THIS WEEK’S WEATHER

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Now through Christmas

Updated Thursday 12/21 @ 4:58 PM — Today’s models have backed off considerably on the chance of showers late Saturday evening and Sunday morning. In fact, at this time, most models with the exception of the ECMWF and ICON-EPS have any showers staying well west and far north of the immediate PHL area on Sunday. Considerable cloudiness is still expected.

Posted Thursday 12/21 @ 9:55 AM — A back door cold front will slip through later today with colder air for Friday. The front will return as a warm front on Saturday into Sunday. I’ve summarized the situation in the graphic caption below—

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. A back door cold front will move through tonight. Colder weather for Friday. The front will return as a warm front through late Saturday into Sunday with scattered showers, mostly far north and west, but a shower here can’t be ruled out. Warmer weather for Sunday, but early morning showers are possible, along with a light shower later in the evening.

For much of Saturday and Sunday we’ll be in the transition zone between warmer and colder air masses and significant cloudiness is expected. Less certain is the amount of shower activity here.


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WEEKEND WEATHER FORECAST

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Sunday Storm Update

Posted Sunday 12/17 @ 3:10 PM — It’s looking like 3-4 inches of rain (even 5″ in a few spotes just to our west) will fall over a large area, according to the majority of this morning’s models.

Here’s the 3 PM MRMS radar. The heaviest rain is expected between 1 and 4 AM —

MRMS radar at 3 PM Sunday.

Sunday Storm Update

Posted Sunday 12/17 @ 9:33 AM — After reviewing the latest model guidance, the forecast remains pretty much intact. Very light drizzle of increasing intensity is visible on radar moving up from the Cape May area. A gradual increase in dampness as the morning proceeds.

The current setup, via satellite water vapor imagery—

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. The main storm is far to our south moving almost directly towards us. (Click on image for a larger view.)

Here are the salient points regarding this storm—

  • light scattered drizzle, increasing late afternoon
  • heaviest rain 2-3 AM tonight
  • rain taper late Monday morning ends after 1-2 PM Monday
  • highest winds after midnight and especially 2-3 AM into Monday morning. Wind gusts 40 mph with some models showing 50mph.
  • Snow flurries, especially north and west daybreak Tuesday. Possibly a coating northwestern suburbs.

Here’s the hourly forecast rain rate in inches per hour (NBM model)—

NBM Precipitation rate (Blue Bell) in inches/hour. Greatest rainfall intensity (and winds) 2-3 AM (Click on image for a larger view.)

Total Rainfall expected—

Today’s 12z NBM total precipitation forecast. Some models show areas of 4″+ Click on image for a larger view.)

Wind gusts—


Sunday Forecast Update

Posted Saturday 12/16 @ 4:55 PM — The high cloud cover today was less than forecast and the NAM-NEST was one of the few models that got this right today (but discounted by me) .

The NAM-NEST continues to forecast showers and drizzle as early as the early to mid morning Sunday, and because of its accuracy today, I’m going with it for Sunday. It’s supported somewhat by the latest ECMWF and to some extent, the latest GFS, but the rainfall it’s predicting early is quite enhanced—

NAM-NEST shows showers and drizzle starting before daybreak and rainfall by noon Sunday is considerably more than several other models. Nonetheless, I’m going with it, based on its performance today. (Click on image for a larger view.)

The heavier rain starts between 5 PM and 7 PM Sunday evening. At that time, the main storm is still in South Carolina moving north. By midnight, wind gusts increase to 40 mph.

By 5 AM Monday morning, the low is an elongated two-center system right over our area—

Latest GFS (18z) shows a two center elongated low at 5 AM Monday. (Click on image for a larger view.)

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