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Friday Forecast Update

Update Fri 03/24 @ 10:38 AM — The showers associated with the cold front have lingered further north than forecast last night. They will likely linger into the afternoon (2-3 PM) in contrast to the 11 AM time frame forecast yesterday. Cloudiness will remain through the afternoon.

This morning’s 12z HIRESW shows lingering very light showers possible at 2 PM. This moves south of the city by 3 PM. (Click on image for a larger view.)

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.)