Somewhere in the back of my mind I thought this might be possible. Before I get going on this, let's not be too depressed if nothing comes out of it. Many ingredients are there for an outbreak, but any number of things may go wrong, namely a lack of rich low-level moisture. It looks like that shouldn't be too much of a problem given the very cold/dry air in the mid levels and the pooling of what looks to be low-to-mid-50's dewpoints along the triple point. One big plus will be the amount of solar insolation - skies look to be mostly sunny ahead of the cold front and surface low, and I wouldn't doubt that many areas in the slight and moderate risks see temps in the low to middle 70's, especially given that places that saw good mixing and some sun today made it to near 80. Lows tonight may only drop to the mid to upper 50's in most areas as well so that further supports warmer highs.
Now for the SPC's discussion:
...THERE IS A MDT RISK OF SVR TSTMS FROM WRN TN / WRN KY NWD ACROSS
EXTREME ERN MO / IL / IN / ERN IA / SRN WI....
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER GREAT LAKES
SWD ACROSS THE MS / OH / TN VALLEYS...
...SYNOPSIS...
NEGATIVELY-TILTED MID-LEVEL SHORT-WAVE TROUGH IS FORECAST TO MOVE
NEWD FROM THE PLAINS STATES INTO THE MIDDLE AND UPPER MS VALLEY
THROUGH THE AFTERNOON / EVENING...AND INTO THE UPPER GREAT LAKES
REGION BY THE END OF THE PERIOD.
AT THE SURFACE...LOW INITIALLY FORECAST OVER NERN KS SHOULD MOVE
NEWD TO ERN IA BY LATE AFTERNOON...AND THEN ACROSS WI OVERNIGHT.
COLD FRONT ASSOCIATED WITH THIS LOW SHOULD MOVE EWD ACROSS THE
CENTRAL / SRN PLAINS AND INTO THE OZARKS THROUGH EARLY
AFTERNOON...ACROSS THE MID MS VALLEY DURING THE MID TO LATE
AFTERNOON...AND INTO THE OHIO / TN VALLEY REGION BY THE END OF THE
PERIOD.
...UPPER GREAT LAKES SWD INTO THE CENTRAL GULF COAST STATES...
SIGNIFICANT SEVERE WEATHER EVENT APPEARS TO BE SHAPING UP FOR PARTS
OF THE MIDDLE MS VALLEY REGION THIS PERIOD. AN 80-PLUS KT SWLY
MID-LEVEL JET IS FORECAST TO SHIFT NEWD ACROSS THE OZARKS AND INTO
THE MID MS VALLEY REGION DURING THE DAY...WITH ASSOCIATED DRY SLOT
FORECAST TO OVERSPREAD THE REGION THROUGH MIDDAY.
MEANWHILE...INCREASING BOUNDARY LAYER MOISTURE WILL SPREAD NWD INTO
THIS REGION AHEAD OF 990 MB SURFACE LOW MOVING ACROSS THE MO VALLEY.
COMBINATION OF MOISTENING BOUNDARY LAYER AND STRONG HEATING BENEATH
DRY SLOT AND ASSOCIATED STEEP MID-LEVEL LAPSE RATES SHOULD RESULT IN
500 TO 1500 J/KG MEAN-LAYER CAPE FROM LA / MS NWD ACROSS THE MID MS
VALLEY.
THOUGH STORMS MAY BE ONGOING ACROSS IA AND VICINITY AT THE START OF
THE PERIOD AHEAD OF MAIN VORT MAX...CAP ACROSS WARM SECTOR SHOULD
INHIBIT CONVECTIVE INITIATION ALONG COLD FRONT THROUGH AT LEAST
MID-AFTERNOON. PERSISTENT LARGE-SCALE UVV AHEAD OF SHORT-WAVE
TROUGH SHOULD SLOWLY WEAKEN CAP...WITH CONVERGENCE ALONG / AHEAD OF
COLD FRONT EVENTUALLY ALLOWING STORMS SHOULD DEVELOP SWD FROM
ONGOING IA CONVECTION. STORMS SHOULD INITIATE ACROSS ERN MO / IL BY
MID TO LATE AFTERNOON...AND INTO WRN TN AND NRN MS BY LATE AFTERNOON
/ EARLY EVENING.
DIFFLUENT FLOW ALOFT AND STRONG DEEP-LAYER SHEAR SHOULD ALLOW STORMS
TO RAPIDLY BECOME SEVERE. STRONG FLOW THROUGHOUT THE LOWER
TROPOSPHERE SUPPORTS A THREAT FOR DAMAGING WINDS -- PARTICULARLY
DURING THE EVENING WHEN SQUALL LINE MAY DEVELOP ACROSS IL / IN.
DURING THE AFTERNOON HOWEVER...PRIMARY STORM MODE IS FORECAST TO BE
SUPERCELLS...WITH VERY LARGE HAIL EXPECTED. IN ADDITION TO 50 TO 60
KT DEEP-LAYER SHEAR...STRONG LOW-LEVEL SHEAR / HELICITY IS
ANTICIPATED...PARTICULARLY ACROSS IL / SRN WI WHERE LOW-LEVEL FLOW
SHOULD BE SLIGHTLY BACKED AHEAD OF IA SURFACE LOW. THIS SUGGESTS
THE POTENTIAL FOR ISOLATED TORNADIC SUPERCELLS...AND AT LEAST SOME
THREAT FOR A STRONGER TORNADO DURING THE LATE AFTERNOON / EVENING
HOURS FROM WRN TN NWD ACROSS IL INTO SRN WI.
OVERNIGHT...STORMS SHOULD SPREAD AS FAR EWD AS LOWER MI / WRN OH /
CENTRAL KY / MIDDLE TN...WITH SEVERE THREAT LIKELY PERSISTING WELL
INTO THE OVERNIGHT HOURS.
See
http://www.spc.noaa.gov/products/outlook/day1otlk.html for imagery and updates.
The little snippet in there about backed winds ahead of the surface low caught my attention when I was looking at some of the 00z mesoscale model runs. Low-level storm relative helicities will be high right along the front, just before winds become nearly unidirectional as it passes. Short-lived, but strong tornades can and often do form in closed/occluded-low scenarios like this. If CAPEs get to where the NAM says they'll be (1000-2000 J/kg) ahead of the front, golfball or larger sized hail seems plausible as well. Looks like a fascinating day here in south-central Wisconsin. Spring is finally here...and is coming in with a vengeance. Expect about 3432 updates from me today! Time for some sleep before the big day!
Andy
