This morning, a strong Sub Tropical disturbance is driving out of the Mississippi Valley and moving towards the Tennessee Valley. This disturbance will eventually reach the southern Mid Atlantic coast by tomorrow morning to bring portions of the Philadelphia metropolitan area a mix of snow, sleet, and rain.
Currently, the disturbance is pulling up moisture from the Gulf of Mexico. The lifting associated with this disturbance is producing severe thunderstorms and heavy precipitation over the Southeast. The Sub Tropical disturbance will be forced to move west to east as a strong Polar trough over the eastern Great Lakes and Northeast will support suppression of the exiting disturbance on Friday morning. This is why the moisture with the developingcoastal low will not make much of a push north tomorrow morning.
The current thoughts with this storm is that the precipitation will be on relatively light as the best dynamics remain over the New Jersey coastal waters. The snow will have a high water content, making accumulation difficult in the best conditions and a mixing of sleet and rain is likely over much of the Philadelphia metropolitan area. Scattered snow showers can be expected over the southern New York City metropolitan area including Long Island but no significant accumulation is expected. Locations over extreme southeastern and southern New Jersey will remain too warm to support frozen precipitation and only rain is expected.
The area of concern likes from central New Jersey through southeastern Pennsylvania including all of Philadelphia. While I do not expect heavy precipitation from this rapidly exiting area of low pressure, the winter mix of snow, sleet, and rain may cause driving issues for tomorrow morning’s rush hour with accumulations up to 2 inches possible from Morris and northern Monmouth Counties of New Jersey through Lancaster County of Pennsylvania. Precipitation will start tonight and continue on through early Friday afternoon.
I will be keeping an eye on this storm through the day and tonight. There is a very slight chance that heavier precipitation will be able to impact central and southern New Jersey than currently expected if the coastal boundary layer enhances the development of the coastal low off the Delaware Coast on Friday morning. If that should happen, then some mesoscale banding would be possible from Monmouth County down through Cape May County of New Jersey before an exit into the Atlantic. I don’t expect this to happen give the progressive nature of the 500 MB pattern, but it is a threat I will keep an eye on.
Otherwise, high pressure will build into the region on Friday night with clear and comfortable conditions through the weekend. A strong cold front will approach on Monday with periods of heavy rain through Monday morning and into the early afternoon hours. Temperatures will warm into the 40’s and possibly lower 50’s on Monday morning ahead of the cold front and then fall through the 40’s, 30’s and into the 20’s as the cold front exits on Monday evening. A turn to colder conditions can be expected on Tuesday and Wednesday as a strong Polar high pressure system takes hold.
A significant shift in the pattern back to a cold and potentially active period of winter weather will begin to unfold next week, leading to a gradual decline in high temperatures each day.
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