Monthly Archives: March 2024

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Quick Weekend Outlook

Update Fri 3/29 11:16 PM — Too many things happening today, including a router malfunction and home electrical breaker issue. So no Weekend Weather Forecast in its usual form. Just want to say that the showers on Saturday won’t arrive until after 6 PM, despite what I’m hearing on TV.

Weekend Outlook Early Edition

Posted Friday 03/29/24 @ 9:48 AM — Today, Friday will be sunny and quite windy.

The first of a series of fast moving clipper disturbances will move across the ridge ridge (see yesterday’s graphic) to bring some light showers late Saturday.

WV image Friday morning shows the first of several clippers that will bring light showers Saturday evening. Another clipper and a warm front will bring a chance of showers and rain Monday through Wednesday. (Click on image for a larger view.)

We should see increasing cloudiness between noon and 2 PM Saturday. Light showers possible after 5-6 PM. High near 60.

Easter Sunday will have sunshine through high cloudiness. No rain. High low 60s.

Friday through Sunday Outlook

Posted Thursday 03/28/24 @ 5:51 PM —

Thu 5:51 PM —Forecast Review — The models over-forecast the rainfall in Philadelphia today. A nose of dryer air kept rainfall to a minimum west of the Delaware river.

I guess the Phillies could have played today, but except for the wind, they’ll have a nicer day on Friday for their season opener.

Friday does look sunny, but very windy, especially in the afternoon. Highs 54º Blue Bell, 57º Philadelphia.

Saturday looks partly to mostly sunny, less wind. There may be a period of cloudiness early afternoon. Some clouds move in again towards evening with showers possible in the mid evening. Some models have these showers staying to our north.

A series of disturbances moving across a somewhat stationary upper air ridge will begin to affect our weather beginning Sunday. Here’s the NAEFS forecast for Sunday—

NAEFS model statistical “mode” version with overlayed GEFS model “bias-corrected” precipitation forecast for Sunday. Disturbances moving over the upper ridge may bring unsettled weather late Sunday through Wednesday (Click on image for a larger view.)

An approaching disturbance will bring a mix of clouds and sun on Sunday. The current forecast has showers moving to our south later Sunday, but this could change.

Thursday Update through Saturday

Posted Thursday 03/28/24 @ 11:01 AM — Current surface analysis shows a stalled front just through Philadelphia with waves of low pressure developing along the front—

Current Surface Analysis with Mean Sea Level pressure, surface winds and surface 3 hour pressure delta (HRRR) I’ve drawn the cold front’s approximate position. (Click on image for a larger view.)

It appears that the eastern track forecast for the heaviest rainfall from this system was the most accurate, and additional rainfall through this afternoon is expected with it being considerably heavier along the Jersey Shore and east of Philadelphia.

The rain tapers off between 4 and 6 PM from Philadelphia westward. Here’s the latest NAM-NEST at 5 PM Thursday—

03-28-24 12z NAM-NEST 1 hour accumulated rainfall at 6 PM (Click on image for a larger view.)

For Saturday, a clipper-type system will bring considerable clouds and showers late—about 6 PM according to some models and a bit earlier, late afternoon, according to some other models.

Thursday Forecast Update- Phillies Opener Rescheduled

Posted Wednesday 03/27/24 @ 5:18 PM — The rain came in slowly on Wednesday, but by 3 PM, most areas from Philadelphia westward were getting rain from this developing coastal system.

Phillies Opening Day has been rescheduled due to the wet forecast. The model trends over the past day have the heavy rain shield even further westward again, with rain likely all day Thursday and well into Thursday evening. The heavy rainfall totals forecast has increased. Here’s the latest NBM —

03-27-24 18z NBM total accumulated rainfall Wednesday into Thursday. (Click on image for a larger view.)
Wednesday Thursday Update

Posted Tuesday 03/26/24 @ 10:14 PM — It looks like light scattered showers slowly move move in from the west on Wednesday, as early as 11 AM but most likely between noon and 3 PM. Rain coverage increases but there may be a lull during the evening until about 3 AM Thursday morning.

Scattered rain through Thursday, much heavier near the Jersey Shore.

The models are converging on a more eastern track for the heavy rain axis. In the city and west, it will be less than 1″. Heavier rain east and at the shore.

Here’s the current GFS forecast rain accumulation through Thursday —

03-26-24 18z GFS rain accumulation through Thursday. Contours are 0.25 inch increments (Click on image for a larger view.)

It’s not looking great for the Phillies opening day.

Tuesday Update

Posted Tuesday 03/26/24 @ 8:04 AM — Last night’s models have less cloudiness from Philadelphia and westward this morning. Thickening clouds still expected during the afternoon.

For Thursday, there’s a range of model forecasts regarding the heavy rain banding. The majority of the models keep the heaviest rain east into NJ and even further eastward. The GFS maintains heavy rain into Philadelphia—

Here’s the latest ECMWF—

Last night’s ECMWF shows the heaviest rain in the Atlantic. (Click on image for a larger view.)

Here’s the latest GFS—

03-26-24 06z GFS accumulated rain forecast by Thursday 10 PM (Click on image for a larger view.)

For last Saturday’s rain, the GFS also had a consistently westward track and was correct, but it had support from other models. This time, the GFS is the most westward. Updates later.

Tuesday

Posted Monday 03/25/24 @ 7:49 PM — A stationary area of low pressure in the western Atlantic will rotate clouds into our area on Tuesday. An approaching cold front will be here on Wednesday.

GFS forecast for 5 AM Tuesday shows a stationary vertically stacked low in the Western Atlantic. Moisture around this low will rotate into our area from the east on Tuesday. A high pressure ridge over our area will block precip from the west and east. The precipitation from the cold front is visible in the western sections of Ohio. (Click on image for a larger view.)

Tuesday -An easterly wind and thickening clouds during the day. Highs 51-53º but high uncertainty with a high NBM standard deviation of ± 3.5º

Some showers move in from the west on Wednesday, but rainfall totals look light.

Incredibly, the models are trending towards another 1″ + rainfall on Thursday, especially for NJ.

Overview

Originally Posted Mon 3:08 PM —Following Monday’s delightfully sunny but cool weather, the week ahead will be cloudier with several systems expected to affect us.

Here’ the satellite current water vapor image—

WV image Monday afternoon. A cold front in the Midwest will have its energy shear off to our north as it passes through Wednesday into Thursday, bringing showers. Low pressure is expected to develop along this front and will bring some rain to our area Thursday, but the main system will be slightly to our east. (Click on image for a larger view.)

A cold front in the Midwest will have its energy shear off to our north as it passes through Wednesday into Thursday, bringing showers. Low pressure is expected to develop along this front and will bring some rain to our area Thursday, but the main system will be slightly to our east.

Here’s the current GEFS forecast for Thursday—

03-25-24 12z GEFS forecast for early Thursday morning. Low pressure will move slightly east of our are, but some rain is still expected here. (Update: latest models Monday show possibility of 1″ rainfall. )( Click on image for a larger view.)
Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx

Saturday Rain Totals

Posted Saturday 03/23/24 @ 5:25 PM — We had a lot of rain in just 14 hours or so. Here’s the MRMS rain totals as of 4 PM—

MRMS combined rain gauge & radar-based measurement 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 I didn’t post these models, the GFS and the Canadian models correctly forecas the placement of the heaviest rain axis just east of the Delaware River into NJ, although the GFS rain totals were too low.

The NBM did well with a forecast 3.6″, as did the HREF forecast (PMM) version, but both had the rainfall axis too far west into Philadelphia and western suburbs. The ECMWF was slightly too far west as well. The experimental RRFS too far west and its rainfall forecast was too high!

Winds will be picking up over the evening hours tonight becoming quite gusty, but subsiding by the afternoon Sunday.

Rain Update

Posted Saturday 03/23/24 @ 12:58 PM — The heaviest rain has entered our area over the past hour or two, about two hours ahead of the model forecasts.

MRMS Instantaneous Precipitation Rate (PRATE) at 12:52 PM. (Click on image for a larger view.)

The latest hourly HRRR suggests that the rain will be tapering off between 2 and 3 PM and ending about 3-4 PM from the southwest.

At noon, many areas already had 2-2.75 inches of rain. according to the MRMS. I’ll post a ‘final’ rainfall total later this afternoon.

Saturday Rain Update

Posted Saturday 03/23/24 @ 8:09 AM — Some areas have already received 0.75 inches of rain and the heaviest rain is still to our southwest—

MRMS instantaneous precipitation rate at 8 AM Saturday. Heaviest rainfall is still southwest in Virginia and will arrive here between noon and 2 PM. (Click on image for a larger view.)

The expected time for the rain to taper off and end is between 4 PM and 7 PM. Clearing will occur from southwest to northeast later this evening.

Here’s the latest rainfall forecast (NBM) —

03-23-24 06z NBM accumulated rainfall by 1 AM Sunday. (Click on image for a larger view.)
Weekend Weather Update

Posted Friday 03/22/24 @ 8:07 PM — A few more afternoon models have come in since my last post. High rainfall accumulation is the trend and the HREF and [experimental] REFS show even higher rainfall for our area than the NBM model (shown in previous post.)

The HREF and REFS are “ensembles”, meaning that they combine and average different model runs, different models and/or different ‘perturbations’ of the same model. Both the HREF as well as the experimental RRFS-ensemble (REFS) also create means (averages) in several ways.

The HREF and the REFS include statistical averaging algorithms called PMM (“probability matched mean”) and LPMM (“local probability matched mean”), mathematical approaches which attempt to eliminate a weakness of ensemble mean forecasts that causes the magnitude of precipitation to be smoothed out in the mean— Important maxima are reduced in magnitude and low magnitude values are spread over too a large an area in simple arithmetic means.

Here’s the PMM and LPMM outputs for today’s HREF model which attempt to correct for problems with ensemble simple means —

HREF- Probability Matched Mean—

HREF Probability match mean (PMM) total precipitation forecast for Saturday. (Click on image for a larger view.)

HREF Local Probability Matched Mean precip forecast for Saturday—

HREF Local Probablity Matched Mean precip totals for Saturday (Click on image for a larger view.)

The LPMM can sometimes create artificially high values and the PMM version is often found to be more reliable. You can see that the PMM version is quite similar to the NBM model (shown just below in the previous post.)

Either way, it looks like a lot of rain tomorrow!

Posted Friday 03/22/24 @ 5:42 PM — This afternoon’s models continue to forecast impressive amounts of rain falling over a 16 hour period. The latest NBM, which tends to be conservative, has the following rainfall forecast through Saturday evening—

03-22-24 18z NBM accumulated rainfall through 11 PM Saturday night. As always, the exact placement of the heaviest rain bands can’t be taken literally, but it gives a good idea what to expect in our region tomorrow.

Saturday

Light rain begins after midnight tonight The heaviest rain about 2-3 PM Saturday, but like the Giant Food ad, where the shopper is being told about the melons, “they’re all good ones”, all areas in the Delaware Valley tomorrow will have heavy rain.

Winds will be elevated along the Jersey shore all day, but around Philadelphia, winds will pickup about 10 PM Saturday evening.

NBM high temperatures: Blue Bell, PA 54º Philadelphia, PA 56º
uncertainty slightly above average (based on standard deviation): ± 2.3º

Sunday

Lingering showers at the shore early morning. Clouds around Philadelphia break for sunshine during the mid to late morning. Temperatures mild early, peaking around noon, then falling during the afternoon.

NBM high temperatures early : Blue Bell, PA 55º Philadelphia, PA 56º

Early Edition- Friday and Saturday

Posted Fri 8:34 AM — Two low pressures systems near the Gulph of Mexico will interact and move towards us late Friday into Saturday.

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. Two low pressure systems will interact over our area .

But first some coverage of today, Friday— It will be sunny with relatively light winds. The area of cloudiness mentioned last evening to move in mid afternoon today is looking less impressive with last night’s models. So sunny for much of the day, with high clouds late.

What will be deceptive today will be the high temperatures. While the the TV/radio forecasts will give you the high temperatures, they don’t often tell you when in the day they will occur. Today, the high temperature will be reached late in the afternoon and it will be fairly chilly through at least noon. Basically, the winds will shift to the south about 2 PM, bringing the warmer temperatures by about 4-5 PM.

Getting back to Saturday, the two systems developing will interact and a supply of Gulph moisture will result in heavy rain on Saturday.

03-22-24 06 z NAEFS model statistical “mode” version overlayed with GEFS model “bias-corrected” precipitation model forecast for 2 PM Saturday. The heaviest rain moves in early afternoon. (Click on image for a larger view.)

Rain moves in 2-3 AM Saturday morning and will be heavy during the day with 2″-3″ inches of rain expected.

The latest NBM confirms yesterday’s trend for heavier rain, with an axis of heaviest rain though the immediate PHL area—

03-22-24 12z NBM accumulated rainfall by 8 PM Saturday. contours are 0.1 inch increments. (Click on image for a larger view.)

It becomes very WINDY after 8-9 PM Saturday. More details later this afternoon or early evening.