11:00 AM | **Dreaded back door cold front brings dramatic changes in temperatures for Sunday…heavy rain event Sunday night/Monday with possible strong thunderstorms**
A major warm up in the DC, Philly, NYC corridor will continue into Saturday, but then temperatures will come crashing down on Sunday as a strong back door cold front slides down the Northeast US coastline from northeast-to-southwest. A more conventional west-to-east moving cold front will then produce a heavy rain event around here on Sunday night and Monday and strong thunderstorms can be mixed into the picture as it turns somewhat milder on Monday ahead of the cold front. In fact, the rain may be so heavy early Monday morning that it could have a negative impact on the AM commute up and down the DC-to-Philly-to-NYC corridor. Much colder-than-normal air will follow the passage of the west-to-east moving cold front for Monday night and Tuesday and highs may struggle to reach the 50 degree mark on Tuesday afternoon.
The dreaded back door cold front
Early in the weekend, very strong high pressure will be expanding from south-central Canada into southeastern Canada. This high pressure system is the anchor of a frigid air mass and there will be significant ice and snow from the Upper Midwest to New York/New England over the next couple of days. This very cold air mass will then begin to slide down the New England coastline later tomorrow from northeast-to-southwest following the passage of a “dreaded back door cold front”. Long-time residents of the Northeast US know very well of the weather phenomenon known as the “back door cold front” and how it has a tendency to take place pretty regularly this time of year. The conventional cold front in this part of the country moves in from the west or northwest whereas a "back door cold front" approaches from the northeast or east.
One of the main contributing factors to this atmospheric phenomenon in mid-April is the still very chilly waters of the nearby western Atlantic Ocean. A shift in wind direction from southwest to northeast – as is typically the case with the passage of a "back door cold front" – can quickly drop temperatures from the 70’s to the 30's in just a matter of hours. This is indeed a real possibility this weekend in places like New York City where temperatures on Saturday could reach the upper 70's and then be generally confined to the 30’s on Sunday. The much cooler air is likely to make it all the way down into the Philly metro region by early Sunday and then into the DC metro region later in the day. In fact, there can be a few hour period on Sunday morning in the DC metro region where temperatures range from near 50 degrees north of the District to near 70 degrees just south of there - eventually the much cooler air will overtake all areas.
Heavy rain event Sunday night/Monday
By Sunday night, a deep upper-level low will head into the eastern states and it will begin to take on a "negative" tilt with its trough axis becoming oriented from northwest-to-southeast and this will generate strong upward motion in the I-95 corridor. At the same time, a strong more conventional west-to-east moving cold front will begin to approach the region and this combination is likely to result in a heavy rain event for DC, Philly and NYC metro regions in the Sunday night/Monday morning time frame and there can be strong thunderstorms included with the rain event. In fact, some spots along the I-95 corridor could end up with more than two inches of rain by the time we reach mid-day on Monday. Temperatures just ahead of the conventional west-to-east moving cold front will turn milder for awhile on Monday after the drop in temperatures on Sunday due to the passage of the back door cold front.
The chill returns
Once the conventional cold front clears the area later Monday, much colder-than-normal air will pour in on strong northwest winds for Monday night and Tuesday and it looks like it’ll stay generally colder-than-normal right to the end of the month. The 06Z GEFS forecast maps of 850 mb temperature anomalies averaged over 5-day periods (days 5-9 above, days 10-14 below) show lots of “blue” (i.e., colder-than-normal) next week and beyond to the end of April and this will take place in much the same region as the first part of the month where colder-than-normal weather was experienced (i.e., much of the eastern two-thirds of the nation).
Meteorologist Paul Dorian
Extended morning video discussion on the wild swings coming over the next few days: