Daily Archives: Sunday, November 29, 2020 10:02 pm

Severe Weather

WILD WEATHER MONDAY


My previous post talked about the tremendous energy expected to converge over our area on Monday as two jet streams phase.  Tonight’s models just becoming available support the possibility of severe weather Monday.

I had to dust off my summer model download scripts for this forecast, as the model parameters that are of interest are the summer severe thunderstorm variety.

The latest HRRR (High Resolution Rapid Refresh) shows highly elevated severe weather parameters, especially Wind Shear, Helicity and CAPE (convective available potential energy) for November.

Two time periods are of interest tomorrow—  From 9-11 AM, extremely elevated Helicity is forecast (black shading)  High winds are likely during the 9-11 AM time period.—

HRRR Helicity and Vorticity at 10 AM  (Click on image for a larger view.)

From 3-5 PM, highly elevated CAPE (for November) is forecast with the possibility of severe thunderstorms with hail —

CAPE and Hail forecast parameter  (Click on image for a larger view.)

Be sure to listen to the NWS for last minute warnings.

Philadelphia Weather Outlook

INTERESTING WEATHER PATTERN FOR PHILADELPHIA AREA

The weather has been mild and quiet recently.  However,  changes are expected over the next week as a highly amplified pattern develops. The trend is a change to much colder weather next week.

Tomorrow, Monday, will be a rainy, windy day.  Jet energy from both the northern jet and southern jet will phase and result in deep low pressure development over the Great Lakes.  Some of that energy will move down to cause GUSTY WINDS (up to 40 mph)  for us on Monday—

GEFS 300 mb (jet level) winds Monday showing jet streak energy from southern and northern streams  (Click on image for a larger view.)   ALSO NOTE THAT THE NEXT IMPULSE IS VISIBLE IN MONTANA

It will still be mild on Monday, but colder air moves in later Monday and Monday night.

Notice that the jet flow makes a loop over high pressure in the Mid-West and another high energy impulse is waiting in the wings for later in the week.

There’s much uncertainty about timing of this next impulse with how these things are going play out later in the week, but some models are showing snow for central and western Pennsylvania.

For us, it will be rainy, windy and cold Friday and unsettled and cold next weekend. NO SNOW for us at this time. Stay tuned.

GEFS Saturday 10 PM (Click on image for a larger view.)