Standing My Ground

I'm just going to go ahead and assume that most of you look at multiple forecasts when you're interested in the weather -- rather than just relying on Rippeology.  If you're doing that, you're seeing some forecasts "back off" yesterday's projected totals a bit, putting southern Wisconsin more in the 5-8 inch range for this weekend's storm.

Here are the National Weather Service snow maps from yesterday and today.  Note the retreat in snow totals.

Yesterday, I predicted 8-11 inches.  I'm sticking with that forecast today for 5 reasons.

First, nothing about this storm has changed in the last 24 hours.  Timing, temperature, intensity and duration are all nearly identical.  The only thing that has changed slightly is the location of the low pressure development (see the last point below), and that actually works in favor of my slightly higher totals.

Second, there are two pieces of energy in play here, and at some point, they will combine into one.  Bernie Rayno from Accuweather did an excellent job of explaining this in his video yesterday.  When and where those two pieces of energy combine makes a huge difference.  As I draw it out on paper, I have them combining somewhere near Waterloo, Iowa (my birthplace!), which bodes well for higher snow totals in southern Wisconsin.  Because...

Third, as the low strengthens and tracks through northern Illinois Sunday, it seems inevitable to me that the low will shoot heavier snow bands to its northeast -- right in the direction of southern Wisconsin.  With southeast winds and strengthening energy to the south/southwest, it just makes sense that some bands in our area will briefly produce snow rates at 1-2" per hour.  That alone can pad snow totals in a short period of time. 

Fourth, this is a 30 to 36-hour storm.  Pretend for a moment that the average snow rate is only a quarter of an inch per hour.  That's 8-9 inches.  Granted, we'll see some periods where the snow rate is .10 to .25 inches an hour...but all it takes is a couple of hours in heavier bands (as discussed above) to rack up the snow totals.

Fifth, this morning's models have the low developing farther south than prior runs, giving it the ability to tap some gulf moisture before heading in our direction.  GFS has the low moving out of the Texas panhandle and into Oklahoma by Noon Sunday.  This, too, suggests the possibility of some heavier bands.

Everybody interprets model data differently, and the dynamics of this storm are only now really starting to set up.  Truth will reveal itself at some point when the snow finally stops while we're all sleeping Sunday night.

~Scott