Category Archives: Weather Updates

Weather Updates

WEATHER UPDATE- SAT AM

[su_box title=”Weather Update Sat 10:30 AM” box_color=”#defcdc” title_color=”#000000″]Based on the latest NAM, showers have ended but widely scattered light sprinkles are possible. Low clouds lifting to brighter skies may be delayed until 2-3 PM today.[/su_box]

from earlier today:

The gusty windy conditions (Gusts to 35 mph) will continue and diminish later in the afternoon.

The rain ends by 11 AM.

Based on the 2 AM (06Z) NAM and GFS model runs, the low clouds should lift between noon and 1 PM, leaving brighter skies and some sun through a layer of higher cirrus clouds.   Continued improvement in sky cover later in the afternoon. High temp 74-76.

Currently, Sunday looks dry except some showers may develop in far western suburbs in the mid afternoon. High 67-69.

Weather Updates

Forecast Update

The latest NAM model data has become available. Light scattered showers are forecast for Sunday, especially for the late morning and early afternoon hours. QPF values are low for these early showers  (0.05 inches)

It will be cloudy and increasingly windy.  There may be some brightening skies briefly late afternoon.  High 70-72 reached later in the afternoon.

Winds increase at night. A strong cold front moves through after midnight.  Heavy rain, thunderstorms and very strong winds will accompany this front.

Commentary, Weather Updates

WEEKEND FORECAST UPDATE -SUNDAY

[su_note note_color=”#d9f2da”]Wow, the clouds never broke today and temperatures remained in the 40s!  Yesterday’s NAM had predicted temperatures remaining in the 40s and I ignored it; I thought it was a modeling error because it was so far off.  So one model was an outlier, yet it turned out to be correct. [/su_note]

from earlier this morning:

The rain will move out later this morning. Some of the models are forecasting a break in the clouds after noontime for a few hours, so we may get some sun.  If not, certainly brighter skies.

I know you may have heard about a high of 61 today.  Only the GFS has been predicting this high.  Most of the models have a high in the low to mid 50s.  I guess we’ll find out.

A cold front will move through between 4 and 6 PM. Widely scattered showers and some cloudiness moves through at that time. Temperatures drop into the low 30s by daybreak Monday.

It will become very windy this afternoon and even more so this evening.

[su_note note_color=”#d9f2da”]

Contrary to an often-heard incorrect explanation on TV forecasts, high winds are NOT due to a “wind tunnel effect”.

High winds and wind gusts are principally due to 1. Rapid changes in atmospheric pressure, specifically, the rate of change of pressure over time.  (dp/dt).    2. Thermodynamic effects that cause a mixing down of normally high winds aloft down to the surface.

If you’re looking for “Wind tunnel effects”, they can be felt on the corner of Walnut and 15th streets in Center City on windy days.

Every time I hear a TV person attribute windy conditions to a wind tunnel effect, I wince.  [/su_note]