Update - One final opportunity for snow before 2013!

Can you believe 2012 is almost over!?

Updated below (most recent 10:45am)

Good Sunday morning to you all.

I hope that everyone got the snowfall amount they wanted from this last system. Some of us in Ohio got a little extra snow than forecasted-- what a treat (most of you blog followers are snow nuts, so I shouldn't have any problems saying that) :-)  We still haven't gotten any appreciable snow to the I-64 "donut hole" area-- in 2 years anyway. Got to work on that.

Today, the upslope snows taper off in the eastern WV mountains and calm returns to the region.

HPC - Surface Map - Sunday PM

As high pressure nudges in from the west, we've got a shot at clearing clouds and sunshine, albeit only between this afternoon and midday tomorrow. Another storm system will be getting its act together and be close to us in time for New Year's Eve. Temperatures will be cold today too-- the mid 30s at best given the snowpack.

This all acts as a backdrop for our next system, that unfortunately has another rain/snow line cutting right through our region. Here's what the models are saying at peak impact:

NAM Model

NAM - Late Monday Night NAM - Tuesday Morning NAM - Tuesday Afternoon

The NAM is indicating a 2-part system, though still relatively weak. We get one shot coming in during New Year's Eve itself, mainly along and north of I-64, and for the most part it looks good as light snow. Then after a little break early Tuesday, a comparatively larger shot of moisture comes through, this one of the rain/snow line variety.

GFS

GFS - Late Monday Night GFS - Tuesday Morning
GFS - Tuesday Evening

The GFS is telling a similar story, albeit smeared around in its own low-resolution kind of way. The GFS may be even a bit more marginal with total precipitation amounts, having shoved most of the juice farther to the south.

ECMWF

ECMWF - Monday Night ECMWF - Tuesday Night

The publicly available products from the Euro have an even poorer resolution than the GFS, but the Euro most often ends up being the closest when looking at the weather 3-5 days down the road. The general gist of things here is similar to the others, with perhaps the exception that the first batch of moisture New Year's Eve also has a rain/snow line tint to it. The Euro is also advertising a continual event lasting through Tuesday rather than a break in the middle, though I am a little more suspicious of that since both the other models are showing the break and have better terrain/grid-space resolution.

So let's go with the first batch arriving more snow than rain (but not a whole lot of total precipitation), then the next batch coming in with a rain/snow line cutting through the tri-state...again.

Using what we talked about with the blog posts on the last storm system, we can use the short-range ensembles to identify the best projection for "critical thickness" values.

SREF - Precipitation Type - Tuesday Afternoon

The good news is that the lines are pretty-much following a straight-laced vertical temperature profile (not creating large inversions that would highlight an icing danger). If freezing rain was going to be the big danger here, we would see the lines flipped over, with the 32F blue line being farthest south and the 0C 850mb line being the farthest north-- indicating warm air overtop of cold air.

Anyway, in this example, given the results of the last event, the rain-snow line marked out by this ensemble mean would be, once again, north of the Ohio River. This time around there seems to be less of a fudge factor that can welcome in counties along I-64 in Kentucky (because the 540 thickness line is also much closer to the 32F line. We obviously still have days before we get to the zero-hour, so any adjustment of these lines can flip folks from rain to snow (or the other way around).

HPC - Projected Total Precipitation

If a location were to be getting all-snow, the conversion rate near the freezing mark is a 10-to-1 ratio. Meaning, you get about 10-times the depth in snowfall given an initial depth of rain-- or said another way, if you melt 1" of fallen snow, you usually have abour 0.1" of water left over. Using that ratio as a benchmark, the highest snow totals peak around 3" on the map above (if it's all snow). That makes this next event another weak-ish one, but as we saw with the last one, those late-inning models runs can come out and signal a change that gets some folks a little snowier. Of course, we can go the other way too, but let's not talk about that. It's still the holidays ;-)

Update (10:45am) - Inspired by a blog commenter, I decided to look up the satellite-based snow analysis from our most recent snow event.

NOHRSC - Snow Depth - 12/30/2012

Unfortunately the best snow algorithms from remote sensing of snowfall only permit for this sort of exponential increments, but you can certainly see the contrast. Note that instead of having the rain-snow line oriented directly along I-64 per se, it was more on a SW to NE line angling from south of Grayson to the Sutton area. Less then 10 miles separates no snow from 2" of snow, and the notorious 'donut hole' shows up clear as day :-)
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Regional Radar/Satellite with Warnings Tracking

Accuweather Radar

From the Storm Prediction Center (below): Click For a Larger Image

Activity Overview Storm Outlook Watches Potential Watches Storm Reports
Temperatures HD Doppler Radar Estimated Rainfall Active Warnings
Current Temperatures HD Doppler Radar Estimated Rainfall Active NWS Warnings
Click For Larger Click For Interactive Radar Click For Larger Click For Larger

Have a great day everyone!

-B

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