Saturday, February 14, 2015

Snow Chances On the Rise for Monday - Heavy Snow in southern Indiana??

A rare late night update tonight to make you aware that I am closely monitoring snow chances for central and especially southern Indiana late tomorrow night through the Monday evening time-frame.  Considering the noted changes in the data, I do not want anyone to feel caught off guard.  On Friday, it really looked like the bulk of any snow would stay well to the south of Indiana..with perhaps a little snow grazing southwest Indiana.  Things have certainly changed in the past 24 hours.  The model trends today and tonight are taking the snow much farther north.  To show you how much things have shifted, I put together snapshots of the last three runs of the GFS.  Shifting northward with each run....









 The model runs coming in tonight are all in very good agreement on our system for Monday bringing snowfall much farther north than earlier thought.  Since we are within about 24 hours of the event getting underway, I will go ahead and show you what some of the model data is suggesting as far as snow accumulations.  As always, I give the disclaimer that this is just forecast guidance!  

NAM model snowfall accumulations:


Graphic courtesy of Earl Barker's model page - WxCaster

This model suggests significant snow accumulations for far southern Indiana with light snow making it to about a Terre Haute to Martinsville to Franklin line.

GFS (American) model snowfall accumulations:


Graphic courtesy of Earl Barker's model page - WxCaster

GFS also suggesting significant snow amounts for far southern Indiana with light snow making it as far north as about I-70.  The entire state of Kentucky gets HAMMERED!

GEM (Canadian model) snowfall accumulations:

The Canadian model also shows heavy snow accumulations in far southern Indiana with light snow making it to the I-70 corridor.


Graphic courtesy of TropicalTidbits

ECMWF (European model) snowfall accumulations:

And the last model for the 00z data suite is in...very similar to all the other models.  Heavy snow in extreme southern Indiana.. with the potential for light snow to make it as far north as the I-70 corridor.  


Forecast uncertainties I have is how far north the snow will go....and the amount of dry air that will eat into the northern extent of the snow.  I will say this.  A lot of the models posted assume snow totals at a 10:1 snow ratio.  With very cold air in place, this will be a high snow ratio event.  With higher snow ratios you get more snow with less moisture.  Essentially "more bang for your buck."  While the cold air helps for higher snow ratios, the cold/dry air mass can also make it tough for the precipitation to overcome the dry low levels.  This will mainly be a potential issue for the northern extent of the precipitation shield.   

Bottom line: I want to be clear that I feel more and more confident that this will be a significant snowfall for portions of far southern Indiana.  The farther south you are, the more snow you will see.  ALL areas south of I-70 are now in play for the potential for some accumulating snow, with the highest confidence across far southern Indiana where this could really end up being a decent snowstorm!

Timing: It appears the snow will push into southwest Indiana at some point after midnight Sunday night, and begin to expand across southern Indiana by daybreak Monday.  The system will be at its peak throughout the day Monday with snow falling across the southern half of the state...with heavy snow possible in far southern Indiana.  There will be a sharp cut-off on the northern edge and where that sets up is to be determined.  The snow would not exit southern Indiana until at some point Monday evening into Monday night.  

Are the models done trending north?  Hmm.  Will be interesting to see if there are any additional shifts in the data tomorrow. 


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