WEEKEND WEATHER FORECAST

Update Sat @ 6:05 PM — Some bright spots occurred today, but none of the sunshine I had though might been possible.

The front expected to move through our region a bit later, between 8-10 PM tonight with gusty winds and briefly heavy rain.

An overlap of high shear/high helicity is forecast by the HRRR in the blue boxed area around 9 PM. Fast moving, strong thunderstorms with high winds possible—

HRRR forecast 9 PM High shear/ high helicity. This area will move east/northeast. (Click on image for a larger view.)

Sunday’s forecast looks good.


Update Sat @ 9:43 AM — Most models this morning maintain the low cloud cover. I still think there’s a chance of sun breaking through in the early afternoon.

This morning’s models have some areas of high shear and high helicity about 6 PM near Philadelphia. Some severe storms could develop at that time—

HRRR forecast 6 PM Saturday. Blue boxed areas are areas forecast to have high helicity (contours) and high shear (shading). Severe thunderstorms area possible. (Click on image for a larger view.)

Wind gust forecasts have been reduced to about 40-45 mph instead of the 50 mph previously forecast.


Update Sat @ 8:22 AM — The new Canadian GEM model now predicts significant sunshine breaking through around 2 PM in areas from Norristown eastward. The cold front moves through 6-9 PM with showers and maybe some thunder. GUSTY WINDS this afternoon and with the frontal passage.


Update Fri @ 9:33 PM — Tonight’s early models have some changes: the heavy morning showers on Saturday, depicted in this afternoon’s HRRR rain graphic (below), now are forecast to move more north and west of the city. So it doesn’t look like the morning showers Saturday will be that heavy around the immediate PHL area.

Another change: the latest HIRESW-FV3 does have some bright spots and breaks of sunshine develop around noon and early afternoon. (mentioned below). If that occurs, expect the windy conditions to be somewhat more pronounced due to ” vertical mixing” of sun-warmed air with strong upper winds.


Initial Post Discussion—[post_published]

A warm front will move through the area Friday night into Saturday morning. Very mild air will move in behind the warm front. A very strong cold front moves through Saturday evening.

Saturday

Saturday’s forecast has changed somewhat since yesterday, especially with likely showers during the morning hours.

The warm front moves to our north about 6-8 AM. The latest HRRR shows some heavy shower activity about 6-9 AM in Philadelphia—

HRRR 1 hour precipitation rate 9 AM Saturday. Heavy rainfall forecast in some areas. (Click on image for a larger view.)

Most of the showers move to our northeast, but the HRRR and NAM-NEST are showing lingering widely scattered light showers/drizzle until late morning. (Earlier forecasts had the showers ending much earlier, then cloudy and windy.)

After the morning rain, most models keep us with low level clouds and very windy. I’ve seen situations where models incorrectly show little clearing following a warm front passage. So I while I would expect cloudy conditions, don’t be surprised if some sun breaks through during the afternoon.

It should be dry between noon and 6 PM.

High temperature 67.7º ± 2.3º (NBM Blue Bell)

It will become very WINDY, with most models having wind gusts of 40-50 mph, although the model blend (NBM) wind gusts are in the 35-40 mph range.

HRRR wind meteogram Blue Bell. High gusty winds forecast. (Click on image for a larger view.)

The front moves through between 7 PM and 9 PM Saturday evening with a quick burst of showers and high wind gusts.

Sunday

High pressure builds in for Sunday. Becoming mostly sunny and seasonably cold. Winds diminish. Breezy. High temperature 47.6º ± 1.1º (NBM Blue Bell)

Looking ahead… next week shows a large upper air ridge developing. Very mild weather likely.

Update Fri @ 9:05 AM — A shift in the model blend (NBM) towards the higher resolution models shows the warm front that moves through Friday night lingering through Saturday morning with fog and light drizzle. Drizzle ends during the morning. Winds pick up during the late morning. VERY WINDY. Most of the afternoon (and possibly early evening) rain-free. Highest temperatures in the late afternoon 68-70º.

Front moves through with showers, possible thunder, about 5-8 PM.

Sunday looks to be sunny and breezy.


Update Thu @ 10:25 PM —The weekend has come within the range of the high resolution models. Saturday is looking very cloudy with low clouds in the morning. The NAM-NEST has light sprinkles/drizzle in the early morning. Most models (but not all) have high temperatures 65°+- 2.5°.. Very windy, as discussed below. Rain showers seem to reduce in intensity with the front late afternoon/evening. Check for my regular weekend weather forecast tomorrow.


Update Thu @ 4:27 PM — The latest NAM-NEST wind meteogram for Saturday—

NAM-NEST meteogram (Blue Bell) Saturday Winds and Wind Gusts. 40-50+ mph! (Click on image for a larger view.)

It’s looking like most of the daytime hours will be dry with the actual cold front moving through about 6-8 PM.


Very mild temperatures still predicted for Saturday with possible recording breaking high temperatures in the upper 60s! Unfortunately, the models are also predicting cloudy conditions for much of the day.

The other big story may be the gusty winds that develop in the morning and continue through the evening. The GFS and NAM are predicting wind gusts in the 40-50 mph range for much of the day.
(The model blend (NBM) is only showing gusts to 35 mph.)

The latest models have the actual frontal passage about 6-7 PM (instead of the afternoon.) Rain and possibly some thunder will precede and accompany the cold front.

NBM12z cloud (black) and 1 hour accumulated rain (blue-green) forecast for 1 PM Saturday. The current NBM has rain overspreading Philadelphia 2-4 PM. (Click on image for a larger view.)