Wednesday, January 9, 2013

Wet and Slick Weather Ahead

Quite a few weather “things” coming to the Midwest over the next five to six days and there are still a lot of question marks as to what will hit the ground.  One thing is for sure, there will be a significant and beneficial amount of rain falling at least through Sunday.  In some instances, upwards of 6” of rain could fall in parts of Missouri, Illinois and Kentucky.

Here is the Hydrometeorological Prediction Center’s precipitation forecast for the next five days.
Click image to see larger version.
If the computer models are correct, the numbers on the map (above) might be on the low side of reality.  Just through Friday, a four computer model average for rainfall is:
  • Cape Girardeau:  0.96”
  • Indianapolis: 0.89”
  • Paducah: 1.32”
  • St. Louis: 0.96”
Considering much of the area is still well below normal (precipitation), the rains will definitely be beneficial.

CLEAR SLICK STUFF

Now  the main reason for writing this post… What comes Sunday/Monday.

In the next 24-48 hours I think you are going to start to hear television meteorologists/weather-peeps starting to mention “freezing rain” (a.k.a. ice).  Freezing rain isn’t fun as it only takes a very small amount to make things slick.

The temperature profile of the atmosphere will be a HUGE factor in determining what type of winter weather will reach the ground.  It is the changing temperatures with height that makes winter forecasting the most difficult.

Instead of going in to detail how each type of winter precipitation is formed, check out the following links for tutorials from the University of Illinois on how the various winter weather types are formed.
Ok, now that you have a better understanding of how the different precipitation types form, let’s take a look at what some of the computer models are advertising for a few select locations.  (Note:  This is just an overview of what a few locations could see.  The data used is coming straight from computer models and is not the forecast.  It is also subject to change, and likely will.)

For the last couple of runs, computer models are hinting at cold shallow air to be in much of the Midwest.  The cold air is scheduled to arrive late Saturday night through Sunday depending on your location.  The models have temperatures slightly above freezing at 5,000 feet and  how thick that “warm” layer is will determine the type of precipitation hitting the ground.

This is a meteogram for St. Louis.  Each line is a representation of a different run of a computer model’s prediction of freezing rain accumulation.
Click image to see larger version.
The light blue line shows the amount of freezing rain accumulation from this morning’s run of NOAA’s global forecast model, the GFS.  Disregard the dark blue line (comes from the 6z GFS which I hold little faith in).

Not shown in the above meteogram is the European forecast agency’s computer model, the ECMWF.  The Euro is suggesting 0.59” of rain may fall while temperatures at the surface are below 32°F.  (Keep in mind that not all precipitation falling accumulates.  That is a reason for difference in numbers.)

Here are meteograms for a few other locations along with how much precipitation is projected to fall by the Euro.

Cape Girardeau, Mo:   Euro – 0.63”
Click image to see larger version.
Indianapolis, In:  Euro – 0.60”
Click image to see larger version.
As we get closer to Sunday the models should get better at predicting the minute details needed for determining precipitation type. 

Bottom Line… What I want you to take away from all of this is that there is a chance we could see freezing rain Sunday in to early Monday morning (timing varies by location).  It could also fall as all rain or sleet.  There are still considerable uncertainty as to what will fall.

I know many are skittish after the 2009 ice storm but as of today I do not think this will be anywhere near that storm.  As you will see below in my “Freak-Out-Meter”, I don’t think you should be freaking out nor should you be stocking up supplies to go weeks without power.  Instead, what I think you should do is keep an eye on the forecast over the next couple of days, maybe beat the lines and grab a can of deicer and a few batteries.  Worst case (for me anyway), this doesn’t pan out and you’ve got an extra can of deicer and batteries.

FREAK-OUT-METER:
  • Southeast Missouri: 2
  • Southern Illinois: 2
  • Western Kentucky: 2
  • Northeast Arkansas: 2
  • St. Louis Metro: 3
  • Central Indiana: 2

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