Wednesday, December 4, 2013

Significant Snow & Ice

Looking over the morning weather data and one word keeps coming out of my mouth.  "Wow!"  Computer models are narrowing in on a target for winter weather Thursday through Friday for southeast Missouri, southern Illinois, western Kentucky and central/southern Indiana.

Let me start by saying there are many facets to this storm.  There will be rain changing over to sleet/freezing rain and then changing over to snow.  Travel could be a MAJOR headache for week's end.

The critical part of the forecast is trying to determine when things change over.  There is going to be PLENTY of moisture to work with.  In fact, the morning computer model runs are very aggressive with the moisture.

Here is a look at the profile for Cape Girardeau from this morning's run of the NAM computer model.

12z NAM for Cape Girardeau
(Click the image to see larger version.)
Green = rain | Orange = sleet | Red = freezing rain | Blue = snow

As you can see from the model, a little bit of everything is showing up.  It does appear that this is going to start out for rain in most locations.  As the colder air arrives at the surface the change will begin to happen.  As the layer of cold air at the surface is shallower, freezing rain will be the concern.  As the layer "thickens" it will eventually change over to sleet.  Once the column is large enough with cold air, it will change over to all snow.  Often times this happens at the tail end of the moisture, but that doesn't appear to be the case this time.

Ice is going to be a concern for several areas.  For places like Cape Girardeau and Poplar Bluff there could be 0.25" of ice before changing over to snow.  In Paducah, 0.5"-0.75" of ice accumulation before changing over to snow isn't out of the question.  Right now, Columbus, Indiana and Bloomington, Indiana look to stay away from any ice.  I do think there will be quite a bit of sleet contamination, which will cut down on the freezing rain accumulation, for areas north of a line from Poplar Bluff to Cairo, IL to Owensboro, KY.

Here is a look at how much freezing rain and sleet accumulation the NAM and the GFS are suggesting.
12z NAM Sleet Accumulation through 6pm CT Friday.
(Click image to see larger version.)

12z GFS Sleet Accumulation through 6pm CT Saturday.
(Click image to see larger version.)

12z NAM Freezing Rain Accumulation through 6pm CT Friday.
(Click image to see larger version.)
12z GFS Freezing Rain Accumulation through 6pm CT Saturday.
(Click image to see larger version.)
As you can see, the models are much more bullish on sleet than freezing rain.  However, even a tiny bit of ice can cause HUGE problems.

Let's take a look at how much moisture will be available during the time the computer models suggest it will be all snow falling.  To be honest, I was a little surprised to see the consistency and the amount across the board.

Here is a matrix of quantitative precipitation forecasts (QPF) for various locations in Missouri, Illinois, Kentucky and Indiana.
Through Friday Afternoon

Through Friday AFternoon
The amounts shown above indicate how much moisture will be available while the atmospheric column is supportive of snow generation.  Yeah, there's a LOT!

Simple snow formulas suggest a 10:1 ratio.  It doesn't look SUPER cold in any of the locations (St. Louis will be a little colder) so I don't think this cause the ratio to slide too much.

Here's another look at some of the data from the computer models.  This is looking at snow accumulation from both this morning's run of the GFS and the NAM.
12z NAM Snow Accumulation through 6pm CT Saturday.
(Click image to see larger version.)
12z GFS Snow Accumulation through 6pm CT Saturday.
(Click image to see larger version.)
As to how much snow I think could fall?

INDIANA:
  • Bloomington: 7"-10"
  • Columbus: 8"-12"
  • Evansville: 9"-14"
  • Indianapolis: 4"-6"
ILLINOIS:
  • Marion: 8"-13"
KENTUCKY:
  • Paducah: 5"-8"
MISSOURI:
  • Cape Girardeau: 7"-12"
  • Poplar Bluff: 6"-10"
  • St. Louis: 1"-2" (maybe 3)
Hope you have the snow shovels ready!  But PLEASE be careful if you are in places that could get ice first.  If you go out to shovel and hit some of the ice, your day may not be overly joyful.

Bottom line...
  • There will be rain, freezing rain, sleet and snow.
  • This will NOT be a repeat of 2009's historic ice storm.
  • Temperatures get much colder.
  • Significant snow will fall over parts of the Ohio/Mississippi River valleys.
  • There could be another round of snow coming through Sunday/Monday. Let's first get past Thursday and Friday before dealing with Sunday/Monday.
FREAK-OUT-METER: (Scale of 0 to 10)
Time to break down the Freak-Out-Meter a little more.  If you've been paying attention to it over the last couple days, it is has been slowly inching up.

INDIANA:
  • Columbus/Bloomington: 6/7
  • Evansville: 7
  • Indianapolis: 5
ILLINOIS:
  • Marion: 6
KENTUCKY:
  • Paducah: 7 (because of freezing rain)
MISSOURI:
  • Bootheel: 7 (because of freezing rain)
  • Cape Girardeau: 6
  • Poplar Bluff: 6
  • St. Louis: 3
Reminder:  To get more weather information throughout the day and night, follow me on Twitter (@johndissauer) where I put out lots of information and thoughts that don't necessarily make it in to my blog.

2 comments:

So glad you still keep us updated here in the bootheel of Missouri (Portageville). I use to follow your live feeds for severe weather to stay informed when you were with KFVS-12. Just wanted to say thanks!

John, thanks so much for your updates! This is a great breakdown of the data. We miss you here in Southeast Missouri!

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