Update Sat 09/03 @ 5:49 PM — The forecast posted Friday still looks good. It does appear that we’re going to luck out: no rain in the immediate PHL area (and the shore) until late afternoon on Monday.
Current weather at 6 PM—
Water Vapor with jet stream level wind streamlines (orange streamlines) with superimposed radar. Moisture and rain flow will move north of our area through Monday. (Click on image for a larger view.)
Sunday afternoon has the showers circling up around the region. We stay mostly sunny through high clouds and dry—
NBM forecast for Sunday 5 PM. Cloud cover is in grey/black. Red contours are spread uncertainty in cloud cover. Rain is green. (Click on image for a larger view.)
For Monday, the rain gradually moves in from the north and west. We’ll have significant cloudiness ,thickening during the afternoon, with rain by 5 PM, according to the latest NBM—
NBM forecast for Monday 5 PM rain moves down from the northwest. (Click on image for a larger view.)
Hard to believe, but the NBM cranks out a widespread rainfall of about 1 inch through Tuesday.
Updated Fri09/02 @ 11:35 PM — The forecast below remains on target.
Updated Fri 09/02 @ 5:45 PM —Not much change in the forecast (see the earlier “outlook” below). The system moving towards us may be even slower to arrive, which means Saturday and Sunday will be dry.
Indeed, the areas from just west of Philadelphia and eastward which have seen the least rainfall in recent months, will continue to be bypassed by any showers.
Saturday
High thin clouds much of the day; occasional periods of more signficant cloudiness. Dry. (There may be some afternoon showers along the NJ, coast according to the latest NAM-NEST.)
High temperature 86.4º (sd 1.3º) NBM model Blue Bell, PA
Sunday
Cloudy early morning, then sunshine by noontime. Increasing cloudiness again later in the afternoon and towards evening. Dry.
High temperature 87.9º (sd 3.2º) NBM model Blue Bell, PA
Monday
Considerably more cloudiness. Some models keep us dry while others have light rain moving in late afternoon or evening. (There’s significant uncertainty with Monday’s forecast.)
NBM Forecast Monday 4 PM. Light showers northwest, cloudy elsewhere. (Click on image for a larger view.)
High temperature 83.2º (sd 3.1º) NBM model Blue Bell, PA
Early Labor Day Weekend Outlook
Previously Posted Fri 10:13 AM —
A weak jet flow will result in slow movement of weather systems into our area.
A somewhat stationary area of moisture in the Mississippi valley will slowly approach over the weekend. Here’s what it looks like Friday morning on satellite water vapor imagery—
Current water vapor image (Friday morning) with stalled stationary front This area of moisture will very slowly move eastward bringing an increasing chance of showers late Sunday and Monday. (Click on image for a larger view.)
The current upper air (jet stream level) map shows a somewhat stationary area of low pressure that will linger out west due to weak jet winds—
ECMWF jet stream level wind forecast for Sunday at 5 AM. Low pressure in the middle of the country with upper winds bringing moisture up from the Gulf of Mexico. (Click on image for a larger view.)
With systems moving so slowly (note the colored, higher speed winds can only be seen in the northwest corner and northeast corners of the map) the upper level low pressure system in Kansas will linger as moisture streams up over our area.
Based on the GFS and ECMWF, we’ll have mostly high cloudiness on Saturday and Sunday. Timing any showers precisely will be difficult. With continuing drought conditions, I expect any showers to stay mostly west of Philadelphia through most of Sunday.
There’s a hurricane in the North Atlantic. From experience, tropical systems with weak steering currents play havoc with forecasts even if they are many hundreds of miles away. I expect forecasts to change over the next few days, likely leaning towards even better weather.
According to the ECMWF, even Monday will be mostly rain-free—
ECMWF forecast for 2 PM Monday. Tropical system in North Atlantic. Rain hangs back into western Pennsylvania. (Click on image for a larger view.)
Updates later today and during the weekend. Stay tuned.
