Wed 09:30 AM Forecast Review — Temperatures started a little warmer than forecast, but dynamic cooling from a high precipitation rate has caused the rain to mix with snow here. So the forecast looks on track.
Latest CMC-RGEM Precipitation Type forecast for 11 AM—
CMC-RGEM Precipitation Type Forecast at 11 AM (Click on image for a larger view.)
Update Tue @ 11:16 PM — Tonight’s models are coming in a bit colder. Rain, mixed with periods of sleet and wet snow, possible. Most of the area will have no accumulation, but a coating to about a half an inch accumulation in upper Montgomery and Bucks counties, according to tonight’s RGEM.
Update Tue @ 6:18 PM — This afternoon’s models continue with the forecast of precipitation beginning about 5-6 AM as rain mixed with wet snow, then changing to all rain by 8-10 AM for most of the area. No accumulation expected for most of the area. Essentially a rainy day.
Update Tue @ 11:44 AM — This morning’s Canadian RGEM has consistently shown Wednesday’s storm to be mostly rain in most of our area, but with wet snow mixed in at start. No accumulation expected here.
This morning’s RGEM showing mostly rain with some mix possible Wednesday 9 AM. (Click on image for a larger view.)
Of greater interest is the large coastal storm expected Saturday. Stay tuned.
Update Tue @ 7:55 AM — Last night’s GFS and Canadian RGEM show virtually no snow accumulation on Wednesday in the Philadelphia area, except for the far northern and western suburbs. While temperatures just above 2000 feet will be cold enough for snow (at times) during the day, overall thermal profiles don’t support snow accumulation. The RGEM is even warmer with mostly rain falling.
High precipitation rates may cause dynamic cooling, enough to allow some of the precip to fall as snow at times, but it will melt on the surface and certainly any roadways.
I’ll keep an eye on it.
Update Mon @ 8:12 PM — So, I’ve been asleep at the wheel regarding Wednesday’s storm… I took a quick look at the forecast, saw the critical thickness line (red line) was north of our area, forecast rain, and I never looked further. But there’s more to this.
I haven’t watched the TV weather in a long time, but I could tell something must be brewing because I noticed a large uptick in my web traffic stats. So, I took a deeper look and I see that snow is possible for Wednesday. But is it really gonna happen?
Monday’s 21z NBM showing precipitation and critical 32º wet bulb temperatures (dark blue) and Bourgouin critical levels (yellow contour). (North of these contours, snow is possible.) We don’t see the 32º surface temperature anywhere on the map because it’s going to be 37º in our area, according to the NBM. (Click on image for a larger view.)
So, will it snow on Wednesday? Maybe wet snow or snow mixed with rain will fall. In favor of the snow are cold temperatures above 2000 feet and relatively high precipitation rate.
Will it accumulate?
I don’t think we’ll get accumulation in the immediate PHL area. We’re up against a March high sun angle and surface temps above freezing.
The NBM has this snow forecast—
NBM snow forecast by 4 PM Wednesday. (Click on image for a larger view.)
I’ll keep an eye on it.
Update Mon @ 6:17 PM — After this evening’s showers, the next storm to affect us will be on Wednesday. Easterly winds and rain expected—
Monday’s 12zGEFS forecast for Wednesday at 1 PM (Click on image for a larger view.)
Of greater interest will be a major storm expected to develop on Friday night into Saturday. This has the makings of a significant coastal storm with snow in western Pennsylvania into parts of New England.
Monday 12z GEFS forecast for Saturday, 11 AM. A deep storm, possible bombogenesis. (Click on image for a larger view.)
While I’m leaning towards, the warmer GFS, the ECMWF shows possible changeover to snow for us. Not so sure about that.
Mon 06:05 PM Forecast Review — The high temperature reached 77º in PHL, but I don’t think surrounding areas were as warm as predicted. The showers came through about 4-5 PM on schedule, but with much lower intensity than expected. Additional showers before 10 PM.
Update Mon @ 9:29 AM — Today’s HRRR shows elevated CAPE northwest of Philadelphia between 4-6 PM as the rain moves in. This suggests the possibility of thunderstorms embedded in the first area of rain just northwest of the city.
Previously Posted Sun 9:45 PM —
On Monday, high temperatures are expected to get to the upper 70s with a some areas possibly touching 80º. A cold front approaches with rain moving in from 4-5 PM. (Considerable cloudiness will limit what could have been even warmer temperatures.)
Today’s 18z Canadian RGEM high temperature forecast for Monday. The RGEM has been doing well with temperatures, but it is at the higher end compared to other models. (Click on image for a larger view.)
The unseasonably warm weather expected Monday will eventually give way to cold weather again over the coming weekend.
During this coming week, we’ll be transitioning from a ridge with a southwesterly flow to an eventual colder trough over the weekend.
GEFS upper air flow (jet stream level 250mb) on Wednesday at 1 PM. Southwesterly flow will bring moisture and several low pressure systems passing just to our south over the week. (Click on image for a larger view.)
Several low pressure systems are expected to form and move up from the southwest. After rain Monday night, we’ll likely see some rain again on Wednesday and yet again Friday into Saturday.
The strong contrast in temperatures is likely to set off some wild weather.
Saturday may have some “interesting weather” for us as a strong cold front moves through, according to the latest GEFS—
Today’s 18z GEFS forecast for Saturday 10AM. A strong cold front moves through with some snow possible in far northern areas. (Click on image for a larger view.)
Update Thu @ 8:09 PM — Previous posts have indicated a warmup for the weekend as the jet flow becomes ridge-like over our area. The southwesterly flow will also bring moisture to our area in the form of clouds and some showers. There’s also the possibility of heavier rain next week.
GEFS (mode) jet stream wind forecast (250mb) for Monday morning showing ridge over northeast. The white area is referred to as a “jet streak”, an area of increased wind speed, this case approaching 198 mph. Rising and falling motions (rain) occur at certain areas of the jet streak. (Click on image for a larger view.)
For Saturday, a warm front is expected to move through our area with significant cloudiness for much of the day. No rain expected.
For Sunday, there has been recent uncertainty regarding the speed and placement of showers on Sunday far ahead of a frontal system.
The ECMWF has been forecasting a period of rain Sunday morning with partial clearing in the later afternoon. It’s forecasting about 0.20 inches of rain.
Today’s 12z ECMWF showing 3 hour rain accumulation at 1 PM Sunday. (Click on image for a larger view.)
The GFS has only a very light shower (< 0.02 inches) and mostly for areas north of the immediate Philadelphia area.
But today’s ICON and Canadian models have joined the ECMWF with the period of light rain in the morning. The NAM has also joined that group.
While ECMWF model is new to me (a limited but substantially increased data set only recently became available to the general public this past January 2022), I’m first learning its biases and tendencies and how to integrate its forecasts with the other main weather models like the GFS and NAM. As recently as last week though, a similar difference between the ECMWF and the GFS turned out in favor of the ECMWF forecast.
So with the ICON and Canadian RGEM leaning towards somewhat more rain, I’m leaning in that direction for Sunday. Most models have clouds thinning in the afternoon with temps in the 60s and WINDY conditions, although the latest GFS maintains a fair amount of cloudiness even in the afternoon.
Update Wed @ 10:30 PM — With the warming pattern expected this weekend, today’s models have quite a wide range of forecasts. There’s pretty good agreement for mostly cloudy conditions on Saturday, but not much agreement about whether we get rain on Sunday. The ECMWF and the GEFS show rain, the operational GFS, ICON and Canadian Global not so much. Too soon to know.
Update Tue @ 7:45 PM — Looking at today’s models, the warmup promised from a pattern transition to an upper air ridge still looks on track for the weekend.
Some showers possible late Wednesday night into Thursday morning, especially northern suburbs.
Saturday will be milder but may have considerable cloudiness. There’s a chance of sprinkles far north and west.
Sunday will be mild but some rain is likely.
That upper air ridge may be persistent with milder temps next week but several chances of rain.
Previously Posted Mon 4:59 PM —
It appears that we will have a quiet weather pattern this coming week.
The jet flow is expected to transition from the current colder trough pattern over the east —
ECMWF forecast jet stream winds (300 mb level) for Thursday at 1 PM. A trough over the northeast with cold air. (Click on image for a larger view.)
to a ridge over the east by the weekend with warmer temperatures—
ECMWF jet stream forecast (300 mb winds) for Saturday at 7 PM. An upper ridge is expected to develop over the northeast. (Click on image for a larger view.)
During the week, several disturbances will pass by to our north, bringing some clouds and weak fronts. Here’s Thursday morning—
Today’s GEFS forecast for Thursday, showing some light rain barely making into our area, with the system passing to our north. (Click on image for a larger view.)
By the weekend the upper flow from the southwest will bring milder temperatures, but also considerable moisture and clouds, and possibly rain by Sunday.
GEFS forecast for Sunday at 7 PM. There is some uncertainty about the timing of this system moving through. (Click on image for a larger view.)
