Currently, temperatures range from around 10 in Mount Pocono, to around 30 in southernmost NJ and Delaware, with stiff northwest winds blowing at around 10-20 miles per hour with gusts to 30.
Not a balmy night, to say the least. This is garbage cold – it’s uncomfortable at best, and useless without a storm to provide us with snow – pure garbage in my book. Fortunately, it won’t last long. By the weekend, most of the area will approach if not surpass the freezing mark for highs, and the 40’s and even a few 50’s will be common for next week – a true thaw, albeit a few weeks late.
Unfortunately, the storm to our southwest will stay too far to the south to have any real affect on the area. The upper air steering currents point to two things that I discussed yesterday – The malpositioned Polar Vortex, barely seen east of Hudson Bay in Canada, won’t let our storm gain any latitude, and the negative PNA as evidenced by a poorly positioned ridge now west of the west coast allows the now dominant northern jet stream to crush the shortwave energy as it slides across the nation’s heartland.
The precip shield will head east southeast from it’s current position and off the SE coast later this week.
Perhaps the Delmarva and extreme SE NJ will be brushed, but given the realtively dry air, I wouldn’t expect much more than a few flurries or a period of light snow at best.
So after the warm up next week, then what? Is winter over? Well, in a word, no. However, that’s not to say that one more major snowstorm is a guarentee, either. I expect the warm up to last through at least late February, with very end of the month and first week of March the next chance of a major storm. Remember, the stratosphere just underwent significant warming, as shown below, by the warm hues towards the top of the chart around February 1st.
Even currently, the stratosphere remains relatively warm. This warming usually takes a few weeks to translate down to the troposphere, or lower portion of the Earth’s atmosphere, where the Earth’s weather occurs. Stratospheric warming favors displacement of the Arctic air southward into the continent (negative Arctic Oscillation, or -AO) and a return of blocking in the North Atlantic (negative North Atlantic Oscillation, or -NAO). This combination (-AO and -NAO) is a calling card for cold and often stormy weather for the Mid-Atlantic. You can see how both the AO and NAO forecasts, respectively, below, are headed generally in a negative direction, but not a slam dunk by any means (but also look at the periods of warming and cooling of the stratosphere and try to match them up with the neagtive and positive phases of the NAO and AO over the past few weeks, remembering the lag):
As an example, look at the stratospheric cooling in late January on the chart above, then look at the NAO index approximately two weeks later – you can see how the NAO went positive relative to the cooling. Logically, since we now have a period of warming, one would expect the NAO to become negative in the next 2 weeks. The same goes for the AO, which is at least headed in the negative direction:
Tonight I also want to introduce another index – one which I seldom talk about – but important nonetheless – the Eastern Pacific Oscillation, or EPO. From the National Weather Service:
“The Eastern Pacific Oscillation (EPO) is the upper wind flow over the Eastern Pacific influenced by the ocean. When in a positive phase, the EPO generally is reflected by dominant stronger zonal flow and/or troughing along the West Coast of the U.S. This combination, in turn, tends to funnel milder Pacific air well inland into the country and thus, limits arctic outbreaks by holding them at bay up in Canada. When the EPO is dominated by a negative phase (as with the NAO), more ridging develops along the West Coast as higher pressure extends from the Gulf of Alaska south along the West Coast of Canada (opposite of the positive phase). This, in turn, encourages a northwesterly flow from Canada into the middle and eastern sections of the US and thus, the delivery of polar or arctic air.”
You can see, by this definition, how the EPO is an important factor in the delivery of cold air necessary for winter storms. Here’s the EPO forecast from the GFS, GFS ensembles, and European models, respectively:
You can take away a few thing all of these. First, the EPO is forecasted to be in a negative state for the next few days, supporting our current Arctic outbreak. After about the 12th of February, the models are in pretty good agreement in forecasting a postive EPO, giving us the warmup I elluded to above. And finally, the models also agree on the restablishment of a negative EPO towards the end of the month. This is one of the reasons why I believe it will once again get cold.
But what about storms? Well, this is why I stated above, a major storm is still not a guarentee. One thing that I do not see in our favor is the PNA. All of the forecasts I can find have the PNA in a negative state through at least the 24th of February. Not a good sign for a major east coast snowstorm:
We also have the added problem of climatology after February, we’re getting late into the winter season, and this starts stacking the deck against us. March snowstorms, although not rare, are less common than those in February, with the first week in March easily posing the greatest threat. They can and do happen – the Superstorm of 93 was in the first week of March – but it requires a little bit more luck than earlier in the season.
In the end, given the current state of the stratosphere, and the expected staes of the NAO and AO, based on this, as well as the EPO forecasts, I don’t think winter is done just yet, but it will definitely take a break for a while after the next few days of cold. Philly could even climb into the 60’s sometime next week. And it’s almost guarenteed that the current snowpack will be gone in the near future. But enjoy it – 60 will feel like 80 after the weeks and weeks of below normal temperatures we’ve just endured. I know I will – I’ll be Spring skiing at Camelback on Tuesday.
I’ll be in and out periodically over the next few days, so if you have any questions, drop a comment and I’ll try to answer them ASAP. If any threats arise before the end of the month, I’ll definitely be back before then. I’ll be in Florida for the last week of February and first week of March, so with my luck, I’ll be delayed at some airport watching the biggest storm of the winter hit the Lehigh Valley (not at all a forecast, just Murphy’s law).