Posted Sunday 04/19/26 @ 11:17 AM — The latest RRFS shows the rain to have exited the area by 2 PM
12z RRFS forecast for 2 PM Sunday (Click on image for a larger view.)
Posted Sunday 04/19/26 @ 10:31 AM — The cold front went through our area before daybreak as forecast. This cold front is what is called an “anafront“. Unlike most cold fronts, where the rain precedes and accompanies the front, an anafront has the warm air rising over the cold air wedge, causing rainfall to fall significantly behind the actual frontal passage.
Current water vapor and radar with superimposed RAP model parameters. The front is well off the coast, but the rain is approaching our area behind the front. (Click on image for a larger view.)
The rainfall is moving to the northeast as the main line of rain slowly moves eastward. The models have revised the total rainfall lower as most of the energy driving the showers moves off to the northeast before it gets here. Total rainfall is likely to be less than 0.20″ in the general Philadelphia area.
This event again captures a tendency towards drought-like conditions for our area, especially for the immediate PHL area and S. Jersey. Regular readers to this site know I’ve been talking about this developing dry pattern over the past month or two.
Weekend Forecast Update
Posted Saturday 04/18/26 @ 10:01 AM — Low clouds lifted a few hours ahead of what had been forecast. Mostly sunny for the rest of Saturday.
For Sunday, rain begins somewhat later than previously forecast, now about 8-9 AM. Rainfall amounts will be somewhat lower than forecast yesterday. Total rainfall about 0.3″. High wind gusts around 10-11 AM!
Rain ends and clouds lift between 3 and 4 PM Sunday.
A Quick Update
Posted Friday 04/17/26 @ 6:09 PM — Some areas saw showers Friday afternoon. Some additional activity may move into our area over the next hour or so. There is some strong support near Philadelphia and just east. We’ll see if they hold together.
Radar at 6 PM Strong area of vertical motion (light yellow contours) just southeast of Philadelphia. With daytime heating waning, we’ll need to see if thsese hold together.
Originally Posted Fri 4:55 PM —High pressure behind the front that broke our early Spring anomalous heat wave will move off to our northeast. An easterly flow will keep temperatures cooler on Saturday. A strong cold front moves through Sunday morning with some much-needed rain.
Saturday
High pressure departs and an easterly flow of air will bring low clouds in the early morning. These dissipate by late morning and we’ll have sunshine through high cirrus clouds. An easterly wind keeps temperature east of the city quite cool.
The winds increase from the southeast as a warm front approaches later Saturday night.
High Temperatures Saturday– warmer further west from the shore—
NBM highs at 4 PM Saturday. Warmer to the west. (Click on image for a larger view.)
Sunday
Cloudy with rain as a cold front moves through the area. Rain begins before daybreak. It becomes windy and gusty by late morning as the cold front moves through. There’s a chance of a thunderstorm embedded in the showers. Currently, about 0.5 inches of rain is expected. Rain ends and skies gradually clear by late afternoon.
Temperatures drop behind the cold front and remain in the 60s falling later in the day. It will be windy.
ECMWF-AI forecast for 8AM Sunday Cold front advances with a dip in the jet stream.. Temperatures drop and winds increase with the front. (Click on image for a larger view.)
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.
RRFS forecast for 4 PM Friday. Light scattered showers moving from the north towards the south-southeast. (Model precipitation forecasts rarely pinpoint the exact location for the scattered rainfall. Later (and earlier) model runs will likely show different areas receiving some light showers.) It’s just a general guide. (Click on image for a larger view.)
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.)
18z RRFS light rain accumulation by 9 PM. Rain moves off to the southeast. (Click on image for a larger view.)
Thursday-Friday
Posted Thursday 04/16/26 @ 12:35 PM — Temperatures today are expected to reach the low 90s.
13z NBM high temperatures at 4 PM Thursday. (Click on image for a larger view.)
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—
Today’s 12z NBM v 5 High temperatures The sd is 1.8º. I wouldn’t be surprised if we hit 93º Fine Black Contours are near ground (2m) temperatures in 1º increments. (Click on image for a larger view.)
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.
WV and RAP model potential vorticity. (yellow contours) The energy will end up along the NY State border with PA. (Click on image for a larger view.)
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.
Water Vapor Upper level with theta 305ºK tracks. Notice the red circled vertical motion (Omega). Negative is downward movement here. There is no support and slightly negative support for these storms as they move closer to Philadelphia. As posted earlier, we may get as much as 0.15 inches of rain close to the city. But they will then fall apart. Notice the curvature of the arrows…the curvature is anticyclonic, also causing the showers to fall apart. (Click on image for a larger view.)
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.
18z HRRR total accumulated rain by 3 AM (Click on image for a larger view.)18z RRFS total accumulated rainfall by 4 AM Wednesday. (Click on image for a larger view.)
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—
Upper level water vapor (channel 8) with Omega at 305ºK. (yellow contours- Positive = triggers) The RRFS below shows these disturbances only make it into central and southern areas of PA/MD. (Click on image for a larger view.)
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—
RRFS forecast at 8 PM. A strong wave (white circle) only makes into Central PA/northern MD at 8 PM. The maroon shading is RH at 700 mb. Purple/red – ‘pieces of energy’ Some activity may make it into western suburbs before falling apart by 9 PM. (Click on image for a larger view.)
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?)
RRFS forecast high temps at 4 PM Fine Black Contours are near ground (2m) temperatures in 1º increments. +(Click on image for a larger view.)
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.
Current RRFS (22z) forecast for midnight– light showers mostly north of the city. (Click on image for a larger view.)
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.
Water Vapor image at XX with superimposed RAP model MSL pressure (black contours), GFS/NAM potential vorticity contours (yellow & violet fine contours) with and surface wind barbs, LIGHT BLUE AREAS WITH ORANGE ARROWS ARE FORECAST TO MOVE OVER PHILADELPHIA . (Click on image for a larger view.)
An area of moisture with some lift will move over our area between 2-4 PM this afternoon. Very widelyisolated 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—
RRFS forecast for 8 PM Monday evening. Short waves (wavy blue lines) along with moisture (dark magenta) and vertical motion (dz/dt) red/yellow areas. (Click on image for a larger view.)
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.
Posted Saturday 04/11/26 @ 9:11 AM — You’ve already heard what a nice weekend we’ll be having. What can I add?
Well, as mentioned over the past week or so, I’m seeing a pattern of very dry weather for our area over the coming months.
The latest ECMWF-AI will be used to illustrate and the pertinent information is in caption below —
06z ECMWF-AI forecast for Thursday. The shading shows the Total precipitation through 2AM Thursday. The path of the rain (green arrows) follow a path that takes it around our area, not through our area.
Notice the contour (faint gold color) that extends and pushes in to our area. That contour is a 500-1000mb “thickness” line— it captures the 3-D shape of the air mass over us in the lower half of the atmosphere. .Most important is the sharp anticyclonic curvature of the line right over us. This anticyclonic curvature is associated with downward motion; rain/showers that move towards this area will fall apart. (Click on image for a larger view.)
Continuing from the caption above, as long as this sharp, anticyclonic curvature remains over our area, rain and thunderstorms will be inhibited. We’ve seen this exact same process in recent past summers during what became drought situations. The best we’ll see with this setup are thunderstorms that fall apart as they approach and rain areas that become very light and scattered.
This pattern of rain ‘avoiding’ our area has been happening for quite awhile. These patterns certainly can change. If it’s part of a recognized climate pattern called the Madden-Julian Oscillation, it could easily last 3 months or more. I’m not liking what I’m seeing.
Weekend Early Edition – Beautiful Weekend
Originally Posted Fri 9:57 AM —A weak front, currently just northwest of Pennsylvania, will pass through about 5 AM Saturday morning. The rain associated with this front will shear off to our northwest. A few very light showers possible northwest of the city around midnight with this front. A negligible amount of rainfall.
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) and radar. (Water Vapor Imagery reveals emitted water vapor infrared TEMPERATURE, NOT REFLECTED LIGHT from CLOUDS.) (Click on image for a larger view.)
High pressure builds in behind the front this weekend. Windy Saturday morning, then winds subside in the afternoon. Sunny with very light winds on Sunday. Highs 64º-68º Saturday and 69º-70º on Sunday. :
Another system comes through Monday. Rainfall again will stay far north and west of the city and South Jersey. We may see some scattered very light showers close to the city.
As I discussed last week, I see signs of a very dry pattern for our area in the extended range forecasts.
One more thing…
With a very dry pattern developing, I expect to see increasingly frequent wildfires forming with smoke issues affecting many areas in the coming months. Here’s the current HRRR smoke model showing wildfires and sources of smoke in the continental US—
12z HRRR smoke model shows sources of smoke- wildfires, other sources. (Click on image for a larger view.)
Weather… and Other Things 'Up in the Air'
Jet Streak illustration; The Right entrance region and the Left Entrance region have ascending flow that enhances precipitation.
