Tag Archives: Forecast Evaluation

WEDNESDAY WEATHER

This post was revised

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.

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

 

PHILLY WEATHER UPDATE 8:15 AM

This post was revised

In my neck of the woods, just northwest of the city, a coating of sleet and freezing rain is accumulating.   The QPF was a bit higher than I  predicted last night; a few heavier areas of precipitation allowed some “dynamic cooling” and some snow flakes were able to develop briefly, but essentially it’s been sleet and freezing rain in PHL and the immediate suburbs.

Temperatures are still expected to rise above freezing about 10 AM or so.   Rain is expected for most to the day, heavier in the afternoon.