Monthly Archives: January 2023

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Thursday

Update Wed 01/18 @ 6:19 PM — Low pressure will move in Thursday morning with rain starting between 7 and 10 AM—

Satellite Water Vapor image at 5 PM Wednesday with superimposed radar. (Click on image for a larger view.)

Rain through the day. Increasingly windy during the afternoon. Total rainfall is still expected to be from 0.5 -0.8″ rain —

Today’s HREF total precip by 2 AM Friday morning. Heavier rainfall to our north. (Click on image for a larger view.)

Friday looks fairly cloudy. Windy!

Today’s New York Times has an interesting article: “Can we talk about how we talk about the weather”. It addresses the increasing hype about storms and the use of exaggerated weather forecast descriptive terms. It touches on the new [absurd] trend in naming ordinary storms and pseudo-scientific, non-specific approach to what are “bomb cyclones” and “atmospheric rivers” and the “polar vortex”. And my favorite: media hype.

Long-time followers of this blog know of my disdain for all of this. I often see this blog as my crusade to cut through this on a regional level.

This blog has a small regular daily following, fairly large when a winter/summer storms loom.

As many of you regulars know, I’ve always geared what you read here towards authenticity, not the most re-tweets [or ‘re-toots’ in the Mastodon world].

Wednesday

Update Tue 1/17 9:39 PM — Tonight’s models are showing both periods of sun and periods of clouds for Wednesday. More sun than previously forecast.

Update Tue 01/17 @ 5:17 PM — A strong upper air flow (jet streak) directly over us on Wednesday with low pressure in eastern Canada will cause mild but cloudy conditions for us on Wednesday. Some strong mid-level disturbances with a strong lower level jet will mix down some of these higher winds.

NBM wind meteogram for Blue Bell PA (Click on image for a larger view.)

So Wednesday looks to be fairly cloudy (with some sun early and some occasional breaks in the clouds.) (More sun east of the city into NJ. ) It will be WINDY. Highs 50º sd 1.2º Blue Bell.

Thursday looks quite rainy. 0.5″- 1″ of rain expected.

No snow on the horizon, but several coastal storms are forecast— next Monday and next Wednesday/Thursday. There’s just not enough cold air for snow here.

Nonetheless, the weather pattern has changed a bit over the past few days and during a more ‘normal’ winter, this pattern would bring us a good chance of snow.

Tuesday Update

Update Tue 1/17 10:59 AM — So much for the showers dissipating.

Radar at 11 AM. More showers than forecast.

Follow up –The showers turned out to be minimal. A few sprinkles.

Update Tue 01/17 @ 10:00 AM — As expected, the radar echos have arrived earlier than forecast. Latest radar, supported by current models, has the showers dissipating as they move towards the immediate PHL area and will pass mostly north and south of us —

RADAR 9:45 AM. Most activity will dissipate as it moves eastward. (Click on image for a larger view.)

Monday -Tuesday Update

Update Mon 01/16 @ 9:45 PM — Tonight’s models are leaning towards very light precip staying to our south. A few sprinkles in the morning possible northern sections.

Tonight’s 00z NAM-NEST accumulated precipitation by 7 PM. Barely anything north of the city. (Click on image for a larger view.)

Update Mon 01/16 @ 5:10 PM — This afternoon’s models continue with the forecast of clouds for Tuesday with some very light rain (0.01-0.02″) moving in between noon and 3 PM. A comparison of the GFS and NAM models with current water vapor imagery suggests the models may be a bit slow with the light showers, so it wouldn’t surprise me if we see some very light showers as early as 11 AM.

Water Vapor image with superimposed NAM potential vorticity (PV) contours (yellow) shows the actual image is more northeastward than the models, suggesting the system is moving somewhat faster than the model forecasts. (Click on image for a larger view.)

I should add that this afternoon’s NAM-NEST has no rain for our immediate area, having the light precip move to our north and south. The German ICON and Canadian RGEM models are similar. So there’s some uncertainty whether our immediate area will get any precip.

Update Mon 01/16 @ 9:05 AM — It’s still breezy/windy Monday and the winds will make it feel colder than the thermometer reading.

As for Tuesday, there’s some uncertainty in the amount (if any) of rain we’ll get in our immediate area. The low resolution models have the rain missing us, moving to the north and south of us.

The higher resolution models do crank out a small total amount of scattered showers (0.01- 0.02″) as captured by the latest NBMv4.1 model—

Today’s NBM 12z 12 hour accumulated rainfall through Tuesday. Very light amounts. (Click on image for a larger view.)

Previously Posted Sun 8:16 PM —

Our snow-less winter will likely continue for this coming week into this weekend. At one point last week, I had posted that enough cold air was building in Canada in the coming 7-10 days that we could could see a change in the pattern with the cold air sagging down into an upper trough.

There is no sign of that happening in the current medium range model forecasts.

This week will continue the pattern of milder than average temperatures, punctuated by low pressure systems that track up to the Great Lakes with their attendant cold fronts moving through each time.

Monday: Fair skies. Still breezy. Temps in the mid 40s.

Tuesday: The first example of this repeating pattern will be on Tuesday with showers moving through. The showers lose upper air support as they pass through our immediate area mid day Tuesday, and it’s uncertain if we’ll get much more than a few sprinkles if anything.

Here’s the current RAP model forecast for Tuesday—

RAP model simulated composite radar for 1 PM Tuesday. The rain is moving into an upper ridge and falls apart. (Click on image for a larger view.)

Wednesday: A mix of clouds and sun. Mild in the 50s

Thursday: A more robust system moves through on Thursday with rain.

GFS model forecast for Thursday at 1 PM. (Click on image for a larger view.)

Friday: Clearing windy and colder.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

Monday

Update Sun 1/15 4:55 PM — Monday will be sunny and milder. Still somewhat breezy.

High temperature 46.3.º sd 1.6º NBM model – for location Blue Bell, PA

Sunday

Update Sat 01/14 @ 4:34 PM — The clouds hung in today.

Skies clear early Sunday morning. Sunday will be sunny, continued cold and still quite windy. Here’s the latest NBM wind meteogram—

NBM wind and wind gust meteogram for location: Blue Bell PA (Click on image for a larger view.)

Update Sat 01/14 @ 10:25 AM —

Water Vapor Image from Saturday shows moisture moving northwestward from intensifying low pressure off the Carolinas. Notice poor alignment of yellow and violet contours (“Potential Vorticity”) with darker-warmer areas of image suggests some modeling discrepancies between the GFS (yellow contours), NAM (violet contours) in our area and the actual upper air situation. Explains some of the differences in cloud cover forecasts. (Click on image for a larger view.)

Update Sat 1/14 8:08 AM — I often don’t watch the TV weather at 10 or 11 PM, but last night, I was curious how they were handling the uncertainty in the cloud cover for Saturday. Now I know how they handle it— they basically avoid the subject. I listened carefully; it just didn’t come up. On the ridiculous single weather picture summary at the end, they had the words, “some sun”. Yeah? When? How much? Where? If you weren’t really thinking about it, you didn’t realize that they didn’t tell you anything beyond it was going to be cold and windy.

So let’s jump to the chase: there’s still uncertainty and wide differences in the cloud cover forecast for today, Saturday. I’m leaning towards cloudiness until about 2-4 PM, where we may see “some sun” in some spots. I’m leaning on the new NBM version 4.1 for this forecast. (The new version 4.1 goes into operational service on Jan 17th).

Update Fri 1/13 9:18 PM — Tonight’s models, just coming in, continue to emphasize considerable cloudiness for Saturday especially from the city and eastward, and even a slight chance of scattered snow flurries.

Current water vapor image correlates to the western extent of the cloud cover forecast from tonight’s NAM and HIRESW models—

NAM and HIRESW models have the current water vapor plume above as the western extent of the clouds tomorrow. Others have it further west.

Previously Posted Fri 5:46 PM —

A cold front moved through on Friday, and a highly amplified jet stream trough will have us in colder weather for the weekend. The sharp trough will induce a low pressure system in the Atlantic. This system will be too far east to affect us, except for some cloudiness, especially at the Jersey shore on Saturday.

Latest GFS (18z) shows deep trough of cold air (as captured by the red 540 thickness line). Low pressure develops in the Atlantic, but too far east to affect us here except for some cloudiness. (Click on image for a larger view.)

Saturday

Cold air with the trough along with the coastal low will bring more cloudiness than originally expected in many areas, especially into New Jersey. It will be quite WINDY and cold. Cloudiness lifts during the afternoon hours.

NBM cloud cover forecast for 2 PM Saturday. More clouds than originally forecast. (darker is more clouds; violet contours are standard deviations) (Click on image for a larger view.)

High temperature Saturday 37.8º sd 1.7º NBM model – for location Blue Bell, PA

Sunday

Sunny, continued quite WINDY and cold.

High temperature 42.0º sd 1.5º NBM model – for location Blue Bell, PA

Monday

Sunny and milder. Still somewhat windy.

High temperature 45.2º sd 2.3º NBM model – for location Blue Bell, PA

Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

Friday

Update Fri 01/13 @ 9:34 AM — The rain has lingered longer than I had forecast. (The latest NBM and HRRR show no showers here at this time. Go figure.) The residual showers should be tapering off and moving off shortly to our northwest by about 11:30 AM

Latest Radar with superimposed Theta-E (yellow contours) and 500 mb wind streamlines (violet) . The tight packing of the Theta-E contours just west of the city shows the position of the front. (RAP model) (Click on image for a larger view.)

Friday and the Weekend

Update Thu 01/12 @ 5:19 PM — The showers and rain have moved in with a warm front, and additional rain will precede a cold front passage early on Friday morning.

The rain ends about 7-8 AM Friday morning.

The models aren’t predicting all that much rain (0.30-0.40 inches) in our area. The big story will be the WIND which is already picking up as I write this.

Gusts 30 to possibly 40 mph towards midnight tonight and windy conditions through the weekend. Here’s the NBM wind meteogram for Blue Bell—

Latest NBM forecast wind and wind gusts for location Blue Bell PA. (Click on image for a larger view.)

Temperatures will drop from the 50s Friday morning to the mid 40s in the afternoon, but the wind chill will make it feel colder. A mix of considerable cloudiness with some sun expected on Friday,

A secondary cold front moves through Friday evening and temperatures will drop below freezing by early Saturday morning. The weekend will be sunny, cold and dry.

One more thing — considerably colder air is finally pooling in Canada and in Greenland. In another 7-10 days, we will likely see some snowstorm activity as the cold air sinks south. (Just conjecture at this time. )

Thursday Through Friday

Update Wed 01/11 @ 5:10 PM — Moisture aloft moving in from the southwest over colder air at the surface will result in light showers or drizzle early Thursday morning. The rest of the day looks to be cloudy with additional showers later in the afternoon.

Thursday night: Rain develops during the evening hours Thursday and becomes heavier around midnight. Look for WINDY conditions to develop as the evening progresses. Thursday into Friday as a warm front approaches.

Friday: The warm front moves through before daybreak and then a cold front moves through Friday morning. Skies begin to clear late morning on Friday. It will be windy and temperatures will slowly drop. Friday will still be relatively mild.

A stronger cold front moves through early Friday evening.

Much colder for the weekend!

ECMWF forecast for Friday at 10 AM. Rain is ending here around that time. A sharp but progressive dip in the jet stream (as captured by the red 540 thickness line) will bring cold air on Saturday and Sunday. (Click on image for a larger view.)

Wednesday

Update Tue 01/10 @ 8:15 PM — Not much happening weather-wise, so let’s see if tomorrow’s cloud forecast does better. Thickening high cirrus clouds in the morning. Cloudiness increases about 10:30 to noon. Cloudy most of the afternoon. (Based on tonight’s 00z NBM and HRRR, just available.) Easterly winds will keep it colder to about 43º for a high.

Tue 5:36 PM Forecast Review — We had less cloudiness than any of the model forecasts had predicted. Cloud forecasts can be challenging.

Forecast Update

Update Tue 01/10 @ 9:25 AM — The cloudiness forecast below for today, Tuesday, has begun moving in. These clouds are the result of an upper air disturbance and trough moving through. High 42-44º

For Wednesday, a similar forecast with partly cloudy conditions giving way to mostly cloudy in the afternoon. High 43-45º

The storm for late Thursday into early Friday will be a rain event. Cold air arrives after the storm has departed. High ~55º

The weekend looks cold, but a moderating trend is expected next week with temperatures again above average. I don’t see any potential snowfall for us in the next week or so.

Previously Posted Mon 4:38 PM —

Overview

A benign weather pattern for us this week through early Thursday as a somewhat flat to ridge-like pattern will prevent any storms from forming.

Monday’s 12z ECMWF jet stream wind forecast for Wednesday at 4PM. Low pressure (L) at the surface and aloft is the remnants of the storm that is battering California on Monday. This low will move eastward as high pressure dips down from Canada. (Click on image for a larger view.)

Temperatures warm up a bit on Wednesday and especially on Thursday with the ridge moving eastward.

By late Thursday into Friday, a sharp upper air trough will develop and spawn a surface low off the coast—

Monday’s ECMWF jet stream wind forecast (300 mb level winds) for Friday at 4 PM Upper low (L) and deep trough will spawn a surface low (blue small L) off the coast. (Click on image for a larger view.)

Currently there isn’t much cold air that will move in before the storm departs late Friday afternoon, so all the precipitation will be rain for us late Thursday into Friday. While this could change, there hasn’t been any model suggestion of early deepening of the coastal low.

Tuesday

For Tuesday, an upper level trough with some disturbances will approach with partly cloudy skies becoming cloudy during the afternoon. No precip expected.

ECMWF 500 mb mid level contours with relative vorticity and humidity (Click on image for a larger view.)

By Wednesday, temperatures begin to moderate a bit.