Update Mon @ 8:05 AM — I spoke too soon. I think I see some flakes out there! Faith in the models restored!
Update Mon @ 7:47 AM — It reached 50º in Philadelphia and 47º in Blue Bell last night between 2-3 AM.
The models show the current showers we’re getting as snow showers, but it’s too warm in the lowest 2000 feet of the atmosphere and it looks like rain to me.
Some radar feeds incorrectly categorize what we’re getting as snow. The MRMS correctly shows what’s happening now—
MRMS current precipitation type. The blue color coding is misleading, suggesting snow. Snow is coded as white. The actual precipitation we’re getting is tagged “cold stratiform rain”. (Click on image for a larger view.)
Look for windy, cloudy conditions today, temps in the 30s.
Update Sun @ 9:15 PM — Snow is changing over to rain. High winds possible after midnight. Temps wise to near 50 before falling back to the 30s. Rain ends before daybreak. Tonight’s models continue to forecast snow showers between 7AM and 11 AM Monday morning (mentioned in my 12:50 PM update today). Temperatures will be above freezing and little or no additional accumulation is expected.
Update Sun @ 7:15 PM — The current radar precipitation type shows that the transition to rain is lagging about an hour or so from the model forecasts. The latest HRRR and RAP models still show the transition in PHL about 8 PM, but the actual transition time may be later.
The next new major model run is the 00z run. The 00z HRRR, NAM, RAP and HIRESW will be available by 9:15. I’ll update if necessary.
Current Radar Precipitation type at 8:05 PM Changeover seems to be happening in PHL. (Click on image for a larger view.)
MRMS Precipitation TYPE Snow is 40 miles southwest of Philadelphia at 2:45 PM (Click on image for a larger view.)
Update Sun @ 12:50 PM — This morning’s high resolution models (HIRESW) show considerable snow shower activity Monday morning with a wet coating possible.
Update Sun @ 8:03 AM — Last night’s 06z models continue with a generally earlier start and transition to rain. Clouds move in between 11 AM and 1 PM. Some snow possible as early as 5 PM, very rapidly changing to a period of freezing rain and then rain by 8 PM in the city and shortly afterwards north and west as temperatures rise above freezing. With heavy rain (1.25-1.5”) late evening, temperatures climb to 47º-50º around midnight. Strong wind gusts about 1 AM approaching 50mph.
Rain ends about 4 AM. Cloudy Monday, windy, temps above freezing in the 30s until evening.
Update Sat @ 9:30 PM — The major model runs are are done at 00z and 12z ( 7 PM & 7 AM EST). Some of the 00z high resolution models have become available. The changes noted in my previous update, with an earlier change to rain, are still expected. Some freezing rain possible about 8 PM.
Temperatures below freezing all day Sunday, will rise into the mid 40s after midnight! About 1.5 inches of RAIN will fall before it ends before daybreak Monday.
Update Sat @ 5:05 PM — This afternoon’s 18z models have become available. The trend is for the system to approach earlier on Sunday. Clouds increase by late morning. Some snow develops as early as 5 PM.
The warm-up also appears to occur 2 hours earlier with a transition to sleet and rain in the city around 8 PM and moving quickly north. By 10 PM, the HREF has mostly rain for our area —
HREF 18z Rain/sleet by 10 PM (Click on image for a larger view.)
By Monday morning, little if any snow will be left after the heavy rain.
Another slight change. Non-accumulating snow flurries/showers likely Monday morning and again late afternoon.
It looks like the coming week will be colder than average with another chance of sleet or snow on Thursday.
Update Sat @ 10:01 AM — The forecast for Sunday evening’s storm is essentially unchanged from the GFSforecast from this past Wednesday. While we still have plenty of time before Sunday evening, the models have done usually well with this storm forecast so far. There weren’t the usual differences among models we often see with winter storms.
The Sunday night period is within forecast range now of the very high resolution models.
Snow starts at about 5-7 PM from south to north. Changes to rain most immediate suburbs by midnight. Here’s the latest HRRR with the snow-sleet transition line at 10 PM Sunday—
HRRR precipitation type (PTYPE) forecast for Sunday at 10 PM. The white contour (32º) is the surface temperature. The lavendar, blue and purple contours are the critical thickness contours. (Click on image for a larger view.)
Previously Posted Fri 5:23 PM —
Very cold air will move in due to the flow around a low pressure system (that missed us) in the Atlantic today.
A storm that is has been forecast since Tuesday to form near Virginia early Sunday will move northeastward across our area. We’ll be on the warm side of the storm.
While the model forecasts for this storm have been remarkably consistent, a possibility exists that a more prolonged period of freezing rain will develop in the very far northwestern suburbs Sunday night due to cold air damming. It should all change to rain during the pre-dawn hours.
Saturday
Embedded in the upper very cold flow is an upper air disturbance. Sunny early morning. Then we’ll have mid-level cloudiness from late morning through much of the afternoon. Very cold. High temperature will be 23.2º ± 2.1º (NBM model Blue Bell, PA). It will be very windy in the morning, but winds should subside in the afternoon.
Previously Posted Fri 5:23 PM —
Sunday
It will be sunny and very cold Sunday morning. Clouds move in about 1 PM. Snow starts between 5 and 7 PM and quickly mixes with and changes to rain about 10 PM. Up to an inch is possible before changing to rain. (Details have not changed since my earlier forecast.) High temperatures in the 20s during the day will rise to 39º by midnight.
The total QPF (quantity of precipitation falling) is predicted to be on the order of 1.25″ water, but only about 0.2-.0.3″ will fall as snow.
Some areas in the far-western suburbs may have a more extended period of freezing rain.
GFS forecast for Sunday at 8 PM. Snow falling will change to rain around 10 PM. Less than 1″ by midnight with a slushy, heavy compacted 1/2″ by Monday morning. (Click on image for a larger view.)NAM-NEST forecast for midnight Sunday showing “PTYPE” (precipitation type) The rain-freezing rain line will continue to advance northward. There is an outside chance that areas in far upper Montgomery/Bucks county may experience a longer period of freezing rain late Sunday night. (Click on image for a larger view.)
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In the Philadelphia area and immediate surrounding counties, it changes to all rain. If you were to go out and measure the snow at midnight, you’d find maybe 1 inch of snow in the immediate PHL area, but with most of the precipitation expected to fall as rain after midnight, there will be about 0- 1/2 inch of heavy, slushy mess by the morning. Rain ends before daybreak.
Latest GFS (18z) with snow totals by Monday 8 AM. (Click on image for a larger view.)
Some snow showers possible during the morning. Temperatures do not go below freezing until Monday evening.
Considerable cloudiness Monday. Some snow showers possible late Monday afternoon or evening. Gusty winds in the afternoon.
