By Chris White

Weather Blog: Since Fredericksburg resides "in the seam" between the Richmond VA and Washington DC media markets this blog is a look at the weather from a Fredericksburg-centric point of view.

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An early Halloween monster storm

PREPARING: FEMA offers advice for getting ready for a major storm.

As promised on Tuesday I am addressing the oncoming “Frankenstorm” (a borrowed term) today.  But before diving into the details there are a couple of critical factors that need to be emphasized:

(1) I very much appreciate your readership, but if this is your sole source of weather information you need to change that situation at once.  Although I tend to slip into the role of amateur forecaster the real purpose of this blog is to discuss and explain local weather in and around the city of Fredericksburg.  For situations like the upcoming major storm you need timely and professional weather information that you can obtain from places like the National Weather Service (my recommendation) from which you can obtain updated local information by typing in your zip code into the box on the top left of their main page.  You can also get emergency mobile updates from a number of sources.

(2) The reason I waited until today – Friday – to discuss this storm is that it is literally a once-in-a-generation event.  There are a lot of moving parts to this scenario that are fascinating to the meteorological community, which is one reason why there has been a rapidly swelling buzz in the media and in the digital world.  The potential effect of this event on the Fredericksburg area populace is still only clear enough (IMHO) to talk about in general terms as forecast model solutions are not in great agreement more than 72 hours ahead.  The risks of waving the danger flag too early include (a) sounding like the boy who cried “wolf” too many times – so people stop listening – and (b) unnecessarily creating a public panic by overhyping a situation that may or may not pan out as thought.  My preference is to do neither, so I make no apologies for treading carefully in situations like this one.

So, what can we expect from this potentially historic weather event?  First, here’s the setup:

In this infrared satellite view you can clearly see the approaching cold front draped across the middle of the country from the Great Lakes to the Gulf Coast near the Texas/Louisiana border.  And, of course, Hurricane Sandy is hard to miss lurking off the southeastern U.S. coastline.

As Sandy moves northward into the colder waters near the Tidewater Virginia area it will begin a transition from a pure tropical system to an extratropical system, slowing down in the process and taking a left turn to hit the East Coast.  Where it will hit is still in contention per the forecast models, the worst case being from the European model which has Sandy‘s center basically hitting the DC area head on.  HOWEVER, the current consensus (yes, it could change as time goes on) is that the center of circulation will strike the coast a bit further north and then merge with the approaching front as shown in this HPC graphic:

So what would this mean for weather in the ‘Burg?  Other than the exact track of Sandy‘s center of circulation there are three other factors to consider:

(1) The conversion from tropical to extratropical that will slow the storm’s forward progress will also increase its residence time in our area.

(2) The storm itself it very large and regardless of where the center goes its overall effects will cover a wide swath of territory.

(3) The full moon is this weekend (no, it has nothing to do with Halloween) which will exacerbate any coastal flooding potential.

Thus the potential effects on the ‘Burg and vicinity will start Sunday night and last through Tuesday to include:

(a) Strong winds gusting to 40-50 mph first out of the northeast before swinging around to the north and northwest, with perhaps an Isabel (2003) reprise IF the worst case scenario occurs. This could bring down tree limbs already weakened from this summer’s derecho event and create power outages just as the temperature plummets behind the cold front.

(b) Lots of rain as shown here (the yellow/orange hue over the ‘Burg is 5+ inches):

This could cause river and small stream flooding during the heavier downpours late Sunday into Tuesday.

(c) Coastal flooding along the western shore of the Chesapeake Bay and the southern shore of the Potomac River, with a lesser degree on the Rappahannock.  This would be from both the full moon – higher tides – and the strong winds, with perhaps a minor contribution from a storm surge up the Chesapeake Bay.

So what won’t we see?  No snow for the ‘Burg…that will be reserved for the mountains further west.  No tornadoes or severe thunderstorms are forecast for Sandy‘s landfall and extratropical conversion process.  And no hurricane force winds, even though tropical storm force winds (>39 mph) are a good bet.

The bottom line is that Fredericksburg and vicinity should prepare for the worst case – another Isabel type storm – and hope for the best (a near miss).   I can’t urge the readers strongly enough to stay tuned to emergency messaging and media outlets to keep abreast of what could be a volatile situation.