Posted Friday 03/08/24 @ 9:36 AM — Sunshine through a thin layer of clouds this morning will give way to sunshine for much of the afternoon Friday. High cirrus clouds move in mid afternoon and cloudiness thickens by 5 PM from the southwest. Light winds today with highs 55º-57º.
An interesting setup for Saturday as two jet streams interact over us—
GFS jet stream wind forecast for 9 PM Saturday. Highly cyclonic northern jet with strong southern jet. Faster areas in the jet stream are called “jet streaks”. The red box is an area called the ‘left exit region’ of the jet streak , an area of maximal upward motion. Heavy rain is most likely in this area, which will be just northwest of the Philadelphia region. Small changes in the position of the jet streak can result in major changes in forecast rainfall. (Click on image for a larger view.)
There’s a wide range of model forecast rainfall amounts for Saturday, depending on each model’s forecast position of the jet. As little as 0.7″ to 2″ is forecast. Hopefully, we’ll have some clarification later.
Today’s NAM-NEST has joined yesterday’s ECMWF in forecasting light drizzle or rain as early as 11 AM Saturday. Likely time is 11 AM to 2 PM.
The above jet stream configuration will spawn strong low pressure that will pass right near us. Colder air behind the low will be give us a windy and cold day on Sunday.
Stay tuned for the Weekend Weather Forecast late this afternoon.
Friday Sunshine
Updated Thursday 03/07/24 @9:26 PM — Sunshine will make its appearance on Friday. There may be a period of cloudiness moving through in the morning hours. Some high cirrus clouds come in from the west around sunset. Somewhat breezy. Highs near 58º in the city, 56º in Blue Bell.
Saturday starts quite cloudy. Light drizzle or rain moves in from the southwest as early as 11 AM (ECMWF) but more likely around 12-2 PM. Heavier rain moves in by evening. Another 0.8″- 1.1″ expected. An easterly wind will keep it temperatures a bit cooler, in the low 50s.
03-07-24 18z [experimental] RRFS 1 hour rain accumulation by 1 PM Saturday. (Click on image for a larger view.)
Colder and windy on Sunday.
Thursday Update
Posted Thursday 03/07/24 @ 9:07 AM — We had a few bright spots and even some blue skies for a brief period west of the city this morning. However, an upper trough will swing through today and a mix of clouds is expected to return with even some drizzle in eastern NJ.
Last night’s HREF model most closely predicted this early brief clearing and here’s its forecast for 1 PM that includes the slight possibility of some drizzle or sprinkles —
03-07-24 06z HREF cloud and simulated radar at 1 PM today. (Click on image for a larger view.)
Sunshine for Friday
Forecasting Sun instead of Rain
Posted Wednesday 03/06/24 @ 4:50 PM — Over the years, I’ve hoped this web site would be come a destination for storm forecasts. After this week, I may need to rethink this and become the destination for when we’ll see the sun again.
The rain moved in pretty much on schedule Wednesday. A generalized 1.1″ to over 2 inches in NJ.
Today’s REFS (experimental RRFS ensemble) total rainfall. (Click on image for a larger view.)
There has been some question about whether the rain would linger well into Thursday.
It now appears that the rain will end during the early morning Thursday. No sun, but maybe some bright spots as varying amounts of low clouds appear to be the current model forecast.
Skies clear for Friday and we’ll see the sun return, but some cloudiness works its way back in Friday afternoon.
Saturday looks cloudy. Rain moves in early afternoon (1-2 PM, earlier western sections)
Wednesday Forecast Update
Posted Tuesday 03/05/24 @ 5:48 PM —The next system to bring rain will arrive as early as 11 AM Wednesday (earlier in S Jersey) . The system now appears to be somewhat elongated and is expected to bring heavy rain through at least Thursday morning. The heaviest rain will be along the NJ shore.
Current satellite water vapor (5:30 PM) mage 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 next system arriving Wednesday morning has become somewhat elongated and rain will linger into Thursday late morning. Some of the models suggest light drizzle and slow clearing, so the ‘rain free’ period for Thursday afternoon mentioned in the earlier update may not occur. Friday still looks good. (Click on image for a larger view.)
Yet Another Update- Looking for Sunshine
Posted Tuesday 03/05/24 @ 11:50 AM — Looking for a break in the rain, the latest GFS suggests that the rain ends late Thursday morning and we may be rain free from that point through Friday.
It looks like we’ll have sunshine on Friday. Cloudy on Saturday with rain mainly far western areas early. Rain moves into the immediate Philadelphia during the mid afternoon Saturday.
Tuesday Rain Update
Posted Tuesday 03/05/24 @ 10:56 AM — Over the weekend, it appeared that we might have some significant breaks between the low pressure systems expected this week. That’s looking less likely through Thursday.
We’ve had the rain since last night (total amounts less than forecast except in NJ) , but currently we have the low pressure center just approaching our area—
Current (~10:30 AM) 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. Additional light rain and drizzle is expected until about 5 PM or so.
We’ll have a break in the rain tonight (still damp) but the models are showing rain moving back in as early as 11 AM to 1 PM on Wednesday—
03-05-24 06z REFS (experimental) 1 hour rain plus standard deviation at 1 PM Wednesday. (Click on image for a larger view.)
An additional system is forecast to move in on Thursday. There may be little to no break in the action .
Rainy Tuesday and Wednesday and Saturday!
Posted Monday 03/04/24 @ 5:51 PM — Low pressure is forming as expected and rain will move in after midnight tonight and likely continue on and off until about 4 PM Tuesday.
Another system seems to have accelerated and will be here on Wednesday. Another system arrives Saturday, possibly sooner.
The latest water vapor satellite image captures the setup—
Current satellite water vapor image (5:30 PM ) with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. Tuesday’s storm (1) is just to our south. Our next storm (2) has accelerated somewhat and will be here on Wednesday. It looks like another rainy Saturday as storm (3) will be ahead of a cold front. (Click on image for a larger view.)
Rainfall on Tuesday will be less uniform than last Saturday’s storm—
03-04-24 06z HREF accumulated rainfall forecast for Tuesday. (Click on image for a larger view.)
Previously Posted Sun 5:47 PM —
This Week’s Weather Overview
This week, we’ll see a continuation of the mild trend started this past weekend with a complex, split jet flow and an upper trough off of the southeastern US coast that will induce low pressure formation.
The latest ECMWF jet wind flow (300 mb level) shows the weak upper trough.
03-03-24 12z ECMWF 300mb wind speed and heights. Forecast is for Tuesday. I’ve drawn the trough axis in blue and accentuated the weak wind flow isopleths outlining the upper trough. Cold air remains above the 500 mb thickness line (dark red contour north ) and mild air southward. (Click on image for a larger view.)
Here’s the NAEFS forecast for Tuesday showing a near coastal low (very similar structured to the system that gave us the rainy day Saturday) —
03-03-24 12z NAEFS with GEFS bias-corrected precip overlay forecast for Tuesday. Low pressure over us on Tuesday. Another forming in near the Gulf will be here on Thursday. (Click on image for a larger view.)
Sun 4:15 PM —Forecast Review — It’s a good thing I didn’t go whole hog into the HRRR cloud forecast— It couldn’t have been a nicer day! The HRRR, since its revision/update almost two years ago , tends to overstate low cloudiness.
I’m looking forward to the HRRR’s replacement, the RRFS, which seemed to do much better—
03-03-24 12z experimental RRFS cloud forecast for today. The grey shading is about 28% cloud cover, closer to reality than the HRRR. (Click on image for a larger view.)
Sunday Update
Posted Sunday 03/03/24 @ 9:06 AM —The models have for the most part turned to a forecast of mostly sunny, (with some occasional clouds) but more cloudiness in northern Bucks county and western Montgomery county.
The HRRR still maintains a fair amount of low level cloudiness developing here this afternoon—
03-03-24 12z Latest HRRR still has clouds developing this afternoon. (clouds are grey black) (Click on image for a larger view.)
Very warm. The NBM and ECMWF have us reaching 65-66º in Philadelphia and 65º in Blue Bell with an uncertainty of ± 2º. If the HRRR is correct, those numbers may be a bit high.
Clouds move in this evening and Monday will be mostly cloudy. A similar wet system to Saturday’s (inverted front becoming a coastal low) brings rain Tuesday.
Saturday Update
Posted Saturday 03/02/24 @ 7:38 AM — Last night’s models continue a trend towards heavier rainfall today (Saturday). The GFS and HRRR have rainfall totals over 1-1.3″.
The [experimental] RRFS has even higher totals—
03-02-24 06z RRFS. The RRFS continues to be improved and is now at beta 0.8 with recent changes in data assimilation. (Click on image for a larger view.)
Rainfall should be ending from south to north about 6-8 PM tonight.
Clouds break for a very nice, warm, sunny March day on Sunday. A few clouds possible in the afternoon Sunday. Highs 62º Blue Bell, 64º Philadelphia (± 2.2º)
Previously Posted Fri 9:36 PM —(Delayed post due to some model data download issues, now resolved.)
As posted yesterday and this morning, our weather will be affected Saturday by an inverted trough along the coast that will become a weak low pressure system moving very near us. Rain starts after midnight tonight and lasts through much of the day and possibly early evening on Saturday.
Saturday
Cloudy with rain until early evening. Mild
NBM high temperatures: Blue Bell, PA 51º Philadelphia, PA 54º uncertainty (based on standard deviation): ± 2º
Rainfall amounts;
NBM rainfall totals through Saturday. (Click on image for a larger view.)
Sunday
There’s been uncertainty with the forecast for Sunday. As posted this morning, it appears now that we’ll have sunshine for much of the morning but with low clouds with breaks of sun developing in the afternoon. Very mild!
NBM high temperatures: Blue Bell, PA 62º Philadelphia, PA 63º uncertainty (based on standard deviation): ± 1.8º
Posted Friday 03/01/24 @ 10:34 AM — The high layer clouds probably won’t move in until after 4-5 PM today, Friday.
Very rainy Saturday with latest models increasing the rainfall amounts to 0.6- 1″ of rain here.
There may be some periods of sun Sunday morning.
Friday and the Weekend Early Outlook
Posted Thursday 02/29/24 @ 5:10 PM — A complicated and split jet flow will result in a weak, slow moving coastal low near our area from Friday into the weekend—
02-29-24 12z NAEFS winds at 250 mb (jet stream level) shows the southern and northern branches of the jet stream winds. The interaction of the two streams as well as blocking high pressure in the Atlantic will spawn a coastal low (L) from an inverted trough . Light rain and an easterly flow will result on Saturday. Clouds move in later Friday. (Click on image for a larger view.)
Friday will start sunny, but very high clouds move in from southwest about 1-2 PM and cloudiness increases slowly during the late afternoon. Plenty of sunshine expected through these high clouds for much of the day. Highs 48º-51º
NAEFS forecast for Saturday at 4 PM. (Click on image for a larger view.)
Saturday looks to be cloudy, damp with rain at times during the day. Despite the low clouds, temperatures will be in the low 50s.
Most models have our rainfall in the 0.3″-0.6″range, but the NAM has been consistently forecasting heavier rain on Saturday.
Sunday dries out but a significant cloud cover may remain. Very mild with highs in the low 60s.
Wednesday Evening Storm Update
Posted Wednesday 02/28/24 @ 5:32 PM — The winds are beginning to pick up and the latest HRRR from 4 PM (the HRRR model is run hourly and takes about 1:20 hours to complete) shows a line of very heavy rain moving through about 8 PM—
02-28-24 20z HRRR (4PM EST model) shows a line of heavy rain at 8 PM. High winds/gusts with this line and afterwards. Above is precipitation and “precipitation rate”. The winds will stay elevated as temperatures drop rapidly. (Click on image for a larger view.)
Wednesday Storm Update
Posted Wednesday 02/28/24 @ 11:22 AM — The cold front is entering northwestern Pennsylvania and several lines and areas of showers precede the front.
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. (Click on image for a larger view.)
The trends from the latest HRRR- heaviest rain between 5:30 PM and 9 PM. Wind gust forecast is now in the 40-45mph range and continues behind the front.
Posted Wednesday 02/28/24 @ 8:46 AM — The forecast remains basically on track. Most areas received about 0.15- 0.20 inches of rain last night. As expected, greater amounts fell far northern Bucks County and northwestward into Allentown.
We may see some bright skies for a period later this morning. More showers will following.
The models are forecasting an additional 0.50- 0.80 inches of rain in our immediate area. This morning’s HRRR just available shows diminished shear and helicity values from last night’s extreme values.
The big impact will be the winds and the plummeting temperatures. The HRRR is still forecasting wind gusts in excess of 50 mph. The Canadian HRDPS interestingly, shows the high winds following the frontal passage, not so much with the rain and front.
The heaviest rain will be with the front, between 5:30 (western sections) and 8 PM.
More on Wednesday’s Storm
Posted Tuesday 02/27/24 @ 7:47 PM — We’ll have several periods of rain on Wednesday. With the cold front moving through between 7-9 PM, expect the possibility of strong, damaging winds especially between 5 PM and 9 PM.
A further review of this afternoon’s models suggests that despite a lack of CAPE, helicity and vertical shear values are predicted to be so high during these hours that strong thunderstorms can’t be ruled out.
Basically, the available high kinetic energy (helicity/shear) makes up for any lack of thermodynamic energy (CAPE) for spawning these storms.
Here’s the HRRR wind gust forecast for 9 PM—
02-27-24 18z HRRR wind gust forecast for 9 PM Wednesday. Exact location and timing of maxima are not to be relied on. (Click on image for a larger view.)
Of greater interest is the severe weather parameters, vertical wind shear and helicity that peak in serious way about 6 PM. The last time I saw these values, we had some tornadic activity. With a lack of CAPE, I’m not really sure what to make of it—
02-27-24 18z HRRR forecast Shear (shading) and Helicity (contours). Helicity values are approaching 900 m2/s2 in the boxed area which is extremely high. If CAPE were forecast to be higher, tornadoes would be likely. Without CAPE, I’m not sure what to expect. (Click on image for a larger view.)
I’ll update this evening if anything else shows up in tonight’s early models. I think we need to wait for tomorrow morning for the final call.
Stormy Wednesday
Posted Tuesday 02/27/24 @ 6:03 PM — While the wonderful mild temperatures have gotten most of the attention on the TV/radio, the real story will be the rather significant storminess on Wednesday afternoon and evening.
A sharp cold front will move through about 6-9 PM Wednesday evening. Plenty of dynamics has been expected but the latest models have increased the possibility of some wild weather here.
What had been expected to be a light rainfall is now in the heavy 1″- 1.5″ range with locally higher amounts.
Over the past several days, I’ve been talking about the high winds expected and the latest models are supporting sustained winds of over 25 mph with gusts 40-50 mph. While thunderstorms are not likely (according to the NBM) with low CAPE values, there’s plenty of wind shear and helicity to fuel some of the downpours. ( We’ll have to see if thunderstorms can form with such low expected CAPE).
NBM total rainfall through 11 PM Wednesday night. (Click on image for a larger view.)
Temperatures will plummet from the upper 50s to below freezing in about 6-8 hours after midnight Wednesday.
More details follow with tonight’s early models.
Tuesday- More Sunshine
Posted Tuesday 02/27/24 @ 8:54 AM — Last night’s models have pretty much converged on a later start for the showers instead of early afternoon. It appears that showers will hold off until about 4 PM (western areas) to 7 PM as forecast yesterday by the HRRR and Canadian models.
Regarding cloud cover, it appears that we’ll see an increase in cloudiness towards noon, but breaks of sun and clouds will remain with us through about 3 PM, at which time the lower level clouds move in.
02-27-24 06z Experimental RRFS-Ensemble cloud forecast at 2 PM. (tan- high cirrus, maroon- mid level clouds) (Click on image for a larger view.)
Current Water Vapor image—
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. (Click on image for a larger view.)
Tuesday Forecast Update
Posted Monday 02/26/24 @ 8:00 PM — This afternoon’s models show a change in the forecast for Tuesday. Some, but not all, models are now showing an earlier start to the showers.
Tuesday starts sunny, but clouds move in rapidly about noontime from the west. Several models (GFS, HREF, NBM, ECMWF and ICON) have light showers moving in as early as 1-3 PM. (The experimental RRFS shows showers 4-5 PM and the HRRR and Canadian models about 6-7 PM.)
I’m going with the earlier start time (1-3PM) for the showers since the GFS tends to be better with timing these things.
Despite the clouds, the NBM is still predicting fairly warm high temperatures—
02-26-24 18z NBM forecast high temperatures for Tuesday. Fine contours are 1º increments. (Click on image for a larger view.)
As mentioned, a sharp cold front will move through Wednesday evening with rain and likely high winds. It doesn’t appear that thunderstorms will be part of the mix. Rainfall for the immediate Philadelphia area is running about 0.6-0.8″ of rain. Not the biggest rainstorm for us compared to recent others.
The big story will be the wind and wind gusts above 40 mph and sharp drop in temperatures Wednesday night behind the front. I realize that lately, some of the model forecasts for high winds just haven’t been materializing. This time around I think it’s a good bet.
Initially Posted Sun 5:28 PM —
A roller coaster experience of weather will unfold this week, beginning with the overnight period tonight (Sunday night). An upper air trough will move through along with a front before daybreak Monday with widely scattered showers, mostly north of the city. (It’s hard to believe since there isn’t a cloud in the sky as I write this. )
A well-advertised warm up is expected Monday through Wednesday. But an abrupt end to the warmup is expected later Wednesday as a strong cold front moves through and the temperatures drop almost 30 degrees after midnight into Thursday.
Here’s the current water vapor image on Sunday afternoon—
Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. Two large disturbances in separate jet flows (1) (2) will combine their energy into an energetic trough by Wednesday. (Click on image for a larger view.)
Here’s what unfolds later Wednesday—
02-25-24 12z NAESF forecast for Wednesday evening. A sharp cold front moves through with rain, possibly some thunder and very strong winds. Temperatures in the 60s drop to near freezing Thursday morning. (Click on image for a larger view.)
The very warm temperatures have talked about, but there’s been little attention to the sharp front and possible stormy weather later Wednesday. I’ll have more coverage as the week progresses.
Monday — Following scattered showers before daybreak, clouds in the early morning becoming sunny by mid to late morning. Here are the NBM high temps—
02-25-24 18z NBM forecast high temps for Monday with standard deviation. (Click on image for a larger view.)
For Tuesday—
02-25-24 18z NBM forecast high temps for Tuesday with standard deviation. (Click on image for a larger view.)
By late Tuesday, some rain may move in. Wednesday will be warm, but with showers.
Sun 05:37 PM Update — As soon as I posted this forecast, the latest GFS model shows the front comes through during the late afternoon Wednesday instead of around midnight. An evolving forecast.
The interesting weather begins late afternoon Wednesday. Stay tuned for updates.
