Posted Sunday 06/01/25 @ 10:37 AM — Ordinarily, I find the the expression “sunshine through high cirrus clouds” to be a useful description of a day’s cloud cover when the predominant cloud type is cirrus. Many people might not notice that the sunshine is filtered by high clouds.
Today, the appropriate sky forecast description is sunshine through smoke. The smoke from wildfires in Canada has made its way to our area in a reduced way. Here’s the latest HRRR smoke model forecast for this afternoon showing plumes of smoke —
Today’s HRRR smoke model forecast for 6 PM. While the 100 x 10 minus 6 kg/m2 doesn’t approach the 480 level we saw a few years ago. the sky will not be the bright blue we’d expect to see with a clean air mass. (Click on image for a larger view.)
Saturday Weather Update
Updated Saturday 05/31/25 @ 9:48 AM — Latest RREF shows the scattered showers as early as 1 PM.
Posted Saturday 05/31/25 @ 9:30 AM — We had the heavy rain last night; rainfall amounts and severity here were not as great as had been forecast possible.
Total rainfall received—
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.)
Additional showers are expected with the passage of a cold front this afternoon. Currently, these showers are in northwestern PA—
RADAR at 9:15 AM with superimposed RAP model parameters. (Click on image for a larger view.)
Most models show two areas moving towards us, as shown above, with the heaviest rain to our north and more so to our south.
Here’s the current HREF forecast for this afternoon—
Forecast for 2 PM this afternoon. Scattered showers, nothing severe. (Click on image for a larger view.)
A dry day for Sunday with sun mixing with instability cloudiness.
The weather really warms up next week, with temperatures in the mid to upper 80s Tuesday through Thursday.
Heavy Rain Possible Tonight
Posted Friday 05/30/25 @ 6:11 PM — One more thing. Helicity and vertical shear values become highly elevated between 10 PM and 1 AM. The potential for severe thunderstorms and even a tornado is possible, most likely in western suburbs.
Posted Friday 05/30/25 @ 6:11 PM — I’m a little short on time for this forecast, so I’m simply going to focus on Friday night at this point.
Showers and thunderstorms are developing to our south and will move in as early as 8-9 PM and will quickly become widespread by 10-11 PM.
HREF 18z forecast simulated radar 9 PM and 11 PM (Click on image for a larger view.)
Flood Watches have been issued for parts of the area. Total rainfall by 8 AM Saturday—
18z HREF forecast accumulated rainfall by 8 AM Saturday. Note that the exact locations and amounts are often not correct, but suggest possibilities. (Click on image for a larger view.)
Following a break Saturday morning, more rain is expected Saturday afternoon. I’ll update tomorrow morning.
Posted Friday 05/30/25 @ 9:53 AM — The clouds should break for sunshine from west to east about 11 AM to noon. Cloudiness develops again about 4-5 PM. Light rain moves in about 7-9 PM. Heavier rain and possibly severe thunderstorms move in about 9 -11 PM Friday evening, according to the latest HRRR.
Today’s 12z HRRR forecast simulated radar- 10 PM Friday evening. (Click on image for a larger view.)
(Problems with NOAA’s supercomputers have been an issue over the past 18 hours, hopefully resolved. This has prevented availability of the RRFS and REFS.)
Update Thu 5/29 10:44 PM — Tonight’s early models suggest that Friday will be relatively rain free. Minimal isolated showers. Heavy rain and potentially severe storms move in and develop in place over our area beginning 6-8 PM.
Active Unsettled Weather Friday Saturday
Posted Thursday 05/29/25 @ 5:27 PM — Several pieces are coming together for some active weather (heavy rain, thunderstorms) beginning later Thursday night through at least Saturday.
The jet stream is forecast to dive south into a sharp trough (somewhat unusual for late Spring). This feature along with a southern stream jet flow will provide energy to spawn low pressure, rain and thunderstorms. Add to this an increasingly moist air flow with some forecast helicity, wind shear and the ingredients are in place for potential severe weather and heavy rainfall.
Today’s 12z ECMWF jet stream flow shows strong jet streak diving south and interacting with south jet flow, spawning waves of low pressure. (Click on image for a larger view.)
Timing of these soon-to-be spawned low pressure waves will be less than exact. As mentioned, the first wave moves through Thursdaynight with showers and some thunderstorms, ending early Friday morning.
A break in the action looks likely Friday morning, but there’s the possibility of some scattered storms forming Friday afternoon. The heavy action now appears to occur Friday evening and night, where severe thunderstorms are possible, especially in NJ. Rain and thunderstorms continue into Saturday. We may get a break on Sunday.
I expect to hear a few severe thunderstorm announcements over the next two days. Stay tuned.
Clearing Thursday- Possible Severe Storms Friday Afternoon
Posted Thursday 05/29/25 @ 8:42 AM — Sky conditions are expected to improve over this afternoon. Cloudiness will become quite variable in many areas between 2 and 5 PM. Enjoy while you can.
More clouds and what looks like possible severe storms Friday afternoon into Friday evening.
RRFS forecast Precipitation rate and upward helicity at 5 PM Friday. Suggestive of severe storm potential. (Click on image for a larger view.)
Wednesday -Thursday Update
Posted Wednesday 05/28/25 @ 4:33 PM — I rarely use the popular TV weather phrase “I’m tracking this [on radar]” to describe the progression of weather.
“Tracking” suggests to me a very non-dynamic process with weather moving from point A to point B, like on a train track. Indeed, the hourly rain depiction on the iPhone weather widget is that level of weather ‘forecasting’. Weather forecasting is much more complex than this.
Case in point is the current radar, which shows the back edge of the rain moving towards us at 4 PM. So, why did they postpone the Phillies game for this evening?
The reason is rain is expected to redevelop over us and increase in intensity despite the back edge visible on radar at this time.
Composite RADAR with RAP model parameters superimposed at 4 PM. Yellow contours depict vertical velocity. (Click on image for a larger view.)
The above radar image above includes RAP model vertical velocity (yellow X) which is expected to move over us during the early evening hours. Heavier rain is expected to redevelop with this dynamic in place Wednesday evening. (I guess we’ll see if it happens.)
The rain is expected to depart by the early morning, but low clouds will linger for much of the day Thursday.
Another possibly heavy rain maker is forecast to begin mid afternoon Friday.
Wednesday’s Rain
Posted Tuesday 05/27/25 @ 6:10 PM — This afternoon’s models are predicting remarkably similar rainfall totals for Wednesday, with higher rainfall to our south (a trend that has been consistent as well.)
To mix it up a bit, here’s the HREF ensemble model rainfall totals through 8 AM Thursday—
Today’s 18z HREF model rainfall forecast through 8 AM Thursday. (Click on image for a larger view.)
With the exception of the Canadian RGEM, most models have rain starting around daybreak Wednesday. As for the Phillies game Wednesday evening, it looks like the rain doesn’t taper until late evening.
The rain ends early Thursday morning, but plenty of clouds are forecast for much of the day, possibly breaking to some sunshine or bright skies late Thursday afternoon.
Tuesday-Wednesday Forecast Update
Posted Monday 05/26/25 @ 7:29 PM —It appears that cloudiness will advance earlier into our area Tuesday than previously forecast. Considerable cloudiness is expected during the morning, with thickening and lowering cloudiness during the day.
Many models have some light sprinkles after midnight into early Wednesday morning with heavier rain developing by late morning and during the afternoon. An easterly wind will make it quite chilly on Wednesday.
Rain will continue Wednesday evening and taper off Thursday morning. Slow clearing with a chance of a shower through Thursday.
12z RRFS-A (pre-release version) total rainfall through Thursday/ (Click on image for a larger view.)
The GFS, Canadian, ECMWF and RRFS are forecasting close to 1+ inch of rain total around Philadelphia, less amounts to our north. The AI versions of the ECMWF and the GFS show lesser amounts, about 0.5-0.75 inches with the heaviest rain south of our area.
Memorial Day through Wednesday
Originally Posted Sun 7:53 PM —Low pressure that slowly departed our area will still influence our weather on Monday, Memorial Day. We’ll see plenty of sunshine Monday, but several models are hinting at some cloudiness developing mid-afternoon into the evening as a short wave associated with the departing low rotates through.
The GFS and pre-release RRFS model show the possibility of a few isolated showers between 3 PM and 8 PM. Most areas will be dry. (The Canadian HRDPS keeps these showers far north of our area.) (Updated Sunday 05/25/25 @ 9:12 PM —Several more of this afternoon’s models keep any isolated showers to our far north.)
12z RRFS-A (pre-release) model forecast for 8 PM Monday. (Click on image for a larger view.)
Tuesday will have sunshine through high cirrus clouds ahead of an approaching low pressure system. (Areas south of the city and in South Jersey may have considerable mid-level cloudiness.)
Also expected Tuesday is an updated NBM model, which will be moving to NBM version 4.3. This updated model will have several enhancements, including an update to cloud cover and improvements in forecasting tropical systems and severe weather.
Here’s the storm taking shape in the Central US as of Sunday evening —
Sunday evening 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. Storm taking shape in south central US. (Click on image for a larger view.)
This storm will bring rain to our area Wednesday. The trend has been for the heaviest rain to move to the south of our immediate area. About 0.5 inches of rain are expected.
Latest GFS forecast for Wednesday (Click on image for a larger view.)
Posted Saturday 05/24/25 @ 9:37 AM — Last night’s forecast still holds. The sunshine this morning will be mixing with clouds by about noon. There’s a chance of an isolated, fast moving light shower about 3-5 PM. although most areas are expected to remain dry.
Current Water Vapor with Radar shows the disturbance expected to move through—
Water Vapor, radar composite and RAP model vertical motion around 9:15 this morning (Click on image for a larger view.)
Previously Posted Fri @ 6:19 PM — —The main low pressure system that affected our weather over previous days is slowly moving away, but the first upper low and a second upper low will bring cool weather and unsettled skies at times through the first portion of the Memorial Day Weekend. Monday should be mostly sunny.
(An upper low can be thought of as a cold circulation of air aloft.)
ECMWF-AI forecast for Sunday at 8AM 1 and 2 are upper low pressure systems. The red lines are called 540 thickness lines, and they demarcate colder average temperatures of the lower half of the atmosphere. In winter, areas north of the 540 thickness lines are cold enough for snow. In late spring, that cold air causes instability to develop with sunshine heating the ground. (Click on image for a larger view.)
We had widely scattered fast moving showers late this afternoon, and with cold air aloft, that possibility still exists for Saturday afternoon. Sunday, any instability showers should remain far north of the Philadelphia area.
It should be noted that any really warm weather isn’t forecast for our area this weekend or even for the coming week.
Saturday Forecast
Sunny in the morning. Instability cloudiness develops before noon and lasts several hours into the afternoon. A few, isolated showers move through at that time. Most areas will be rain-free. It will be windy during the mid-day hours.
NBM high temperatures: Blue Bell, PA 63º Philadelphia, PA 66º Uncertainty:average (based on standard deviation): ± 1.9º
Sunday Forecast
Partly sunny, although the experimental RRFS shows considerable cloudiness south of the city and in Southern NJ. Less windy but still breezy.
NBM high temperatures: Blue Bell, PA 68º Philadelphia, PA 70º Uncertainty: average (based on standard deviation): ± 1.8º
Memorial Day
Sunny. Winds subside further but still breezy. High thin cirrus clouds move in late afternoon.
NBM high temperatures: Blue Bell, PA 68 72º Philadelphia, PA 74º Uncertainty: low (based on standard deviation): ± 1.4º
