Yup, It's Going to Snow

Happy New Year from Rippeology!

Here's hoping you had a chance to enjoy to the 24th warmest and 4th driest December on record in Madison.  Both temperature and precipitation trends are about to turn in the opposite direction.

Southern Wisconsin will see its first winter storm of the new year this weekend, and a pretty strong cold blast will follow in its wake.  Here's how I'm sizing up the 4 most important factors in winter storm development, specifically for our area:

Storm Track: very favorable
Storm Intensity: moderately favorable
Surface Temperature: very favorable
Speed of Track: somewhat favorable

So, the two things that prevent this storm from being a real whopper are A) intensity, or barometric pressure of the low; and B) the speed with which the storm will come and go.

Nonetheless, a low pressure system is taking shape right now in west Texas.  It's a somewhat disorganized storm at the moment, and will take another 36-48 hours to really wind up.  When it does, it'll head northeast toward Chicago.  If you need a refresher on Texas Panhandle Hooks, see this post from mid-December.

Based on current path, I think this means 3-5" of snow for southern Wisconsin, starting around 6pm Saturday and finishing up around Noon Sunday.  As is always the case with panhandle hooks, narrow bands of heavier snow can pad the totals in localized areas.

Here's the probability map of 4" or more of snow, ending Sunday afternoon.

So, far southern Wisconsin is in that 50/50 area of 4" or more.  If you're in far southeastern Wisconsin, you may actually see some mixed precipitation at the storm's outset, but locations near Lake Michigan may also get some lake effect snow as the low pulls northeast into Canada and winds switch to the northeast.

This model shows the anticipated position of the low over northern Illinois overnight Saturday.  Models have been gradually ticking the low farther west over the last few days.

This model supports that track, meaning that for the most part, there's far less disagreement about storm track than most storms we've seen this year.

It's possible that the National Weather Service out of Sullivan may issue a Winter Storm Watch for our area.  If they're going to do that, it would likely be issued with this afternoon's 3:35pm forecast, or tomorrow morning's 3:35am forecast.  Issuing the watch is a strong indicator of computer model consistency, and therefore, forecast confidence.

So there you have it.  On a side note, I'll be tracking my own forecast accuracy throughout 2015.  For winter storms, I'll post a specific snow amount (to a tenth of an inch) 24 hours before the storm starts.  My goal is to be within 1.5 inches on these projections (based on official Madison airport totals).  You'll see running accuracy results in the right sidebar of the blog throughout the year. 

Also for 2015: more video forecasts from Rippeology!

Watch for the final snow prediction here and on Facebook, to be posted Friday afternoon.