Category Archives: Philadelphia Weather Outlook

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

Rain Totals

Update Mon 06/12 @ 8:16 PM — The rainfall totals were somewhat similar to the model forecasts in a general way. The models captured the rapid decrease of rainfall in New Jersey and this morning’s emphasis on a westward maxima was somewhat correct. Even the rain maxima in Delaware county was somewhat captured, although no model had that rain location as the local maximum.

It was much needed rain!

While it’s still raining in Bucks county and northeastward, here’s the MRMS estimate of rainfall that fell today through 7 PM—

MRMS rainfall through 7 PM (Click on image for a larger view.)

Good news…there’s more rain possible on Wednesday. More about that tomorrow.

Monday Storm Update

Update Mon 06/12 @ 4:02 PM — The rain arrived before 3 PM and the current radar suggests that the heaviest rain axis may be further east, through Philadelphia as forecast last night’s models, instead of a more westward track, as forecast with today’s models.

Demonstrating this is the current MRMS radar composite with superimposed vertical velocity pressure (white box) from today’s RAP model—

RADAR at 3:45 PM with superimposed vertical velocity pressure from RAP model (Click on image for a larger view.)

Generalized severe weather still doesn’t appear likely, but some severe localized cells always possible. We could definitely use the rain.

Monday Storm Update

Update Mon 6/12 12:54 PM — So my 12:12 update indicating a later start and a westward axis of rain appears to be an error of inadequate model spin-up time. I’m going to lean back towards the earlier model run forecasts with a 2-3 PM onset and heavier rains extending into Philadelphia. I guess we”ll see. We need the rain.

Update Mon 06/12 @ 12:12 PM —The latest models are moving towards a more westward position of the heaviest rain. Additionally, the rain is now expected to move in at 3-6 PM range rather than the earlier start time.

This trend is more in line with the GFS, ECMWF and ICON models, but I’m not sure if the change in the mesoscale models is just a manifestation of inadequate model spin-up time.

Here’s the latest HRRR precipitation forecast —

12z HRRR total rain forecast. These model distribution of the rain should never be taken literally. The immediate Philadelphia area is in the red circle. (Click on image for a larger view.)

The latest live MRMS with superimposed RAP model moisture convergence and omega (vertical velocity) supports this westward emphasis—

Monday Storm Update

Update Mon 06/12 @ 9:08 AM — The trends listed last night continued with the 06z model runs early this morning.

There are large differences in forecast rainfall between the low resolution global models (which tend not to have explicit convection (thunderstorm) parameterization) and the high resolution mesoscale models which do.

This event will have significant convection and I’ll be leaning towards the HRRR, NAM-NEST, HRDPS and HREF models with explicit convection.

Timing: light showers, as forecast by the HRDPS yesterday are moving through the area this morning. Showers and thundershowers move in to western suburbs as early as 11 AM to noon. Heavier activity moves in 2-3 PM and continues with a peak between 5 PM and 7 PM.

Precipitation Amounts: Heavy rain from this system appears to be the major component. Here’s the latest HREF model total precip forecast, which is on the higher end of the HRDPS and HRRR—

06z HREF precipitation totals. (Click on image for a larger view.)

Severity— As mentioned yesterday, the severity parameters are in the moderate range with some very localized moderate-severe in a few locations between 5-6 PM. Wind gusts are not forecast to be as high as other recent events. That doesn’t mean severe weather can’t happen. Overall, severity possibilities are lower than recent severe events.

HRRR
Severity
Parameter		Sept 1 , 2021
Tornado Outbreak
(example of highly severe)		Recent
April 1st 2023 Tornadoes
(Example of severe)
(06-12-23)
Today’s
06z HRRR Forecast		Impact
CAPE
Joules/kg		 3500-4200 900-1100 900-1100⇩⇩
Helicity
m^2/s^2		 1350 655406⚐
Vertical Shear
1/sec		40-4640-4518-20⇩
Precipitable Water 2.7″0.83”2.0″⇑ ⚑
Lifted Index
º K		minus 6minus 9.3ºminus 3.3⇩⇩
HRRR Hail
inches		1.91.41.5⚑
Peak Wind Gusts
mph		 40-5040-5035.5⚐
Storm Motion Shear Vector
Alignment		Aligned – ~ 90ºAlmost alignednon-aligned↓
250 mb
Jet Stream Wind
mph		6313542⇩⇩
Severity Parameters Impact: ⚑ indicates favors Severity ⚐ indicates Possible Severity
↓ indicates works against Severity ⇩ Significant, but less impact

Monday — Finally Some Rain!

Update Sun 6/11 10:54 PM — A quick update. Tonight’s early models have the following trends—

  1. High resolution models have the heavy rain through Philadelphia.
  2. Low resolution models keep the heaviest rain west of Philadelphia
  3. As forecast by the earlier HRDPS, some showers possible in the morning.
  4. Several models have the heaviest rain in the evening.
  5. Several models have significantly less rain in New Jersey.

Updates tomorrow morning.

Previously Posted Sun 5:56 PM —

Over the past week, the models have been advertising a significant rain event for us on Monday with a frontal passage. If nothing more, one should be impressed that this weather event has been consistently forecast almost a week in advance.

The real grit lies in the details, and there’s increasing evidence that much of the area will get 0.6″ to over 2.0 inches of rain, much more rain than most areas have seen in over a month.

As is often the case, the models’ grasp on the forecast severity parameters (vertical shear helicity CAPE PWAT Lifted Index ) tend to become more meaningful within 18- 24 hours of the event. That’s been the case with tomorrow’s event.

Here are the trends—

• There has been a general trend towards higher amounts of rain, both in eastern PA and NJ.

• There has been a general increase in what I call the severity parameters. However vertical shear values have remained at the low end.

• The actual cold front comes through about 9 PM (Blue Bell) but most of the rain comes well ahead of the actual front.

There’s still a range of model timing with the Canadian model having a line of thunderstorms move through as early as 11 AM to 3 PM, with a second line moving through about 6- 8 PM with the cold front.

Our NOAA models (e.g. HRRR) have scattered storms from about 2 PM through 10 PM with more emphasis on late afternoon and early evening for the heavy activity.

Latest HRRR—

Sunday’s 18z HRRR total rainfall forecast for Monday. The exact placement of these heavier rain bands should never be taken literally. (Click on image for larger view.)

Sunday afternoon’s HREF model—

18z HREF total rainfall through 8 PM Monday. (Click on image for a larger view.)

Check back on Monday for updated forecasts and my “severity table”.

#weather #paweather #wx #pawx #philadelphia #phillywx

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia #phillywx

Friday Forecast Update

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.