THURS HEAVY RAIN & WEEKEND OUTLOOK

With a complicated forecast, let’s try a different approach. I’m going to use two different model’s meteograms showing precipitation for Blue Bell, PA. (remember that a meteogram only shows the weather for one specific location; the Jersey shore’s meteogram may look much different for the same time frame.)

Both show heavy rain (1 inch) starting about 2 PM Thursday afternoon.

The ICON shows significant rain again on Saturday. The model blend does not. (Not shown here, the GFS has showers in the late afternoon Saturday.) Both show Sunday and Monday essentially rain free.

ICON model—

ICON model rain meteogram for Blue Bell, PA Is it over-doing the rain on Saturday? (The GFS only has rain in the afternoon on Saturday.) Why the ICON model? It did well with last night’s rain, while the GFS model totally over-predicted last night’s rain. (Click on image for a larger view.)

Important clarification: the meteogram times indicate prior 1 hour accumulations. If you were to take those times as literal (and you shouldn’t), it would mean that the actual rain start times could have been as much as 1 hour earlier. Accumulation also does not show light rain that might not have accumulated enough to show in the scale of the meteogram.

NBM

NBM meteogram for Blue Bell PA (Click on image for a larger view.)

So after some heavy rain Thursday and early Friday, much of the Fourth of July weekend may be relatively rain free. (Considerable clouds on Saturday with possibly some showers in the afternoon, according to the GFS.)

Sunday and Monday look much better weather-wise.

It will be cool on Saturday (high in the 70s) and still below average highs on Sunday (about 80º)

THUNDERSTORMS & HEAVY RAIN

Wed 09:42 PM Forecast Review — Not all models were onboard with very heavy rain tonight. I think the GFS overdid the rain forecast for tonight. But most models agree with a forecast for periods of heavy rain starting Thursday afternoon, 1-3 PM.  

Updated Wed 3:32 PM with precip map

A quick post here….As described in my previous post, a front will move through and stall just south of the Philadelphia area.

Some scattered pop-activity possible late this afternoon.

The main frontal activity will move in this evening (Wednesday evening). Latest models have storms affecting immediate PHL area from about 8 PM through midnight, starting in far northwestern suburbs earlier. Severe activity possible far northwestern suburbs; heavy activity here.

GFS Accumulated Rain forecast at 1 AM Thurs morning. Note that the GFS is forecasting additional 1-2 inches of rain in some areas Thursday afternoon into Friday. Please note that weather models cannot exactly predict precise location and amounts of rain, but it gives an idea of the general quantity. (Click on image for a larger view.)

Not all models are on-board with the above GFS forecast of excessive rain.

Main event appears to be Thursday mid-afternoon (2-3 PM) into night with additional heavy rain/storms.

Stay tuned for updates.

Weather… and Other Things 'Up in the Air'