NY NJ PA Weather Forecasts

Strong to severe thunderstorms expected through the day

7:24 AM

Overcast to broken clouds dominate the skies as widely scattered showers and weak thunderstorms develop through out northeastern Pennsylvania this morning.  A warm front is currently driving towards the forecast area this morning and will move through the region by early this afternoon.  Behind this warm front; warm, moist, unstable air can be found, which will support the development of strong to a few isolated severe thunderstorms, especially over northeastern Pennsylvania, northern New Jersey, much of Southeastern New York, and Connecticut.  While I don’t expect much of an increase in high temperatures, humidity will significantly increase which will support an environment favorable for heavy downpours.

Of course, there is another important factor to consider this afternoon and for that, we look at this morning’s water vapor satellite.  This morning, an upper low is forming and dropping south through the Great Lakes and towards the forecast area.  This same upper low will drive a cold front through the forecast area this evening, which will produce lifting throughout the region.  However, I want everyone to take note of the area I circled in yellow.  This area is dry, cool air at 500 MB.  When this cool, dry upper level air interacts with the warm, moist air moving into the surface this afternoon, the atmosphere will rapidly destabilize.  The cold air aloft will support an environment for large hail to form along with strong wind gusts.  The good news is that I think the threat for severe weather will be limited and will be highly dependent on the amount of sun shine that can break out this afternoon ahead of these thunderstorms.  Wind shear is not all that impressive, so I don’t expect any super-cell thunderstorms, and besides the cold air aloft, the set up for severe thunderstorms is not as impressive as other events this past summer.  However, the threat is still there and will have to be monitored.

The most significant threat from the thunderstorms this afternoon will be very heavy downpours, large hail, wind gusts over 55 mph, and frequent lightning.  The thunderstorms will rapidly develop and will have the most significant, wide spread impact this afternoon after 2 PM.  However, as we can see this morning over northeastern Pennsylvania, the threat for showers and thunderstorms will be present through the entire day.

The trough will begin to weaken tonight into tomorrow morning as the strong upper low lifts north.  This change in the structure of the upper level trough will eventually lead to a shift in the trough axis further to the west.  However, before that happens, another round of disturbances will impact the region.

The disturbance on Friday will be generally weak with widely scattered showers and thunderstorms, especially in the afternoon.  The lifting for the thunderstorms at the surface will be a weak cold front, which will lose support as it moves through the forecast area.  By the time the boundary exits New Jersey, only a slight wind shift can be expected with little change in the air mass.

A much strong disturbance will move through the Mid Atlantic on Saturday, which will spawn a developing coastal low on Saturday.  This pattern appears to be more fall-like than a typical pattern in July.  The low pressure system will intensify over the southern Mid Atlantic and will bring a period of moderate to heavy rainfall in the afternoon on Saturday.

As the low pressure exits on Sunday morning, high pressure will slowly build into the region from the west.  High pressure will provide clear skies and dry conditions Sunday afternoon through early Monday afternoon.

A new pattern will take hold by late Monday afternoon and will continue to impact the Mid Atlantic through next Wednesday.  Surface high pressure will reposition off the Atlantic coast and support southwesterly winds over the forecast area.  Meanwhile, the trough orientation will have the axis of the trough positioned well to the west of the forecast area.  What this means is that region will be under the influence of a warmer, more humid pattern through this period.  As weak disturbances moving east and northeast from the trough interact with the warm, moist air mass in place; scattered showers and thunderstorms will develop and impact the region.  At the surface, cold fronts will approach and then stall to the west of the forecast area, much like what was seen in mid May.  The cold front will become focal points for showers and thunderstorm development and may lead to a pattern will flash flooding may be a concern.

So the pattern does shift to a slightly warm regime, however the wet and active conditions remain with more humidity in the air mass to contend with.

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