10:45 AM | ***Icing threat in the Mid-Atlantic region later Thursday after a 3-day mild break...winter's comeback will continue in late February and likely well into March***
Paul Dorian
“Cold air damming” will set up later in the week and this can result in an icing event on Thursday in much of the Mid-Atlantic region. Map courtesy NOAA, tropicaltidbits.com
Overview
It’ll be quite mild in the Mid-Atlantic region through mid-week, but then it turns much colder on Thursday and that cool down could be accompanied by some icing in much of the area. Temperatures today should make it into the 50’s and they’ll remain on the mild side on Tuesday, but it’ll become quite wet as well with a decent rainfall on the way from later tomorrow into tomorrow night. The warmest day of the week is likely to be on Wednesday ahead of the next cold front with temperatures likely to climb well up in the 60’s, but then big temperatures changes will take place by Thursday. Looking beyond the possible ice event later Thursday, numerous signs point to a continuation of winter weather conditions in the eastern states as we wind down the month of February and then flip over to March. In fact, there is a good chance for a very cold air mass to arrive in the east by early next week and it could be preceded by some snowfall.
The warmest day this week in the Mid-Atlantic is likely to be on Wednesday when temperatures could soar past 65 degrees in the DC-to-Philly-to-NYC corridor. A cold front, however, will be poised to the northwest (left map) and it will usher in a colder air mass (right map) for Thursday potentially setting the stage for icing. Map courtesy NOAA, tropicaltidbits.com
Three days of mild and then an ice threat
After a cold weekend, temperatures today should jump well up into the 50’s in the DC-to-Philly-to-NYC corridor and they’ll remain on the mild side on Tuesday and Wednesday. The mild conditions on Tuesday and Tuesday night will be accompanied by a decent rainfall for us as low pressure pushes from the Great Lakes area to the southeastern part of Canada. On Wednesday, temperatures could easily soar to 65+ degrees in DC, Philly and NYC, but a cold front will drop through the region later in the day and it’ll turn noticeably colder on Wednesday night following the passage of the front.
The upper air wind flow later this week will generally be from west-to-east in the Mid-Atlantic region and this may make it difficult for the next cold air mass to penetrate too far to the south while it does make it down the spine of the Appalachians at low-levels of the atmosphere (i.e., “cold air damming” and potentially setting the stage for an icing event). Map courtesy NOAA, tropicaltidbits.com
It is at this time that the weather pattern gets more active in the Mid-Atlantic region and also more interesting with a difficult forecast on our hands. Strong high pressure will build across the Great Lakes on Wednesday night and Thursday and it’ll have an extension into the southeastern part of Canada. From this position, low-level cold, dense air will be able to make its way down the spine of the Appalachian Mountains in an atmospheric set-up known as “cold air damming”. At the same time, the influx of the cold air in the upper part of the atmosphere will have some trouble advancing to the south as the upper-air wind flow from southwest-to-northeast will tend to inhibit its push in that direction. “Cold air damming” this time of year can lead to icing issues if indeed there is the combination of low-level cold air and slightly warmer (i.e., slightly above freezing) layers in the upper part of the atmosphere. Another feature of “cold air damming” is the formation of low pressure off the Mid-Atlantic coastline and this is a possibility later Thursday into Thursday night.
12Z GFS forecast map of total accumulated freezing rain from this late week event in the Mid-Atlantic region. Map courtesy NOAA, Pivotal Weather
The best chance for icing (sleet and/or freezing rain) on Thursday appears to be from the northern half of the DC metro region to central Pennsylvania. Farther to the north, in places like northern Pennsylvania and interior southeastern New York, it may be cold enough at all levels of the atmosphere for accumulating snow to fall – at least at the onset of the late week storm system.
There is still a few days to go before this potential wintry weather event and fine-tuning on the details is always necessary when dealing with a wide variety of conditions over a small area raging plain rain-to-freezing rain-to-sleet-to-snow…stay tuned.
One sign for additional cold air outbreaks later this month and during March is the teleconnection index known as the Eastern Pacific Oscillation (EPO). The forecast trend is to put the EPO into negative territory as we flip to March and for a sustained period of time which is more favorable for cold air outbreaks to push into the central and eastern US from northern Canada. Plot courtesy NOAA, Weather Bell Analytics
Looking ahead…winter is not going away
The cold air outbreak that arrives later in the week will not be the last for the eastern states as we head from the end of February into the month of March. Some of the signs that point to more winter weather during the month of March include an unfolding stratospheric warming event that was highlighted in our posting’s of last week and the continuing forecast trend of the Eastern Pacific Oscillation (EPO) teleconnection index into negative territory.
Looking ahead, many signs point to a continuation of winter conditions in the eastern states as we transition to the month of March. A very cold air mass is destined to arrive in the eastern states in about a week’s time to end the month of February on a very cold note. Map courtesy Canadian Met Centre, tropicaltidbits.com
Cold air masses that form over the northwestern part of Canada and Alaska have a much easier time of making their way into the eastern US if the EPO is in negative territory for a sustained period of time as indicated by some of the latest computer forecast models. When the EPO is in this favorable territory for cold air intrusions into the eastern US, there tends to be a ridge of high pressure over eastern Alaska, the Gulf of Alaska and far northwest Canada. This pattern tends to establish a flow of Arctic air from Alaska (and possibly even from Siberia across the pole) into the central and eastern portions of Canada and then ultimately into the central and eastern portions of the CONUS. In fact, there is a good chance that a very cold air mass can reach the eastern US by early next week and it could be preceded by some snow.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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