9:43 AM

A strong upper low stationed over the central Great Lakes is driving several strong disturbances and a slow moving cold front towards the forecast area today.  The large scale trough combined with the strong upper ridge over the western Atlantic is supporting a persistent southwesterly jet stream from 850 MB to 250 MB , which is drawing deep tropical moisture into the forecast area.  At the surface, winds are from the south and southeast around 5 to 15 mph and humidity is high with relative humidity over 75% to close to 95% throughout the forecast area.  In other words, it is warm and humid this morning.

This afternoon, the cold front which is currently still over the Ohio Valley, will continue to slowly drift to the west.  Disturbances associated with the upper low will move along and ahead of the cold front, which will help to destabilize the moisture rich atmosphere over the region.  As a result, strong to severe thunderstorms will rapidly develop this afternoon.  The wind direction throughout the atmosphere indicates that there is little in the way of directional vertical wind shear throughout the mid and upper levels, however there is some slight direction wind shear between the surface and mid levels.  As a result, there is a threat of super cell thunderstorms to develop especially over the Delaware River Valley this afternoon.  However, the main threat with these thunderstorms today and this evening will be the heavy rainfall, strong wind gusts, and some large hail.  The saturated atmosphere will supply the thunderstorms will plenty of fuel to remain strong for several hours, and the southwesterly winds at the mid and upper levels will mean thunderstorms will be slow to move east, into the Atlantic and may train over the forecast area for several hours as well.  This is why a flash flood watch has been issued for many locations in the forecast area this morning, specifically the Delaware River Valley, the New York City metro, the southern Hudson Valley, and Connecticut.  Rainfall amounts from these thunderstorms will produce rainfall amounts exceeding an inch of rain in many locations, and possibly exceeding 2 inches in isolated locations.

The thunderstorms will develop as individual super cells initially over eastern Pennsylvania, but will eventually form into a solid line of strong to severe thunderstorms that will march slowly to the east.  These thunderstorms will have the potential for strong wind gusts over 55 mph, heavy downpours, frequent lightning, large hail, and an isolated yet weak tornado.  Tornado threat is very low though, but wind shear must be acknowledge.

The rest of the week is going to sound like a broken record.  The cold front never really gets to the coast this evening and will basically weaken into a stationary boundary, wavering over eastern Pennsylvania and western New Jersey through the week.  The long wave trough axis at 500 MB will remain well to the west, which means the forecast area will remain in a deep southwesterly jet stream through all of next week.  So while plenty of low and mid level moisture will continue to move into the region along with various upper and mid level disturbances, the upper level winds will inhibit cold front from move at any great speed to the east.  Therefore, by the time the cold front makes it to the coast, the frontal boundary is barely a wind shift line at best with little change in the air mass behind it.  As a result, the forecast area can expect similar conditions to what is being experienced today through all of this week.  For those that like warm, humid days.  Well, this week is for you!