Updated Sun 9/11 10:54 PM — Additional rain, possibly heavy, will move through Monday evening. Another inch of rain, possibly two inches, may fall.

Update Sun 09/11 @ 11:03 AM — Please look at the comments link just above for some information that regulars to this blog might find interesting!

Update Sun 09/11 @ 11:02 AM — Current radar shows rain has overspread much of the area

Current Hybrid Radar Sunday 10:15 AM Most of the heaviest rain will track to our west. (Click on image for a larger view.)

The rain should continue.

ECMWF 06z rain forecast for Blue Bell, PA (Click on image for a larger view.)

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  1. Hey Glenn. I am your neighbor, Pauline’s husband, and Cyan’s friend. I am also the volunteer administrator for the James Turrell “Greet the Light Skyspace” at CHFM. One of the most challenging responsibilities is predicting precipitation. We can’t open the roof and run the lighting sequence if there is any risk of precipitation during the the 65 minute window the roof is open. We try to give ticket holders a few hours advance warning if we can’t open since some travel from as far away as Washington and NYC. 85% of our programs run Sunday evenings, starting at sunset. I’m wondering if we might be able to plug into your expertise to predict the precipitation risk for our events?

    1. Hi George, I’m sure I could provide some direct help and we should talk.

      Perhaps some of the best help I could provide would be to give you some readily available online links to find the forecast rain probability. One of the best is the direct NBM (Model Blend) text output. The NBM is considered the best model for rain probability and the data is updated every few hours.

      I’ve pre-configured the URL for you to provide the model output for Philadelphia Airport, Wings Field Blue Bell, and Northeast Philadelphia airport.


      While direct model output for a specific location is not available from this site, the output here is close enough for your needs.

      It provides hourly probability (P01) in percentage (on an hourly basis, anything greater than 18% and increasing is meaningful) and the amount (Q01) in hundredths of an inch.

      The tricky part is converting to the UTC time to Eastern standard or Eastern Daylight time. So in the example below, this is the NBM model from 0700 (3 AM) and the first row (labeled UTC) and the column labeled “14” is 10AM today.

      Looking down the probability is 48% and the quantity of rain is 2= 0.02″


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