10:45 AM | ***Accumulating snow late Saturday night into mid-day Sunday with influx of Arctic air…very cold Sunday night/Monday/Monday night…a look ahead with teleconnection indices***
Paul Dorian
An Arctic air mass begins to filter into the Mid-Atlantic region later Saturday and the full brunt will be felt on Sunday, Monday and Tuesday. In fact, the coldest core of the Arctic air mass will be overhead on Monday making for a Valentine’s Day that will feature temperatures way below-normal for the middle of February. Map courtesy NOAA (12Z NAM), tropicaltidbits.com
Overview
It stays mild in the Mid-Atlantic region into the beginning of the weekend, but an Arctic front will slide through the area on Saturday and its passage will bring about much colder conditions for Sunday, Monday and Tuesday. Low pressure is going to form along the Arctic frontal boundary zone by tomorrow night and this system should generate accumulating snow in the Mid-Atlantic region from late Saturday night into Sunday likely on the order of a coating to a few inches in most spots. The core of the Arctic air mass will move overhead by Monday and temperatures on Valentine’s Day will be way below-normal for the middle of February. The Arctic chill wanes by mid-week and then signs point to a big time warm-up by late next week although it is likely to be accompanied by some rain by week’s end.
Low pressure will form along an Arctic frontal boundary zone this weekend, but the “phasing” together of northern and southern systems is likely to take place a little too late for any significant snowfall in the Mid-Atlantic. Map courtesy NOAA (12Z NAM), tropicaltidbits.com
Details on the weekend and next week
After a very mild day on Friday, the weekend will begin on the mild side in the DC-to-Philly-to-NYC corridor; however, an Arctic cold front will slide across the area on Saturday and this will set off some changes that will result in much colder conditions for Sunday, Monday and Tuesday. Temperatures may hold onto mild levels for at least the morning and mid-day hours on Saturday in the I-95 corridor, but don’t be surprised if they drop some during the afternoon hours and dew points (a measure of overall moisture content) are quite likely to drop in the PM hours which is typical of an incoming (dry, cold) Arctic air mass.
Low pressure will form along the Arctic frontal boundary zone by tomorrow night and snow should break out late Saturday night in the I-95 corridor - perhaps as a brief period of rain at the onset. Snow can continue on Sunday morning before winding down as the low pressure system pushes northeastward to a position out over the western Atlantic Ocean.
12Z NAM forecast map for early Sunday morning with snow (shown in blue) in parts of the Mid-Atlantic region. Map courtesy NOAA, tropicaltidbits.com
In terms of snowfall amounts in the DC-to-Philly-to-NYC corridor, it appears that accumulations will likely end up in the range of a coating to a few inches in most spots by mid-day on Sunday. If there are to be any surprises on the up side with this system in terms of snow accumulations, it would likely be in the region from DC’s immediate south/east side-to-the Delmarva Peninsula-to southern New Jersey (and yes, that has been kind of a repeating pattern this winter). There are a couple of limiting factors that will likely prevent anything more significant in terms of snow accumulations. First, the “phasing“ of two upper-level waves of energy (one in the northern stream and one in the southern stream) looks like it just won’t happen in time for an inland intensification of the low pressure system. Rather, much of its strengthening is likely to take place when the low pressure center is off-shore. Second, the low pressure system that will push along the frontal boundary zone will move along at a pretty good clip - inhibiting its chances for producing significant snowfall in the I-95 corridor.
The Arctic chill coming for the Sunday, Monday and Tuesday time period will ease at mid-week in the eastern US and it’ll turn much milder by next Thursday and Friday. Map courtesy NOAA (06Z GFS), 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 temperature now at Philly Intl Airport (PHL) is 43 degrees, at Reagan National Airport (DCA) it is 47 degrees, and in Central Park (New York City) it is 41 degrees]. It stays cold on Tuesday and then the Arctic chill really begins to wane at mid-week. It looks significantly warmer by next Thursday and Friday with 60+ degrees on the table for highs in the DC-to-Philly-to-NYC corridor, but rain may also accompany that warm up at week’s end.
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 be noticeably 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 much 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 again for cold air intrusions into the eastern states…stay tuned.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
Follow us on Facebook, Twitter, YouTube
Video discussion: