Winter Storm Watch Issued

***Winter Storm Watch issued from 6 AM Friday to Midnight Saturday morning***

The National Weather Service in Louisville, KY has issued a Winter Storm Watch for Warren, Simpson, Logan, Butler, and Edmonson Counties valid from 6 AM Friday to midnight Friday night/Saturday morning. The NWS forecast calls for 2-4″ of snow accumulations and up to 0.25″ of ice. This will likely change over the next 24 – 36 hours.

What We Know

A strong cold front will move through the region late Thursday night and into early Friday morning. This will lead to the rapid changeover from rain to freezing rain, then to a mix of sleet and snow, then finally to all snow Friday morning, which is pretty sweet if you’re into that kind of thing.

h/t giphy.com
h/t giphy.com

Okay, time to get serious. A longwave trough is currently located over the Rocky Mountains. This is spreading warm, moist air into the region. If this were early spring and temperatures were a bit warmer, we’d be concerned about potential severe weather.

As the trough progresses eastward a jet streak will move into the backside of the trough and cause a secondary shortwave to form.

NAM Upper Level Pattern - Valid Thursday Evening - pivotalweather.com
NAM Upper Level Pattern – Valid Thursday Evening – pivotalweather.com

A surface low pressure area will form in response to strong divergence aloft. This secondary area of low pressure will form to the south of the region and move northeast with time. Notice the circled red region in the map above is co-located with the low pressure area in southern Arkansas and northern Louisiana in the map below.

NAM Surface Model - Valid Thursday Evening - pivotalweather.com
NAM Surface Model – Valid Thursday Evening – pivotalweather.com

This is the ideal low pressure track to give the Ohio Valley a significant winter storm. This increases confidence in the overall scenario.

What We Don’t Know

There are a few things that weather models are having trouble with. For example, we’re not exactly sure where the secondary low will track. A shift of 50 miles will make a huge difference in snow and ice totals. Each dot in the southeast United States represents a model’s idea of the location of low pressure. That’s a lot of dots over a large space.

NOAA WPC
NOAA WPC

We’re also not sure how strong that secondary low will be. If the low is stronger, cold air should wrap around the backside quicker. This scenario would lead to quicker changeover to all snow. A weaker low could signal the potential for more sleet and freezing rain.

h/t giphy.com
h/t giphy.com

The last big thing we’re unsure of is the location of what is called the “deformation band”. This is the location of heavy, banded precipitation to the northwest of the area of low pressure. If a deformation band forms, it could lead to enhanced snow totals over a very narrow band of the region.

NAM Surface Model - Valid Friday Evening - tropicaltidbits.com
NAM Surface Model – Valid Friday Evening – tropicaltidbits.com

Bottom Line

The bottom line is that while we’re unsure of where the heaviest precipitation will occur, and potential amounts, we are sure that travel will be disrupted Friday morning and throughout the day on Friday.

h/t giphy.com
h/t giphy.com

As always, we’ll update you with the latest information as it becomes available!

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