A complicated and powerful storm is targeting the northern Mid Atlantic today through early tomorrow morning with heavy rain, strong winds, and possibly a few severe thunderstorms.
The primary low pressure system is located just south of the central Great Lakes and will be moving towards southeastern Quebec, Canada by tomorrow afternoon. This storm is complicated due to the fact that three air masses will be interacting with each other for this storm. The first air mass is the cool, stable marine air mass that has been in place since yesterday morning. The second is a very warm, moisture loaded, unstable air mass that is driving north from the Southeast and Gulf Coast into the southern Mid Atlantic. The third is the Polar/Pacifica air mass that is driving through the Plains and Mississippi Valley this morning. All three of these air masses will clash over the northern Mid Atlantic, leading to what is called an occluded front where the stable cool, wet air mass is at the surface, the warm, unstable air mass is elevated, and the dry and cool Polar, Pacific air mass behind the occluded front. This type of environment leads to elevated thunderstorms that produce very heavy rainfall and powerful wind gusts.
The first batch of rainfall is currently approaching eastern Pennsylvania late this morning. Consider this rainfall as the preview and not the maine event as warm air drives over the cool marine air mass in place. The rain will be moderate to heavy at times on and off through the day as this rain approaches. Meanwhile, due to a high pressure system over the Canadian Maritimes, winds will continue to increase from the east and southeast through the day around 10 to 20 mph with gusts over 30 mph. Temperatures will hold in the 50’s for highs.
Tonight, the occluded front will approach and move from west to east with an area of intense heavy rainfall and embedded thunderstorms. This area of rain and embedded thunderstorms will produce high rainfall rates leading to urban and small stream flash flooding. In addition, winds from the mid levels will be mixed down in the embedded thunderstorms leading to powerful wind gusts over 50 mph. The worst conditions will be from 9 PM tonight through 6 AM tomorrow morning from west to east. Rainfall amounts will range from a half an inch over extreme southeastern New Jersey to over two inches over portions of northeastern Pennsylvania and northwestern New Jersey where orographic lifting will help to enhance rainfall rates. Sustained winds of 15 to 25 mph can be expected with gusts easily over 40 mph, over 50 mph in embedded thunderstorms. These conditions are dangerous and I strongly suggest staying in doors for this storm.
The good news is that this low pressure system will move quickly into Canada which will allow high pressure over the Southeastern United States to build into the region with clearing skies and decreasing winds. Under the influence of sinking air behind the storm, temperatures will warm into the 60’s throughout the region for highs tomorrow.
However, the pleasant weather conditions will not last long. A cold front over the Great Lakes will stall over the northern Mid Atlantic from Monday afternoon on through Wednesday morning with variable clouds, scattered showers, and temperatures near to slightly below normal in the upper 50’s to mid 60’s for highs and 40’s to lower 50’s for lows. The cold front will lift north as a warm front on Wednesday afternoon leading to warmer conditions with highs by the afternoon in the 70’s. However, a cold front from the west will approach by Wednesday evening with the potential for strong to severe thunderstorms.
High pressure will take hold for Thursday and Friday with clear skies, light winds, and temperatures near normal in the lower to mid 60’s for highs and mid 40’s to lower 50’s for lows. However, the pattern is set up to repeat itself for the weekend with yet another potential rain storm by Saturday night.
For details on your location, visit the NY NJ PA Weather Local Seven Day Forecast!