#Philadelphia #weather #PAwx #PhillyWx

Friday Forecast Update

Posted Friday 04/17/26 @ 11:03 AM — A weak upper air disturbance will combine with some moisture and instability CAPE to set off some showers about 3-5 PM. The showers will be scattered and not every area will receive some precip.

The latest ECMWF is forecasting showers for Sunday with likely greater areal coverage and amounts. Stay tuned for my regular “Weekend Weather Forecast” later today.

Friday

Posted Thursday 04/16/26 @ 9:43 PM — A weak cold front will move through after midnight. Showers and thunderstorms in central PA will fall apart as they move towards Philadelphia. The immediate Philadelphia area may see a few scattered drops before daybreak.

Friday will have periods of sunshine and periods of clouds. It will be considerably cooler, but still above average temperatures in the upper 70s.

For Friday, the RRFS remains the sole model predicting a weak low pressure circulation to form associated with an upper trough. A few scattered showers may develop late afternoon. (The latest HRRR and the GFS keep us dry.)

Thursday-Friday

Posted Thursday 04/16/26 @ 12:35 PM — Temperatures today are expected to reach the low 90s.

A weak cold front and upper trough will pass through around or after midnight Thursday night. Once again, a line of storms will fall apart as they approach Philadelphia. Little or no rainfall expected.

The upper trough that moves through Friday may close off or spawn a surface low right over us. Some much needed rainfall is possible late Friday afternoon.

Several periods rain forecast earlier this past week have fallen apart. We’ll have to see if Friday’s forecast holds.

Wednesday Forecast Update

Posted Wednesday 04/15/26 @ 10:26 AM — The record breaking temperatures are on the way, according to the NBM—

Despite the temperatures, Heat Indices (“Apparent Temperatures”) will be cooler (87º-90º) due to dew points in the low 60s. If you factor in the wind, it will feel even cooler than that.

As for thundershowers or any rainfall, the energy is available, but the track of the disturbance will be far north of Philadelphia today, mostly in NY State.

Showers Tuesday Night Update

Posted Tuesday 04/14/26 @ 8:16 PM — There are showers and thundershowers to our west. Looking at the track, you’d think this rain will move in here. See caption below.

As of tonight, this may be the only rain we get this week. Next chance is Sunday and the rainfall totals aren’t looking too heavy for Sunday.

This tendency for rain to fall apart as it reaches this area is a trend and a concern for this current season. We need some rain.

Showers Tuesday Night

Posted Tuesday 04/14/26 @ 5:25 PM — Despite the overall pattern that works against precipitation here, there’s enough energy moving over the ridge of high pressure to induce some showers tonight, mostly from 11 PM to 3 AM near the city. There’s increased confidence that we’ll see something with both the HRRR and RRFS cranking out a small accumulation.

The main energy dissipates after moving through Lancaster and Berks counties; the models are forecasting some rain here despite the collapse of the trigger.

Our high today was 88º KPHL (Philadelphia airport) and 85º (KLOM- Wings Field Blue Bell, PA). That was close to the mean + standard deviation of the NBM.

If we look at the mean + standard deviation for Wednesday, that brings us to 93ºF KPHL (airport) and 91º Wings Field KLOM. Dew points will be low and it will be breezy, so the ‘feels like’ will be about 2º less.

Tuesday Forecast Update

Posted Tuesday 04/14/26 @ 8:58 AM — The high temperatures forecast for today still look to be on-track according to the latest NBM version 5. (For reasons unclear to me, the RRFS and REFS forecast lower high temperatures by about 3-4ºF ).

As for any rainfall, we remain in an unfavorable upper air pattern for showers/thunderstorms in Philadelphia and especially S. Jersey. Looking at the upper water vapor image (channel 8) there are a few triggers that are in Ohio that may move in later today, between 6 PM and 8 PM—

The RRFS shows these triggers to fall apart after 8 PM, only making into central PA and Maryland. A few ‘pieces of energy’ may make it into western suburbs of Philadelphia—

Tuesday

Posted Monday 04/13/26 @ 8:30 PM — The warm air arrived late Monday afternoon with an increase in humidity. Mostly sunny through high clouds on Tuesday; occasional periods of cloudiness, especially northwest of the city and later in the afternoon. The NBM is forecasting some light scattered showers/thundershowers from 5 PM into the evening. (Can we believe it?)

It will be windy. The winds will make it feel cooler than the actual temperatures.

Interesting Weather Monday

Mon 8:24 PM —Forecast Review — It looked threatening at 2 PM, but few areas saw any precipitation. The showers that had been forecast for this evening have materialized to our far north and west but are not here as had been forecast. The NAM-NEST, the HRDPS and the RRFS are still showing some light shower activity around midnight; most of the showers will move off to our north- Northern Bucks and northwestern Montco may see the most in the way of light showers.

Originally Posted Mon 8:50 AM — The forecast has changed from what I heard on TV last night. Signs of this change were showing on last night’s early models.

There are some areas of energy to our WEST this morning. These are forecast to move towards the Philadelphia area this afternoon and this evening.

An area of moisture with some lift will move over our area between 2-4 PM this afternoon. Very widely isolated showers and thundershowers are possible at this time.

A more organized area of moisture and vertical motion (omega) will move down over our area about 7-10 PM, causing slightly more widespread showers and thundershowers—

While precipitation may be overall light and scattered, we need any rain we can get.

This set up looks interesting and some localized strong storms sometimes occur with these setups as a ‘surprise’. Stay tuned.

#Philadelphia #weather #PAwx #PhillyWx

Monday into Tuesday

Posted Monday 04/06/26 @ 12:18 PM — A weak upper air disturbance with associated light showers is far northwest of our area this morning.

This disturbance will move through between 11 PM and 2 AM Monday night with light scattered showers in our area.

Colder air follows behind this disturbance for Tuesday.

Originally Posted Sun 5:27 PM —The cold front that went through Sunday afternoon preceded large high pressure that will move in for much of the week with cooler than average temperatures.

It’s notable that temperatures might drop below freezing Tuesday nigh; it’s still too early to plant some spring plants and flowers.

Temperatures moderate Thursday into Friday.

Another front moves through Saturday, but the showers associated with this front may not have upper air support, so little in the way of precipitation expected.

There appears to be a significant warm-up for the following week.

#Philadelphia #weather #PAwx #PhillyWx

Sharing Excellent Question/Comment Submitted

From Brian Friday, February 20, 2026 10:40 am at 10:40 AM

Thanks for sharing your love for weather with the broader community. It’s always fun to hear your perspective on the raw data.

Just curious: do you ever peek at the NWS forecast? Other than you 🙂 I think of them as the gold standard. They’ve been consistently forecasting on the lower end for my area–shocking close to the blend median.

Also I’m curious if you’ve focused on the air temp during the bulk of the precipitation. In my area, it is forecast (who knows what really will happen!) to be decently above freezing–in the upper 30s. Is that a factor in the argument for lower totals? Does that suggest that even if we get a decent snow, a lot of it will be on grass and not roads and sidewalks?

Just trying to get a handle on the practical implications for whatever is coming.

Hi Brian, Excellent questions and comments. Let me address them—

1: NWS: I am totally impressed with the forecasters and scientists of the NWS. And I DO more than peek at their forecast discussions on a regular basis. But I find myself unduly influenced if I read their forecast discussions before I make my own conclusions.

Their forecasts have legal weight in case of public injury and destruction and I find that they need to protect people and property first, often erring on the side of over-stating certain forecast risks. Severe Thunderstorm warnings are the perfect example. When it comes to snow storm risks, they also focus on the economic impact of a wrong forecast. So they don’t move towards excessive snowfall extremes until they have to.

As you’ve seen, I’m currently inclined towards the NBM median but it may be too low.

2. Temperatures and Snow: I’m totally focused on temperatures with snowstorms. But near-ground temperatures (actually 2m above ground is what the ground temperatures really mean) are meaningless when the upper level temperatures from 1500 feet to 10,000 feet are below freezing. (It will snow 50% of the time when near ground temperatures are as high as 36.5º and the temperatures from 1500 feet to 10,000 feet are at or below freezing.)

The red, magenta and yellow lines on my maps are “critical thickness” lines which show the freezing temperature at various levels (actually thicknesses) of the atmosphere. If all three lines are south of your area, temperatures aloft are cold enough for snow even if it’s above 32º near the ground. Where ground temperatures come into play is whether the snow accumulates, compresses and/or melts. Model algorithms try to take that into account.

Interestingly, I was going to unveil a new algorithm I worked out over recent weeks with Claude AI for GFS snowfall totals. I will run this algorithm on the GFS data I’ve scripted to download and process 4x daily. I may try it with today’s 18z GFS totals. Temperatures aloft are a major part of this algorithm, as is the temperature near the ground. (I’ve set the cut off to be 33º, BTW.)

Thanks for your questions. I may share it and your response in the main blog.

Storm Update

Posted Friday 02/20/26 @ 10:02 AM — There has been some improvement in the forecast, as far as the NBM is concerned. But there are general trends and differences that remain—

• The ECMWF maintains a weaker storm until it passes us by. It’s track has moved somewhat closer to us, but still low snow totals are forecast (1-3″)
• The GFS continues to forecast a major storm with snow totals over 6″ in our area and more at the shore.
• Disturbingly, the NAM has the energy jumping over our area, keeping the snow totals very low.
• Similar to the NAM, the RRFS shows very low snow totals with a far southern track.
• The Canadian RGEM and GDPS AI area all in the low accumulation camp.

Here’s the ECMWF forecast at 1 AM—

The GFS maintains a monster of a storm with heavy snow in our area—

The other models have similar to slightly less snow accumulations as shown in the table from yesterday.

Here’s the latest ECMWF-AI forecast—

At this time, I’m going to depend on the Model Blend (NBM) and I’m leaning towards the median snowfall forecast. Here’s the latest—

Here’s the latest NBM mean forecast—

The median and mean have become much closer lending higher confidence. But I still can’t get past the NAM and new RRFS that show minimal snowfall here.

Updates this afternoon.

Snow Storm Update

Posted Thursday 02/19/26 @ 8:54 PM — The latest ECMWF has moved in the direction of the GFS, as has the latest ECMWF-AI and the AIGFS. A major snowstorm is being predicted by all four models.

The latest ECMW-AI snow accumulation forecast—

I’m not ready to share the GFS totals. It’s either wrong or we’re headed for a whopper of a snowstorm.

We’ll have to see if tonight’s model runs are continuing with the current trend. Stay tuned!

Sunday Storm Update

Posted Thursday 02/19/26 @ 4:48 PM — The forecast for the coastal storm on Sunday continues to evolve. Here are some of the latest trends—

There you have it. Clearly, the NBM model blend is highly influenced by the GFS.

I’m leaning towards the NBM median at this time:

Of interest is the wide disparity between the GFS and the NAM. (I dusted off my download code to retrieve and process the NAM. The NAM will be retired this year.)

For many years, I relied exclusively on the GFS and NAM for my snow forecasts. What I distinctly remember- the NAM tends to over-forecast snowfall and an average of the NAM and GFS usually served well when their forecasts were close. But, when the NAM is forecasting a miss (as is the case here), the lesser NAM forecast was the more accurate model.

The GFS has undergone many revisions since this observation. The NAM hasn’t been updated since 2017. So that past experience may not hold.

Latest Thoughts on Potential Sunday Snow

Posted Thursday 02/19/26 @ 9:30 AM — As last night’s Quick Update indicated, several models which leaned towards the southern track (missing us) moved back towards a somewhat more northern track. This includes the ECMWF-AI, GFS, German ICON, Canadian GDPS-AI Spectral, HGEFS, AIGFS. and GEFS.

The latest ECMWF maintains a southern track, but shows some light snow in our area with the upper air low. The ECMWF has been the most consistent which earns it some respect in this forecast puzzle and is the least “phased” system.

The latest GFS has moved back to a forecast of substantial snow possible—

With the ECMWF’s consistent southern track, it is worthwhile to see what the statistical ensemble of the ECMWF shows regarding surface low position and location of most uncertainty—

The mean position of the low in the ensemble is more northern than the regular ECMWF and the greatest spread of the ensemble members is towards the northwest of the mean position, suggesting a strong possibility of a more northwestern track.

So we can’t ignore the ECMWF, but there’s too much uncertainty within the model variants to assume it to be correct.

Later today, the storm time horizon is coming within the forecast range of the NAM, RRFS and Canadian RGEM (all forecast out to 84 hours.) We’ll probably have a better handle on the forecast at that time. Updates later today.

Note— Most updates on this site are cross-posted on social media. To save time, posts labeled “Quick Updates” are not.

Quick Update

Updated Wednesday 02/18/26 @ 11:34 PM —Tonight’s GFS has returned to forecast of significant snow lasting into Monday. Updates tomorrow.

Uncertain Sunday Storm

Posted Wednesday 02/18/26 @ 5:26 PM — Over the past day, we’ve gone from a potential whopper of a snow storm to a highly uncertain forecast. With the advent of AI modeling, it had been my hope that this sort of great uncertainty with coastal storms would be a thing of the past. Apparently, the AI models are just as fickle as the older numerical models.

Regarding the storm forecast for later Sunday, the ECMWF maintains a southern track and suppressed development. The latest available 12z run shows it totally missing our area—

The latest GFS has reversed some this morning’s trend towards the ECMWF forecast and now shows a storm capable of greater than 6 inches snowfall—

The latest ICON model was closer to the ECMWF and the latest Canadian Global Spectral AI was in-between the GFS and the ECMWF.

The latest ECMWF-AI model is closer to the GFS than it’s own regular ECMWF.

So we have a highly uncertain forecast at this stage with snowfall forecasts ranging from zero to over 6 inches.

The storm is still over 110 hours in the future. We’ll need to wait for the event to come into the range of 84 hours for some input from the other higher resolution models. Stay tuned.

Sunday Storm Update

Posted Wednesday 02/18/26 @ 12:33 PM — It’s interesting that the lone outlier model (ECMWF) in yesterday’s cache of medium range models was actually leading the pack in forecasting a southern track and a somewhat delayed intensification of Sunday’s possible storm. The list of models forecasting a major storm have moved in the direction of the ECMWF today. Here’s the latest GFS—

There’s still plenty of time for things to change, but a southern track would be most consistent with the storm track pattern we’ve seen in recent weeks. Stay tuned.

Updated Wednesday 02/18/26 @ 6:48 AM —A quick update on Sunday’s potential storm. Last night’s models have moved towards the ECMWF with a more southerly and easterly track with less development offshore. Still stormy but much lower potential snow accumulation (4 inches or less). I’ll update later this morning with the new models runs (12z runs).

Weather Update: Wednesday-Sunday

Posted Tuesday 02/17/26 @ 7:21 PM — A warm front will move through Wednesday. Temperatures will reach the low 50s, but with the warm front, light showers and drizzle in the morning, some additional showers are expected in the mid to late afternoon. There may be some breaks of sun around noontime.

Following a weak cold front with high pressure to our north, an easterly flow on Thursday will drop the temperatures down with plenty of low clouds.

Another rather wet system approaches on Friday with rain for much of the day. A continued easterly flow will keep temperatures in the 40s.

Saturday looks cloudy in the morning, sunshine in the afternoon. Temperatures in the upper 40s.

Most models are predicting a deep coastal storm to form on Sunday. The exception is the ECMWF, which keeps the storm to our south.

Unlike the the past system that brought us light snow this pastSunday night, (and whose prior forecasts kept changing), this Sunday system is is being consistently forecast.

It seems that less a question of whether the storm will form, but whether it will be snow/rain or a mix with near-ground temperature forecasts uncertain. That said, many models are forecasting 6-12+ inches of snow at this time with the storm lingering into early Monday. I’m not ready to hang my hat on these high snow totals.

Here’s the latest GFS forecast for Sunday—

The following models currently have a similar forecasts to the GFS above— AIGFS, ECMWF-AI, Canadian Global AI-spectral, NAEFS, German ICON, HGEFS. They differ in temperature forecasts and have slight differences in track and intensity. An interesting system that bears watching, especially with the ECMWF being the exception.

Brief Transitional Week – Much Needed Rain by Friday

Originally Posted Mon 7:15 PM —I’ll call this week transitional: a transition from cold and dry to more seasonable temperatures and two possible chances for much needed rain. Unfortunately, there’s the possibility of a reversion back to snow and cold by late Sunday.

We’ll see plenty of clouds this week, starting Tuesday. There may be some clearing in the afternoon.

Milder temperatures, exceeding 50º on Wednesday will also be accompanied by clouds. The RRFS has much of the rain Wednesday afternoon staying far to our north.

Expect additional clouds Thursday with an approaching rainy system on Friday.

While it’s a long way off, the ECMWF-AI shows a potential snow event for Sunday.

I expect the forecast to change as the week progresses. Stay tuned.