Thursday, December 6, 2007

THE WEATHER HAS BIG PLANS FOR YOU


The problem is...those plans are fraught with peril over the next 2 weeks. But since this is a site dedicated to basic weather for busy people, let's get right to it, shall we.

EVENT # 1- FRIDAY 12-7: LOOKEY WHAT WE HAVE HERE.
Go ahead, take a look on the radar, you'll like it. While you're at it, check out current surface temperatures across the Mid-Atlantic, bitter me timbers on a Friday morning. Where oh where have I seen this before? No, not the clipper we just had... but January 4, 2003. A very similar setup tomorrow and I have to go out on a meteorological limb here and tell you this could turn out to be the second surprise snowfall in 1 week. Four years ago, on Sunday the 4th, we went to church in the Baltimore area under some light snow courtesy of an upper level low, the NWS forecast was for perhaps 1/2 inch. It was only expected to snow a few hours, and snow it did.. leaving 5 INCHES between 9AM and 5 PM. The event caught everyone so off guard that school was closed on January 5th.

Now fast forward to 2007. Unlike that storm, we already have a fresh snowpack driving down overnight temperatures, and another system with enough moisture to produce 1-3" snows in central Ohio. What do I think will happen? Upper level lows have a way of "activating" precipitation at the surface given the right conditions. If we take a 1:20 liquid to snow ratio, and multiply by current projections of .03" liquid for this event, it translates into over 1/2 inch of snow. That's assuming the system does not incorporate moisture from the bay, which I believe the clipper did, and this one will too. Read the Baltimore-DC NWS current forecast discussion to read between the lines and see what I see. Perhaps the radar is just showing virga (when the precip is falling but not reaching the ground), or is there a chance that evaporative cooling turns a "rain snow mix" into an all snow event?

EVENT # 2 - THE LONG ICE STORM COMETH? Intriquing animation of precip type based on a merger of analysis from the GFS and NAM computer models, definitely check this out.

I know your local forecasts are printing out the chance of a deluge for days starting Saturday and continuing into next Thursday. At this time of the year, when there's a lot of battle going on between cold and warm..do you really think it's just going rain for 6 days straight? Let me put it in simple terms... a 1033 mb High in Eastern Canada pressing down on a frontal boundary draped across the US from New Jersey to Missouri is a forecast fraught with peril. From Saturday to the middle of next week, (8th to 12th) computer models are already projecting a significant to extreme ice event from Illinois to New York, including most of Pennsylvania. This could end as a surprise snowstorm o the New England coast toward end of the week. Potential ice accretion of 1/2" over many many metropolitan areas stretching back 1000+ miles. In Maryland, if that cold air can penetrate the stationary front, a multi-day rain event could turn into a multi Tylenol ice event in no time flat. What does it mean for you?... might want to have extra batteries on hand now, I'm totally serious. There will be more on this event posted over the weekend.. but closely monitor your NWS forecast site for changes, as I think this is a dangerously evolving situation.


EVENT # 3 - THE PRE-SOLSTICE SNOWSTORM?

Dec 07 Storm 3

A major US government computer forecast model, called the GFS (for Global Forecast System) has been for several days now advertising an extremely significant coastal storm in the 17th-18th time frame. Liquid potential is 1 - 2 inches depending on your location, (closer to 1" liquid in the Mid-Atlantic, and 2" in Northeast and New England). As forecasters at Accuweather have already pointed out, climate indices are aligning to provide a nearly ideal setup (a positive PNA and negative NAO) which I will explain in more detail over the weekend. It also appears that extremely cold air will make itself available for a portion of the storm, making ratio calculations (considering possible 20:1) right now a bit premature, but at least fun.


That's all for now. Over the weekend, please consider posting in the comments what your local TV forecasters are reporting, because we have one heck of a week coming up if you like surprises.

1 comment:

E.H. Boston said...

Here in Woburn, we got a surprise 1/2" of snowfall tonight...4-6PM.

Some places got over 1".

The funny thing is, this wasn't even shown on the GFS or NAM last night.