Rain changes to snow: Sloppy accumulations today

This is going to be an interesting weather system to watch unfold.

Our latest warm December weather system spins northeast toward Minnesota today. The telltale rotating comma-shaped cloud signature is impressive as the low pressure circulation rides northward from Kansas City toward Wisconsin today.

The surface maps tell the story. Low pressure, a rain-to-snow transition as we roll through the day. By late afternoon the low sits near La Crosse, Wis., and the rain snow line has shifted east into western Wisconsin.

Over-achieving system?

The big forecast question today revolves around precisely when the change form rain to snow occurs in the metro. The latest model runs suggest it could happen sooner rather than later, perhaps by lunchtime for parts of the metro. It's looking like all snow in the metro this afternoon.

This system is also looking a little stronger near the center than it appeared yesterday. Strong upward 'forcing' (rapidly rising air) near the inbound storm center may create enough extra lift to produce some moderate to at times heavy snow bands today.

The Twin Cities NWS has recognized that trend as well, and has some interesting perspective on the potential for heavier snows in the early morning forecast discussion.

THERE SHOULD BE A NARROW AREA OF MODERATE TO HEAVY SNOWFALL IN THE AFTERNOON...WHICH SHOULD LEAD TO A NARROW STRIP OF 1 TO 4 INCHES OF ACCUMULATION IN EASTERN MN AND WESTERN WI. THE THERMAL PROFILE IS RIGHT ON THE RAIN/SNOW THRESHOLD...AND MODEL QPF IS ALSO VARIABLE...SO ONLY ISSUED A WINTER WEATHER ADVISORY ONLY A FEW COUNTIES IN WESTERN WI WHERE 2-4 INCHES SEEM REASONABLE. AREAS SOUTH OF THIS ADVISORY COULD ALSO SEE A QUICK BURST OF SNOW THIS EVENING... AND SOME GUIDANCE HAS A FEW INCHES OF ACCUMULATION...SO MAY NEED TO UPDATE THE HEADLINES IF THIS TREND CONTINUES.

and...

THE BEST POTENTIAL FOR ACCUMULATION SNOW IS ALONG AND EAST OF I-35. SNOW RATIOS SHOULD BE

LESS THAN 10:1. THE 90 PERCENT SNOWFALL PROBABILITIES RANGE FROM 4-6 INCHES IN THE ADVISORY AREA AND EAST METRO. IT WILL BE INTERESTING TO SEE HOW THIS PLAYS OUT...BUT THE SYNOPTIC SETUP CERTAINLY HAS THE POTENTIAL TO OVER-ACHIEVE IF THE TRANSITION TO SNOW OCCURS SOONER THAN LATER.

Translation? A coating of sloppy snow is likely today, but the potential is there for this system rev up into a much more significant snow producer with several inches of sloppy snow accumulation in or near the metro.

Here's the early NWS thinking on snowfall totals.

More detail here and the prospects for the next system due Christmas night.

Higher potential?

Some of the model guidance is cranking out higher snowfall totals in snow burst like conditions today. We'll need to watch the higher end potential of this system as the afternoon unfolds. With temps hovering just above freezing most roads will probably be wet, but it could be a much more "interesting" afternoon commute if the heavier snow scenario unfolds.

Bottom line: Rain changes to snow across the metro today. Wet sloppy accumulations are likely.  1 to 3 inches of sloppy accumulation seems like the most likely metro range, but the system has the potential to produce higher snowfall totals if the changeover occurs sooner and snow intensity builds.