Monthly Archives: February 2023

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia

Monday

Update Mon 02/20 @ 9:45 AM — No change in yesterday’s prediction of sun breaking out around noontime. The latest NBM supports this—

This morning’s 12z NBM showing cloud ceiling (shading) and cloud cover (contours) Movement to the southeast (arrows) Clear skies after the front moves through. (Click on image for a larger view.)

The weak cold front that is causing the clouds this morning will move back as a warm front tonight and Tuesday. Several periods of rain tonight and again Tuesday.

The weekend system is looking less impressive regarding any snow here.

Previously Posted Sun 5:51 PM —

Overview

This week’s weather will be influenced by an extremely strong jet stream flow (by Thursday into Friday, the jet streak winds approach 225 mph!) and generally southwest to northeast flat to upper ridge. The warm- cold boundary will be right near us and any movement of this frontal boundary will cause changes in the forecast. With such high jet stream winds, such waves in the frontal boundary are bound to occur.

NAEFS forecast for Thursday morning showing jet stream winds (at 250 mb height). Superimposed is the 540 thickness line (red line) captures the general position of the cold-warm boundary . (Click on image for a larger view.)

I think this week’s weather will turn out to be ‘interesting’, fast moving and probably difficult to forecast accurately.

(I’m still watching the system expected to approach us next Saturday. Timing differences have already developed between the various models that were strangely similar yesterday. A mixed precipitation event changing to all rain still possible Saturday or Saturday night.

With things so fast moving, I’m just going to look at Monday and Tuesday to start.

Monday

A cold front moves through late morning. Cloudy in the morning, then sunshine by the afternoon. High 58-60º

Tuesday

A warm front moves back through in the early morning with showers in the morning. Then sunshine by the afternoon. Very WINDY. High 58-60º

Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

#weather #paweather #wx #pawx #philadelphia

Update Sun 2/19 8:40 AM — As alluded to last night, the model cloud algorithms predicted cloudiness for today, but the vertical relative humidity field values were not all that high, so I was curious about how much cloudiness we would actually see today. So far, not much. While a few periods of cloudiness are still possible, I don’t think it will be as cloudy as the radio forecasts are suggesting.

Previously Posted Sat 8:45 PM —

Some Cloudiness Sunday… Watching next Saturday

Today’s models continue with a forecast of considerable mid-level cloudiness during the day Sunday. This sort of cloudiness can be the sort that lets dim sunlight through. The models also show some areas where there will be intermittent clear skies.

The cloudiness forecast is the result of several weak upper air disturbances moving through.

I’m sort of curious how much cloudiness we actually get, since the relative humidity vertical profiles are not that impressive. I guess we’ll see. High temperatures around 53º (Blue Bell). It will become fairly windy during the afternoon and evening.

Watching Next Saturday

There seems to be usually high agreement with today’s global models (GFS, GEFS, ECMWF, ICON, GEPS, NAEFS) that a ‘cold air damming’ setup will develop early next Saturday as warm air rides over cold air at the surface. This is a snow –> sleet–> rain scenario for the immediate PHL area. An inch or so of actual snow is possible, as currently forecast, but it will all be washed away by rain later in the day. Temperatures rise the next day.

This is the most substantial setup for a bit of snow that I’ve seen this entire winter. Many lesser possibilities have faded into oblivion this winter. (This setup was originally forecast by some models to occur this coming Thursday, but that faded away.)

We must not forget that this is about 7 days away. In the weather world, that’s considerable forecast lead time. Much can change in that time frame. Stay tuned.

NAEFS forecast for nest Saturday at 10 AM. Critical temperatures contours (red, white, violet, blue, light blue) are all supporting snow at the onset. But temperatures expected to warm up as the day progresses. (Click on image for a larger view.)