12:00 PM (Saturday) | ***Accumulating snow from late tonight into mid-day Sunday with influx of an Arctic air mass…very cold Sunday night/Monday/Monday night***
Paul Dorian
A strong jet streak aloft will play an important role in tomorrow morning’s snowfall in the Mid-Atlantic region as it will promote strong upward motion in its “right entrance” region (i.e., over the Mid-Atlantic). Map courtesy NOAA, tropicaltidbits.com
Overview
The day started off quite mild in the Mid-Atlantic region, but the passage of a pair of cold frontal systems will bring about big changes in the overall temperature pattern for the next few days. Temperatures will likely peak by early afternoon and then drop slowly later this afternoon as an Arctic air mass begins to filter into the region following the passage of these two cold fronts. An upper-level trough of low pressure will then dig into the eastern US tonight and low pressure - aided by a strong jet streak aloft - will form along the Arctic frontal boundary zone. Precipitation will break out later tonight in the DC-to-Philly-to-NYC corridor and Sunday morning is quite likely to feature accumulating snow throughout the region which can last into the mid-day hours in most areas. Very cold conditions will follow on Sunday night, Monday, and Monday night with Valentine’s Day high temperatures generally confined to the 20’s - well below-normal for mid-February. The Arctic chill will disappear at mid-week and then it turns much milder on Thursday, but that warm up looks brief and it may be accompanied by some heavy rainfall with the arrival of the next strong cold front.
The surface weather map early today featured a pair of cold fronts in the northeastern states (boxed region) and the passage of these will bring about much colder conditions for Sunday, Monday and Tuesday. Map courtesy NOAA/WPC
Details
One surface cold front pushed through the I-95 corridor this morning and a secondary front will arrive later in the day. Temperatures started off at very mild levels this morning, but may begin to drop during early afternoon as an incoming Arctic air mass slowly begins to filter into the region. In the upper part of the atmosphere, a trough of low pressure will begin to deepen from later tonight into Sunday as it reaches the eastern states from the Great Lakes region. An important factor in the formation of low pressure by early tomorrow along the frontal boundary zone will be a strong upper-level jet streak that will promote upward motion (right entrance region) in the DC-to-Philly-to-NYC corridor resulting in a breakout of precipitation later tonight and continuing into mid-day on Sunday.
The precipitation may begin as a brief period of rain sometime between the hours of 10pm and 2am, but it should be all snow by sunrise on Sunday and the precipitation shield will expand in areal coverage by daybreak. Accumulating snow should continue through the morning hours on Sunday in the DC-to-Philly-to-NYC corridor and then likely wind down in most spots around mid-day or early afternoon. Road conditions may be slippery in the morning and mid-day hours, but they should improve later in the afternoon after the snow ends and in time for most “Super Bowl” traveling plans. “Winter Weather Advisories” have been posted by the National Weather Service for the DC metro region and I would expect them to be issued in the Philly and NYC metro regions as well at some point later today or tonight.
Precipitation may begin as a brief period of rain later tonight, but should become all snow (shown here in blue) by early Sunday morning as depicted here by the 12Z NAM for 7AM. Map courtesy NOAA, Pivotal Weather
In terms of snowfall amounts for the DC-to-Philly-to-NYC corridor, it appears to me that average accumulations by mid-day Sunday will end up in the 1-3 inch range. Isolated higher snowfall amounts of 4 or 5 inches are possible during this “Super Bowl” Sunday weather event, Initially, the snow may have some trouble sticking on the ground after these past couple of unusually mild days, but soon after, with Arctic air getting better and better established, accumulations should be no problem on all untreated surfaces (e.g., grass). Another wave of energy in the upper atmosphere will push overhead later Sunday night and this could result in additional snow shower activity in parts of the Mid-Atlantic region…perhaps even a heavier snow squall.
The core of the Arctic air mass will be overhead in the Sunday night/Monday/Monday night time frame for the Mid-Atlantic region. Map courtesy NOAA, tropicaltidbits.com
The core of this Arctic air mass will be fully entrenched in the Mid-Atlantic region for the Sunday night/Monday/Monday night time frame and temperatures on Valentine’s Day (Monday) will be way below-normal for mid-February with highs generally confined to the 20’s. [Normal high temperatures now are 44 degrees at Philly Intl Airport (PHL), 48 degrees, at Reagan National Airport (DCA), and 42 degrees at Central Park in New York City]. It stays cold on Tuesday and then the Arctic chill disappears at mid-week. It looks like significantly milder conditions will arrive here on Thursday, but that warm up is likely to be brief and it may be accompanied by some heavy rainfall as another strong cold front arrives. It turns seasonably cold again by the end of next week and for the weekend to follow.
Two teleconnection indices that provide information with respect to the temperature, wind and pressure patterns over the Pacific Ocean tend to climb to into positive territory during the second half of February and then back down into negative territory during the first half of March. This forecasted trend of the Western Pacific Oscillation (WPO, left) and the Eastern Pacific Oscillation (EPO, right) suggests that while it may turn warmer for the second half of February in the eastern US (relative-to-normal), there may be more in the way of cold air outbreaks once again during the first half of March. Maps courtesy Weather Bell Analytics (Meteorologist Joe Bastardi, Twitter), NOAA
Looking ahead with teleconnection indices
Looking ahead, there are signs that the second half of February will in general be warmer (relative-to-normal) compared to the first half of the month. The cold air outbreaks that we have been experiencing recently in the eastern US originating in northern Canada will likely become less frequent during the latter half of the month, but this won’t necessarily mean that the threat of winter-like weather will be over. In fact, forecasted trends of two teleconnection indices (WPO, EPO) that provide information on the temperature, wind, and pressure patterns over the Pacific Ocean suggest that while there may be a warmer pattern during the second half of February for the eastern US, it just may flip back to a colder pattern during the first half of March. When these two Pacific Ocean teleconnection indices move into positive territory the high pressure ridge over western Canada tends to disappear and this change would be unfavorable for cold air outbreaks to make it all the way into the eastern US from Canada. On the other hand, when these indices are in negative territory - as depicted for the first half of March - the upper air wind flow is likely to become more favorable once again for cold air intrusions into the eastern states…stay tuned.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com