The 1 am model runs have changed the QPF significantly. The NAM and GFS are down to a 0.30 inches QPF, occurring late morning into evening. Expect about 2-3 inches. Wow, this is a tough business!
8:30 AM Update: Some snow pellets are falling near my home, just northwest of the city. Upper air temperatures still on the borderline for snow, but they are still expected to drop.
Ground surface temperatures have not decreased as much as expected last night; This likely will reduce accumulations on sidewalks and roadways, since any snow initially falling will melt until surface temperatures chill.
Air temperatures near the surface are still expected to drop to the 30-32 and upper air temperatures should drop to support snow by late morning.
The snow totals should still be 2-3 inches, but perhaps towards the lower range.
The latest NAM data has become available. QPF totals have risen to over 0.50 inches water. Upper atmosphere temperatures marginally support snow or snow mixed with sleet and ice pellets early morning in the immediate PHL area. Inner western suburbs willl likely be all snow.
The upper atmosphere cools causing precipitation to be all snow by late morning or early afternoon.
Surface temperatures about 30-32 degrees for much of the day. Winds will be light. It will feel like less of a “storm” and more of a light gentle snowfall that accumulates over the duration of the day.
Snow starts before daybreak with a coating to an inch expected by daybreak. The snow or snow/sleet continues at a light rate becoming all snow by afternoon. Slightly heavier snow during the mid to late afternoon before ending about 7-8 pm.
Depending upon the amount of morning sleet, snowfall totals 3-5 inches, possibly 6 if it’s all snow.
The GFS data becomes available in about an hour . I’ll update if things change.
10:45 pm update GFS model similar enough that I’m sticking with the above Forecast.
The afternoon run of the NAM just became available. QPF values for PHL are now over 0.5 inches water. The critical temperatures of the upper atmosphere are now not as warm as the earlier run from PHL and westward. Still slightly warm for dry snow—some sleet or ice pellets will mix in reducing snow totals. Approximately 3-5 inches possible for PHL and immediate west is the current call.
The afternoon model runs are not the best, since they don’t incorporate new radiosonde upper air data. (That’s those weather balloons.) Will have a better handle on snow totals with the evening runs. Will update by about 9:30 PM tonight.
