Category Archives: Forecast Review


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.



Yesterday’s cloud base did lift and thin, but we never saw the degree of clearing that was forecast by the HRRR or NAM-NEST models. Showers moved in, as expected, about 5 PM, but the northern-most extent and their duration into the evening hours was greater than predicted by any model.

For today, (similar to last Sunday), several upper air disturbances are causing the cloud deck right now.  Sun should break out later this morning, but another upper air disturbance is expected about 4 PM (not talking about the Eagles here.)  So, another period of cloudiness possible later.

The coastal storm for mid-week mentioned in last Friday’s post remains difficult to forecast.  The NAM and Canadian GDPS have 1-2 inches of snow (less in the city) late Tuesday afternoon into evening.  The GFS shows less development and a coating at most. The GFS has done the best this season with these storms.  This storm is still beyond the range of the shorter range models.  Stay tuned.


Happy New Year!

I got up this morning and saw the clouds and even some very light snow flurries.   Last night’s models did not show these clouds or flurries.   Nor did the higher resolution just-run hourly models like the HRRR or RAP show it.

Did the models capture anything that could explain the weather this morning?

They did, but apparently the model’s algorithms didn’t translate a strong upper air disturbance and moisture into the clouds and flurries that we have.

Last night’s GFS shows a strong area of vorticity (“an upper air disturbance”) passing through along with increased moisture in the upper and mid levels.

GFS 500 mb vorticity 8 AM Wed.   Click for larger image

GFS humidity – several upper levels  8 AM Wed

Add the humidity, vorticity and upper air cyclonic flow together and you get the weather we have this morning.

If the models were somewhat better, this combination of parameters should have triggered its cloud algorithm to show the clouds we have.   But it didn’t.

Based on the same thinking and parameters, the GFS shows humidity and vorticity move off between 12 – 2:30 PM.  We should see more sun by that time.

[su_note note_color=”#defcdc”]Update Wed 10 AM: This morning’s high resolution NAMNEST finally shows the light precip and clouds we already know about.

NAM NEST precip and cloud forecast for 11 AM Wednesday