Feb 202013
 

Main Precipitation Threat Tonight/Thursday

All of the Ozarks are under some short of winter storm warning this morning for later tonight and Thursday. Ice accumulation is still a concern.

A huge amount of humidity is being lifted over a dome of cold air which will result in lots of rain aloft, which will transition to a mess in the Ozarks on the ground in the form of sleet and freezing rain.

Layout of Precipitation

There is an expected transition of precipitation type for many in the Ozarks. When the initial wave comes in tonight, it’s expected to be snow and some sleet.  This will probably stay snow in areas from let’s say Lamar to Camdenton northward.

As for Springfield, snow will give way to sleet and eventually freezing rain (ice) by dawn on Thursday.

Freezing Rain vs. Sleet: What’s the Difference?

 

Areas of northern Arkansas and south-central Missouri will hold on to freezing rain the longest and have the biggest threat of significant ice accumulations.

Totals

I expect Springfield will see several inches of snow/sleet overnight tonight with a glaze of ice on top of that starting sometime in the early morning hours of Thursday.

The snow up north could amount to 1-3″.  This of course will become a major snowstorm north and northwest of the Ozarks.

Ice accumulations will be between .10 and .40″ I think with the higher amounts in the area specified on the graphic.

Information Today/Tonight

I will post a winter storm update after the morning computer model runs come out, right around noon.

I will post a video review/blog by late afternoon.

Also, look for a live web show tonight to discuss the situation. Details coming up later today!

Feb 192013
 

Winter Precipitation Depends on Temperatures Above

When I use the phrase “winter mix”, it refers to some combination of snow, sleet or freezing rain (ice).

The term is used whenever any of these are possible over a certain time frame.

Both sleet and freezing rain require a layer of above freezing air aloft.  The difference is in the depth of the sub-freezing layer touching the ground (lower blue areas on diagram)

While the “general” layout is for snow to occur closest to the colder air with sleet, freezing rain and rain occurring in bands toward the warmer air (usually in a southerly direction), there are exceptions.

One is terrain. An increase in elevation means colder temperatures which can change the precipitation type.  Or the opposite, occasionally cold air becomes trapped in valleys and alters precipitation type.

Also, convective (rain/thunder) bands tend to cool a column of air near the ground and turning what might be a freezing rain situation into sleet.

Here are the definitions:

Sleet

This is liquid (rain) aloft which falls into subfreezing air near the surface deep enough to freeze the drops into ice balls.  Sleet “tings” when it strikes windows.  Sleet accumulates like snow but because it is essentially little ice pellets, it doesn’t accumulate nearly as fast. It actually offers some increased traction on roads when compared to snow.

Freezing Rain (Ice)

Nearly the same as sleet except that the drops stay liquid falling into a much shallower subfreezing layer at the ground. These “super-cooled” rain drops will then freeze on contact with surface objects, especially those off the ground such as trees and wires.  Freezing rain producing ice accumulations over a half inch can cause branches and wires to snap from the weight. An ice storm is born!