Category Archives: Philadelphia Weather Outlook


#weather #paweather #wx #pawx #philadelphia

Thu 9:44 PM Regarding tonight’s storms Folks, I was asleep at the wheel regarding tonight’s substantial thunderstorms. I was focused on Friday and I hadn’t even looked at tonight’s forecast in detail.

There goes my second career!

Anyhow, now that I’ve looked at the models from this afternoon again, it should have been pretty clear that thunderstorms were likely, even some heavy storms. Helicity values were very high (~ 700 m2/s2) and shear values were very high (approached 40).

(During last summer’s dry period, we didn’t even come close to values like this to get a thunderstorm.)

Strangely, the NBM gave a only 3% chance of thunderstorms tonight, probably because CAPE values were only in the 300 J/Kg range.

It shows you can get some strong storms with very little CAPE, if you have the other ingredients.

Friday Forecast Update

Update Thu 03/23 @ 5:24 PM — Today’s models continue with the forecast of a cold front dropping through our area Thursday night and stalling as it moves south of Philadelphia. Waves of low pressure will ride along this front on Friday. It will be quite chilly on Friday, as temperatures will be in the mid to upper 40s.

The rain, for much of the day Friday, will affect mostly southern areas, although during the morning (before 11 AM or so) , some light rain may spill northward as the disturbance moves by to the east.

The latest NAM-NEST below captures the forecast scenario for Friday and is very much in-line with yesterday’s HRDPS and the latest NBM—

Today’s 18z NAM-NEST simulated radar forecast at 11 AM shows where most of the rain will be on Friday, although it will be a bit further north during the mid-morning hours. (Click on image for a larger view.)

The front will move back as a warm front on Saturday before another cold front moves through.

The stream of moisture will continue through parts of Saturday. The overall flow is captured by this water vapor image—

Today’s water vapor image, showing the flow of moisture into our area through Saturday.

A mix of sun, clouds and showers expected on Saturday. Details tomorrow.

Thursday – Friday Forecast

Update Wed 03/22 @ 7:59 PM — The showers mentioned last night showed on radar at 8AM Wednesday but evaporated before reaching the ground.

For Thursday, a mid-level disturbance will bring some rain Thursday morning but there should be some partial clearing Thursday afternoon, after 1 PM. Temperatures may reach 70º (Canadian Model) or 68º (NBM)

As mentioned last night, cold front moves through Thursday night with more showers. The front slows down and stalls just to our south. Rain will move along the front.

Depending upon the position of the front, Friday may just be cloudy, or may have considerable shower activity. The Canadian high resolution model (HRDPS) has the northern extent of the rain just reaching areas of Montgomery county—

Canadian HRDPS Precipitation Rate forecast at 1 PM Friday. (Click on image for a larger view.)

Too soon to be sure about the location of the showers on Friday.

Update Tue 3/21 11:24 PM —Tonight’s high resolution models show some showers early Wednesday morning with the warm front.

Previously Posted Tue 9:00 PM —

The incredible weather we’ve had for the past two days will decline from perfection from Wednesday through Saturday.

A warm front is approaching from the southwest as a major storm sets up in the middle of the country.

Wednesday will feature a mix of clouds and sun as a warm front moves through. Most of the cloudiness will lift in the afternoon, after the warm front passes to our north. Highs will again reach the low 60s.

Following the warm front passage Wednesday, things become a bit more uncertain, as a backdoor cold front will slowly move through late on Thursday night with light rain at times during the daytime.

On Thursday, despite the rain and considerable cloudiness, temperatures will approach 70°.

A back door cold front moves through Thursday night—

GFS shows temperatures (shading) and the winds shifting from southwesterly to northwesterly at midnight Thursday into Friday morning. (Click on image for a larger view.)

This front will set up somewhere in our region, slowly drifting southward as waves of low pressure move through our area on Friday—

GFS showing rain moving in during the day Friday Notice the white box area (wind direction change) is down past southern Delaware. (Click on image for a larger view.)

Saturday, another system in the Great Lakes will push a cold front through. More showers and windy conditions.

GFS Saturday 2 AM (Click on image for a larger view.)


#weather #paweather #wx #pawx #philadelphia

Update Mon 03/20 @ 9:42 AM — Spring begins at 5:24 EDT today and we’ll be seeing milder temperatures (actually, much milder temperatures) beginning Tuesday.

With all the talk on the radio about how warm it will be later this week, there’s not as much being said about the expected significant increase in clouds and likelihood of rain, perhaps as early as Thursday.

Currently, most models are showing rain moving in during the day Thursday with possible periods of moderate rain Friday and especially Saturday.

Today’s 06z NAEFS – There’s been good run to run consistency with this ensemble forecast for Friday and Saturday. The ECMWF and GFS operational models also show this multi-centered series of low pressure systems moving into our area. (Click on image for a larger view.)

Previously Posted Sun 5:03 PM —

A quiet first part of the week is expected, as high pressure that brought us the cold weather on Sunday moderates Monday through early Wednesday. Fair skies with moderating temperatures Monday through much of Wednesday.

Here’s the current forecast (SREF) for Tuesday evening—

SREF forecast for Tuesday evening. High pressure over the east coast will move out to sea. A cold front with some moisture (1) will bring some light showers here late Wednesday. A series of disturbances (2) on the west coast will eventually move eastward. Friday and next Saturday look to be wet at this time. (Click on image for a larger view.)