MESO: Mesoscale Discussion 0440

ACUS11 KWNS 110740
SWOMCD
SPC MCD 110740
MNZ000-WIZ000-IAZ000-SDZ000-111215-

MESOSCALE DISCUSSION 0440
NWS STORM PREDICTION CENTER NORMAN OK
0240 AM CDT THU APR 11 2013

AREAS AFFECTED...SRN MN...ERN SD...NWRN IA...EXTREME WRN WI

CONCERNING...HEAVY SNOW

VALID 110740Z - 111215Z

SUMMARY...MODERATE/OCCASIONALLY HEAVY SNOW WILL INCREASE IN COVERAGE
EARLY THIS MORNING...WITH RATES OF 1-1.5 IN/HR POSSIBLE. IN AREAS
WHERE SNOW IS NOT ALREADY UNDERWAY...RAIN/SLEET IS EXPECTED TO
CHANGE TO SNOW BY 09-10Z.

DISCUSSION...LATEST WV IMAGERY DEPICTS A CLOSED UPPER LOW MOVING
SLOWLY ENEWD ACROSS THE CENTRAL PLAINS...WITH MULTIPLE EMBEDDED
VORTICITY MAXIMA ROTATING WITHIN THE LARGER CIRCULATION. ONE OF
THESE EMBEDDED FEATURES IS CURRENTLY PROGRESSING NWD ACROSS THE MO
VALLEY OF ERN NE/WRN IA. AHEAD OF THIS FEATURE...INCREASING ASCENT
HAS RESULTED IN AN EXPANDING SHIELD OF PRECIPITATION WITH LOCALLY
MODERATE/HEAVY SNOW ALREADY REPORTED. STEEP LAPSE RATES OF AROUND 7
DEG C/KM IN THE 3-6 KM LAYER /SAMPLED UPSTREAM IN THE 00Z DDC
SOUNDING AND ALSO DEPICTED IN AVAILABLE FCST SOUNDINGS/ WILL FAVOR
SOME CONVECTIVE ENHANCEMENT OF PRECIPITATION RATES.

SNOW IS ALREADY FALLING ACROSS ERN SD INTO SWRN MN AND NWRN IA.
AREAS FURTHER TO THE EAST ACROSS S-CENTRAL AND SE MN ARE CURRENTLY
REPORTING A MIXTURE OF RAIN AND SLEET...DUE TO A COMBINATION OF
ABOVE FREEZING SFC TEMPS AND A WARM NOSE IN THE 800-700 MB LAYER.
WHILE SIGNIFICANT COOLING OF THE WARM NOSE IS NOT EXPECTED...RECENT
HI-RES GUIDANCE /NOTABLY THE EXPERIMENTAL 11/00Z SSEO AND 11/04Z
HRRR/ AND FCST SOUNDINGS SUGGEST SUFFICIENT LIFT WILL OCCUR TO COOL
THE COLUMN AND ALLOW THE PRECIP TYPE TO BECOME PREDOMINATELY SNOW BY
09-10Z...THOUGH A MIXTURE OF SLEET MAY PERSIST LONGER OUTSIDE OF
HEAVIER PRECIP BANDS. MEANWHILE...ADVECTION OF COLD/DRY AIR IN THE
LOW LEVELS WILL ALLOW TEMPS TO FALL TO NEAR OR BELOW FREEZING.

SNOWFALL RATES OF 1-1.5 IN/HR WILL BE POSSIBLE THROUGH 12Z...WITH A
SLOW DIMINISHING OF PRECIP FROM SW TO NE EXPECTED AFTER 09Z AS THE
DRY SLOT IN THE WAKE OF THE EMBEDDED VORT MAX APPROACHES THE
AREA...THOUGH PRECIP WILL LINGER WELL PAST 12Z ACROSS THE ERN
PORTION OF THE MCD AREA.

..DEAN.. 04/11/2013

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...ARX...MPX...DMX...FGF...FSD...ABR...

LAT...LON 42429493 42859650 43699730 44429798 45279784 45879679
45829518 45749401 45519286 45139205 44369163 43739217
42949321 42479414 42429493

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
To unsubscribe from WX-STORM send e-mail to LISTSERV@LISTSERV.ILLINOIS.EDU with
"unsub wx-storm" in the body of your message. For more information write cnovy@cox.net.