Posted Sunday 05/18/25 @ 9:21 AM — A beautiful day ahead with temperatures in the low to mid 70s, sunny skies and low humidity.
I’m keeping an eye on the upcoming weekend and the Memorial Day Weekend. Here’s the current water vapor satellite with radar and select RAP model parameters superimposed—
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. Flow from the southwest will affect us by late Tuesday. (Click on image for a larger view.)
An unsettled period, late Tuesday night through Thursday with rain at times. Depending upon the exit of another cut off upper level low, things should improve by the Memorial Day Weekend, however, it’s looking rather chilly for May.
I also wanted to post the MRMS rainfall total for the heavy rains received this past Friday—
MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch) (Click on image for a larger view.)
Saturday Update
Posted Saturday 05/17/25 @ 9:41 AM — The showers that developed (only forecast by some of last night’s 00z models) with the cold front this morning are moving through.
Current Radar with satellite water vapor and RAP model 300 mb vertical velocity pressure (omega) superimposed. (Click on image for a larger view.)
Sunshine should break out shortly. I wish the forecast for the rest of Saturday was clear cut, but it’s not. Several models have some scattered showers and thundershowers mid or later this afternoon. The latest HRRR which just became available keeps any scattered pop showers far west of our area. The Canadian HRDPS, which was correct about these showers this morning, still forecasts scattered light showers as late as 7 PM. We’ll have to see.
Posted Saturday 05/17/25 @7:35AM — I was off-duty last night but the models showed some light showers with this morning’s cold front.
Low pressure in Canada will move east and will drag a cold front across the area late Saturday morning. High pressure builds in for Sunday.
Saturday Forecast
Cloudy early morning. Clouds break for sun about 10 AM to noon. Somewhat breezy.
NBM high temperatures: Blue Bell, PA 83º Philadelphia, PA 86º
Sunday Forecast
Sunny and somewhat windy. Cooler.
NBM high temperatures: Blue Bell, PA 74º Philadelphia, PA 76º Uncertainty (based on standard deviation): above average
Posted Friday 05/16/25 @ 4:38 PM — The first short wave moved through around noon. It kept together better than I had forecast. A second short wave will bring showers and thunderstorms here, also a bit later than had been earlier forecast.
Here’s the current radar at 4:50 PM—
Radar with superimposed RAP model Omega (Click on image for a larger view.)
The HRRR and NAM-NEST have these storms dissipating before getting here between 8 and 9 PM. The RRFS and Canadian HRDPS have the storms moving into our area. I’m leaning towards the RRFS.
Posted Friday 05/16/25 @ 11:45 AM — There’s strong upper level support for the storms currently in western sections, but lower level support is lacking as it moves eastward at 11:44 AM. Let’s see which will prevails.
Radar with upper level RAP model Omega contours at about 11:44 AM (Click on image for a larger view.)
The models are showing less distinction between the original two short waves, now predicting showers and thunderstorms through the afternoon and early evening hours.
Posted Friday 05/16/25 @ 9:06 AM — A quick update. Latest radar shows a bow echo associated with the first of two short waves that will move across our area today.
The current area of fast moving heavy rain rain/ strong storms is expected to weaken as it moves into Philadelphia later this morning. Some rain still possible with this batch. Current RAP model shows moderate downward motion ahead of this impulse consistent with some weakening.
Current composite radar at 9 AM with superimposed RAP model 700 wind streams and low level Omega. Omega is negative in our area, indicating weakening. (Click on image for a larger view.)
Another impulse expected later this afternoon (2-6 PM) will be fueled by higher CAPE values and higher vertical wind shear. Some stronger storms expected with this second short wave. I’ll update around noon with newer models.
Revised ForecastPosted Thursday 05/15/25 @ 7:40 PM — After reviewing the afternoon (18z) models which became available after my previous posting, I have to revise my forecast.
It appears that there will be two waves of energy that pass through on Friday. The first, in the late morning, will be strong in far western areas, but several models have this rapidly diminishing in intensity as it encounters a weak mid-level ridge over Philadelphia.
A second impulse moves through between 2 and 5 PM, as noted below, which appears to have more mid-level support, causing some very strong storms as it moves into NJ. We’ll see how it all plays out. I’ll update tomorrow morning.
Posted Thursday 05/15/25 @ 5:15 PM — A potent disturbance will move through during Friday afternoon. Previously expected around noon, the latest models have it moving through about 2-5 PM, earlier to our far west.
The upper air will support strengthening as it approaches, but it’s forecast to hit a weak mid-level ridge right over Philadelphia. Some models (HRRR) have it weakening and moving to our north and south over this ridge. The latest RRFS (experimental) maintains some of its strength and has it further intensify as it makes it across the river into NJ.
So this disturbance (called a “short wave”) is not looking as intense as it was yesterday, but some of the thunderheads may reach 50,000 feet according to the RRFS with fast onset heavy rains and winds.
RRFS 700 mb (10,000 feet) level short wave and Relative Humidity (shading) at 10,000 feet. Not shown are CAPE values which are in the 1000-1500 joule level and areas of vertical shear which exceed 25 1/sec. All the ingredients for storm formation. (Click on image for a larger view.)
The weather clears for Saturday, but a few widely scattered late day thunderstorms still possible.
Thu 5:11 PM —Forecast Review — We had the sun break out about mid afternoon, as forecast. Some areas, especially in New Jersey have been seeing some showers and low level thunderstorms.
We’ve had quite a bit of rain over the past three days. Here’s a final summary, based on the MRMS—
MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED over the past 72 hours. . Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch) (Click on image for a larger view.)
Thursday through Friday
Posted Wednesday 05/14/25 @ 5:28 PM —Following some scattered showers Thursday morning, many of us may finally see some sun Thursday by mid afternoon. Unfortunately the upper air will be cold and thermal instability will lead to scattered showers and thundershowers between 2 and 6 PM. A mix of clouds. sun and scattered storms sums it up for the afternoon.
Friday, a strong impulse rotating around the upper low near the Great Lakes will result in potentially some strong fast moving storms here around noon. Here’s the RRFS, which suggests a bow-echo formation around noon—
12z experimental RRFS simulated radar forecast for noon Friday.
The potential for damaging winds Friday with this impulse needs to be watched.
Wed 5:20 PM —Forecast Review —The experimental RRFS did better than the HRRR today regarding its forecast for lingering moisture and rain around Philadelphia this afternoon.
Posted Wednesday 05/14/25 @ 12:14 PM — Opted against going to the afternoon Phillies game. The morning models support a dry slot developing, and current radar/water vapor imagery shows dry slot advancing northward—
Satellite Water Vapor with superimposed composite radar at noon. (Click on image for a larger view.)
The hold-out for improving conditions is the experimental RRFS. It still shows some showers during the afternoon game. (Perhaps we’ll see why it’s still ‘experimental.)
14z experimental RRFS simulated radar at 2 PM. Could this be right?? (Click on image for a larger view.)
What about the Phillies Games today?
Posted Wednesday 05/14/25 @ 9:10 AM —It does look like there will be a relative ‘dry slot’ develop beginning about 2-3 PM today in the city. The latest HRRR (11z) shows rain exiting to the northwest.
Here’s the simulated radar forecast for 1 PM. There may be some showers at the scheduled game start—
11z HRRR simulated radar forecast at 1 PM As we always see, exact placement of forecast rain is more frequently than not inaccurate. (Click on image for a larger view.)
The latest HREF model, which is a statistical ‘ensemble’ of the HRRR, NAM-NEST and RAP models shows minimal rain for the hour preceding 2 PM —
06z HREF forecast 1 hour prior rainfall at 2 PM. (Click on image for a larger view.)
Additional rain is expected during the evening, but the models are leaning towards it being somewhat west of the city.
As for total rainfall so far for this event, this has been the most significant widespread rainfall we’ve had in a long time. Here’s the latest 48 hour total estimate—
MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch) (Click on image for a larger view.)
Wednesday Forecast Update
Posted Tuesday 05/13/25 @ 5:19 PM — The weather is unfolding as forecast, with a stream of increasingly heavy showers moving up from the south southeast around a closed upper low to our west.
The latest ECMWF-AI model has rain continuing tonight and becoming quite heavy by early morning Wednesday. Some thunderstorms may be in the mix on Wednesday. A total of almost 2″ of much needed rain is forecast for our area through midnight Wednesday.
ECMWF-AI forecast for 2 PM Tuesday. Heavy rain over our area. (Click on image for a larger view.)
It looks like some rain/showers continue on Thursday as the upper trough axis moves over us. Thunderstorms also possible.
Tuesday Forecast Update
Posted Monday 05/12/25 @ 5:56 PM — The forecast appears to be generally on-track with rain expected in the immediate Philadelphia area on or before 5 AM Tuesday morning.
Here’s the current satellite water vapor image—
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. Upper level low (L) will gradually move north-northeast. Bands of rain will rotate up over our area at least until late Wednesday and likely into Friday. (Click on image for a larger view.)
Light showers to start, then bands of heavier rain move in later in the morning and continuing, with some breaks, through the afternoon and Tuesday night. Rain tapers off somewhat on Wednesday, but thundershowers will likely develop during the afternoon.
Total rainfall around 1 inch possible in and around Philadelphia, by Wednesday morning. more west of the city.
Posted Monday 05/12/25 @ 7:40 AM — This week’s model forecasts continues to evolve, with a shift towards some heavier rain in the immediate Philadelphia area by Wednesday. (I’ll have to see it to believe it.)
For today, sunshine through high cirrus clouds, with clouds thickening between 4 PM and 7 PM from southwest to northeast. Rain begins here before daybreak Tuesday, but much of the rain will be showery in the morning.
The chance of more moderate to heavy rain waits until later on Tuesday and most likely Tuesday night into Wednesday morning.
06z REFS (experimental( shows only light rain likely here at noon on Tuesday. At least initially, the heaviest rain will be west of our area. (Click on image for a larger view.)
Originally Posted Sun 8:17 PM —Monday will have sun through high clouds, then increasing cloudiness by 4PM. High temps similar to Sunday, near or just above 80º. Rain begins after midnight early Tuesday morning.
An active weather week ahead, where another upper level closed low will bring good chances for rain from before daybreak Tuesday through Friday.
Despite this forecast, it’s not entirely clear whether the needed heavier rain will be in and around Philadelphia, or continue a long standing pattern for the heavier rain to remain to our far north and west. Some models are showing heavier banding right over Philadelphia, but others (Canadian and various runs of the German ICON model and the RRFS) show the heaviest rain to our far northwest.
Today’s 18z GFS model forecast total rainfall through daybreak Wednesday. Greater accumulations by Friday. (Click on image for a larger view.)
Some models show just intermittent showers on Tuesday, while others are forecasting periods of moderate, continuous rainfall here. Too early to be sure.
There will also be the possibilities of thunderstorms during the week; the higher dew points, available moisture aloft and instability will set the stage for these storms, especially late afternoons and evenings.
Posted Sunday 05/11/25 @ 9:40 AM — A beautiful Mother’s Day. The weather couldn’t be finer. Light winds, low humidity. Highs near or above 80º
05-11-25 12z NBM forecast high temperatures for Sunday (Click on image for a larger view.)
Enjoy the great weather today, because the AI models are forecasting several days of rain, potentially heavy, from before daybreak Tuesday through Friday.
Clouds move in during the afternoon Monday and rain begins shortly after midnight early Tuesday morning.
Posted Saturday 05/10/25 @ 9:22 AM — Enjoy this wonderful (but somewhat cool and, initially, rather windy) weather that we’ll have through Monday. The models are consistently forecasting rainy weather from before daybreak Tuesday through early Thursday—
06z ECMWF-AI Single forecast for Tuesday at 8 AM. A slow moving system associated with another closed upper level low (Blue L) will move in before daybreak Tuesday. (Click on image for a larger view.)
Previously Posted Fri @ 5:33 PM — —Low pressure that gave us the rain on Friday will depart Friday night. High pressure builds in on Saturday. The pressure gradient between the departing low and the building high will cause windy conditions on Saturday.
NAEFS forecast for Saturday at 2 AM. High pressure will be in play over the weekend, keeping the developing low pressure system near the Gulf of Mexico Gulf of America Gulf of Mexico to be suppressed to our south. (Click on image for a larger view.)
Saturday Forecast
Sunny and windy.
NBM Winds and gusts
NBM high temperatures: Blue Bell, PA 71º Philadelphia, PA73º Uncertainty (based on standard deviation) : above average ±2º
Sunday Forecast
Sunny and less windy.
NBM high temperatures: Blue Bell, PA 75º Philadelphia, PA 78º Uncertainty (based on standard deviation): above average ±2º
