A dip in the jet stream, will usher in a cold front late Tuesday into Wednesday.  Tonight’s models are suggesting the possibility of some heavy rain and imbedded thunderstorms, some could be impressive.

While available energy (CAPE) is on the moderate to low side, other severe weather parameters such as helicity and vertical wind shear are expected to become highly elevated after 10 PM Tuesday evening.  The possibility of thunderstorms with high wind gusts exists.

Heavy rain Tuesday night will reduce to showers that may linger into Wednesday afternoon.

Stay tuned.

[su_note note_color=”#ffffff”]Updated Thu 03:23 PM — Today’s models keep the most intense thunderstorms far west of Philadelphia on Friday evening.  Some models showed that yesterday.

The models seem to show  weakening of the storms as they move into the immediate Philadelphia area later on Friday evening, after 10 PM.   I’ll keep an eye on it.

Substantially reduced as it gets here 2-3 hours later—

[/su_note]

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.

[su_note note_color=”#bceaed”] 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. [/su_note]

[su_note note_color=”#d9f2da”]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. [/su_note]

from earlier Tues morning:

[su_note note_color=”#d9f2da”]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. [/su_note]

from yesterday…

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.

The frontal passage and thunderstorms in Philadelphia expected today will be well-handled by the NWS.

So, what value-add can I offer this early in the day?

Reviewing the models from earlier this morning, the following characteristics and trends exist:

There’s a possibility of some earlier scattered showers and thunderstorms as early as 12-2PM.

Increasing  areal activity is expected between the hours of 4 PM and 8 PM.   A line of storms should develop by 5-6 PM and move through the Philadelphia area, according to the latest RAP and HRRR models.

The severe weather parameters (cape, helicity, shear, precipitable water) are all elevated, but not as elevated as seen a few weeks ago with the tornado development.

Some low pressure centers are expected to develop in this line of storms and additional activity may linger until after 8 PM.