Monsoon Martin’s Forecast Update: Vanilla Thunder or Mixed Bag?

Friday, 14 December 2007

First, a comment on yesterday’s storm: we ended up with a quickly-called early dismissal yesterday (my school at 9:30), which may or may not have been necessary—but was surely appreciated and well enjoyed. Slightly warmer surface temperatures caused much of the precipitation to be liquid with ice mixed in, rather than the snow and ice with rain mixed in that I’d expected. Around my parts, northern Lancaster County, we saw rain turn to sleet and freezing rain, then to rain, and back to ice for a bit before tapering and ending by five in the evening. I did not experience any slipping on the roads, though I had slowed it down a bit for most of my commute home. Did any of you have problems with icy conditions, power outages, slip-and-falls, etc.? Let me know by posting a comment at the end of this entry.

And now to discuss the next system, Saturday to Sunday…

This is still a challenging forecast because there are some competing low pressure systems and the wildcard factor of warm air infusing into the mix on Saturday overnight complicating matters. I think what we have to remember (and what we saw in action yesterday) is that it’s still autumn and conditions aren’t quite right for a major, snow-bombing, Vanilla Thunder, foot-plus Nor’easter; these are far more common in February or March, for a variety of reasons.

Here’s my thinking as of today, with the understanding that a shift in the track of a low pressure system of even 25 miles one way or the other could alter it dramatically. (But I’m not waffling: what appears below is what I really think is going to happen.)

Saturday begins clear, cold and dry with temperatures in the upper 20s. Clouds will increase in the afternoon as temperatures rise only to about 34. Look for snow showers beginning by 7 or 8, scattered and flurrying at first. Sleet will begin to mix in by 9 or 10; precipitation will change over to sleet and then freezing rain (perhaps even plain old rain in Lancaster and southern Berks Counties) overnight. We’ll actually sleep through the “heart” of this storm, and a lot of precipitation will fall between Saturday night and early Sunday morning. Winds will increase to 20mph by Sunday morning, and 30 by Sunday afternoon—with gusts above 40.

By the middle of Sunday morning, the system will begin to pull away. Expect rain and freezing rain showers to late Sunday morning. Precipitation will taper on Sunday afternoon, changing to snow and ending by 3pm or so.

Predicted snow totals:

• Greater Reading and southern Berks County: 2-4 inches of snow and sleet accumulation with moderate icing, particularly overnight and Sunday morning; perhaps another inch of accumulation during “wraparound” snow period on Sunday afternoon
• Montgomery and Chester Counties, Philadelphia, South Jersey: mainly sleet to rain south and east; a coating of accumulation at most with little driving hazard.
• Poconos: 12-15 inches of mostly snow.
• North of Reading, Schuylkill County, Carbon County: 4-8 inches of snow and sleet with significant icing; perhaps another inch or two of accumulation during “wraparound” snow period on Sunday afternoon.
• Lancaster, Lebanon and York Counties: brief periods of snow followed by freezing rain and rain, accumulating to an inch or two of slushy mess at most.

Worst driving times (confining my analysis to the Berks and Lancaster County region):

• Saturday night from 10pm to Sunday morning 10am, I would say you want to avoid being out and about; it will be icy and increasingly windy, with wind chills in the teens.
• There may be a few brief periods of reduced visibility on Saturday evening and Sunday afternoon during steadier snow showers, but I think one could safely drive with caution at these times.

I do not believe we are likely to have delays or cancellations on Monday at Mifflin or Muhlenberg; perhaps delays in outlying districts like Hamburg and Blue Mountain.

Beyond all this, high pressure builds in. We’ll see sunny and dry but very cold conditions, with highs in the low 30s and lows in the teens and low 20s throughout first half of the week. By the weekend, temperatures will moderate a bit, but I’m now tracking a potential system for Sunday the 23^rd. Very cold for Christmas Eve and Day (but no snow, it doesn’t seem), but Thursday the 27^th into Friday the 28^th may hold more snowfall…

Have a great (and safe) weekend!

Monsoon