Philadelphia Area Weather Forecasts

Philly Winter Weather Update 7 AM

So the issues with last evening’s model runs continue with the 1 AM reruns of the GFS and NAM.

Here are  the contradictions and forecast dilemma:  Both models have high QPF values (GFS about 0.50) and  NAM (increased to over 0.60 inches water) but they differ in the handling of the low pressure development.  The GFS has us waking up to 2 inches of snow Tuesday morning.   The NAM has us waking up to a light coating at best.  They differ by almost 18 hours for the heavy QPF.   So something is wrong, possibly with both models handling of this developing system.

If this were a different scenario, I would change my current forecast from the current 1-3 inches to the QPF-based 5-7 inches when all is said and done Tuesday night.

Essentially, I don’t think the models are right and the 1-3 inches is a hedge on what could be a fizzler of a storm.   HOWEVER,  a small voice is beginning to say, “don’t ignore the models QPF”

(I heard KYW’s forecast this morning and they’re going with the same “1-3 ….with 6 inches in some locations”.   Hey, what locations??   Wow, talk about a hedged forecast!  Yet another forecast from them ‘sanitized for your protection’. )

So here’s where we are at:  If this morning’s models continue to crank out high QPF values, we have to start taking this seriously and expect higher snow amounts on Tuesday.  I’ll update sometime mid day today….(this is not my full-time job).

 

 

 

Weather Updates

Philly Winter Weather Update

Latest NAM shows the inconsistency of the modeling of Tuesday’s snow. The NAM has moved the snow to the afternoon and evening on Tuesday. Additionally, the secondary low develops far from the coast.

The QPF is about 0.48 inches water, but I wouldn’t hang your hat on that number.   Despite the QPF,  I’m thinking 1-3 inches snow by late Tuesday evening.   This “storm” could just fizzle out.

11 pm: Latest GFS maintains a similar QPF, but has the heaviest snow before daybreak on Tuesday. These are large differences and model inconsistency in this time frame suggests that neither is correct. This snow remains low confidence.

Winter Storm Outlook

Winter Weather Update – Sunday Noon

I’ve been thinking that the Tuesday snow from the ‘secondary low’ wouldn’t amount to much (1-3inches) but the latest NAM and GFS data is available and both models crank out 0.50 and 0.54 inches respectively, as the QPF.

That ordinarily translates to about 5-7 inches of snow, but the models have it coming is dribs and drabs over a 30 hour period from late Monday night into Tuesday night and I’ve seen those sort of things over-done with other storms.

4:45pm: Based on this afternoon’s NAM, I’m still thinking 1-3 inches total by Tuesday eve, despite higher model QPF values.

That said, the words to keep in mind are “low confidence” and “notoriously unpredictable” when it comes to a secondary low precipitation QPF.   Not only is the QPF unreliable, but it is especially so for any particular location.

So, according to the latest,  the snow starts after midnight early Tuesday morning, we wake up with about 2-3 inches of snow Tuesday and light snow continues throughout the day into the evening.   The temperatures support snow instead of rain or a mix.    I’ll update again this evening.

Weather… and Other Things 'Up in the Air'