Updated Sun 09/17 @ 6:03 PM — It appears that some rain will linger here in the Delaware Valley until about 10-11 AM Monday. Cloudiness will linger longer…until about 2-3 PM.
More info in This Week’s Weather to be posted this evening.
Update Sat 9/16 10:51 PM — It looks like rain will only affect eastern NJ and the shore on Monday. but clouds linger here with some clearing in the afternoon.
Update Sat 9/16 9:39 PM — This evening’s models are showing showers moving in as early as 3-4 PM Sunday.
A large dip in the jet stream will spawn a coastal low pressure system late Sunday and it may affect our weather with rain Sunday evening through early Tuesday.
Water Vapor image (channel 9) captures mid and upper level flow (jet stream level) Saturday afternoon. White arrows show the general location of the jet stream. A low pressure system (blue L) will be form and move up the coast later Sunday through Monday with rain.
Sunday
Sunny in the morning. Increasingly cloudy beginning 12 to 2 PM. Showers move in from the west between 5 PM and 7 PM.
Model temperatures have a higher than usual uncertainty (spread) due differences in forecast cloud cover. sd =2.5º
High temperature 76.7º ( NBM model— location Blue Bell, PA) High temperature 79.3º ( NBM model— location Philadelphia, PA)
Updated Sun 09/03 @ 9:36 PM — High temperatures Sunday were 1º shy of last night’s NBM forecast (within the forecast standard deviation). The heat wave cranks up a notch on Monday.
The latest NBM forecast (00z) just became available and it’s consistent with past forecasts—
Tonight’s 00z NBM forecast high temperatures for Monday. Standard deviations (uncertainties) are about 1º again for Philadelphia and about 1.5º for the surrounding areas. (Click on image for a larger view.)
High temperatures are forecast to rise about 1º each day through Wednesday and possibly Thursday. Here’s the NBM forecast for KPHL—
NBM Forecast temperatures/dew points/heat indices (“apparent temperatures”) The apparent temperatures (over 100º) are likely too high because the NBM has been over-estimating the dew point temperatures. (Click on image for a larger view.)
Here’s the latest ECMWF forecast temperature meteogram for Philadelphia Airport—
ECMWF (18z run) through Wednesday. Temperatures Philadelphia Airport. A little lower temperature than the NBM forecast for Monday but much higher for Tuesday and Wednesday. (Click on image for a larger view.)
Update Sat 9/02 11:12 PM — The forecast remains on track for Sunday and Monday. I’m raising the expected high temperatures for Sunday. Monday’s forecast highs still look right.
Sunday
High temperature 91º ( NBM model— location Blue Bell, PA) High temperature 93º ( NBM model— location Philadelphia, PA)
Monday
High temperature 94º ( NBM model— location Blue Bell, PA) High temperature 96º ( NBM model— location Philadelphia, PA)
Previously Posted Fri 5:21 PM —
This is a fairly simple forecast and the details haven’t significantly changed over past days.
Following a delightful Saturday, the “heat dome” that has made the weather headlines this summer will expand eastward and northward, affecting our area starting Sunday.
This afternoon’s Satellite Water Vapor (which shows the upper atmosphere) with superimposed RAP model jet level windstreams and the 500-1000mb thickness line (thick orange contour). Note the 576thickness line. South of this line is hot/tropical air. This tropical air will expand towards us. (Click on image for a larger view.)
Expect unseasonably hot weather from Sunday through at least Thursday. On the positive side of things, dew points over the weekend will NOT be oppressive.
Saturday
Sunny and beautiful!
High temperature 82º ( NBM model— location Blue Bell, PA) High temperature 83º ( NBM model— location Philadelphia, PA)
Sunday
Sunny and unseasonably hot, but with comfortable humidity.
High temperature 90º ( NBM model— location Blue Bell, PA) High temperature 92º ( NBM model— location Philadelphia, PA)
NBM high temperatures Sunday. This may be a degree too low. (Click on image for a larger view.)
Monday
Sunny and quite hot. Increased humidity with dew points in the mid 60s.
High temperature 94º ( NBM model— location Blue Bell, PA) High temperature 96º ( NBM model— location Philadelphia, PA)
