Winter Storm Watch Sun 4pm - Mon 7pm

Latest QPF maps from the HPC also shows increased moisture with this H5 closed low. The dark blue indicates greater than 0.5" liquid precip and the brighter blue greater than 0.75" liquid. This confirms that narrow banding we see so often with clipper systems.

From the NWS in INDIANAPOLIS:

VERY HIGH Q VECTOR DIVERGENCE OVER SOUTHERN CWA FROM TONIGHT INTO
MONDAY...WHICH CORRESPONDS TO STRONG ISENTROPIC LIFT AT LEVEL 285.
ALSO TROWAL EXPECTED TO BE OVER SAME AREA...AND AT 925 MB SEE BAND
OF RELATIVELY HIGH EQUIVALENT POTENTIAL TEMPERATURES ADVECTING IN.

TAKEN TOGETHER...THIS SUGGESTS RELATIVELY HEAVY SNOW WILL
FALL...ESPECIALLY WHERE TROWAL AND HIGH EQUIVALENT POTENTIAL
TEMPERATURES LINE UP. AS OFTEN WITH TROWALS...THIS BAND MAY BE
NARROW.

AVERAGE PRECIPITABLE WATER SOUTHERN CWA OVER THE PERIOD ABOUT THREE
TENTHS OF AN INCH...WHICH MORE OR LESS CORRESPONDS TO MODEL QPF. DUE
TO RELATIVELY COLD TEMPERATURES OVER AREA AGREE WITH BUFKIT WE MAY
SEE LIQUID SNOW RATIOS ON THE ORDER OF 20 TO ONE...

If Bufkit is right and we get a 20:1 ratio, that 0.84 precip around Louisville would mean 16.8" snow!! Bear in mind that not all of this will fall as a 20:1 ratio. That ratio will settle in as colder weather moves in with the H5 low after the surface low and associated cold front passes mid-day on Sunday. Still think that a good solid band of 5-7" with locally higher amounts over Dubois, Crawford, Pike and counties along that east-west line is a good call.

NWS in Louisville has issued a Winter Storm Watch for nearly all counties bordering the Ohio River. It appears as though a Winter Weather Advisory will likely be issued tomorrow or overnight. Might not also be surprised if that was even upgraded to a warning at some point.

EXPECT SNOW INTENSITY TO START PICKING UP LATER IN THE AFTERNOON...
THUS HAVE STARTED A WINTER WEATHER WATCH AT 4 PM SUNDAY. FOR AREAL
COVERAGE...HAVE THE HIGHEST TOTALS OVER THE NORTHERN TWO-THIRDS OF
THE CWA AND THUS THE PLACEMENT OF THE WATCH FOR ALL BUT THE SOUTHERN
TWO TIERS OF COUNTIES. THESE AREAS LIKELY WILL GET AN ADVISORY
ISSUED EITHER TONIGHT OR TOMORROW FOR SUNDAY NIGHT AND MONDAY.

Updated Snow Map

The latest 00z model runs from the NAM and GFS have started to take quite a varying path. Somebody is going to get some major snow! It's a question of who at this point. On the left you find the NAM and the GFS to the right. The dark blue indicates greater than 0.5" liquid precip. The NAM takes this right into the heart of our area, while the GFS has pushed it further north the past two model runs. Frankly it's a little late in the game to be pushing a system over 100 miles north of where it has been for several runs consistently. There could be many explanations for this, but it'll be interesting to see if the next runs due out later overnight track it back south again. I tend to believe the NAM is more reliable at this point.

Because of the updated last three model runs, I am going to have to up my snow totals. Models are all in agreement that somebody is going to get a heavy band of snow. The H5 low is now poised to go just south of Louisville and that would set us up in the perfect zone for the heavy snow. With a clipper system, the heaviest bands of snow usually occur just north of upper low. It would not be a shock to see some spots get greater than 7" with this system. A good swath of 3-5" still seems likely for much of the area.

Here is the latest 7 day forecast created by me on Sat 2/13/2010 at 6pm.

Major Winter Storm Valentine's Day

The latest model data shows a major winter storm from a strong Alberta Clipper moving into the region late Sunday evening lasting into Monday evening. A winter storm watch is now in effect for most of Southern Indiana and Kentucky from 4pm Sunday through 7pm Monday. The snow events will come in three waves, with the first beginning Saturday night into Sunday morning. Accumulations of 1-2" are possible. The main event will come Sunday afternoon into Monday morning with most of the snow coming from this time frame. Some wrap around moisture may come on Monday evening bringing another quick inch of accumulation.

At left is the latest probability from the HPC of at least 4" of snow. Prob of 8" is center and prob of 12" is far right.
Red = 70%
Green = 40%
Blue = 10%

With that said, here is my forecast graphic for what to expect. Going to go with generally 3-5" across our area, though locally higher amounts could easily be possible depending on how high the snow to liquid ratios become. With the first wave from the surface low tonight, a 10:1 ratio is probable. However ratios could be as high as 16:1 or even 20:1 as the cold, arctic air begins to set in behind the front. As of right now, the NAM is churning out 0.22" liquid and the GFS is at 0.36". The NAM seems to be underestimating the liquid as it has in some previous winter storms this year. I like the GFS much better. At at 20:1 ratio, that could mean as much as 7.2" and 5.76" at a 16:1 ratio! Because some of this will occur at the 10:1 to start, going with 3-5" generally across the area, but won't be surprised at locally higher amounts.