Category Archives: Weather Updates

Weather Updates

WEATHER UPDATE THURS AM

[su_note note_color=”#d9f2da”]Thurs Noon update: Wow, more snow than I had forecast! The low level atmosphere temperatures are at or below freezing. The NAM upper atmosphere critical thickness level seems to have fooled me this time around. It works in the winter, apparently not in November.    😱         I’ll make a note of it!

So, let’s try this again. Based on the latest NBM (which I’ve been ignoring, except for the precipitation start time), the changeover to sleet and then rain will occur about 1 -2 PM in PHL.    This is a tough business.

[/su_note]

Based on the latest NAM and NBM model data, the forecast from last night is on track.

Precipitation is moving in, as shown on radar, at 10:30 AM.  On this radar image, it’s easy to see how the precipitation is hitting a wall of cold air, eroded at the northern edges—

Radar Thurs 10:20 AM, courtesy of Weathertap.com

This is a sleet to rain event, with some snowflakes possible at the start.   The latest NAM supports the possibility of a brief change to snow before daybreak Friday.  (Little or no accumulation.)

 

 

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.