Category Archives: Weather Forecasts


Update Sun @ 6:37 PM — Today’s models have also backed off on any snow for Tuesday. Next interesting period to watch is Friday into Saturday.

Update Sat @ 9:33 PM —Tonight’s models has backed off to just snow flurries Sunday evening.

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Originally Posted Fri 5:04 PM


Sunny and continued very cold. Gusty winds in the morning, subsiding in the afternoon. High temp 28.6º ± 2.6º (NBM model Blue Bell)


An upper air trough axis moves through.

Some cloudiness in the early morning, especially north and west of the city. Then partly/mostly sunny. Continued cold. Gusty winds. Clouds move in late afternoon.

The GFS is forecasting an upper air disturbance possibly bringing a dusting/coating of snow late evening Sunday, towards midnight. The NAM has some light snow earlier in the evening.

High temp 32.3º ± 2.5º (NBM model Blue Bell).


Update Thu @ 7:25 PM — One more thought about the forecast gone wrong….. Most models got the onset timing correct and the end of the precipitation correct. They also got the general QPF (quantity of precip falling) correct. They went very wrong on the thermal profiles.

As for the weekend, as previously mentioned, the models have been in consistent agreement with the storm early Saturday staying to our south.

We’ll have very cold weather this weekend. High temps likely won’t exceed freezing. At times, there will be cloudiness due to an upper air trough moving through with additional weak cold fronts/upper air disturbances. Otherwise dry.

The next period of interest is Tuesday, where secondary low pressure may develop off of the coast. This period also has the potential to be a mixed-precipitation event with icy conditions or sleet. Just a possibility now.

Look for my regular, weekly “Weekend Weather Forecast” Friday afternoon or evening.

Thu 08:35 AM Forecast Review —  So…most models got this forecast wrong.  BUT there’s always something to be learned. 


First, which models did the best here?  As was the case a few weeks ago, the ICON  and the new Canadian GEM model correctly predicted the temperatures warmer and more precipitation as rain.

Canadian GEM model from Wednesday evening forecast for 8 AM today correctly predicted the above freezing temperatures and precipitation type being mostly rain (green) vs snow (blue). Note its 32º line is also closer to what we saw today.  (Click on image for a larger view.)


Of our major models, the NAM and NAM-NEST were the closest. 

The HRRR, RAP, GFS, SREFHIRESW and HREF  groups had the 1-3″.   Of course, since the NBM is a composite or ensemble model of other models, it steered its snow totals towards the greater population of high snow accumulation models.   Our new GFS v 16 model has been very disappointing.

Another thing to learn with the NBM:  the 25 percentile snow totals seems to be surprisingly accurate lately here.  I have to admit, yours truly ignored the low-end NBM percentile and I discounted the warmer Canadian GEM and ICON as total outliers last night. 

(BTW, last night’s ICON and GEM had predicted most of our precip as rain with just a coating possible.)

I may have to add to my mantra: “never ignore the NAM, GEM and ICON” 


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Update Wed @ 9:27 PM — Tonight’s early models have become available.

Rain about 3 AM with the arctic cold front passage will change to snow from northwest to southeast between 6 and 8 AM.

Snow continues until about noon.

Of interest is the trend of this afternoon’s NAM and the new NAM and NAM-NEST which just became available.   It has less than an inch throughout the region. The reasons are:

  • The ground will start off wet.
  • The ground will be warm, above freezing, to start
  • Snow-water ratios will be low until it gets colder
  • Compaction of wet snow will occur initially


Latest NAM Model forecast (Click on image for a larger view.)

Regulars here know my mantra: “Never Ignore the NAM”

The latest NBM model is below and it captures most of the models forecasts from today. —

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Another impulse in the Gulf of Mexico may also slide to our south on Saturday. Again, we appear to be on the northern fringe.

In both cases, the currently forecast jet configuration is positively tilted and significant low pressure development near the coast is not currently forecast.

I’ll keep an eye on things. Check back during the week.


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.

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It looks like the coming week will be colder than average with another chance of sleet or snow on Thursday.

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Originally Posted Fri 5:23 PM


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.)


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.