What originally looked like a cold, chilly, and at worst showery event on Tuesday into Wednesday is now becoming a more nasty storm for a couple of reasons.
(1) The upper air trough that is responsible for the upcoming cold shot is sharper in nature than what computer models were forecasting over the past few days. A sharper trough is not only stronger and more potent in terms of energy which would support a stronger storm to develop but also would change the movement of the storm itself. Earlier guidance had the storm moving more north-northeast but recent computer guidance is suggesting a movement more to the north.
Because the trough is stronger and also deeper, the upcoming low pressure center will intensify more rapidly. Earlier guidance had suggested the low would be more disorganized as the upper air trough would be less potent.
(2) The sharper trough is also moving in more slowly. This is important because the coastal low will develop closer to the region than earlier anticipated. As the low was earlier forecast to develop closer to Cape Cod more recent model guidance suggests the low develops closer to the coast. Since the low will be closer and stronger than before the Mid Atlantic and Philadelphia will see greater impacts from the storm.
What will the impacts be from this stronger storm?
(1) Rain will move in later this evening and become steadier as the night progresses. By morning, rain could be moderate if not heavy in a few places.
(2) Rain will be more widespread in the morning hours on Tuesday but gradually will be becoming more occasional and scattered in coverage during the afternoon as the storm system lifts northward.
(3) Winds will increase through the night, becoming very gusty tomorrow with north and northwest winds at 15-30 mph, gusting possibly to 40 in places.
(4) Across the higher elevations north and west of Philadelphia, rain will mix with snow across the hills around the Lehigh Valley on Tuesday and across the Poconos late tonight and tomorrow. Snow may accumulate in the highest elevations of the Poconos during the day tomorrow and an inch or two of accumulating snow is possible in Carbon and Monroe Counties. It's possible some snow mixes in the higher elevations of the suburban counties north and west of Philadelphia but the odds are we see rain during Tuesday.
(5) As the storm lifts northward, precipitation will become more showery Tuesday night and with colder air draining south from Canada we could see a few flurries at times in the Philadelphia suburbs mixing in with those showers.
It will be cold tomorrow, with temperatures moving little during the day from morning temperatures in the upper 30's and low 40's. Temperatures may even fall slowly during the day north of the city. Combined with those gusty winds, it will feel quite winter like out tomorrow despite the calendar saying it's October 28th.
I'll provide another update on the storm tomorrow morning.
Update, 11 PM: Snow is already being reported at Mount Pocono and in Tobyhanna. They will likely more than the inch or two quoted above...could be quite a few inches of snow in those areas.
