SIGNIFICANT SNOWS COMING TO AREAS NORTHWEST OF I-95 FOR SATURDAY AFTERNOON INTO SUNDAY MORNING

A very weak area of low pressure will move from the Mississippi and Tennessee river valleys to the west of the area tomorrow afternoon through tomorrow night. This will spread moderate to heavy precipitation into the norther Mid-Atlantic region starting just around lunch through early afternoon from west to east, initially in the form of snow for almost everyone.

Yesterday’s overnight model runs first started picking up on the amount of cold air that would be in place prior to this storm. They continue to see the influence of this cold with each run and are nearing a consensus. In general, the upper atmosphere will be cold enough to support snow for everyone; however, with the low pressure center tracking to our west, warm air that initially rides up and over the cold dome producing the snow will eventually make inroads in the lower portions of the atmosphere, first in southern and eastern areas and I-95, then further northwest, to a point.

The problem in this case, and arguing against a more substantial I-95 snowstorm comes at 925mb, or about 2500 ft up in the air, down to the surface.

925NAM

You can see on the above map from the latest 12z run of the NAM that 925mb temperatures go above 0c (32F) in southeastern PA and all of DE and southern and parts of central NJ around 7pm EST (0 Zulu time). Snow will fall though the majority of the atmosphere until it reaches approximately 2500 ft, and then begin to melt on it’s way to the surface, (surface temperatures also very closely mimic the map above for this storm). So, it’s safe to say, based on this model, that PHL and surrounding areas in southeast PA will start to transition to rain, after a very brief period of ice, around 7-8pm in the evening Saturday. Those farther south, it will be earlier after a very brief thump of snow, before changing to plain rain, while those farther north will hang onto snow longer and in some cases for nearly or all of the duration of the heavy precipitation. The 0c/32F line at 925mb and at the surface gets to about the blue ridge/ just north of I-78 during the large majority of the precipitation, and not much farther than that. Looking across the board at the models, there is near consensus on these variables on the NAM, RGEM, and European. The GFS I believe is just too warm, given the extreme cold preceding this storm and deep snowpack particularly in the northern 2/3 of Pennsylvania.

So what exactly does this mean? Precipitation will start sometime around or just before lunchtime for those farthest west, and early afternoon for those further east in New Jersey. It will start as snow for everyone, but quickly change to rain for those well southeast of I-95, within an hour or two (probably by 4-5 pm). In and around the city of Philadelphia including southeast PA and central NJ, expect the changeover to occur sometime around 7-8pm. Farther north and northwest, including places like Lancaster, Doylestown, Trenton, up towards NYC, expect a changeover around 10-11pm. The Allentown-Bethlehem-Easton area will changeover in the early morning hours, in the realm of 1-2am, if the changeover occurs at all. I suspect that in these areas, it may be a case of snow to drizzle/freezing drizzle, and really not that much of substantial rain/ice, but that’s kind of a tough call. Even if it does rain in these areas, it won’t be for more than an hour or two. IN the Pocono mountains, expect all snow, from start to finish.

Given all of the above, I think 2-4″ is a good call in and around PHL and southeast PA and its immediate eastern and southeastern suburbs. This will include the NYC area, and the central NJ coast just below the city as well.

Southeast of that, down toward the pine barrens and inland sections of NJ, expect 1-2″, and along the coast of southern NJ, little to no accumulation.

Farther north and west, in the Lehigh Valley, the Lancaster and Harrisburg area, and the Poconos, expect 4-8″, with the least in the south (places like Quakertown/Lancaster), and most in the north (along the blue ridge and obviously in the mountains to the north of that themselves).

Following the storm, expect relatively mild (by the past several weeks standards) temperatures on Sunday, in the mid 30’s to low 40’s from north to south. Then, it’s back into the deep freeze for the foreseeable future, with additional chances at snow around the 25th/26th and March 1st/2nd.

More as we get closer as needed, if there are any substantial changes.

 

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HIGH WINDS, BRUTAL COLD, SOME SNOW TO AFFECT THE MID-ATLANTIC THIS WEEKEND

Just a quick post this morning to make sure everyone’s aware…

There’s a high wind watch this weekend, just issued a few hours ago for all of eastern PA, northern MD, all of DE and NJ into New England:

URGENT – WEATHER MESSAGE
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
528 AM EST FRI FEB 13 2015
…A POSSIBLY DAMAGING HIGH WIND EVENT COULD OCCUR SATURDAY NIGHT
INTO SUNDAY…
…HIGH WIND WATCH REMAINS IN EFFECT FROM SATURDAY EVENING
THROUGH SUNDAY AFTERNOON…
* WINDS…NORTHWEST 20 TO 30 MPH WITH GUSTS UP TO 60 MPH.
* TIMING…THE HIGHEST WINDS SHOULD OCCUR LATE SATURDAY NIGHT
INTO SUNDAY MORNING.
* IMPACTS…BE PREPARED FOR POWER OUTAGES… POSSIBLY LASTING FOR
MORE THAN 24 HOURS. TREES AND TREE LIMBS WILL BE KNOCKED DOWN.
MINOR STRUCTURAL DAMAGE TO HOMES IS POSSIBLE. DO NOT PARK
VEHICLES WHERE TREES CAN FALL ON THEM. MAKE SURE ALL CELL PHONE
AND ELECTRONIC DEVICES ARE FULLY CHARGED. IF YOU HAVE
GENERATORS… PLEASE MAKE SURE THEY ARE WORKING PROPERLY AND
PROPERLY VENTILATED. EXPECT BRIDGE RESTRICTIONS.
* SNOW…TWO TO FOUR INCHES OF SNOW EXPECTED SATURDAY AFTERNOON
INTO SATURDAY NIGHT. A BURST OF ONE TO TWO INCHES OF SNOW
WITHIN AN HOUR IS POSSIBLE AROUND DINNER TIME SATURDAY. THE
WIND WILL CAUSE SOME BLOWING AND DRIFTING PROBLEMS.
* WIND CHILLS…AROUND 10 BELOW ZERO ON SUNDAY MORNING.
PRECAUTIONARY/PREPAREDNESS ACTIONS…

Here’s the 6z GFS wind gust forecast for this time period:

GFS wind

 

There will be anywhere from 2 to as much as 6 or 7 inches of snow late Saturday into Saturday night, followed by very gusty winds, as high as 60-65 mph, as you can see above. This will cause widespread blowing and drifting of any snow that does fall, and more importantly, possible power outages, with temperatures in the 0-15 degree range, and and wind chills well below zero. It doesn’t take a rocket scientist to figure out this could be a big problem.

So make sure you have an alternate heat source other than electricity, or if not, make arrangements to stay with someone who does have one, just in case. Fill all your vehicles with gas, and charge all cell phones. Make sure generators work and there’s gas for them. If you do need to leave your home due to power loss, shut off the water and open all spigots in an attempt to prevent pipe bursts. Hopefully there won’t be widespread outages and it won’t come to that, but better safe than sorry. Regardless, it will be getting dangerously cold starting tomorrow.

And anyone planning to travel up towards Boston or Maine, my advice is not to. They will have the same conditions except with 1 to as much as 3 feet of snow, particularly along the coast of Maine.

More as warranted and as we get closer…

 

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MAJOR GROUNDHOG’S DAY SNOW AND ICE STORM TO AFFECT THE NORTHERN MID-ATLANTIC AND NEW ENGLAND

We have quite the storm already developing across the central US, which you can see on the latest national radar stretches from eastern Nebraska, all the way to Ohio, and south to the Gulf coast. This low is currently centered over Missouri and will track east-northeast into the southwest most portion of Pennsylvania while gradually strengthening.

meso3

 

radar

 

This generally east to west track is the result of blocking in the form of a double barrel, or banana high pressure to our north and northwest, a low pressure system over the Canadian maritimes (our recently departed clipper), and the Polar Vortex situated over Hudson Bay in Canada. Once the low reaches SW PA, it will jump to the coastal water of New Jersey. While this is going on, copious amounts of moisture will spread into the area from the west, with scattered snow showers developing later this afternoon, and more steady snow coming this evening during the superbowl. There are several factors at play here as to who gets what when it comes to snow, ice, or rain, or a combination of the three.

It’s already plenty cold here, with temperatures ranging from near 20 in the northern areas to near 30 in the Philadelphia region, not to mention we are just recovering from a rather brutal Saturday with very cold temperatures and wind chills thanks to a fresh Arctic air mass that invaded behind our last clipper. The ground is VERY cold, and even it some areas get slightly above freezing tomorrow. Additionally, there is a healthy snowpack from the Lehigh Valley on north, which will help to keep temperatures from rising that quickly. These are the reasons why I’m worried that ice will be a problem even in the face of above 32 degree temperatures.

Meso2

 

Additionally, the strength of the high to our north, and the position of the low our the Canadian maritimes are of paramount importance in the evolution of this storm. Both prevent the low from gaining latitude, and any deviation in position or strength from the general model consensus will result in big differences in the snow/ice/rain forecast. Models tend to underestimate cold air, especially low level cold air, and given how cold its been, and a new area of high pressure sliding into our region as the storm does, these factors will be a problem when it comes to ice.

European2

 

As warm air rises up and over the colder air at the surface, snow will initially break out, but then as warmer air continues to invade, the snow will change over to sleet and then freezing rain, from south to north. The questions become how far north does this complete changeover line get, and how long does the freezing rain hang on given the above factors.

Right now, I think the models are removing the cold air too quickly, as they often do, and even when the temperature rise to 32 or 33, the ground is cold, and ice will continue to accumulate, at least for a time. The image below is from the overnight European model run, and it shows you where the snow/ice/rain lines line up approximately during the height of the storm.

European1

 

All this being said, I think the complete changeover line (from snow to ice and/or rain) gets somewhere within the region of I-78 in the Lehigh Valley. It may be a few miles north, or a few miles south of this area. And that’s not to say it will be all snow above this line either, as I believe there will be some mixing with sleet even in parts of the Poconos.

Philadelphia should go to rain after an inch or two of snow. This includes the immediate southern and eastern suburbs of the city, as well as western southern NJ and northern most Delaware, and those along the PA/MD border farther west. Just outside of the city in the northwest suburbs, as well as central NJ including Trenton, 2-4″ should fall, followed by the changeover to ice and eventually rain. Farther north than that, up into the southern Lehigh Valley, the Reading area, and more northern NJ from Phillipsburg to the NYC area, 3-6″ will be the rule. 6-10″ is quite possible in the northern Lehigh Valley, and 8-12″+ in the Poconos and NW New Jersey. Please note that the lower end of snowfall accumulations will occur if there’s an earlier changeover or more mixing, whereas the higher end will occur if it is indeed colder than modeled. It will be all snow north of that into NY state and New England. I am very concerned about icing in the northwest suburbs of Philadelphia, from the area of the east-west turnpike into the Lehigh Valley, particularly below I-78, and central NJ, where I do not think ground temperatures warm up enough to prevent at least moderate ice accumulations.

The 75th percentile map below from the WPC is probably a good estimation of snow amounts, although the southern and northern fridges are likely overdone.

WPC SNOWThe large majority of this storm will occur overnight tonight into tomorrow morning, with things tapering off around and after lunchtime. Be careful later tonight after the superbowl, because it’s very likely there will be snow and/or ice falling no matter where you are, with the exception of central and southern Delaware and far southern NJ. The commute tomorrow morning will be a nightmare for those north and west of the city, particularly in the Lehigh Valley and Poconos.

After the storm departs, the cold will hold into the foreseeable future, with several more chances of winter weather in the coming weeks.

More later if warranted.

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SIGNIFICANT TO MAJOR WINTER STORM TO AFFECT THOSE ABOVE THE MASON DIXON LINE INTO SOUTHERN NY STATE AND SOUTHERN NEW ENGLAND LATE SUPER BOWL SUNDAY INTO MONDAY…

Energy ejecting out of the southwest United States will move out to the northeast and spawn a weak area of low pressure in the mid Mississippi valley. The low will head towards the Ohio river and West Virginia initially, while strengthening gradually. Once it reaches this position, it will transfer its energy to a coastal low off the Delmarva. Meanwhile, the eastern flank of a banana high pressure will be located to our north and northwest, and low pressure which is now exiting our our this morning will be over the Canadian maritimes, as the Polar Vortex spins centered around Hudson Bay Canada. These three features will act to effectively block the initially low from gaining much more latitude, and force it to move to the coast.

EuroSuperBowl

There should be ample moisture available to the storm initially from the Gulf of Mexico, and then the Atlantic as the coastal low forms and strengthens. The cold source will be there in the form of high pressure to our north and northwest, and there will be at least some blocking present given the 3 features described above. This will result in some rather significant snowfall accumulations particularly north of the Mason Dixon line in the northern mid-Atlantic into southern New England, including the I-95 cities from Philadelphia to Boston, initially in the form of warm advection snows, then as a result of the coastal low taking shape. Right now, a general 6-12″ of snow looks likely, and this includes nearly all of the state of PA, central and northern NJ, southern NY state, and much of Massachusetts, Connecticut, and Rhode Island.  This snow will be falling with temperatures primarily in the 20’s (and in some cases colder) in much of PA, northern NJ, and coastal New England on north, and therefore snow ratios will be higher than the 10:1 shown on most snow accumulation maps, probably in the 12-15:1 realm. South of the Mason Dixon line, there will be some mixing or a changeover, and this includes DC and Baltimore, as well as most of Delaware, particularly south of New Castle County, and South Jersey especially areas south of Atlantic City. I could see mixing go as far north as within a few miles of the PA turnpike, but I don’t think the rain/snow line gets much farther north than that. There is very close to universal model agreement in this scenario, somewhat of a rarity this season, with the exception of the Canadian model, although it’s ensembles are in agreement with the other models. Systems like these have the ability to overperform, especially on the front end, and that’s something we’ll have to watch for regarding QPF increases in the modeling over the next 48 hours and on radar once the storm forms late Saturday and Sunday. Snow should start from west to east around the time of the Superbowl (be aware it may very well be snowing after the game for most) and last through at least Monday afternoon, which is a relatively long duration event.

So given what happened with the last storm, you are probably asking, what can go wrong or right, depending on your perspective with regards to snow. The position of the Polar Vortex is key in this situation, and any deviation farther north or south will result in the initial low moving more north or south, and result in a warmer (more mixing and less snow south) or colder (more suppression and snows farther south, less north), respectively. That’s the one wildcard, but right now, given the rather good model agreement, I don’t expect things to change significantly. And could the storm be a miss like the last one? That’s VERY unlikely, as this storm will actually be formed with a large precipitation shield BEFORE it reaches our area. The last storm was dependent solely on redevelopment of a clipper low which had a paltry amount of snow before the coastal low rapidly intensified, and in our case for the northern mid-Atlantic, too far east to really affect us.

Beyond this storm, I see no significant warm ups in site. Weak Modoki El Nino winters are almost always back loaded, with the greatest degree of cold and snow coming in March and February, and in some cases into early April. Given this fact, and the SST profiles which continue to be very warm off the west coast and in the Gulf of Alaska, similar to last year, and additionally those in the northern Atlantic, which remain favorable for blocking, as well as the inevitable weakening of the -QBO in the next few weeks, I see winter extending well into March if not early April. So there is plenty more snow for those who love it. For those who love Spring, I think they’re disappointed much like last year, especially if they were hoping for early warmth.

More on the late weekend storm as warranted.

 

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HISTORIC ROAD CLOSING BLIZZARD TO AFFECT NEW JERSEY THROUGH MAINE

I wish I had time to get more in depth here, but unfortunately I just haven’t had the time given work and everything else in between, so this will have to be quick.

The storm is currently streaking over Kentucky and by tomorrow will be redeveloping off the Virginia Capes and then RAPIDLY deepen as it heads just east of due north.

Meso

Once it reaches our latitude, the 500mb or upper level low will close off somewhere around the Delmarva peninsula, which subsequently will capture the surface low and cause it to slow down and meander around near the 40/70 benchmark, just southeast of eastern Long Island. Where and how rapidly this upper level low forms will determine how far west the heavier snow gets with respect to eastern Pennsylvania. The European and its ensembles have been rock solid consistent in this scenario, which is typical for nor’easters, and I’m leaning heavily on their outcomes. I just don’t buy the further east solution of the other models given the insistence of the Euro and the very warm ocean temperature just off the east coast, which storms like this feed off of.

Euro1a

 

euro1b

 

Assuming the European and its ensembles are correct, and I think they will be, expect lighter snows to begin in the early morning hours and then continue through most of the day Monday. There may be a lull in the action Monday afternoon, and then Monday evening things will dramatically pick up in intensity from southeast to northwest as the coastal storm ramps up. Heavy snow, where it does fall, will occur from Monday evening through at least Tuesday afternoon. The worst weather will be near the coast, where 2-3 feet is likely from central NJ up into southern Maine. Farther west, at our latitude, snowfall will drop off, and there will likely be a rather sharp cutoff along the western fringe of the precip shield. The hardest area to forecast for our area will be on a line from about Scranton to Hamburg to West Chester PA. Within just 10-15 miles of this line, one could got from 6-7 inches of snow to well over a foot. There is the possibility that this storm gets its act together more quickly, and the 500mb low develops faster and farther southwest, resulting in a slightly further west surface low track, but I’m not ready to go there yet. I will be watching tomorrow though as the storm develops for this possibility however.

That being said, I like NOAA’s forecast below for this storm. Extreme eastern PA should see double digits, in the realm of 10-18 inches, greatest along the Delaware river, least further west. Farther east, amounts of 2-3 feet will be common, but given the gale and storm force winds associated with this storm at the coast, after you get beyond 18 or 20, let’s be honest, it’s rather hard to measure. Farther west there should be 6-12″ along the Scranton-Hamburg-West Chester line I described above. Accumulations will likely drop off from there as one heads toward and beyond the Susquehanna river.

NOAAsnowfall

 

After the storm winds down, colder air will follow with some moderation towards the end of the week, and another chance of snow come later Thursday into Friday. This will be followed by the coldest air of the season, likely quite brutal, next weekend into the first week of February. Winter has truly returned.

More tomorrow as warranted…

 

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BLIZZARD FOR AT LEAST PART OF THE NORTHEAST EARLY NEXT WEEK? YES, I THINK THERE WILL BE….

As the storm from overnight departs us, leaving a healthy dose of snow, there’s a good possibility of another, even bigger storm for someone in the northeast US come Monday and Tuesday. A rather potent clipper low will race across Kentucky and southern Virginia during the day on Monday, and provide light to moderate snow to the north of it’s track, across most of the mid-atlantic states.

Once this low reaches the North Carolina coast, the fun begins. Just 24-48 hours ago, all models had this storm exciting out to sea stage right. However, over the last 24 hours, the upper level pattern has been changing and favoring a low which develops faster and closer to the coast from NC northward. We’ll look at the NAM, although honestly, all of the models are showing similar trends across the board:

1/23 18z NAM 500mb:

NAM1

1/24 0z NAM 500mb:

0z NAM

1/24 6z NAM 500mb:

NAM3

1/24 12z NAM 500mb:

NAM4

All of the troughs over the east coast late Monday afternoon are negatively tilted, which will allow any storm that forms to ride north and parallel the coastline. But looking closer, the trough axis (or position) has moved west with each successive run of the model. Furthermore, the trough is becoming progressively deeper and sharper over time as well.

Now, lets look at the surface maps:

1/23 18z NAM surface:

NAM5

1/24 0z NAM surface:

NAM6

1/24 06z surface:

NAM7

1/24 12z surface:

NAM8

The increasingly deeper and farther west position of the trough at H5 allow the low to begin development further southwest and closer to the coast. As a result, you go from a storm out to sea on the 18z NAM last evening to a blizzard over New England on the most recent 12z run today.

18z last evening, low harmlessly going out to sea:

NAM9

12z today, blizzard for New England and Long Island:

NAM10

So you can see the importance of the trough depth, sharpness, and its position. As I said before, ALL of the models are trending this way. Do I think this will continue to trend to the point that it affect most of the Mid-Atlantic with heavy snows? Outside of maybe eastern NJ and New York City, no, not at this time – but, it’s definitely something to watch over the next few days. One thing is becoming more and more likely – southeastern New England and at least eastern Long Island is going to be hit pretty hard with this one.

More on Facebook at doctoochweather as warranted….

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Winter cancel? Not by a long shot….

So I realize I’ve been shirking my usual blogging duties lately, but to be honest, there hasn’t been a lot to talk about up to this point, particularly along the coastal plain into the I-95 corridor of the Mid-Atlantic. I’ve been lucky enough to have about 12 inches of snow collectively fall from the pre-thanksgiving storm, and a few other minor storms, up here in the foothills of the Poconos, but other than that, there hasn’t been any big threats. However, winter, after all, is just beginning – the winter solstice was just the other day. So why all the complaining?

Most of it comes from people just pining away for snow at all costs – they see the majority of meteorologists talking about how the winter is set to be another bad one, and if that call for cold and snow doesn’t start in November, and last into April, well, then winter is just not happening. A complete epic fail. Climb the bridge. It’s over. Maybe next year.

Except, winter just started, and we’re just entering it’s prime months. So, all is not lost. In fact, there are still plenty of signs out there in the short, medium, and even the long range that are favorable. There are still some question marks, but lets get to what is going right.

 

THE ALASKAN RIDGE, THE MEGA HIGHS, AND THE EL NINO

The first thing I’m noticing is the re-establishment of big, strong Arctic highs coming out of northwest Canada, and with them, extreme Alaskan ridging (-EPO) in the 8-10 day period. These two features were the HALLMARK of last year’s winter, trumping the lack of a -NAO and the relatively non-contributory ENSO state we saw last year. You can clearly see them on the latest run of the GFS below (surface map first, 500mb to follow):

 

GFS surface

 

GFS 500mb

You may think, sure, but it’s the GFS; however, these features are on all the models, and many have them very strong. I often will chastise this model when it comes for east coast storms, and for good reason, as it regularly performs horribly in the medium range for such systems. But it’s performance last year was actually pretty good against the famed european model when it came to seeing the strength of these large highs coming down out of Canada in the longer range. It’s been nice to see them appear in the 10-15 day forecast on the GFS and see them hold throughout and into the 8-10 day forecast, as well as see them on other models. In fact, I will be watching the strength of these highs on the european as we get closer in time, and it would behoove you to do the same. Last year, they actually increased in strength from run to run, and were overall weaker initially when compared to the GFS.

The importance of these highs (and the Alaskan ridging) can’t be overstated. One only has to look at the 500mb map above and if you follow the contour lines over Pennsylvania and NY state back to the west, and see the source region for these upper level winds is in fact coming from north of Alaska, the north pole, and even crossing the pole from Siberia. That’s serious cold, and that’s what this setup is capable of over the next 2 weeks, beginning around December 29-29th, and onward – and we all know you can’t get the snow without the cold, especially for our friends in the I-95 corridor.

These changes at 500mb are the result of the warm sea surface temperatures seen below in the area labeled #1, which as you’ve known from earlier facebook posts, promote ridging in Alaska and northwest Canada, which in turn allows the cold air to pour into the United States (which is well established over the pole and Siberia thanks to above normal snowpack in these areas). Additionally, also discussed earlier this year, the warmer waters off the Baja of California, and the weak west based el nino state of ENSO (labeled #2 and 3) promote an active subtropical jetstream, and the moisture source for the winter storms we all live for (well, some of us).

GlobalSSTENSO

 

THE COLD PRESS AND THE SOUTHEAST RIDGE

Even with that, one can look at the relatively warmer European, and to a much lesser extent the GFS, and think, but about the southeast ridge that keeps showing up? Isn’t that an issue? The answer is, yes, in most situations, but given Arctic advance associated with the Alaskan ridging and the Highs coming with it, it actually can be beneficial. Whenever you have such extreme cold air, in this case from cross polar flow, there’s always the chance that it can overwhelm the pattern, and suppress the storm track far to the south. So, you want that SE ridge to flex its muscles, because without it, you get a lot of ‘garbage cold,’ or temperatures in the teens and 20’s and wind and flurries. Not exactly a party for snow lovers, let alone anyone who doesn’t like winter.

EUROSURFACE

The question becomes, how strong is this ridge, and how much does the cold air press? Unfortunately, the answer is not apparent this far out. Will there be a “storm” on December 29th exactly as depicted above on the Euro? Probably not. But something similar to this is very possible, and in fact from right before New Year’s until well after, there may be a few of these possibilities. The question becomes how much energy comes out of the southwest US – if it’s a lot, the rain snow line is shunted northwest of the one on the map above. If it’s less, the line and precip is shunted south.

And now to the question marks….

THE NEGATIVE NAO

Most forecasts included a negative NAO this year, but we just haven’t seen much in the way of Atlantic blocking. The sea surface temperature (SST) over the north Atlantic remain favorable (see below, where we have warm waters in the Davis straits (labeled #1) and around Iceland (#2), and cold waters in the central Atlantic (#3), but we have yet to see a sustained -NAO, which as most know promotes slower, longer duration storms by blocking there quick escape into the Atlantic Ocean.

GlobalSSTs

Time will tell as to whether this occurs. Typically, in my experience, such a pattern tends to become more established as we get into mid to late winter, usually late January through March. Additionally, as discussed below, the stratosphere is becoming more favorable for blocking. So while although it has yet to really come on, there are signs that it will shortly.

 

THE QBO AND THE PACIFIC JET

Much has been made over the Quasi-Biennial Oscillation, or QBO, over the last few days, and it’s affect on the warm Pacific jet stream that has dominated the pattern over North America over the past few weeks, starting after Thanksgiving.

So what the hell is the QBO? I don’t pretend to be an expert on it, but the best most useful I’ve found is from Dave Tolleris at wxrisk.com:

“The Quasi-Biennial Oscillation (QBO) is a BAND of wind over the equator of the globe that was discovered over 50 years ago.  This band of wind exists the very top of the atmosphere about 15 miles up where the pressure is about 30mb or just 3% of its surface value.  The QBO  has a “ cycle”  to it.  It runs from east to west  (the negative  phase) then after  reaches some sort of Max negative value … the  QBO   moves back towards neutral. Then  the winds reverse and the QBO runs from West to east (the positive phase) . The cycle takes approximately somewhere between 18 and 27 months  but sometimes it can take longer or shorter.”

QBOsample

The bad news so far this late Fall and first few days of Winter is that the QBO has been markedly negative, in the -20’s range, for quite some time.

QBO

This is bad because it promotes a strong Pacific jet, with it’s zonal pattern and associated milder Pacific air, to flood the continental US every time a colder pattern tries to take hold.

But, there is good news on the QBO front as well. It is after all, an oscillation, which implies that at some point these values should begin to decline. Such declining more moderate negative values promote more amplification at 500mb and more blocking. I remember discussing this with a few of the EPAWA meteorologists a few months back and wasn’t worried about the highly negative values of the QBO even back then. Why? Because one only has to look at the QBO values over the past few decades (see below) to see that after about 5-6 months, such highly negative values ALWAYS fall back toward neutral within the subsequent 2-3 months.

QBO2

So I knew that as we enter the heart of the winter, things should fall into place and the Pacific jet should relax, and more blocking should be the rule.

 

SUDDEN STRATOSPHERIC WARMING (SSW)

I also wanted to briefly touch on the Stratosphere and its warming implications for us going forward. The behavior of the stratosphere in relation to the troposphere, or where we live, is somewhat complex, but I like to think of the SSW events themselves as kind of like a sledge hammer. They in effect split the polar vortex, which when displaced from the north pole (hence the name), can bring large chunks of arctic air along with it. A few weeks ago, quite a few people were excited about the SSW that was occurring over the northern hemisphere, but in fact on the wrong side of the globe, centered over Russia, and not over the pole or North America. If there’s one thing that I learned from the winter of 2011-2012, it was the the location of such an event is as important as the SSW event itself. It’s no wonder December has been rather blah when it comes to cold and snow from a stratospheric standpoint. The Polar Vortex has been in an unfavorable position away from North America, and there’s been a lack of arctic air this past month almost nationwide.

However, there seems to be good news here as well. As you can see below, the latest forecast from the ECMWF (courtesy of WSI) shows another SSW event, but this time directed more over the pole, rather than on the other side of the globe.

SSW

This would promote splitting of the polar vortex into a more favorable position for cold for us, and a more negative NAO (blocking) and AO (cold) as we go into mid to late January, given the 2-3 week lag time that is usually the norm for such events.

 

THE MADDEN JULIAN OSCILLATION(MJO)

Finally, we come to the MJO. The MJO is characterized by an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian and Pacific Ocean. The implications of this cyclical pattern of tropical rainfall are neatly shown in the following two graphics:

MJO3

MJO

One can clearly see that the phases 8, 1, 2, and 3, and to a lesser extent 7, are favorable for cold in the eastern US. Phases 1, 2, and 3 are particularly wet as well.

Right now, the MJO impulse is currently in the eastern Indian Ocean and is forecast to be in phase 4/5 over the next few days. This is why we are seeing a southeast ridge pop up on many of the models. However, there are signs it will indeed propagate into and beyond phase 6 as we go through mid January, again, favoring cold on our side of the country.

 

CONCLUSION

So, with all that being said, you can see winter isn’t in fact canceled, but just getting started. The mega highs and Alaskan ridge is there, just like it was last year. This will initially cause the cold to bleed southeast, on the heels of a broad based trough, and while the MJO is in its warmer phases, the southeast ridge to fight back. The QBO is markedly negative, yes, but it WILL start to move towards neutral, promoting a relaxation of the Pacific jet, and more blocking as we head into the heart of winter.  The stratosphere is forecast to warm in a more favorable location for us, also favoring more blocking and a -AO. And the MJO should propagate into more favorable phases for cold and snow as we head towards mid-January. Fun times are indeed ahead.

Watch for things to get interesting beyond December 28th/29th. More as warranted as usual.

Special thanks to Mike DeFino and Bobby Martrich of EPAWA who contributed to this discussion.

 

 

 

 

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Why is a major snowstorm still very possible in the MidAtlantic and New England?

Some media outlets have been waffling back and forth between the possibility of a significant or major storm and just the nuisance variety, based mostly on what the models at a particular hour are saying. I have not however. I still believe a major snowstorm across a large portion of the northern MidAtlantic and New England is likely Thursday into Friday, and below is a major reason why.


The first map below is the upper air pattern at hour 60 from the afternoon run of the NAM (12z) for this Thursday evening. It shows a positively tilted shallower trough, with it’s base/axis in the central part of north Georgia. The ridge out west is less amplified as well.

 photo 12znam500mb-hgt_rvort_us-60_zps91a6426a.png

Now, compare that to the next image below from this evening NAM (18z). The trough is less positive and more neutral, with the base is slightly west and south in the western portion of central Georgia, meaning it is slightly deeper, and also a little sharper (lines in the upper midwest are steeper along the front of the trough).

 photo 18znam500mb-hgt_rvort_us-54_zps703aedda.png

So most would think – who cares? Not that big of a difference, right? And you’d be correct, it isn’t a big difference. But that’s the point. These little differences higher in the atmosphere at 500mb can have profound effects on what happens at the surface.

The third map below corresponds to the first 500 mb map we looked at, yet at the surface, for the 12z NAM. The low center is directly south of Prince Edward island, Canada, and the precip shield is sparse to non existent over the Mid-Atlantic. 

 photo 12znam-mslp-qpf6-us_hr60_zps3330476f.png

Now look at the last map in the series below. This is the surface depiction off the 18z NAM. Those subtle changes at 500mb produce quite a difference at the surface, with the low about 150 miles west of its position versus the 12z. Additionally, the precip shield is much more robust, producing moderate to heavy snow over most of the area. 

 photo 18znam-mslp-qpf6-us_hr54_zps128ac938.png

Now, these differences were only 6 hours apart between two model runs. And all of the runs did this this afternoon at 500mb. So you can see how the next 12-24 hours may make quite a difference as more accurate data comes in and the models adjust. I expect that the models will continue to adjust a quite a bit of wind blown, high ratio snow is on the way for most of us. 

 

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QUICK LUNCHTIME UPDATE

Quick lunchtime update, but first a statement from the National Weather Service:

THERE IS SOME RAIN ON THE SOUTHERN PERIPHERY OF THE NORTHERN
STREAM SYSTEM ALSO IN PARTS OF WESTERN PA AND EASTERN OH. BASED
ON THE MEAN FLOW SEEN IN 12Z UPPER DATA…THE AXIS OF THE HEAVIEST
SNOW MAY BE SHIFTING EVER SO SLIGHTLY MORE WEST AND NORTH THAN
CURRENT FORECAST. LOTS OF CONVECTION OFF THE CAROLINAS WHICH COULD
CONTINUE THE ENHANCED DOWNSTREAM UPPER RIDGING THAT COULD SHIFT
THE SURFACE LOW TRACK AND ASSOCIATED RAIN/SNOW LINE AND DYNAMICS
JUST A SLIGHT HAIR WEST AND NORTH OF CURRENT FORECAST.

Translated, the storm appears tracking a little farther west than originally thought. Now, I know that many of you in the western portions of the area have seen nothing at all, and are thinking, ‘how can that be?’ The reason for this has to do with the low to our west – the sinking air between the coastal low and the western low effectively prevents any precipitation from occurring.

HOWEVER, the energy from the western low is currently being absorbed or phasing with the coastal low. This coastal storm is now undergoing rapid intensification, and there is intense convection over SE NJ moving NW at this hour. As the storm deepens and moves up the coast, the precip shield will expand northwestward. This will take some time, but snow should develop from southeast to northwest. Because the low may track slightly further west, this can shift some of the heaviest snows slightly west.

But, unfortunately, its not that simple. There will also be mesoscale banding developing, which in layman’s terms is where one town can get 2 or 3 inches of snow in an hour or two, and another a few miles away gets nearly nothing (again due to sinking air). There is no way to predict this ahead of time. Regardless, everyone in eastern PA will see snow this evening, with the most the farther east and north you go.

This is a complicated storm to say the least, but it is far from over, and in fact, is only just getting started. The heaviest snows will be occurring from late afternoon into the overnight hours. We’ll have more updates periodically as warranted. [doc]

Image

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HISTORIC NEW ENGLAND BLIZZARD LOOMS – BUT WHAT ABOUT US? SOME TRENDS AND OBSERVATIONS THAT SNOW LOVERS WILL LIKE

By now, most have heard of what’s about to happen in southern and central New England – 2-3 feet of wind blown snow with blizzard conditions this Friday and Saturday. This storm will be the biggest in decades for them and will likely shut down that part of the country into next week.

Given the relative lack of snow the past two years in the northern mid-Atlantic, the obvious question for snow lovers – and haters for that matter –  is what about us? Can we expect some of the same? Well, the answer is no – not 2-3 feet, and not blizzard conditions for our area. However, there are some things am I following which suggest we still can get a significant to major snowstorm in most of eastern PA and central and northern New Jersey.

Let’s start with the models.  The European model has by far been the most consistent, bringing this storm up the coast for the past 10 days now:

 ecmwf850mb-mslp-tmp_48_zps429f0946.png

Prior to this point in time, it is prudent to look at the upper levels of the atmosphere, at 500 mb, to see whether this models forecast coincides with whats happening in real time. This is the 500 mb map for 4 am eastern time from the overnight run of the European:

 Euro5009z_zps9bb2362e.jpg

I drew over the height lines over the southeast US. I know it’s somewhat difficult to see, but you get the idea of the rather gentle SW to NE orientation of the upper level winds at 500 mb as forecasted by the european at 4 am.

Now let’s look at the real time 500 mb chart (also at 4am):

 Meso500mb_zps75589771.gif

You can see that the orientation of the upper level winds is sharper, and pointing more up the coast, than out. Yes, it’s not a large difference, but it’s differences like this at the infancy of a storm that can change forecasts down the road.

Now let’s look at the 0z GFS upper air map at 4 am:

 gfs500_zps3bdbadcc.gif

Also flatter, in fact a little more flat than the European, and definitely flatter than the current upper level pattern above. It’s no surprise then that the GFS pushes the storm even farther east and offshore when compared to the European (see above) at the same time:

 gfs-mslp-qpfshort-us_hr48_zpsc926ac77.png

So, we have a current 500 mb (or upper level wind field) which is pointing more up the coast than certainly the GFS forecast at this point in time, but more importantly, the European model, which brings the storm the closest to us. An interesting observation, and one that would favor a storm closer to the coast, and more snow as well, for eastern PA and NJ.

How about the pressure, strength of the low over the northern gulf? You can see that the low is about 1009 mb just SW of New Orleans, LA at 4 am:

 mesoNOW_zpsb1b8cea6.gif

Compare this to the GFS forecast at 4am, at about 1012 mb:

 gfs-mslp-qpfshort-us_hr9_zpse7644d75.png

and the European at 7am, 3 hours later, with still a low of 1011-1012 mb:

 ecmwf850mb-mslp-tmp_12_zpsb364b985.png

Both have pressures slightly higher than what is actually happening at this point in time. Not a big difference, but something to watch.

And finally, lets look at the current radar at 4:45 AM:

 969ca12f-5502-4aa5-a05c-7eb63c3e0777_zpsad02db62.jpg

You can see that the southern precip shield is much larger than modeled (compare to the maps above), extending into the western half of Georgia, and even up into Kentucky. Additionally, precipitation to the north and west looks healthier than predicted by both models as well. Moisture is beginning to be drawn into the system from the Atlantic just NE of Jacksonville, FL in the form of thunderstorms.

In summary, we have upper level winds pointing more up the coast than out, favoring a storm track closer to the coast, more like the European model. We have a developing low slightly stronger than modeled. And we we have a more expansile precipitation field than forecasted.  I’ll be watching all of these factors throughout the day. Current observations and comparisons with the modeled forecast will be critical. How much snow will we get? I think at least 6 inches is a good start in eastern PA, which includes the Lehigh Valley, with as much as foot in the eastern counties along the Delaware river, especially in northeast PA, and in northern New Jersey, IF things come together just right. Southeast Pennsylvania will see the least, with perhaps 3-4 inches in the city of Philadelphia an it’s immediate suburbs.  Southern NJ and Delaware will see very little. These numbers can and will probably change, but regardless, this will be the biggest storm of the year for many here.

More updates on my facebook page(http://www.facebook.com/DocToochWeather) and at Eastern PA Weather Authority (http://www.facebook.com/easternpaweatherauthority and http://www.epawablogs.com)

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