Update Fri @ 1:13 PM — Latest models have the rain likely ending in the immediate PHL area between 12 and 2 PM Saturday. Clouds break later in the afternoon. There’s still a lack of complete consensus regarding when the rain ends. A steep gradient with the rain— southern areas will receive much more rain than areas north of Philadelphia.
Today’s 12zHREF shows back edge of rain (1 hour prior accumulation) moving southward about 1 PM. Clouds are black, dark grey. (Click on image for a larger view.)
Updates this evening with the regular Weekend Weather Forecast feature.
Updated Thu 9:28 PM —The latest ECMWF just became available. It shows a very rainy Saturday, quite different than the GFS and NAM-NEST.
Today’s 18z ECMWF rain accumulation 2PM Areas of flooding rains in Maryland and Delaware (Click on image for a larger view.)
Update Thu @ 8:27 PM — Friday looks to be very warm and humid. Most models have us fairly rain-free during the day, but the model blend has widely scattered showers. High near 87º ± 2.2º
Rain moves in after midnight Friday. Heaviest rain south of Philadelphia.
There are large differences in timing and placement of this rain. Also uncertainty about when it clears up on Saturday. The NAM-NEST keeps the rain south of us and has it lingering The GFS has rain in our immediate area but tapers after 11 AM. The model blend (NBM) has considerable rain throughout the day, but I’ve seen the NBM overly prolong rain duration.
NAM-NEST Forecast for Saturday at 2 PM. Plenty of clouds (black shading), till raining in some areas. (Click on image for a larger view.)GFS forecast (simulated radar) and clouds (white) for 11 AM, showing rain departing PHL area but clouds linger into afternoon. (Click on image for a larger view.)
So uncertainty about clearing on Saturday, but I’m leaning towards the GFS. Updates Friday.
Updated Thursday Forecast, Wed 10:43 PM —The high resolution models are available again tonight. Several show an area of rain showers moving through western, southern suburbs and Philadelphia before daybreak and ending about 11AM Thursday. (The HRRR keeps all the rain south of our area.) The sun breaks out after noon.
Update Wed @ 8:58 PM — Several changes to the forecast. (FYI, there have been problems with NOAA data servers this afternoon. Many models were unavailable at their usual times. Some models are still giving errors during download. With so many models missing, I’m not going to attempt to retrieve them; this forecast is based heavily on the GFS, Canadian RGEM , German ICON and ECMWF models.)
For Thursday, except for the possibility of some light very widely scattered showers mostly in the morning, much of the area and the day will be dry.
For Friday, the front that was expected to bring rain will arrive much later in the day. Much of Friday will be rain-free.
Unfortunately for Saturday, the front will be slow to move south. Some showers and considerable clouds on Saturday into early afternoon, especially areas south and east of the city. Areas of Maryland and Delaware will have very heavy rain in the morning. Some clearing during the afternoon.
Update Wed @ 9:40 AM —There are changes in the forecast for Thursday through Saturday. Significant differences exist between the ECMWF and the GFS regarding the position of boundary that is to our south and the disturbances that will ride along it for tonight and Thursday.
Water Vapor Satellite image 9 AM shows boundary (dotted red line) with weak low pressure in Illinois. Low pressure expected to form (white circle) late Wednesday night into Thursday. It’s unclear whether much rain will make it into our area on Thursday. The ECMWF is more aggressive with the rain, the GFS not so much. (Click on image for a larger view.)
It now appears that showers to our south will not make it into the general Philadelphia area tonight. It’s unclear how much rain (if any) moves into our area on Thursday. The ECMWF is more aggressive with the rain Thursday than the the GFS. Will have to wait until more model runs come in.
Also unclear is the forecast for Saturday. Both the ECMWF and GFS have considerable clouds now for Saturday with a lingering chance of showers, especially in the afternoon and at the Jersey shore. So what appeared to be a clear cut forecast last night for the next few days will be not so clear cut. Updates this evening.
Updated Tue 9:53 PM — A diffuse, stalled frontal boundary just to our south and will remain quasi-stationary through Friday. Upper air disturbances will move along this boundary to our south on Wednesday. Any showers will essentially stay to our south through Wednesday.
It will be quite humid on Wednesday morning. Dew points above 70°, but will drop in the afternoon.
Thursday: This diffuse boundary will attempt to move back northward Wednesday night with some showers that will linger into Thursday morning. The boundary won’t make much progress, but with it somewhat further north, we’ll be in the path of additional upper air disturbances. Showers and thunderstorms likely late Thursday afternoon.
Friday: A stronger kicker will move through on Friday with showers and thunderstorms.
The weekend looks good.
Update Tue @ 5:48 PM — An unsettled week weather-wise coming up. No strong systems. Several chances of some showers or storms. The upcoming weekend weather looks good!
Tue @ 5:46 PM — Forecast Review— As expected, the storms moved off mainly to our south and north. Not much happening in the immediate PHL area. The showers stayed together in NJ more than forecast but no strong thunderstorms with such low CAPE values. The HREF forecast graphic below probably did the best.
Update Tue @ 3:47 PM — Latest HRRR continues with the strongest storms moving south of Philadelphia and another batch north of Allentown.
18z HRRR Strongest storms (6PM) move south of Philadelphia and then dissipate in NJ. Only lighter showers in other areas. (above graphic shows accumulated 1 hour precipitation) (Click on image for a larger view.)
The lower resolution ECMWF does show some activity into Philadelphia. (I waited years to get some access to the ECMWF data. Adding the ECMWF to my forecasting toolkit this past 6 months hasn’t really improved my forecast accuracy, whether it be forecasting snow storms or thunderstorms.)
Update Tue @ 11:34 AM — The morning high resolution models are showing any storms will be scattered in two groups and less impressive than even previously forecast. Many areas may not receive any rain.
12z HREF forecast shows lowering CAPE eastward and scattered storms in two groups. Many areas may not see any rain. (Click on image for a larger view.)Latest HRDPS (12z) shows storms at 6 PM diminishing in intensity as they make it into Philadelphia. Diminishing CAPE value (shading) as one goes eastward. (Click on image for a larger view.)
Update Tue @ 9:50 AM — This morning’s models continue with a forecast of a scattered group of storms affecting our area this afternoon and night. This likely will NOT be an organized solid line of storms.
As was the case last night, the high resolution models show two scattered groupings of storms, one that moves north (Allentown area) and another that moves mostly south of us.
The NAM-NEST shows the storms move through in two waves. One about 5 PM and another about 11 PM. They also move through in two general groupings, north and south of PHL.
NAM-NEST showing the earlier (5 PM group of storms) mostly north of us and the 11 PM group of storms (2)
The latest HRRR shows a somewhat similar scenario for 6 PM—
12z HRRR showing two groups of storms at 6 PM with significant helicity just south and west of PHL. Color shading is CAPE. (Click on image for a larger view.) 12z HRRR showing elevated vertical shear just south of Philadelphia. Also shown is storm motion vectors and Shear direction vectors. (Click on image for a larger view.) Any storms that develop in this area may be severe, although CAPE values still diminish significantly in NJ.
As discussed just below, CAPE values diminish significantly from west to east. Storms will diminish as they move into NJ.
Previously Posted Mon 9:09 PM —
A complex disturbance will affect our area late Tuesday afternoon or evening. There are large differences in the model forecasts, with a number of models having any storms either weaken and/or move off to our north.
The overall jet flow is depicted here —
GEFS jet wind forecast (250 mb winds) at 5 PM Tuesday. Jet flow breaks up and circles back north of our region. (Click on image for a larger view.)
The jet flow complexity over our area is shown in the current water vapor imagery—
Water Vapor image Monday evening shows disturbance (1) that may affect us on Tuesday afternoon. The breakup of the jet flow with a bend eastward is captured by the fine high level water filaments bending back (2) (Click on image for a larger view.)
The models have one thing in common: they’re forecasting CAPE values that are high west of Philadelphia but rapidly diminish east of the city.
Here’s the HRDPS which captures this—
Canadian HRDPS forecast surface CAPE values for 5 PM Tuesday, moderately high west of the city and diminishing just east to near zero. (Click on image for a larger view.)
The trajectory of the impulse visible on water vapor (1 above) varies with each model. The NAM-NEST has strong storms north of our area, near Allentown.
The latest RAP and HRDPS show strong thunderstorms about 4-6 PM moving into the city, but dissipating as they move east. The ICON has the storms closer to 7-9 PM and the ECMWF has most of the strongest activity moving to our north, like the NAM-NEST.
HRDPS forecast for 5 PM Tuesday, showing a line of heavy rain and storms. This line is forecast to fall apart as it moves further eastward. (Click on image for a larger view.)RAP model forecast for 5 PM Tuesday- simulated radar superimposed on CAPE values. (Click on image for a larger view.)
The impulse expected to trigger these storms is quite a distance away at this moment. I expect significant changes in the forecast by tomorrow morning. A couple of things worth noting: CAPE values to our west are high and vertical shear is also forecast to be highly elevated. Helicity values also elevated, especially northern Bucks county. Precipitable water (PWAT) values also very high (2.2-2.4″) indicating potential for heavy rains.
Updated Thu 10:34 PM — The forecast continues to evolve for the weekend. First, an upper air wave moving through on Friday will trigger showers and thunderstorms in far northwest areas mid Friday afternoon and these storms will move near the immediate PHL area late afternoon into the evening. Most but not all of the activity northwest of the city.
CAPE values are forecast to exceed 2200 j/kg, so strong storms are possible, but severe not expected.
The front sinks slowly through our area on Saturday. Strong storms and showers possible throughout the day, but late afternoon and evening are the most likely times.
Sunday and Monday are looking better and better. Tomorrow’s Weekend Weather forecast will nail things down
Updated Thu 7:42 AM — The forecast for the weekend continues to improve, as the GFS now shows more spotty precip during the day and the heaviest rain during the evening hours. Most models show clearing by Sunday afternoon. Monday looks good.
Updated Wed 10:03 PM — A cold front will sink towards us late Friday and stall over our area for Saturday and at least part of Sunday as waves develop inducing showers and thunderstorms for Saturday and part of Sunday. Some significant rain for Saturday. The ECMWF is the most optimistic for Sunday, the GFS less so. Things look better for Monday. Stay tuned.
Updated Tue 10:34 PM — Cancel those showers. Tonight’s models have no showers for Wednesday afternoon.
Update Tue @ 9:27 PM — For Wednesday, a weak front (trough) moves through the area late in the day. The models have been back and forth on the chance of showers late afternoon, but the afternoon models are showing a chance of showers between 5 and 8 PM in the northwest and far northwest suburbs.
18z HREF shows showers northwest suburbs at 7 PM. Most models keep these north of the immediate PHL area. (HREF 1 hour precipitation + spread in contours) (Click on image for a larger view.)
FYI — Tomorrow, June 28th, the NWS-NOAA will launch its new supercomputers into operation, beginning with the 8 AM EDT (12z) models. The system being upgraded is referred to as WCOSS (Weather and Climate Operational SuperComputer System) The increase in speed/capacity is quoted as 3x the current system.
I’m not sure if this will result in a faster model release schedule (as an example, the 00z GFS currently takes 3 hours 44 minutes to create the first 24 hour forecast, not available until 11:44 PM EDT. It sure would be nice to have that earlier in the evening.)
Surely, new models expected for release in 2023 will be more complex and higher resolution. Exciting stuff!
Update Mon @ 5:48 PM — The balance of the week looks to be fairly nice and increasingly warm. There’s an increased chance of scattered thunderstorms Wednesday evening; otherwise quiet.
Todays’ GEFS jet stream winds forecast (250mb) for Sunday July 3. A slight cyclonic upper flow will interact with moisture moving up from the southwest. A frontal boundary right over us. (Click on image for a larger view.)
Unfortunately, the weekend may be affected by a front that somewhat stalls out. Current model forecast is that much of Saturday will be OK, but we may have showers and thunderstorms late afternoon Saturday through much of Sunday.
Way too early to hang our hats on that forecast. Monday, the 4th, looks good.
Forecast Review— Overall, most areas had 0.25-.50 inches of rain with several areas in NJ getting over an inch.
Update Mon @ 11:07 AM — The frontal boundary is on schedule with showers and thundershowers expected to enter the immediate Philadelphia area between 12:30 and 2 PM.
Water Vapor image shows upper air ‘trigger” for some shower intensification this afternoon (Click on image for a larger view.)
Heavy rain in some areas but no severe weather in the immediate PHL area. Stronger storms possible east of the Delaware during the afternoon.
12z HREF 2.5 km showing simulated radar and accumulated rain (green contours) at 2 PM. (Click on image for a larger view.)
Showers should end about 3-4 PM in the city with areas of sun breaking out in some locations.
Updated Sun 11:22 PM — Tonight’s models show thunderstorms of greater intensity as the front moves into New Jersey early afternoon.
Update Sun @ 7:38 PM — Most models show the timing of the front as described below. But, the latest RAP model and GFS have the main wave of the front moving through much earlier. The GFS has showers starting as early as 10-11 AM and the RAP as early as 8-10 AM.
Update Sun @ 5:44 PM — A cold front will move through our area Monday morning through early afternoon with showers and thunderstorms.
The front is likely to come through in two waves— an early period 6-8 AM with very widely scattered showers and storms. Another wave approaches about noon to 2 PM with a more distinct line of showers and thunderstorms. No severe storms expected here. Heavy rainfall (1-1.5 inches) in some locales will be the main impact.
Today’s 18z NAM forecast for 2 PM showing heavier rains (3 hour totals) north of the immediate PHL area as well as southward. Some areas may have 1.5″ rain, some may have less than 1/2 inch. (Click on image for a larger view.)
Since the front is coming through early, daytime heating effects will be minimized. This will reduce the likelihood of any severe weather. The energy with this front is distributed in two waves, also reducing severity. Possibly stronger storms will be nearer the Jersey shore and southward into Delaware.
Updated Thu 10:35 PM — Tonight’s models have moved away from widely scattered showers for Friday. Additionally, they’ve moved away from Friday’s cloudiness as well. Looking at the humidity fields, I wouldn’t be surprised if there’s some periods of low clouds on Friday. I guess we’ll see.
Updated Thu 7:30 PM — Friday’s weather forecast will be interesting. Many models show sunshine and fair weather clouds. The higher resolution models show sunshine with periods of clouds and very widely scattered sprinkles from mid morning into the afternoon, especially northern areas.
Update Thu @ 11:40 AM — The moderate rainfall we’re getting Thursday morning will taper off about 2-3 PM Thursday afternoon. Clouds linger with a few very widely scattered showers.
Things improve considerably Friday through Sunday as the low pressure system that has been persistent will move away. High pressure will dominate through most of Sunday. A southwesterly flow of more summer-like air will move in.
GEFS (mode) forecast for 2 PM Sunday. Cold front in Ohio Valley moving eastward will arrive late Sunday or Monday. High pressure in western Atlantic (H) has replaced the upper low and will bring much warmer, summer-like temperatures.(Click on image for a larger view.)
Update Wed @ 7:58 PM — The most recent models show rain lingering into early Thursday afternoon before ending. We may see some light rain as late as 2-3 PM. Considerable lingering cloudiness. Some heavier rain expected in the morning Thursday; here’s the latest RAP model accumulated rain—
Today’s 21z RAP model accumulated rain forecast. (Click on image for a larger view.)
Updated Wed 6:02 PM — Current radar and water vapor imagery around 5:40 PM looks pretty close to the 06z HREF forecast (2 AM run) from this morning—
Radar/water vapor imager from 5:40 PM Wednesday shows the lack of rainfall in the immediate PHL area. The similarity with this morning’s HREF forecast (image below from 7:42 AM) is probably as good as it gets.
Update Wed @ 7:42 AM — With the backdrop of low predictability, today’s weather: partly sunny with increasing cloudiness during the afternoon. Most of the shower activity holds off considerably in our area, as we’ll be in the middle of two areas of showers. Any showers we get will be light and scattered before 6 PM and any evening showers look light and scattered as well.
This morning’s HREF forecast for 6 PM shows Philadelphia between two areas of rain. This feature is shown by several models. The heaviest rain remains far west of Philadelphia today and as it moves into our area from the west late tonight, much of the heavier activity diminishes as it moves towards us by Thursday morning.
Updated Tue 6:59 PM — The lack of precise predictability of the upper level low’s position off the New England coastline is already affecting today’s forecast— the narrow band of showers expected to move in here this evening will likely pass to our east.
The same upper low is now expected to spawn a surface low near the Carolina coast; the path of this low is expected to move northward. As you can tell, this is a complex scenario.
As best as we can predict, the next band of showers will set up in central Pennsylvania on Wednesday and will mostly stay to our west, although some shower activity may affect our area, especially late afternoon and evening on Wednesday.
The shower activity late Wednesday will be with us Thursday morning, but things dry out by Thursday afternoon.
The upper low is expected to reform in the same general position as it is in now. Forecast uncertainty will remain.
Currently the weekend looks good.
Update Tue @ 9:30 AM — This week’s forecasts are totally dependent upon the movement of an upper level low off the New England coast. Last night’s models show this low moving southwestward back towards us on Wednesday.
In the meantime, a warm front in western PA will attempt to move closer to us this afternoon with showers and possibly thundershowers breaking out this afternoon between 5 and 9 PM.
Water Vapor image Tuesday morning: Warm front (red line) will attempt to move closer towards us as an upper air disturbance ( blue area with white arrow) moves over us late Tuesday afternoon, sparking showers and possibly thundershowers. The upper low (L) will move closer to us on Wednesday, impeding the movement of the warm front. (Click on image for a larger view.)ECMWF upper wind forecast (jet stream) for Wednesday evening shows the upper low (L) having moved southward and westward.
The difficult to forecast position of the upper low and the difficult to time disturbances moving down from the north will determine our weather over the next few days.
Updated Mon 10:41 PM — Tonight’s models have clouds with some breaks on Tuesday. Much reduced chance of showers during the day, but several models have showers moving in between 4 and 8 PM.
Update Mon @ 4:59 PM — The models continue to keep the very hot weather in the center of the country with a upper low pressure trough in the northwest Atlantic.
For a change of pace, we’ll look at the ICON model which captures the current pattern and the outlook—
Monday 12z ICON model forecast for Thursday: large hot ridge over Texas with impulses moving across the top (2). Upper low and highly amplified trough (1) in the western Atlantic. “Bermuda High” pressure(3) not really near Bermuda. The uncertainty around the position and configuration of (1) and the impulses (2) makes for a highly uncertain forecast for later in the week. (Click on image for a larger view.)
Tuesday’s forecast has already changed from what it was a day earlier. While much of Tuesday will be cloudy, the trend has been for any showers to be very light and widely scattered.
However, there is an increased chance of showers, possibly thunderstorms, about 5 PM on Tuesday.
Water Vapor imagery Monday afternoon shows disturbance ahead of warm air (orange-red). We’re on the eastern edge of a warm front boundary. Whether it moves west or east will depend upon the position of the trough in the northwestern Atlantic. This will determine both the amount and timing of any showers and storms this week. (Click on image for a larger view.)
Wednesday looks to have more rain than Tuesday.
Thursday may continue to have showers., especially east into NJ. Again, this week’s forecast is unusually low confidence.
Stay tuned.
Previously Posted Sun 9:51 PM —
The persistent pattern of an upper ridge in the mid section of the country and an upper trough over our area will shift a bit over the week, but we’ll still be in the upper trough to some extent. Temperatures in our area will be near or below average.
ECMWF jet stream winds (250 mb) on Monday. The uncertainty for the week: in what position the upper low north of Maine will be later in the week. The strong accentuation of this eastern trough will diminish and there’s large uncertainty whether the low will cut off and move southward or even southwestward! Too much uncertainty between models. (Click on image for a larger view.)
As the caption above explains, there’s uncertainty in the forecast for us.
Tonight’s Water Vapor image shows the forecast dilemma. We are in the very dry flow from the north. If the jet position shifts slightly eastward, we’ll be in the path of numerous disturbances moving in from the Great Lakes. (Click on image for a larger view.)
So far, the models are showing several periods of showers/rain: Tuesday, late Wednesday into Thursday and maybe even a period on Friday.
Needless to say, this past weekend wasn’t typical weather for June and the coming week won’t be either.
No sign of the usual summertime Bermuda High effect; it’s well out to our east.
I expect changes in the forecast as the week unfolds. Much depends on the position of that upper low. Stay tuned.
