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12/12/2013

Snow Accumulation Likely In Parts Of Our Area In The Next 48 Hours! I Have My Snowfall Totals Inside...

We have talked about the Friday night / Saturday storm for days now and it is finally time to get the storm into our area. I feel confident some of us will see accumulations, so in tonight's blog I will talk about when to expect the storm in your area, who could see snow, and how much could accumulate.

 

Friday Night / Saturday's Winter Storm

 

First I will say that this is not a winter storm for the whole area. For southern KY, this is simply a rain system, but our northern counties will have the biggest problems. The reason we have been able to generate these storms is because we have two jet streams that have been converging in our area. The northern branch brings the cold and the southern branch brings the moisture. The storm of interest is now moving into Arizona / New Mexico.

 

SATRAD

 

While there is quite a bit of cold in our area now, the winds will shift to the southwest over the next 24 hours and that will try to bring in some warmer air for Friday. Notice the temperatures in the 40s near Little Rock, AR. What you also see is the snow pack in southern and central Indiana creating considerably colder temperatures.

 

Temps - Regional 2

 

Finally, the other big player for this storm will be the dry air in place over our area right now. Notice the dewpoints remain in the single digits over nearly all of our region.

 

Temps - Regional - Dewpoint

 

 

A Timeline For The Friday Night / Saturday Storm

 

There are two critical parts to note with this storm. First, we have a snow pack in southern Indiana and second, we have incredibly low dewpoints in the area. The snow pack's impact on the temperatures is obvious, so southern Indiana would be most likely to see accumulating snow on this system. The dry air plays a very different role. We will peak near 41 tomorrow and won't go below freezing Friday night, so how can it snow? The answer is the dry air. The precipitation will fall into this dry air and evaporate. As it evaporates, it cools the air and this gives Louisville a window when snow could fall. As I see it, that window is late Friday through around 6 am on Saturday and then we go to rain. That window stays open for southern Indiana through mid morning when you will go a rain-snow mix. For Bedford, IN to Seymour, IN to North Vernon, IN, you will likely stay as all snow on this storm system. AdvanceTrak again is handling this storm very well. You can see the evaporative cooling work as the temperature in the metro drops 4 degrees from 9 pm to 11 pm Friday night when the precipitation tries to start. Notice the timestamp on the top right part of each image.

 

AdvanceTrak 1

 

AdvanceTrak 2

 

AdvanceTrak 3

 

AdvanceTrak 4

 

AdvanceTrak 5

 

AdvanceTrak 6

 

AdvanceTrak 7

 

AdvanceTrak 8

 

AdvanceTrak 9

 

AdvanceTrak 10

 

 

Computer Model Snowfall Totals

 

I want to be very clear, these snowfall totals are from the computer models and not my forecast. I mention this because everytime I have a technical discussion about snow, I get tagged with some snowfall total from the computer models. As we look, the NAM is showing the highest snowfall totals, but we also know it has the greatest resolution to deal with the snow pack in place. In all the computer model data, we see snowfall totals are the greatest in our northern counties.

 

EURO Computer Model Snowfall Through Late Saturday

 

EURO

 

GFS Computer Model Snowfall Through Late Saturday

 

GFS

 

NAM Computer Model Snowfall Through Late Saturday

 

NAM

 

AdvanceTrak Computer Model Snowfall Through Late Saturday

 

AdvanceTrak Totals

 

 

My Thoughts On Our Storm System Friday Night / Saturday

 

With this storm system approaching the NWS has blanketed southern Indiana and Trimble / Carroll counties in Kentucky in a Winter Weather Advisory. This advisory goes in effect at 7 pm on Friday and lasts through 10 am Saturday for most of our area. Jackson/Jennings/Lawrence counties in Indiana expire Saturday at noon. I think the winter weather advisory is well placed, but I will say that it may need to move 1 county further south just to cover the snow that falls in Louisville Friday night.

 

Warnings

 

We have a complicated forecast Friday night. The snow pack and dry air create some complexity in this forecast. I do not think Louisville will ever go below freezing in this setup and that means accumulations that occur would be much more likely on grassy areas. Looking at the pavement temperatures, you can see most of KY has pavement that is well above freezing despite all the cold we have seen.

 

Pavetemp

 

Next, we can see the snow depth is far higher in southern Indiana that most of Kentucky.

 

AdvanceTrak 1

 

All of this together point toward a better chance of snowfall accumulation in southern and central Indiana.

 

Timelime...

As I see this storm, it will start late tomorrow in our western counties near 9 pm, Louisville from 11 pm to 2 am, then our eastern counties near 2 am. Now let's detail the timeline...

 

  • This will start as a rain-snow mix or only rain in our southern counties like Leitchfield, KY to Campbellsville, KY to Columbia before rapidly change to all rain pre-dawn on Saturday.
  • For areas in central KY like Hardinsburg to E-town to Lawrenceburg, you will start as a rain-snow mix. I think you will change to all rain near 5 am on Saturday.
  • For areas along the river like Tell City, IN to Louisville, KY to Eminence, KY, you will start as snow and that can likely continue through around 6 am on Saturday.
  • For southern Indiana including Jasper, IN to Jeffersonville, IN to Clarksville, IN crossing the river into Carrollton, KY, you will start as all snow and it will stay snow through around 8 am - 9 am on Saturday.
  • Our northern counties including cities like Bedford, IN to Seymour, IN to North Vernon, IN, I expect you to stay as all snow in this storm system.

 

Snowfall Totals...

Now let's talk about how much could accumulate. Southern Indiana will definitely see the most since you have the snow pack in place. It will stay colder longer and you have slightly colder pavement temperatures. I think Louisville is on the line, but the data does suggest Louisville could see an inch or possible two on the north side of the city. Here are my specifics.

 

  • I have mainly rain with near no accumulation for Leitchfield, KY to Munfordville, KY to Hodgenville, KY to Campbellsville, KY to Columbia, KY.
  • For areas in central KY like Hardinsburg to E-town to south Louisville to Lawrenceburg, I think you will see up to 1" of snowfall accumulation. I also want to note that most of that will wash away with the rain on Saturday.
  • For areas along the river like Tell City, IN to North Louisville, KY to Eminence, KY, I think you could catch from around 1" to 2" of snow. Keep in mind, the accumulation on grassy surfaces here will be much higher than on the roads.
  • For southern Indiana including Jasper, IN to Jeffersonville, IN to Clarksville, IN crossing the river into Carrollton, KY, I have you in the 1" - 3" snowfall total.
  • Our northern counties including cities like Bedford, IN to Seymour, IN to North Vernon, IN, I have you in the 3" - 5" snowfall total. You will be the big winner on this storm system with most of you in the 3" to 4" range.

 

Snowfall accumulations area-wide will be higher on elevated surfaces and grassy surfaces especially near the Ohio River. The northern counties stay colder longer and therefore your totals are the highest for our area. I hope this helps you know what to expect from this storm!

 

 

 

It is winter storm season and if you want to be one of my storm spotters, you can join me on my facebook or twitter page. Just follow the link below and click "like" or "follow".

 

If you ever have any question, please remember I can be reached on facebook or twitter easily! Just follow the link below to my facebook or twitter page and click "LIKE/FOLLOW"!

 

https://www.facebook.com/pages/Marc-Weinberg/171330336238674#!/pages/Marc-Weinberg/171330336238674

 

http://twitter.com/MarcWeinbergWX

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