Friday, September 07, 2012

The Wind Threat With Saturday

Last evening's post on Saturday's rain and thunder made a passing reference that despite a lack of severe weather risk (at the time) for Saturday, winds could be gusty as a line of thunderstorms moved through tomorrow afternoon. The Storm Prediction Center has upped the ante on the forecast for Saturday's wind threat -- stating there's a three in ten shot at severe weather within 25 miles of any point tomorrow for much of the region.

The severe threat tomorrow is predominately a wind threat with a much lower threat for hail.

The reason for this is that the storm system that approaches tomorrow will be in the process of intensifying as it moves through the Great Lakes.  A rather robust low level just will push ahead of the storm system, with winds at 5000 feet above the ground as high as 70 mph just east of the low center tomorrow afternoon.  The graphic below shows the winds at 5000 feet (in nautical miles per hour, so divide by 1.15 to get mph).  The core axis of wind will be from Ontario south into Northern Pennsylvania, although winds aloft will be robust down into the Delaware Valley.  A lower level jet streak will develop below this 5000 foot layer nearby later in the day tomorrow as well, helping provide us the opportunity to get in on a squall line of sorts later in the day.

Not all of Saturday will be awful -- it will be breezy at times with increasing clouds in the first half of the day.  If you have a community event or some sort of morning activities, you should be able to get those in before 1 or 2 PM locally.  However, as we work into the later afternoon the front itself will approach from the west...with the squall line or quasi-squall line developing.  The high resolution NAM (below) shows its thinking for 5 PM, with a line of solid rain (wind) and some thunder stretching across New York and Northeast Pennsylvania, followed to its south by a broken line of thunder and rain.

Timing the thunder threat locally, it looks like 4-8 PM is when our region gets in on the "fun" from this frontal system.  Winds could reach 50 mph or higher with any storms that do develop.  There could also be a downburst or tornado that drops within the squall line as there is some indications that wind shear will be present.  The odds of that will be higher up towards Scranton and Williamsport than they will be here but there's a slight chance of that here as well. 

Yeah, the heavy rain threat still exists with tomorrow but it will mostly be with the squall line and not so much with multiple lines of storms firing and training over the same areas.  Rain could be quite heavy at times as the front moves through as well.   However, rainfall totals at this point look to be less than an inch locally...and an inch or more from the Poconos north.