The [relative] warm-up mentioned in my posting last week is on track to arrive late Friday. Unfortunately, the milder temperatures will be accompanied by low pressure and rain.
The low pressure system arriving late Friday will be interacting with a cut-off air upper low in the southeast. Much of the heavier rain will be Friday night and it may taper on Saturday.
There’s much uncertainty with the specifics and timing of this rain, because interactions with upper closed lows are difficult to model.
There’s some suggestion that the upper low may spawn another low pressure system for part of Sunday. Too soon to tell.
Milder temperatures will persist into next week, with a bit of a roller coaster effect as cold air dips in several times. It will be milder, then a day or so of cold, then milder again.
Real changes back to winter are forecast to occur around Christmas Eve with a large storm and deep cold returning.
Tonight’s models show the southern storm brushing southern Delaware on Sunday. (Interestingly, the new FV3-GFS had hinted at this all week.)
Sunday will be mostly cloudy with considerable mid and high level clouds. Temperature highs only 36.
Surface high pressure with an upper broad cyclonic flow will provide colder than average temperatures, light winds and sunny skies
this weekend on Saturday and some cloudiness on Sunday in Philadelphia.
Saturday will be sunny and cold. High 39. (Average high is about 45). Winds will be light.
Sunday will be similar- sunny and cold with light winds. High 39.
Updated Fri 10:30pm Sunday will have mid and high level cloudiness based on the GFS model. High 38
Outlook: A cold and dry week ahead. Some heavy precipitation (likely rain or mix to rain) next Friday into Saturday.
The coming weekend is going to be unseasonably cold and dry. The coastal storm’s track has consistently been forecast to pass south of the Philadelphia area late Sunday into Monday.
Despite my winter long range climate forecast
for a cold winter in Philadelphia posted last weekend, the latest climate models show the balance of December to be somewhat milder than average. This change is predicted to occur later next week.
We’ll see if this happens.