Sun 08:01 PM Forecast Review — The rain stayed along the coastline of Southern NJ today. Instead of moving back as a warm front there are indications that the front will be joined by a cold front in western PA. This setup will allow the remnants of IDA to approach our area on Wednesday.
Updated Sat 10:30 PM— Tonight’s models show more clouds than previously forecast on Sunday and some sprinkles in the morning. A chance of some heavier showers in the early afternoon, especially from PHL and eastward.
The slowly moving frontal boundary just to our south has spawned a somewhat stationary weak low pressure system off the Delaware/Maryland coastlines.
Sunday will start cloudy, but enough dry air will filter in on Sunday to give us a mix of broken clouds and sunshine by noontime. Some widely scattered showers are possible later Sunday afternoon (mostly in NJ) due to instability but most areas will be dry.
It will be very humid. High 83.0º ± 1.8º NBM, Blue Bell PA
Hurricane Ida’s track looks like it will begin to affect our area late Tuesday through early Thursday.
If and when Hurricane IDA becomes a threat to our area, I’ll have a link to follow the storm’s effects.
Update Sat 8:10 AM— Some areas had heavy rain after midnight. For Saturday, the HRRR continues with areas just to the west of Philadelphia being relatively rain-free with most of the rain from PHL into NJ. The NAM-NEST have a more westward extent.
The HREF which blends these models shows the rain today as just that, a blend—
HREF Dark Blue is low clouds. Green/yellow is rain/radar. Green contour lines area standard deviations in rain. (Click for larger image)
Update Fri 10:40 PM — The axis of predicted heavy rain tonight has fallen about >50 miles to the south. Tonight’s HRRR optimistically keeps the rain on Saturday out of the western suburbs.
The NAM-NEST and HIRESW-ARW are not as optimistic—
NAM-NEST Saturday precip
The weather on Saturday may be better than previously forecast.
A frontal boundary is attempting to move to our south Friday evening. The boundary is resulting in showers and thunderstorms as had been expected. These chance of these storms will linger through the evening and night as the front barely makes it south of our area.
Unfortunately, the high pressure system behind the frontal passage will remain to our north as it encounters a firmly entrenched upper air high over the middle and southeastern section of the country.
NAM surface forecast for Saturday at 2 PM Showing the upper High to the northeast and the Bermuda high to our south. The Philadelphia area will be in the convergence zone of moisture and winds. (Click on image for a larger view.)
The NAM-NEST shows maximum moisture convergence and upward vertical velocity about 9 AM Saturday. The NAM-NEST also shows a weak coastal low pressure system forming off the Delaware coast on Saturday, lingering into Sunday.
NAM-NEST moisture convergence and upward vertical velocity 9 AM Saturday. (Click on image for a larger view.)
What does this all mean?
Saturday
Clouds, rain and thunderstorms from Friday night into at least the early afternoon of Saturday with a lower chance later in the afternoon. High 77.9º ± 2.8º NBM Blue Bell PA
Sunday
The low pressure system that forms off the Delaware coast will remain nearly stationary Saturday night into most of Sunday. Considerable cloudiness in the morning. Some bright skies and sun in the afternoon with a chance of showers/thunderstorms on Sunday afternoon. High 82.4º ± 1.8º NBM Blue Bell PA
Update Fri 7:30 PM : I’ve gone with the NBM model for cloud cover on Sunday. Some models have much more cloudiness Sunday afternoon.
If and when Hurricane IDA becomes a threat to our area, I’ll have a link to follow the storm’s effects.
