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
Update Fri 06/09 @ 9:20 AM — A disturbance rotating around the upper low over eastern Canada will bring a mix of cloudiness and sunshine late morning into the afternoon and evening. Most models keep any showers too far to our west, but the Canadian models have been consistently forecasting the possibility of light showers around here, most likely during the evening—
Canadian HRDPS accumulated rain forecast by 11 PM Friday. The Canadian models are on the high end of the spectrum in predicting shower activity near Philadelphia. Most areas will receive no rain. (Click on image for a larger view.)
Showers, if any, will be light and scattered. Update Fri 06/09 @ 9:47 AM — This morning’s RAP and HRRR are more similar to the above HRDPS. showing more shower activity in and near Philadelphia.The RAP shows a line of showers/thundershowers about 8-9 PM passing through Philadelphia.
As for smoke, here’s the very latest smoke level forecast at near-ground level for 4 PM Friday—
Today”s 12z HRRR. Some areas, mostly in Chester county and areas south of the city will have elevated smoke at near ground level. (Click on image for a larger view.)
The weekend is looking much warmer and currently, no rain is forecast. A change in the general weather pattern still on-track for next week.
Philadelphia Smoke & Friday Forecast Update
Update Thu 06/08 @ 5:58 PM —Smoke levels improved this afternoon, but it appears that more smoke and particulates will move through through this evening, before the end of the Phillies game.
This evening’s smoke levels—
18z HRRR smoke forecast for 10 PM this evening (Thursday) Shading is total column smoke concentration while white contours are areas of significant near ground level smoke. The worst areas will be far southwest of the city this evening.
For Friday evening, about 24 hours later, smoke levels improve significantly—
Friday —As for the weather, some scattered showers and thundershowers are possible Friday afternoon and evening. Most of the activity will be far west of the city and near the Jersey shore.
Philadelphia Smoke Forecast Update
Update Thu 06/08 @ 7:25 AM — Here’s the latest HRRR extended smoke forecast. This is the forecast for smoke at ground level to 8 meters above ground level (about 26 feet above ground)
06z HRRR forecast for NOW (7 AM) Thursday. Still very high smoke concentration. This is forecast smoke at 8 meters above ground height(26 feet) (Click on image for a larger view.)
By noon, the air quality at ground level is improved, especially west of Philadelphia—
06z HRRR smoke forecast at ground level at noon (Click on image for a larger view.)
The forecast above is for smoke levels 8 meters above ground. While the ground level smoke will be significantly reduced in some areas today, the sky will look quite hazy and smokey due to high levels of smoke still being present at mid and upper levels of the atmosphere.
Unfortunately, the HRRR shows low level smoke increasing during the second half of the Phillies game tonight at 9 PM—
06z HRRR smoke forecast at 9 PM Thursday evening. (Click on image for a larger view.)
Regarding rain on Thursday, while some areas far northwest and in Delaware/Maryland may get some showers this afternoon and evening, little to no rain is currently expected in the Philadelphia area today.
Philadelphia Smoke Forecast Update
Update Wed 6/07 @ 10:22 PM — The latest HRRR shows the Philadelphia area in the thick of smoke at 10 PM—
Tonight’s HRRR smoke at near ground level near maximum tonight. (Click on image for larger view.)A
The HRRR shows that things improve temporarily Thursday afternoon near ground level—
HRRR smoke forecast for 2 PM Thursday. The sky will still look smokey because upper levels will still have plenty of smoke. (Click on image for larger view.)
Update Wed 06/07 @ 8:35 PM — As I mentioned earlier, I never thought I’d be programming for HRRR smoke model downloads for Philadelphia. I’ve gotten a better handle on these specific parameters and I’ve updated the graphics.
This afternoon’s HRRR shows things improving at the surface during the early afternoon Thursday, but things get nasty again during the evening.
18z HRRR total smoke near ground at 1 PM Thursday. Things improve temporarily during the afternoon as somewhat cleaner air moves in from the west. (Click on image for a larger view.)
Most HRRR model runs only forecast out to 18 hours. The next HRRR model run that forecasts out to 48 hours will be available after 10 PM. I’ll update later this evening with the new HRRR regarding the smoke forecast for tomorrow.
As for the weather pattern change, it’s still on track. Some showers are possible later Friday and some rain later Monday, as the jet stream finally flattens and the blocked pattern breaks down by next Wednesday.
Philadelphia Smoke Forecast
Update Wed 06/07 @ 5:50 PM — I never thought I would have to download a smoke forecast parameter for the Philadelphia area. But the HRRR model has a separate model for smoke (particulate matter- fine) and I’ve spent a fair number of hours today leaning how to program the download and process this parameter.
It appears that the current HRRR model keeps the heavy smoke with us through most of Thursday, with some improvement early Thursday evening in southern areas as some cleaner air punches in from the west.
HRRR forecast Particulate Matter Fine (smoke) for Thursday evening at 7 PM. A tongue of somewhat cleaner air punches in from the southwest Thursday evening. I have no experience with this sort of forecast and I don’t know how accurate the HRRR is in forecasting smoke. (Click on image for a larger view.)
Where there’s smoke there’s fire
Update Wed 06/07 @ 9:42 AM — The current smoke situation here is a serious health risk. All the result of the incredible stretch of dry weather that has affected the local Philadelphia region but also areas in Canada.
One of the many capabilities of the HRRR is low level smoke concentration forecasts. Here’s the current HRRR analysis at 8 AM today—
HRRR smoke analysis shows the Philadelphia area in a relative maxima of smoke concentration. Each contour is increasing/decreasing smoke concentration. (Click on image for a larger view.)
Unfortunately, more smoke is on the way. Here’s the HRRR forecast for this afternoon and evening—
HRRR smoke near ground forecast for 6 PM Wednesday. (Click on image for a larger view.)
Update Tue 06/06 @ 5:40 PM — Despite some radar echos, most areas had little rain. Perhaps the RRFS will be a big improvement in forecasting when it’s released the end of this calendar year?
Radar image at 4:38 PM suggests that some areas were getting rain. Most of those echos were caused by rain evaporating before it reached the ground. Most areas had no rain, including areas with radar echos.
Wednesday looks to be sunny and continued cooler than average, with highs in the mid 70s.
Several models are now forecasting a large scale change in the stagnant jet pattern and are predicting rain for our area next Monday and Tuesday. A significant change in the jet stream pattern is expected by next Wednesday through Friday.
Update Tue 06/06 @ 7:23 AM — The uncertainty with the isolated/scattered showers this afternoon continues. Capturing this is a forecast comparison between the NAM-NEST (also shown below) and the new RRFS model (still experimental)—
The RRFS (Rapid Refresh Forecast System) and the NAM-NEST total precipitation forecast comparison for today, Tuesday. As mentioned last night, the NAM-NEST is in the high end of total precip forecast for today, Tuesday. (Click on image for a larger view.)
There’s another chance of showers this Thursday afternoon or evening.
As mentioned over the weekend, there are signs that the long-standing blocked pattern we’ve been in for over a month will be breaking down between Monday and Wednesday of next week. Expect a change to warmer and possibly wetter weather.
Update Mon 06/05 @ 5:32 PM — It’s been back and forth with the chance of showers on Tuesday. There’s a range from little to nothing with the GFS, while the NAM-NEST is forecasting the most shower coverage. Showers possible as early as 2 PM, but 4-6 PM is most the most likely time frame. Most areas will see no showers.
Here’s the NAM-NEST total accumulation forecast for Tuesday which is at the high end—
Today’s 18z NAM-NEST model forecast total precipitation for Tuesday afternoon and evening. (Click on image for a larger view.)
The Canadian HRDPS is probably the closest to the HREF and HRRR and is probably closer to the the likely actual amounts and coverage—
Today’s 12z Canadian HRDPS total rain forecast for Tuesday. (Most areas get nothing.) (Click on image for a larger view.)
The experimental RRFS has almost no shower activity.
Update Sun 06/04 @ 8:37 PM —I think l need to retract that ‘dry’ forecast for Tuesday. Several of this afternoon’s models (18z) are showing scattered shower/thundershowers, similar to what we had the other day.
Previously Posted Sun 5:08 PM —
The blocking pattern (Omega block Ω ) that’s been with us for weeks will maintain it’s hold over our weather through the coming week.
(There are finally signs that the block will break down between the 10th and the 15th of this month and we’ll see a change to a more typical summertime pattern likely next week —More heat, more humidity, maybe more thunderstorms.)
Monday looks to be mostly sunny to partly sunny/partly cloudy in the afternoon.
Tuesday: Regarding the current blocking pattern, a deep upper cyclonic flow currently over New England will rotate a disturbance around its center resulting in the formation of a surface trough moving through our area on Tuesday.
Sunday afternoon Satellite Water Vapor image shows upper low near coast of Maine. and the potential disturbance that will move through on Tuesday with what appears to be a low possibility of some showers. A similar scenario for Thursday. (Click on image for a larger view.)
For Tuesday, the latest GFS, ECMWF and today’s earlier NAM-NEST have some potential showers moving through, both earlier in the day and especially late afternoon Tuesday. We could use the rain.
Unfortunately, the latest NAM-NEST, Canadian GEM and the still-experimental RRFS have little in the way of showers for us from this system. (Little in the way of clouds too.) I’m leaning towards a fairly dry Tuesday for us.
After a sunny Wednesday, another disturbance may rotate through on Thursday with more clouds and maybe some sprinkles.
