Category Archives: Philadelphia Weather Outlook

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia

Friday – Saturday Update

Update Fri 03/31 @ 9:13 AM — The cloudiness is moving in as expected and the rest of Friday will be cloudy. No rain expected in our area until around or after midnight.

For Saturday— rain in the morning with a sharp clearing line moving through from west to east about 1-2 PM. It now appears that the second line of showers moving through about 5:30 – 8 PM will have the possibility of strong (not severe) thunderstorms, especially from Philadelphia and eastward into NJ.

I’ll update this evening with my regular Weekend Weather Forecast.

Friday – Saturday Update

Update Thu 03/30 @ 7:34 PM — A major low pressure system approaches and moves through the Great Lakes and Canada. Some changes in the forecast. Friday may have some early sun, but thickening cloud cover by late morning and the rest of the day. Temperatures will actually warm as the day progresses with highest temperatures towards evening.

Most models have the rain now starting somewhat earlier on Friday than previously forecast and have the rain move in about 7-10 PM, but the NAM and NAM-NEST have the showers moving in during the mid afternoon. These models appear to be outliers right now.

Heavier rain on Saturday morning still appears to abruptly end about 1-2 PM with the sun breaking out. (The ECMWF keeps shower around; I’m not going with that.) Some additional showers expected with the actual cold front moving through about 5-8 PM Saturday. It will be VERY WINDY on Saturday and high temperatures will be in the low 70s.

Today’s 18z GFS shows an abrupt back edge of the rain at 1 PM Saturday. (Simulated radar- clouds) (Click on image for a larger view.)

Thursday- Forecast Saturday Outlook

Update Wed 03/29 @ 8:42 PM — A cold front comes through tonight. Thursday will be sunny but chilly.

Friday: A major low pressure system approaches and moves through the Great Lakes and Canada. Increasing clouds on Friday. Rain begins around midnight.

Saturday: Rain in the morning. Rapid clearing about 1 PM. Very mild but extremely WINDY. High 72-75º. Another line of showers may move through about 6 PM Saturday evening with a sharp cold front.

NBM wind meteogram for Blue Bell PA. Note 45-50+ mph gusts on Saturday. (Click on image for a larger view.)
Wednesday Forecast

Update Tue 03/28 @ 7:30 PM — High pressure builds in for mostly sunny skies on Wednesday. Some cloudiness mid to late afternoon ahead of a weak cold front and moisture aloft approaches. Highs mid to upper 50s.

Showers with the cold front are forecast to stay to our north Wednesday night.

Thursday looks a bit cool again.

A warm front moves through Friday. Just clouds expected with the warm front. Rain arrives late afternoon Friday or Friday evening. The rain may depart early Saturday afternoon (GFS) or linger longer (ECMWF).

Tuesday Forecast

Update Mon 3/27 11:28 PM — Tonight’s high resolution models show some light showers possible Tuesday morning

Update Mon 03/27 @ 8:20 PM — The showers moved in about 3 PM and the heavier rain moved in about 5 PM.

A front moved through today and cooler air on northwest winds will bring temperatures down the lower 50s on Tuesday. A few upper air disturbances will also bring considerable periods of cloudiness.

Dry conditions expected through sometime on Friday.

Update Mon 03/27 @ 9:59 AM — Last night’s models suggest the rain moves in later today, closer to 5 PM closer to 4-5 PM.

Today’s 12z HRRR Precipitation Rate at 4 PM. (Click on image for a larger view.)

A series of low pressure systems will affect our weather over this coming week.

Rain from the first system moves in between 2 and 5 PM Monday. The GFS and RAP hold off the rain until after 5, but the majority of the high resolution models bring the rain in earlier, about 2 PM. (Still earlier in western areas)

Today’s 18z GEFS forecast for Monday afternoon showing this week’s systems. (Click on image for a larger view.)

Another system (2) looks to be to our south on Tuesday. A weak cold front (3) moves through late Wednesday. By Friday afternoon, a large system (4) may affect us through Saturday.

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia

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.)