Philadelphia Weather Outlook

WEEK WEATHER OUTLOOK

Update Tue 7:25 AM— The forecast models have all moved away from a coastal storm for Thurs night and the weekend. Any storm developing will move south and east, away from us.

Update Mon 8:12 PM — Watching the low possibility of a coastal low this weekend.

Cold air descending from Canada will cause a dip in the jet stream and bring colder, below seasonable average temperatures to our area from Tuesday into Friday. (Average seasonal highs are in the 58-59º range.)

The front that precedes that colder air will bring some showers on Tuesday.

GEFS jet stream winds (250 mb) showing dip in the jet flow over the NE and southern stream jet flow over Florida. Currently, the streams are not expected to phase, with only weak low pressure possibly developing in western Atlantic (white circle). (Click on image for a larger view.)

Most models show that any possible low pressure development from interaction of this jet flow with a southern stream jet impulse will be weak and remain off-shore.

Of interest is the current SREF and ICON models, which show enough cold air to the north aloft to support snow (red line is the 540 thickness line) but surface temperatures currently forecast well above freezing. (Click on image for a larger view.)

SREF Model forecast showing weak low pressure bringing possible frozen precip just north of our area late Thursday night/Friday morning. although current surface temperatures are forecast too be too high for snow or sleet. (Click on image for a larger view.)
This afternoon’s NAM shows low pressure with a precipitation shield overspreading our area after midnight Thursday/early Friday morning. Temperatures aloft support snow (red line is the 540 thickness line) but surface temperatures currently forecast well above freezing. (Click on image for a larger view.)

Stay tuned.