Evening Snow Potential Update

Posted on: 9:12 pm, January 16, 2013, by

We are watching the evening forecast model guidance come in this evening, and things are still looking good for snow in Alabama. There will be some adjustments to the amounts of snow forecast for specific areas, but the general idea of heavier snowfall in the higher elevations (higher than 1200′) in northeastern Alabama is still on track.

There will be some who miss out on this event, and there will be some that get more mixed precipitation than anything else leading to little or no accumulation whatsoever.

There is a trend with the late-day and early evening model guidance to shift the core of this low a little farther south; that does not mean the chance of snow is gone. We have seen heavy snow on the north, west, and south sides of different upper lows in the past, so we maintain a chance of some significant snow with a “catch:” some of us are just going to get a mixture while others get solid snow.

The white areas on the map indicate little to no significant snow accumulation.  Pink indicates around an inch on the grass with wet roads; blue indicates areas of higher snowfall in the mountains of Northeast Alabama and East Tennessee.  It gets tough to pinpoint each town in this region because terrain varies so greatly, but the general idea is at least an inch to 2 or 3 inches on the high spots.  A few isolated communities (Lookout Mountain especially) could get between 3 and 6 inches of snow by Thursday evening.

Here’s the evening adjustment to the map to refine it and explain it a little better:

1

The Adjustments:

First of all, the evening run of the NAM suggests a little southward jog in the core of the low; that naturally gives us a decision to make. The best ideas still keep some snow, mainly light in the lower elevations west of US 231 through parts of Morgan, Cullman, eastern Limestone and Madison Counties. West of there, it will be tough to get any appreciable snow:

0Z Nam

0Z Nam

With that look, we will pull the higher accumulations down a bit, but understand that up until the last minute, we will be adjusting this forecast.

When Will We Know For Sure?

Great question. Upper-air lows are notorious for surprises. Sometimes the surprise is a lot of snow, sometimes it is rain, and sometimes it is nothing at all. It comes down to a lot of complicated factors that are not measured very well by our data network. We will be doing the best now-casting we can on Thursday. A lot of this will become more certain in the wee hours of the morning as snow begins in Mississippi.

What About Road Conditions?

If you are traveling on the major highways tomorrow, we expect mainly wet roads from Southern Tennessee south all the way to the Gulf Coast. There will be some places (mainly higher terrain) where snow falls hard enough in a short period of time to create some temporary road ice. I-65, I-565, US 72, AL 20, I-59, US 11, and most of US 411 will be passable on Thursday with only limited exception.

Soil temperatures are in the 40s, so anything that falls (even if there is a temporary accumulation) will begin melting as soon as the snow stops falling.

A re-freeze is possible late Thursday night for wet roads that don’t dry off (or ice doesn’t melt).  The wind will be up around 10-20 MPH in the evening as precipitation ends, so most highways will have a chance to dry off before temperatures dip into the 20s by Friday morning.

Usual spots where water is standing after a heavy rain event (and in places that have been flooded this week), patchy ice is a good bet on Friday morning.

-Jason
Connect with me!
Google+: Jason Simpson
Facebook: Jason Simpson’s Fan Page
Twitter: @simpsonwhnt