October is typically a month of volatility in temperatures over a period of time -- we are prone to occasional warm spells and cool spells, with this year a noted reminder that those can come in quick succession as we went from near 80 in the city on Saturday to the low 50's on Sunday.
We're due for some rebound in temperatures later this weekend and early next week as the pattern becomes a bit more zonal, fast-moving, and the powerhouse trough in Northern Canada winds down a bit. Tomorrow will be a bit milder than the past three days but that warmth will be fleeting as a cool front shoves east, sending us back into the 60's for the duration of the week. Strong high pressure will quickly scoot across the Great Lakes and Northeast, bringing us a very cool Friday night that may result in frost in the burbs as winds slacken off and skies will be clear. The city will avoid frost in all likelihood but we could see low temperatures approach what we bottomed out to on Monday morning.
That high quickly scoots out into the Atlantic. A storm system that was in the Rockies on Friday will quickly race northeast through the Midwest and into Southern Canada by Sunday night. The "cool" front in the wake of this storm system will lack any bite as the pattern behind the front is zonal and relaxed for a couple of days. The resulting push of warmth that this weekend low pressure system brings will result in highs back into the 70's in the Delaware Valley starting Sunday, continuing through a good chunk of next week. It would not shock us if a day or two in that stretch pushed the upper 70's around Philly. Not record warmth (those are in the 80's) but certainly a mild spell.
A stronger storm system, which you can see in the Pacific on the above graphic, will gradually cross the US next week and impact us in the latter portions of next week. That could cool us back down a bit for the weekend of the 20th but after Friday and Saturday it looks like chilled air may take a bit of a break around here.