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Thursday Evening Update

Posted Thursday 07/03/25 @ 6:11 PM — As forecast this morning, much of the energy and moisture for thundershower formation is north of our area.

Here’s what it looks like at 6 PM—

The latest REFS still shows some showers here around 8 PM, but it might be over-forecast.

The Fourth of July Weekend is looking quite nice, sunny but increasingly warm. Near 90º on Saturday, low 90s and more humid on Sunday.

Thursday & Fourth of July Extended Weekend

Posted Thursday 07/03/25 @ 9:38 AM — A front will move across the area with an upper level trough Thursday evening. Most of the energy and moisture will move to our north. Compared to recent thunderstorms, precipitable (cloud water) will be in the 1.4″ range compared to 2.1″ in recent storms, so rainfall amounts will be lighter.

With the exception of New Jersey, which may see some isolated storms this afternoon, the area of showers and storms moves through the immediate Philadelphia area between 7PM and 11 PM, with the latest REFS leaning towards 9-10 PM —

The Fourth of July Weekend is looking quite nice, sunny but increasingly warm, especially by Sunday.

Wed 9:30 AM —Forecast Review — Rainfall over the past several days was impressive, exceeding all model estimates. More amazing is the fact that we couldn’t get much of any rain here at all just a year ago.

Here’s the latest MRMS rainfall estimate over the past 72 hours. (It’s still raining in eastern NJ, so these numbers aren’t final.

What difference does a year make? Last year at this time, we were ascending on the solar cycle curve, something well-studied and associated with decreased rainfall.

This year, we’re descending on the same cycle curve, having peaked a few months ago. We’ve just passed the solar maximum of this cycle. This climate change is especially prominent over periods of two solar cycles– the double cycle is called the Hale Cycle (The Hale Cycle refers to the magnetic polarity of sunspots that reverse every two solar cycles). Is this Hale Cycle the reason for last season’s drought and our recent rainfall pattern change? Maybe.

Wednesday Update

Posted Wednesday 07/02/25 @ 9:51 AM — The models still show lingering rain in eastern NJ while clouds are expected to thin and break for some sun from west to east about 12 -3 PM

Wednesday Forecast

Posted Tuesday 07/01/25 @ 7:37 PM — The cold front hangs up along the coast as weak waves of low pressure move up along it. Expect additional light showers this evening and overnight into Wednesday morning. The sun will break through clouds from west to east on Wednesday afternoon.

Here’s the REFS cloud level forecast at 2 PM Wednesday—

Tuesday Forecast

Posted Tuesday 07/01/25 @ 7:49 AM — Multiple rounds of showers and thunderstorms gave our region significant rainfall in some areas—

A cold front moving through today. Some differences in the timing of the frontal passage with the HRDPS having the front move through about 4-5 PM, while the GFS has the front moving through about 8 PM with the showers and thunderstorms moving in 4:30PM to 7 PM

Similarly, the HRDPS has some showers moving through as early as 1 PM, especially just east of the city. The main line of showers and thunderstorms move through 3 PM -6 PM.

Based on yesterday’s model performance, I’m leaning towards the REFS and HRDPS which has showers and thunderstorms beginning at 3:00 PM to 4:30 PM, with some scattered activity possible as early as 1-2 PM mainly east of the city.

All models have rain and thunderstorms continuing through the evening and night as low pressure develops along the front. Some rain may continue into early Wednesday morning. Heavy rain is expected.

Some thunderstorms may be strong to severe, but current forecasts of helicity and vertical wind shear are in the low- moderate range only.

Tuesday Forecast

Posted Monday 06/30/25 @ 5:41 PM — Showers and thunderstorms moved in from the south between 2:30 PM and 4 PM.

Very few of this morning’s models accurately predicted the timing and location of this afternoon’s storms. I always like to look back and see if any specific model did well. The HRRR, our best high resolution model, didn’t perform too well today, nor did the NAM-NEST. (The AI models don’t have the high resolution needed for thunderstorms.)

Looking back, the Canadian high resolution model (HRDPS) did reasonably well. The experimental REFS also did surprisingly well.

So with that, the REFS becomes “the model of the week”. It is currently forecasting showers/thunderstorms to return between 3 and 5 PM Tuesday afternoon. Some may be strong to severe. Stay tuned.

Monday Forecast Update

Posted Monday 06/30/25 @ 9:07 AM — Yesterday’s Model Blend (NBM) proved to be correct about the lack of showers this morning, and I’ll stay with the NBM for today’s forecast, with individual models showing a range of forecast times for showers and thunderstorms.

Pop up storms can occur anytime after 1 PM today with peak activity between 5 PM and 8 PM.

The latest NBM shows activity near the city picking up about about 1-2 PM just east of the city.

A considerable increase in coverage will occur later in the afternoon. Some areas may receive heavy rain in a short period of time.

Likely focus of heavier storms will be central areas of South Jersey in the mid afternoon and areas north of the city in the late afternoon.

Originally Posted Sun 8:50 PM —The ‘cold’ front that moved through Saturday has stalled just to our south and thunderstorms have been breaking out in South Jersey for much of Sunday, especially near the Delaware Bay and Cape May.

The front will return as a warm front on Monday. Large differences in the forecast exist for Monday morning. The AI version of the ECMWF and the latest GFS have scattered showers breaking out early Monday morning, while the regular ECMWF, the AI version of the Canadian GDPS keeps us dry until 2-4 PM.

The experimental RRFS has scattered pop-up storms in the morning; this may be an example of its tendency to over-forecast convective rain.

The ECMWF-AI has so much precipitation and clouds in the morning that it keeps our high temperatures in the mid to upper 80s instead of the low 90s forecast by the drier forecasts.

The model blend (NBM) keeps us dry Monday morning as well, and I’m leaning towards its forecast. Its high temp in Philadelphia is 90.5º

It’s a tough call.

The models all come together by Monday afternoon with showers and thunderstorms popping up anytime between 1 PM and 4 PM and continuing into the evening. Peak time is about 6 PM according to the NBM.

Tuesday looks even more interesting, as a cold front moves into very moist and unstable air over the Philadelphia region. Stay tuned.

#Philadelphia #weather #PAwx #PhillyWx

Thursday Thunderstorms

Posted Thursday 06/26/25 @ 5:13 PM — The NWS has issued a severe thunderstorm watch. Some strong thunderstorms have developed far northwest of Philadelphia. Latest radar at 5 PM—

The models have only been so-so with today’s forecast. Many models have forecast areas of storms that have not materialized late this afternoon. That’s particularly true of the experimental RRFS which forecast many areas of rain at this very time.

The trend mentioned in this morning’s update suggests the heaviest activity will remain just west of Philadelphia, as shown in the NBM graphic earlier.

The latest HRDPS and NAM-NEST capture the most likely forecast, again keeping the heavy rain to our west.

These things are tough to forecast with high precision. I guess we’ll see what happens in the next few hours.

Thursday Forecast

Posted Thursday 06/26/25 @ 9:44 AM — Nailing down the forecast locations and timing of thunderstorms yesterday met with mixed results; the additional storms forecast towards midnight didn’t materialize.

Today, Thursday, presents another thunderstorm forecast challenge. Model forecasts range from storms developing as early as 2 PM near the city to storms mostly staying to our west and south (and South Jersey) through most of the afternoon and evening.

The NBM total rain accumulation captures the overall trend of any showers and storms staying to our west, south and east—

In contrast to this NBM forecast is the latest ECMWF-AI model, which does have showers and storms in the immediate Philadelphia area by mid afternoon.

Also in contrast to the NBM is the Canadian GDPS- with “AI spectral nudging” which has thundershowers in and near Philadelphia between 3 PM and 7 PM.

A tough call. I guess we’ll find out.

Wednesday Night into Thursday

Posted Wednesday 06/25/25 @ 8:16 PM — Isolated to scattered storms developed. Very low wind shear has resulted in the storms forming and then collapsing. (Wind shear is needed to keep thunderstorms alive.)

Current radar at 8:10 PM

Today’s HRRR was unusually poor in forecasting the current storms. The experimental RRFS did better. Continuing with the RRFS, it is shows additional scattered short-lived storms through 3 AM as the backdoor cold front slowly moves through.

Thursday will have a mix of clouds and sun. Isolated to scattered storms are expected to begin to pop about 3 PM into Thursday evening. More details tomorrow.

Wednesday into Early Thursday

Posted Wednesday 06/25/25 @ 8:30 AM — As described yesterday, the heat dome will retreat late Wednesday as cooler high pressure slowly noses in from the northeast (backdoor cold front). Before that time, temperatures will again approach high levels, between 98º to 100º in and near the city.

Dew points will be higher today at peak temperature time, and I’ll have to resort to the Heat Index temperatures to capture the full impact. (I avoid posting heat index values since I think they’re often used to unnecessarily sensationalize, exaggerate heat episodes on TV broadcasts. Maybe not so today.)

As for thunderstorms, high heat, high humidity and several short waves ahead of the approaching backdoor cold front will create conditions ripe for thunderstorms with heavy rain. The latest HRRR is least on-board with storms here, but the AI models, the NAM-NEST, Canadian RGEM,and the RRFS show the possibility of isolated storms (especially in the wind shift/convergence zone in NJ) as early as 2PM.

Increasingly thunderstorm coverage expected late in the afternoon and especially in the evening hours (6 PM to midnight) where they should become more numerous. Not everyone will see a storm, but those that do will likely see some heavy rain. Severe winds, always a possibility, are not expected at this time.

To convey the scattered nature of the storms, here’s another model parameter that attempts to predict the strength of individual thunderstorm cells at 7 PM.

Wednesday- Heat Early Afternoon Reduced by Thunderstorms

Posted Tuesday 06/24/25 @ 7:57 PM — Disturbances moving across the upper heat dome are expected to bring showers and thunderstorms to our area Wednesday afternoon and evening. Some may be strong.

High temperatures of 99º and possibly 100º in parts of the city will be reached early, before 2 PM.

Thunderstorms develop and move in from the northwest and develop in place as early as 2 PM and continue into the evening. Impressive thermal instability (negative 8 “lifted index” and near 40 K index) and high CAPE values approaching 3000 J/Kg could make any storm strong to severe.

I’ll update Wednesday morning.

Tue 4:30 PM —Forecast Review — Another hot day, where the AI models were more accurate with their temperature forecasts than the very advanced NBM statistical Model Blend. (Although the Model Blend did fine when you factor in the standard deviation.)

Here’s the RTMA temperatures at 3:45 PM—

Here’s the official readings from the NWS Philadelphia Airport KPHL—

Heat Continues

Posted Tuesday 06/24/25 @ 9:26 AM — Many models have similar high temperature forecast for today. The latest Model Blend (NBM) just became available. Here’s its forecast highs with degree of uncertainty (standard deviation) for today, Tuesday—

Here’s the latest ECMWF-AI model high temperature forecast—

Here’s the new Canadian CMC GDPS-AI forecast—

Heat Recap

It really felt hot today! Temperatures seem to have only reached 99º in this area, but dew points were 70º (and where highs were only 96º, e.g. Blue Bell, the dew points were closer to 74º and 75º

Here’s the RTMA @ 3:45 PM, capturing the area’s temperatures—

The NWS has modernized their website for KPHL airport, now showing temperatures every 5 minutes—

Of interest is the localized area of showers that developed, as predicted by the new Canadian GDPS-AI along with the wind convergence zone—

It’s interesting that the experimental RRFS did not predict these showers in Cape May. (The NAM-NEST did predict these as well.)

For Tuesday, here’s the latest ECMWF-AI temperature forecast—

Stay cool!

Originally Posted Mon 9:22 AM —Yesterday’s high temperatures were diminished by the unexpected and unforecast clouds and showers.

The heat will be here for sure today.

Continuing with the “experiment” from yesterday, here is the new Canadian GDPS-AI along with the Model Blend (NBM) forecast high temps for today. likely about 3-4 PM—

Here’s the Model Blend (NBM) high temps—

The “Open Data” version of the ECMWF-AI single is very similar to the above.

Just to see if the Canadian has any unique insights, it is forecasting some thundershowers to develop in NJ at 3-4 PM due to the development of a moisture convergence zone—

Stay cool!