THE NEW GFS MODEL IS LOOKING PRETTY GOOD!

Over the past several days, I’ve mentioned the new “parallel” GFS v 16 model and specifically wondered whether it was going to provide new insights into today’s weather forecast, specifically what sort of ‘precipitation type’ (the model parameter referred to as “PTYPE”— rain, sleet, freezing rain or snow) we would get with today’s storm.

The GFS v16 was one of the few models that were predicting snow at the precipitation onset; most of the higher resolution models (NAM, NAM-NEST, HIREF and HIRESW) were predicting freezing rain or rain. Indeed, I thought there might be a ‘cold bias’ with the new GFS that would need to be discounted. But not so. The GFS v16 also has correctly predicted the snow and the changeover to rain that is occurring as I write this. (The GFS PTYPE forecast from Saturday afternoon was posted in yesterday’s update.)

Let’s look at some other model forecasts from last night:

Here’s last night’s RAP (Rapid Refresh model)—

Sat evening’s RAP model (00z) showing snow and a mix.

 

And here’s last night’s HRRR

Last night’s HRRR 00z (high Resolution Rapid Refresh) showing mostly rain.(Click on image for a larger view.)

 

In retrospect, last night’s model blend (NBM) correctly captured the snow onset instead of rain—

Saturday evening’s NBM (model blend) 00z for today, showing mostly snow or a mix. at the start.

So, if we ever get any real snow this season, we have the new GFS, RAP and NBM to rely on.

While we’re on the subject, the latest GFS 16 has the following snow totals by 1 AM Monday—

GFS v16 snow depth forecast for 1 AM Monday morning   (Click on image for a larger view.)

As mentioned in another post, the temperatures north of us are running way too warm.  The Climate models show above average temperatures to our north for the next month or two.  So we might not be talking about all that much snow this season.  Then again,  warmer than average temperatures don’t necessarily translate into less snow or fewer storms.  I guess we’ll see.

 

WEEKEND WEATHER FORECAST

Sat 04:50 PM Update — Looking over more advanced models than the NAM and NAM-NEST, the consensus is that it will be too warm for freezing rain in the immediate Philadelphia area tomorrow morning, nor is precipitation expected to change back to snow before ending Sunday evening. (Areas north of Allentown may see some snow.)   Rain will start 7-9 AM Sunday morning and will end in the evening.  (The new GFS v 16 still shows a chance of snow as the precip starts at 7 AM, then a quick change to rain.  See second graphic.  Possibly a ‘cold bias’.   We’ll find out.)
HIRESW-FV3 (Pre-release) Precipitation Type 9 AM Sunday (Click on image for a larger view.)

 

New GFS v16 still shows snow at 7 AM Sunday, then a quick change to rain..  Probably a “cold bias’ in the model.   I guess we’ll see tomorrow morning.

Sat 09:38 AM Update — This morning’s models show the following
  • Saturday— Clouds move in around noontime Saturday.
  • For Sunday, precipitation starts between 7 and 8 AM with some areas north and west of the city getting freezing rain to start, then a change to rain.
    NAMNEST 8 AM Sunday RED=Freezing rain   White line 32º (Click on image for a larger view.)


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Our area saw rain today, on schedule between 12- 3 PM, although some areas far to the west and north had a wintry mix, as temperatures remained below freezing. The mix did not occur as close to PHL as forecast.    Here’s the surface temperatures at 3 PM today—

RTMA (real time) Temperatures 3 PM Friday  (Click on image for a larger view.)

For the weekend—

Saturday,  a strong flow of relatively mild air moves in.  Original forecasts showed significant sunshine for Saturday, but the latest GFS suggests considerable cloudiness, a period of sun mid to late morning, then  a mix of clouds and sun at times in the afternoon.  There’s high uncertainty about the cloud cover Saturday, as captured in this NBM graphic—

NBM cloud cover standard deviation -spread or uncertainty- is high just north of Philadelphia (Saturday 5 PM)

With more clouds forecast, the high temperature looks to be 51.4º (NBM) and 49º (GFS) (Seasonal average high is 40º)

For Sunday, a secondary low forms off of Virginia. Precipitation moves in between 7 and 9 AM, starting as light snow or a rain mix. Changes to rain for most of the immediate PHL area. A change back to light snow is possible Sunday evening, with a coating at most.

NBM Snow totals Sunday evening. White line is the 1 inch line The immediate PHL has none or a coating at most.

(It appears that the new GFS may have a cold bias and the snow totals posted yesterday are incorrect and over-done.)

Any other winter, we’d have snow, but a lack of cold air to our north will keep it mostly rain.