Monthly Archives: February 2016

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.

Winter Storm Outlook

Winter Weather Update

An update on the potential snow for Monday through Wednesday.

The models have come together in having the southeast coastal storm pass east of us, missing us early Monday.

The secondary low expected to develop late Monday into Tuesday looks weak and diffuse.  Exact location of development and the amount of precipitation is uncertain, but looks to be light, at most, 1-3 inches, according to the NAM. The GFS cranks out much more, with a QPF of 0.48 inches water, but I think it’s overdone.

Philadelphia Area Weather Forecasts

Philly Weekend Weather Forecast

High pressure builds into our area for the weekend, but an upper air low pressure system to our west will affect our weather.

On Saturday, the upper air low with some upper air vorticities will bring mid-level cloudiness (altocumulus).  It will start out sunny, but expect the mid-level cloudiness for much of the day on Saturday.  High 42.

There wasn’t as much cloudiness as I predicted.

On Sunday, it will be mostly sunny and a bit milder. Some cloudiness moves in during the late afternoon.  High 44.

All models are showing a coastal storm to form off the southeast coast and move east of our area, missing us early Monday.  Not much variation with the various models, but it we must keep in mind that the same models didn’t capture the westward track of this morning’s snow.   So right now, no snow is expected from this storm.

Later Monday, the upper low to our west is expected to spawn a weak secondary surface low around Delaware bay, giving us light to moderate snow late Monday through Tuesday.   This is a low confidence forecast.

Here are the concerns: 1. The initial southeast low tracks closer to the coast than the models currently forecast.  2, The upper low phases with the coastal low that tracks closer instead of spawning a separate weaker low in Delaware on Tuesday.  While this is not the current expectation, this possibility needs to be watched, especially since the models did so poorly in advance of this morning’s snow.  

I’ll keep an eye on this, but right now, the models are going with a diffusely organized secondary low with snow on Tuesday.