By Lauren Casey

PHILADELPHIA (CBS) — Enjoy our last mild day today for quite an extended stretch as arctic air arrives by tomorrow afternoon and lingers into midweek next week. The dramatic cool-down will commence with a snow event for the Delaware Valley on Friday.

A Winter Weather Advisory is in effect for the far northwestern suburbs, Berks County and the Lehigh Valley from midnight tonight until Noon on Friday and for the Poconos from 8 p.m. this evening until 10 a.m. Friday morning.

The precipitation will begin in the Lehigh Valley and Poconos after midnight, briefly as a wintry mix then changing to all snow. A wintry mix is likely to develop along the I-95 corridor by 5 a.m. on Friday with a transition to all snow thereafter.

Expect a steady period of snowfall for Philly and surrounding suburbs, including South Jersey during prime commute time from 7 a.m. to 9 a.m.

The swath of uniform precipitation is set to clear the area by late morning but scattered snow squalls are likely to re-develop during the afternoon due to a strong northwesterly wind flow.

Snow squalls will locally reduce visibility and contribute to addition snowfall accumulation.

Plan for 1-2 inches in Philadelphia through the day with higher totals to the north and west. The Lehigh Valley is forecast to pick up 2-4 inches of snow and generally a coating to an inch along the coast.