Monthly Archives: March 2021

Philadelphia Weather Outlook

WEEKEND WEATHER PREVIEW & DAYLIGHT SAVING TIME

A cold front will move through around daybreak Friday. Light rain is expected with the frontal passage (less than 0.20 inches).

Skies are expected to clear after the frontal passage and should remain sunny and cooler Friday.  A secondary cold front moves through early Saturday. 

The weekend should be mostly sunny, windy and cooler although some cloudiness is possible during part of the day Sunday as a weak upper air disturbance moves through.  High 48-50º Saturday and 53-56º Sunday.

The fairly dry weather pattern is expected to continue.

Of course, Sunday morning is the beginning of Daylight Saving Time.  I love the extra daylight at the end of the day, but for “weather people”, Daylight Saving Time means the models come out an hour later. (Weather models are run at UTC – Coordinated Universal Time).   For “weather people” on  Eastern Daylight Time, the models really come out a little too late!  I’ve written extensively about this in past years—

Little Known Facts about Daylight Saving Time and TV Weather Forecasts

Daylight Saving Time and Weather Models

“Check Back at 11” TV weather and Daylight Saving Time

The new GFS version 16 launches on March 17th. Due to the increased complexity of the new model, (there are new parameters and it’s computed at many additional levels -layers of the atmosphere), the GFS v16  will take an additional 8 minutes to compute its forecasts.  Several models that depend upon the GFS for their “initial conditions” will also run later.   

That means the GFS model’s next day forecast (for the next 24 hours) won’t be available until 11:45-11:50 PM EDT, way past the 11 o’clock TV news and past bedtime for most of us! 

 

Philadelphia Weather Outlook

WEEK WEATHER OUTLOOK

Outlook Updated Tue 5:58 PM — Current models do have the cold front pushing precipitation out of our area for Saturday.  (There had been the possibility that the front would hang up right over us, keeping things cloudy and wet.)  Sunday also looks good right now.   Cooler, more seasonable temperatures for both Saturday and Sunday.

from Sunday….

As mentioned in my previous post, a transition in our area from a jet stream trough to a jet stream ridge (warmer weather) will occur during this week.

GEFS Model 300 mb wind forecast for Wednesday morning.  The phasing of jet streaks (1)  will cause a low pressure system to develop in the Midwest.  The eventual track will affect next weekend’s weather. (Click on image for a larger view.)

 

This ridge will allow temperatures to reach into at least the 60s (and possibly near 70º) for the Philadelphia area by Wednesday. 

The current Model Blend forecast high temps (Blue Bell -Wings Field, add about 1 to 2º for Philadelphia.)


Wednesday — 62º
Thursday — 66º
Friday — 66º 

 The uncertainty with these temps is high.   The  Model Blend standard deviation is 3º-5º.  In these situations, the NBM can be on the low side.

For Next Weekend:  Also uncertain is the eventual development and track of a deep low pressure system in center of the country from confluence of the southern and northern jet streams.   We may enter a prolonged period of rain that goes into the weekend, OR we may have a cold front push far enough south to suppress the moisture to our south and give us a dry, cooler, and windy weekend.