Category Archives: Weather Updates


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Sun 8 AM : The short range high resolution models have the clouds coming in somewhat earlier than the FV3-GFS and GFS. About 2-3 PM. The FV3-GFS still about 7 PM. It will become quite windy today.  Areas to the north of Philadelphia will be sunny most of the day.

Current RAP (Rapid Refresh Model) cloud composite for 2:30 PM Sunday

Tonight’s NAM keeps the main cloud deck just to our south for much of  Sunday.  High clouds at times, but lower clouds aren’t forecast to move in until 4-7 PM. High 76-78

The WRF model, just available, has the clouds moving in about 1-3 pm, earlier just south of the city.


I’m always on the lookout for the best forecast model. (Anyone into weather is probably on this ongoing search.) The issue is that some models do better in different weather patterns.

The only model that got close to predicting the thundershowers last night that affected the northwest suburbs and some of the Philadelphia area was a model that I haven’t until recently focused upon- the WRF with its two variants- the WRF-NMMB and the WRF-AFW.

The WRF (Weather Research Forecast) model is a short range (48 hour) model that has a high resolution. It’s only run twice a day for the US.

It did well last night and also with the storms last week. So let’s see how it does today.

The WRF is forecasting showers and thunderstorms to develop as early as 2:30 PM (earlier far northwest suburbs).  Most likely time for Philadelphia is 3-5 PM.  High temperature forecast for today is 84-85 before the showers move in.


Tonight’s models are doing extremely poorly predicting the thunderstorms that are on our doorstep at 11 PM.

NEXRAD radar image 11pm Saturday (

This doesn’t bode well for Sunday’s forecast; if the models can’t get the 3 hour forecast correct, what confidence can one have for the 20 hour forecast?

There’s a wide range of times for the thunderstorms expected on Sunday.  They may start as early as 2:30 in the afternoon, or they may move through as late as 7 PM.  A low confidence forecast with tonight’s models.



A weak warm front moved through before daybreak. Dew points have already started to climb and winds have shifted to the south.

The general consensus is a mix of sun and some clouds at times today.  High temperatures somewhat lower than predicted by the GFS (87)- most models are in the 82-83 range and the NBM consensus comes in with a similar range.  The statistical EKDMOS comes in at 83-85.

A line of thunderstorms will develop late this afternoon/evening mostly in the Pottstown/Reading Allentown areas to our west. These storms will intensify and train in the area.  It’s unclear how far east these will move. Some models have the storms approaching Philadelphia about 8-9 PM but diminish in intensity significantly.  Some models keep the storms to our west.   NJ may not see much of anything tonight from these storms.