Tuesday, March 6, 2012

3/5/12 Clipper Recap

The one thing about clippers is that they can bring some surprises.  They can be huge busts, or end up over-producing.  The fact that they usually don't carry a lot of moisture is complicated even more by the mountains and their tendency to significantly weaken clippers as they cross the WV/VA state line, before eventually redeveloping east of the Blue Ridge.  Track is also important, with the heaviest snows being just north of the low.  Clippers have narrow bands of precipitation, so 25-50 miles north or south can mean a big difference.  Here's my first and only snow map I made for this storm Sunday morning:
I felt pretty confident with this map through the day Sunday, although a few runs of certain models began to keep all of the precipitation well south of I-64, with no snow making it into Harrisonburg, Charlottesville, northern va, maryland, DC, etc).  Clippers do usually trend north, so I was holding on to that.  A few of these same models were also very bullish with snow totals for central/SE Virginia, which I just did not see happening.  If this event was happening in say late December/January, when the sun angle was not as much of an issue, then sure, I might have took them into account.  But no, we are in March.  This storm was also going to be starting as the sun was coming up in those areas.  The gfs/ukmet/cmc/euro began to creep the northern edge of the precipitation just a bit during the day runs on Sunday.  The nam continued to keep all precipitation confined to a line from lynchburg to richmond, leaving out locations north of there.  Then last minute, the Sunday night 00z run of the nam suddenly brought the northern extent of precipitation to the VA/MD border.  Although a lot of people threw out this run, saying that models were pointless this close to an event, the fact that the nam had been the southern outlier and came north was worthy of pointing out.  At this time, the water vapor loop of the storm also appeared to show that the clipper had turned the corner.  Once this happens, it's usually pretty safe to draw a horizontal line of where the the northern extent of precipitation is located on radar and bring that line due east.  The clipper had turned the corner with precipitation all the way into southern Ohio, a big signal that areas north of I64 would in fact see snow, which they did.  Here is a map from the national weather service depicting snow fall accumulations:
This map doesn't do the best job showing exactly how much fell from a narrow band from around charlottesville to just west of fredericksburg. In this narrow area, there were reports of 6-10" of snow.  I'd say that I64 and just north was my biggest bust area for this storm.  The rest worked out pretty well.  Here's a link to some of the more impressive totals in VA:

Clipper snow totals

The most important thing I've learned from the past two events is to not ignore last minute trends of models.  It is a myth that they don't matter, with some exceptions of course.  Glad this clipper over-produced for just about everyone, because it's the last snow storm Virginia is getting this winter.  Before I had held out on calling it quits, because I did think an event like this could/probably would happen. I'm now officially ready to call off winter.  It's over.  Enjoy Spring! -hv

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