Monthly Archives: November 2018

Winter Storm Outlook

WEATHER UPDATE 6PM

Here’s the latest, based on the most recent NAM and NBM models:

Precipitation starts later, now between 9-12 noon on Thursday (earlier south of the city).

Precipitation will be principally sleet and some freezing rain, then rain.  There may be some snowflakes at the beginning, but this is a sleet—> rain event.

Temperatures during the day hover near and above freezing, then low to mid 30s.  Temperatures rise near 40 Thursday night.

Rain will be heavy in the afternoon and evening.  QPF values are 1-1.5 inches, mostly falling as rain.

The upper atmosphere chills before daybreak on Friday as the upper low merges with the coastal storm. Some snow may mix with rain briefly before daybreak Friday and before ending early morning.

I’ll update later this evening with the new NAM runs, about 9:30 PM.

Weather Updates

WINTER WEATHER UPDATE- WED 8AM

Last night’s models have changed little from previous runs.   (Please see my previous posts.)

Light precipitation starts about 8AM Thursday in PHL (earlier to the south).  Low level temperatures remain at or below freezing for an extended period of time, while the temperature profile in the upper atmosphere is too warm to support snow.

While the precipitation may start as some light snow, it will quickly change over to all sleet in PHL and the immediate surrounding counties. Some freezing rain is also possible early.  

QPF values in the morning are about 0.20 inches water and during the afternoon, 0.70 inches water.   Much of this will fall as rain. 

The sleet will mix with and eventually change to rain. Cold air damming scenarios have sometimes lasted longer than predicted by the models, so it’s difficult to tell when this changeover will occur.   An extended period of sleet can occur in far northern and western suburbs. (Allentown)   East of the city, in NJ, any sleet will change to rain even earlier.

Surface temperatures at or below freezing about 7 AM Thursday but rise slowly into the mid 30s.

The expected secondary storm formed by the merger of the upper low Thursday night now appears to be too warm for any snow.   Rain is expected late Thursday night into Friday morning.

I’ll update tonight about 9:30 PM.