A warm front will move through the area Thursday night. Showers and some thunderstorms are possible late Thursday night or Friday morning before daybreak.
Very warm and humid weather on Friday is expected with high temps 83º-85º and dew points near or above 70º.
A strong cold front moves through Friday evening. Very high instability and a very moist atmosphere will fuel the development of some impressive, severe thunderstorms Friday evening. Very high precipitable water values (“PWAT”) of over 2.1 inches water will cause locally heavy rain over a short period of time. There’s enough available energy for high winds with these storms.
Some models have the storms shearing off to our west, while others have the line moving through the immediate PHL area Friday evening. Will need to keep an eye on this.
During the Covid-19 Pandemic shutdown, I had been doing daily forecasts. This blog has returned to its regular Weekend Weather Forecasts & Outlooks focus along with Significant Storm Forecasts
I hope you’ve found the daily forecasts over the past weeks useful and informative.
Tues 10 AM Update: This morning’s RAP (Rapid Refresh) model has thunderstorms breaking out 3-4 PM around Philadelphia and continuing on and off until 8-9 PM. Over past weeks, the morning RAP model has had a fairly good track record.
from earlier Tues morning:
Tues 8 AM Update: Last night’s models have backed away from the severe weather in the immediate PHL area. The severe parameters (Helicity, Vertical Shear) have reduced from yesterday’s model runs; the expected lack of sunshine will reduce the chance of severe weather in our immediate neck of the woods.
One can still expect showers and thunderstorms to develop as early as noon and continue into the afternoon. Some of the rainfall may still be locally heavy in spots. It may be very windy in some thunderstorms.
As mentioned yesterday, the heavier dynamics now appear to develop to our south and east.
Tuesday has been in the crosshairs for severe weather for several days. The bullseye for the severe weather had been the immediate Philadelphia area, but the latest models show that the most extreme aspects looks to occur to the south of us, near the Washington DC area.
That said, there are plenty of ingredients that are poised to come together in our area.
A warm front will pass through Tuesday morning, possibly causing showers and thunderstorms before daybreak with another possibility around noon. A cold front associated with a low pressure system moves through during the late afternoon and early evening hours.
Thunderstorms with heavy rain and high winds are possible both during the afternoon and early evening. Some of the severe weather parameters (helicity, vertical shear) are highly elevated giving us a risk of high winds and slight risk of tornados. Luckily, we may not have that much sunshine, limiting the available energy and reducing the potential for very extreme weather.
The models are still evolving and have changed their forecast considerably over the past 24 hours. The NWS does a great job with these events and it’s suggested to stay tuned to their forecasts.
This afternoon’s models have backed off on the extreme weather just a bit. Most of the severe activity will move in between 8-12 midnight. Accumulated precipitation values have come down a bit to 1-2 inches of rain with additional rain on Thursday afternoon and evening.
Shear, Helicity and Vertical Velocity values have reduced a bit from yesterday’s posted graphics with the heaviest activity now predicted to occur in the northern suburbs of Philadelphia, Berks, Lehigh and Bucks counties and into central/ northern NJ and New York City.
That said, these locations are hard [impossible] to pin down precisely in advance. There are differences in the models.
It’s a good thing I don’t usually “do thunderstorm forecasts”. This would have to become a full-time job!