Monday, December 24, 2012

6:40pm Weather Update - Snow Matrix Update

The chunk of energy to spawn the Post-Christmas snow storm is over the four corners region of the United States southwest.  The low is expected to develop early Tuesday morning over eastern Texas and then move northeast.

I am working on my forecast numbers but not sure if I'm going to have them out tonight.  I still have quite a bit of uncertainty as to the placement of heavy snowfall.

I have been talking about a concern for a layer of warm air coming in.  I am seeing data that is confirming that concern.  NOAA's global forecast model is suggesting a layer or temperatures at or slightly above freezing coming in at 3,000 feet and at the surface for 2-3 hours Tuesday evening in southeast Missouri and early Wednesday morning for central Indiana at 3,000 feet .  This would allow for sleet to develop in Indiana and rain in southeast Missouri.  Sleet is a nightmare for forecasters.  It drastically reduces snow totals.  This doesn't mean everyone in the locations mentioned above will see sleet/rain.  In fact, many places will see all snow.  However, the introduction of sleet and rain makes putting together accurate numbers difficult.

The Hydrometeorological Prediction Center has updated their snow probability charts.  These cover 6pm CT Tuesday through 6pm CT Wednesday.

4" or greater snow probability:

(Click image to see larger version.)

8" or greater snow probability:
(Click image to see larger version.)

12" or greater snow probability:
(Click image to see larger version.)

The afternoon run of the high-resolution RPM computer model (21z) is in.  Here is what it is projecting for snowfall through Thursday afternoon.
(Click the image to see larger version.)

Now for the snow matrix.  This is updated with morning and afternoon computer model data.

CITY
18z RPM
9z RPM
12z GFS
Cape Girardeau
9.3”
0.2”
11.7”
Cairo, IL
11.1”
1.5”

Columbus, IN
7.9”
8.0”

Bloomington, IN
10.9”
8.3”

Dyersburg, TN
3.6”
1.5”

Indianapolis
9.6”
5.2”
6.6”
Lafayette, IN
5.8”
2.4””
4.5”
Marion, IL
13.9”
0.7”

Muncie, IN
5.8”
6.6”
5.9”
Paducah, KY
14.0”
4.2”
0.6”
Poplar Bluff, Mo
4.0”
0.1”
11.0”
St. Louis
0.5”
0.1”
0.8”
Union City, TN
3.9”
4.1”


I will try to get updated information out later tonight after the evening data is available.  Not sure how much I will be able to update tomorrow.  Look for an update later in the day.

Have a Merry Christmas!

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