A strong cold front will move through Thursday evening. Heavy thunderstorms, especially in the far northwest suburbs (Allentown) are possible from late this afternoon and especially between 8 and 11 PM Thursday evening. Winds will be gusty to 40 mph.
High pressure builds in behind the front for Friday. Friday will be sunny, windy and cool. High 73-75
A unusually strong upper air high pressure system will center itself over Alabama and Georgia this weekend. Around this upper air high pressure system, areas of disturbance, rotation, (“vorticity”) or eddy currents will rotate around this upper high, bringing us breaks in an otherwise fair weather pattern.
Saturday will be sunny and warm. High 88-90. 78-80. An area of vorticity will approach Saturday night. Showers are possible, but the upper air confluence of flow will cause much of the precipitation to fall apart as it gets to our immediate area.
Sunday: Skies will clear by Sunday morning. Sunday will be sunny and very warm with highs 88-90. Clouds increase mid-afternoon as another, stronger area of vorticity and a weak cold front approaches Sunday late afternoon. There’s a chance of showers late afternoon Sunday, especially west of the Philadelphia area. Some showers will make it into Philadelphia by Sunday night.
Currently, the greatest uncertainty in this forecast is the extent and timing of the showers Sunday afternoon and evening.
Monday: The front moves off the coast and skies clear during the morning, later at the shore. Delayed clearing possible southern shore areas. Sunny. Light winds. High 83-85.
Fri 8 am. Last night’s models have increased the chance of thundershowers early this evening and have decreased the high temperatures expected for Sunday into the low 80s.
The forecast for the weekend, especially Sunday, has been anything but consistent and similar to last week, I’m glad I waited until today to take a stab at the weekend outlook.
A cold front will move through Friday late afternoon/evening. Some showers and thunderstorms are possible with the frontal passage.
High pressure will build in for Saturday. Saturday looks to be a beautiful day with high temperatures near 76.
The front that moved through Friday moves back as a warm front before daybreak Sunday. Several times during the week, it appeared that showers would be likely during the morning Sunday.
However, the latest models have the wind shift occurring without any showers.
Sunday is forecast to be fairly hot, with the NAM forecasting 90 degrees and the GFS and NBM 86. The EKDMOS has a temperature range of 88-91. Dew points move to the mid-60s and possibly approach the uncomfortable 70 degree range by Sunday evening. Sunday will feature a mix of clouds and hazy sunshine.
The FV3-GFS shows some thundershowers late afternoon Sunday; the NAM doesn’t at this time.
Tonight’s NAM has joined the FV3-GFS in predicting moderate rain for Sunday morning. See forecast below for context.
Significant differences exist between the models for this weekend’s forecast.
(Not surprising, since the forecast– predicted high temperatures (86) and the predicted thunderstorms for today, Thursday, weren’t too accurate – only the GFS had the high temperature near 86 and the higher resolution models had the thunderstorms suppressed to our south today and predicted the 80-83 we actually saw.)
Back to the weekend-
Updated with GFS: For Saturday, cloudy but dry (perhaps some light drizzle in the morning) with an easterly, cooler wind.
For Sunday, large differences between the models. The latest GFS, NBM, and NAM suppress most of the showers and rain to our south. The still experimental FV3-GFS has heavy rain on Sunday. I’ve liked the FV3-GFS over the winter, but it’s currently an outlier.
This post will be a ongoing collection of observations and thoughts about the upcoming weekend weather.
Wed PM – Tonight’s NAM shows no thunderstorms for Thursday and highs near 82. Tonight’s NAM has the rain tapering early Sunday morning.
Wed AM – Very warm on Thursday. Looking towards the weekend, it looks like an easterly flow will keep temperatures not as warm as previously expected. It appears that most of the periods of rain will occur during the nighttime hours, although it may linger into Sunday morning.
Tues PM – Tonight’s NAM shows a change of forecast -The warm front that moves through Wednesday returns as a backdoor cold front Thursday night. Friday not as warm as previously thought.
Tues AM -A warm front will slowly move north of our area on Wednesday, opening up a flow of moist, warm air from the southwest. Weak impulses embedded in this southwesterly flow will give us a chance of showers Thursday through Sunday morning. The main low pressure system is expected to move over our area on Saturday night.
So, there’s a chance of showers almost every day, according to the EKDMOS. We are getting into the season where the normal “background probability” is about 20-25%, but this is looking higher.
Temperatures may reach into the mid to upper 80s on Thursday. Reviewing the FV3-GFS, we may be lucky and the showers occur mostly during the evening and night time hours.