Tonight’s early NAM data just became available. Little has changed from my earlier post.
Precipitation starts later, now between 11-1PM on Thursday (earlier south of the city).
Precipitation will be principally sleet, then rain. There may be some snowflakes at the beginning, but this is a sleet—> rain event.
Temperatures during the day hover near and above freezing, then low to mid 30s. Temperatures rise near 40 late Thursday night.
It will become windy late afternoon into the night.
Rain will be heavy in the afternoon and evening. QPF values are 1-1.5 inches, mostly falling as rain.
The upper atmosphere chills before daybreak on Friday as the upper low merges with the coastal storm. Some snow may mix with rain briefly before daybreak Friday and before ending early morning.
Saturday AM Update: Today’s high temperatures will be near their current range (39-41F) and windy. Still unclear how much instability stratocumulus will develop, although the models maintain sunny skies.
Sunday will be more tranquil.
The latest FV3-GFS has brought back the chance of snow flurries (no accumulation) for Tuesday night after the coastal low departs.
A strong cold front will approach Friday afternoon and move through Friday night. Heavy rain is expected Friday afternoon.
Much colder weather will arrive for the weekend as high pressure builds in on Saturday. However a strong upper cyclonic flow from the departing low pressure system bring windy conditions for Saturday. Winds 15 mph with gusts to about 30mph are possible. Temperatures will struggle to reach 40.
With the cold air and cyclonic flow, instability stratocumulus clouds may also develop on Saturday, limiting the sunshine, although the models are down-playing this right now.
For Sunday the winds calm down but still expect unseasonably cold temperatures with highs about 44 with sunny skies.
A significant coastal low will develop and approach early Tuesday , giving us another round of windy, rainy conditions for all of Tuesday. Current track is that we will get heavy rain, but areas in Western PA may receive snow.
The FV3-GFS and NBM were suggesting the possibility of wet snow squalls or flurries moving through with the cold frontal passage Tuesday night, although today’s FV3-GFS has backed away from that.
Wednesday will be winter-like with very cold temperatures in the 30s!
Things have clarified with the timing of the frontal passage and the associated rains. A cold front finally moves through Friday evening into night with heavy rain as a low pressure system rides up the front.
The front clears our area a few hours before sunrise Saturday. The rain ends early morning and skies are expected to clear giving us partly to mostly sunny conditions. (We may have some instability cloudiness at times.) It also becomes windy and gusty. The NBM shows wind gusts as high as 27 mph from the west-northwest during the early afternoon. High 55.
Winds die down Saturday night and temperatures chill to 37.
Sunday will be a beautiful Fall day — sunny and more tranquil. High 54.
The average high for this period is 58 and average low is 42 for Philadelphia.
Daylight Saving Time ends Sunday morning. One of the few things good about that is that the GFS output starts becoming available at 10:40 PM instead of 11:40 PM. (We’ll need that earlier GFS for those future snow forecasts!)
Sunday 12 noon: Considerably more clouds today than had been forecast, with tonight’s low pressure system’s cloudiness already moving in. We may still see some bright spots and sun today.
Yesterday, we had a dry slot allow some brightening about noon before the drizzle and light showers moved in as expected.
I had hoped to get some time outside on Saturday, but it looks like the weather won’t cooperate. Those following this blog have seen the forecast change from rain through Sunday morning to rain ending late Saturday morning.
Things seem to have settled on heavy rain Friday night into Saturday morning, tapering to showers late Saturday morning.
There’s a high probability of light intermittent showers continuing into the late afternoon Saturday. It will be very windy in the morning and it will be mild despite the predicted heavy cloud cover. High
60. 52 (Average high is around 60.)
Sunday will be partly cloudy/partly sunny and seasonably mild. High 58.