Posted Sunday 07/28/24 @ 10:00 AM — Except for the HRRR, the models are holding back the clouds at the shore until this evening. Sunny skies with haze from wildfire smoke here in the city. (The smoke levels here are not anywhere near the levels of last summer. )
The upper level low to our east will result in some instability showers/thundershowers late Monday afternoon. Increasing chances of showers and thunderstorms Tuesday and Wednesday due to an approaching warm front.
Forecast Update
Posted Saturday 07/27/24 @ 5:20 PM — Today’s ample supply of “fair weather clouds” were courtesy of the upper level cyclonic flow around the developing closed low, as discussed below.
The forecast for Sunday remains mostly on-track. There will probably be more “fair weather cloudiness” around the city and this afternoon’s higher resolution models are predicting increasing high and mid level cloudiness at the Jersey shore about 3 PM—
Today’s 18zNAM-NEST cloud forecast for 4 PM Sunday. (Low clouds- blue, mid-level clouds- maroon, high clouds- yellow tan) (Click on image for a larger view.)
Posted Saturday 07/27/24 @ 9:32 AM — Last night’s ECMWF has backed away from a strong westward movement of the upper closed low on Sunday; it has joined most of the other models with a northward or west-northwest motion.
As a result, clouds with this system should remain offshore until Sunday late afternoon or evening. (Only the experimental RRFS has cloudiness at the shore Sunday afternoon.)
FYI, some of the haze in the sky over the past day or so is from smoke and particulates from the wildfires in Jasper Canada. A plume sunk south of us this morning—
12z HRRR smoke – integrated vertical column smoke/particulates . (Click on image for a larger view.)
An general increase in smoke particulates is forecast. Smoke at the ground level is not currently forecast.
Originally Posted Fri @ 5:24 PM — —This looked to be a weekend where the forecast required no meteorologist; anyone could make a slam-dunk forecast for sunny skies both days with just a barometer and a wind vane.
However, things are looking a bit more interesting for later in the day Sunday, especially at the Jersey Shore.
First, high pressure builds in for Saturday with sunny skies—
NAEFS model statistical “mode” version with overlayed GEFS model “bias-corrected” precipitation forecast for Saturday. (Click on image for a larger view.)
For Sunday, there’s now some uncertainty regarding the cloud cover, especially east towards the Jersey shore on Sunday afternoon due to the formation of a closed low in the mid and upper atmosphere—
NAEFS upper 500 mb mid-level closed low Sunday 2 PM. This may cause cloudiness east into NJ and at the Jersey Shore. (Click on image for a larger view.)
The position of this closed upper low is also uncertain, with the latest ECMWF model having it closer to the coast and with a track that retrogrades it westward going into Monday.
So not a slam dunk forecast. Still likely sunny and quite nice in Philadelphia.
Saturday
Sunny and quite nice. Warmer.
NBM high temperatures: Blue Bell, PA 87º Philadelphia, PA 88º uncertainty (based on standard deviation): very low ± 0.9º
Sunday
Mostly sunny in the morning, some increasing cloudiness in the afternoon, especially east towards the Jersey Shore. Slightly more humid with dew points near 60º
NBM high temperatures: Blue Bell, PA 89º Philadelphia, PA 90º uncertainty (based on standard deviation): very low ± 0.9º
Posted Thursday 07/25/24 @ 6:56 PM — The majority of models got it right today with the rain suppressed to the south and east; the exceptions were the Canadian RGEM and HRDPS which were surprisingly very wrong.
There’s a slight change in forecast for Friday. The front will hang up a bit to our south. There will be sunshine on Friday, but sunshine through high cirrus clouds. especially from the city southward. Areas to the north of the city will have blue skies.
It looks like sunshine and blue skies return for Saturday and Sunday.
Posted Thursday 07/25/24 @ 8:52 AM — No significant change in the forecast. The vast majority of today’s models continue to show showers in areas southeast of the city, in Delaware, Maryland and southern South Jersey. The exceptions, not to be ignored, are the Canadian RGEM and HRDPS, which show some showers as far north as Philadelphia. The timing is between 3 PM and 6 PM.
Here’s the HRDPS precipitation forecast through 6 PM. An outlier of a forecast, but the HRDPS has a history of sometimes being correct with when the NOAA models show no precip—
06z HRDPS total precip by3- 6 PM tonight. The lighter yellow-green is convective (thunderstorm) precip. Just food for thought…this forecast is an outlier. (Click on image for a larger view.)
CommentaryPosted Wednesday 07/24/24 @ 4:53 PM — I’ve been wondering when all those hurricanes predicted for this season are going to form?
There’s still one more week in July, but there will need to be a significant increase in tropical activity in August, September and October to reach the expected number of named Atlantic storms forecast this season. Somehow, I expected more activity by this time.
Right now, the Atlantic is quiet. Seems somewhat strange.
Forecast Update
Posted Wednesday 07/24/24 @ 4:32 PM — A few upper air disturbances triggered showers today, but the heavier rainfall was spotty and was not enough to break the rainfall deficit we’re in.
A few additional showers are developing late this afternoon and evening ahead of a surface front moving through tonight.
NEXRAD radar 4 PM Wednesday
Winds will shift to the west and then northwest during the day Thursday reducing the chance of showers to isolated, as drier air moves in. The upper level trough still has to move through, so periods of lingering clouds mixed with some sun are expected. Heavier showers possible in Delaware.
Friday looks to be sunny and seasonably warm with much lower humidity.
Wednesday Forecast
Posted Tuesday 07/23/24 @ 5:54 PM — As I had forecast this morning, our area didn’t have any showers or thunderstorms; we had considerable sunshine.
As for showers, there’s a wide range of model forecasts, but overwhelmingly the trend is for any heavy rain to be south and east of Philadelphia. The latest HREF captures this—
18z HREF model showing total precip forecast through 11 PM Wednesday evening. Light precip is unlikely to change our overall dry conditions. (Click on image for a larger view.)
Earlier models had forecast some heavier showers in the immediate Philadelphia area before daybreak Wednesday into the morning hours. The latest Canadian models have backed off of that, but I think it’s still a possibility, based on the HREF.
More definite is the chance of scattered showers and thunderstorms, late morning, early afternoon and especially Wednesday evening.
As I’ve been saying for several days, this pattern is diffuse and the triggers are mostly upper air disturbances that are difficult to predict and time. Check back Wednesday morning for an update.
Tuesday Update
Posted Tuesday 07/23/24 @ 9:00 AM — Some areas had showers Monday night but most of our area received little rain.
For today, Tuesday, the clouds we have may break for some sun or sunshine through clouds. Despite the forecast I heard on the radio this morning, I don’t see much in the way of showers or thunderstorms during the daytime hours today, based on the models.
That said, there are disturbances in the upper air flow that could theoretically result in showers, so no guarantees of a dry day.
Current 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. The weak low over northeastern PA will exit. The next round of showers this evening is at the bottom left corner of the image. (Click on image for a larger view.)
There’s much more chance of showers and storms tonight, especially south and east of the city.
Tuesday Outlook
Posted Monday 07/22/24 @ 7:30 PM — The first round of rain on Monday mostly missed the Philadelphia area and immediate surrounding counties. Here’s the MRMS Precipitation Estimate for the past 12 hours—
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.)
While some showers are moving in this evening, most of the rain this evening will remain to our west… and to our east. The latest HRDPS captures this—
18z HRDPS shows rain in NJ and in Central PA tonight. Little activity right here near Philadelphia. Just clouds (black grey) and light showers. (Click on image for a larger view.)
The daytime on Tuesday looks to be just cloudy with perhaps some sun through high and mid-level clouds. There’s a chance of showers mostly north of our area.
I’m going to be taking the forecast day by day. This weather pattern is a bit too diffuse to try to forecast more than 36 hours in advance. It does look like more rain is likely on Wednesday, timing to be determined.
Monday Update
Posted Monday 07/22/24 @ 9:04 AM — Based on last night’s models, the main bolus of rain will come in this evening and its trajectory is to keep the heaviest rain south and east of the immediate Philadelphia area.
That’s probably correct in part, but the latest radar shows showers and some embedded storms several hours ahead of the model forecast—
Radar/MRMS at 8:45 AM Monday (Click on image for a larger view.)
Getting the timing right with this system is going to be a challenge. But I would expect some spotty showers by early this afternoon and sooner in South Jersey. It doesn’t look like this first bolus of rain today will impact our overall dry conditions.
Originally Posted Sun 9:16 PM —An upper level trough combined with a stationary front to our south will result in unsettled conditions for much of this upcoming week.
A moisture riding over the stalled front will bring showers and possible thundershowers late Monday morning and continue for the balance of the day. Showers will be spotty in our area, while areas west (central PA) will have heavier rainfall.
Weak low pressure will form on Tuesday.
GFS forecast 2 PM Monday. (Click on image for a larger view.)
Additional waves of low pressure and moisture moving over the stalled front will bring additional periods of shower, rain and thunderstorms Tuesday through Thursday. Exact timing of these waves of moisture and the axis of heaviest rain to be determined.
Right now, the heaviest activity seems to be timed for the evening and nighttime hours, but that could easily change.
