Mesoscale Discussion 21

Issued

Jan 20, 2010, 10:34 AM CST (16:34 UTC)

Expired

Jan 20, 2010, 2:30 PM CST

In force

4 hr

Issued by

the Storm Prediction Center

The Quad Cities radar (KDVN), 53 km from the middle of the area, began a volume at 16:37 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

470 
ACUS11 KWNS 201635
SWOMCD
SPC MCD 201634
INZ000-ILZ000-WIZ000-IAZ000-MNZ000-202030-

MESOSCALE DISCUSSION 0021
NWS STORM PREDICTION CENTER NORMAN OK
1034 AM CST WED JAN 20 2010

AREAS AFFECTED...NERN IA...SWRN WI AND NRN IL

CONCERNING...FREEZING RAIN

VALID 201634Z - 202030Z

FREEZING RAIN WITH RATES OF 0.02-0.05 IN/HR ARE FORECAST TO SPREAD
NEWD INTO PORTIONS OF NERN IA...SWRN WI...AND NRN IL THROUGH 21Z.
THEREAFTER...RATES ARE EXPECTED TO DECREASE IN INTENSITY BY 21-00Z.

A LOW AMPLITUDE S/W TROUGH OBSERVED IN WV IMAGERY HAS BEEN LIFTING
NEWD INTO THE MID MS VALLEY REGION THROUGH THE MORNING. MODEST
SURFACE CYCLOGENESIS OVER THE CENTRAL PLAINS ATTENDANT TO THIS UPPER
FEATURE HAS AIDED IN FOCUSING A ZONE OF LOW LEVEL WAA ACROSS
CENTRAL/SRN IA INTO WRN IL. FORCING FOR ASCENT ASSOCIATED WITH THESE
FEATURES HAS RESULTED IN AN ELONGATED BAND OF PRECIPITATION LIFTING
N-NEWD ACROSS IA AND IL...WITH THE PREDOMINANT PRECIPITATION TYPE
BEING FREEZING RAIN DUE TO THE PRESENCE OF AN ELEVATED WARM NOSE
SPREADING NWD ACROSS A SUB FREEZING SURFACE AIRMASS. SUBSTANTIAL ICE
ACCUMULATIONS HAVE BEEN OBSERVED THROUGH THE EARLY TO MID MORNING
HOURS ACROSS THE SRN HALF OF IA...AND MODERATE FREEZING RAINFALL
RATES /UP TO 0.02-0.05 IN PER HR/ WILL LIKELY CONTINUE THROUGH 21Z
AS THE SHIELD OF PRECIPITATION CONTINUES TO SPREAD NEWD INTO NERN IA
AND SWRN WI/NRN IL.

IN ADDITION...LOWERED STABILITY WITHIN A DRY SLOT OBSERVED IN WV
IMAGERY ADVANCING INTO ERN IA/NWRN IL IS ALSO FAVORING THE
DEVELOPMENT OF THUNDERSTORMS...WHICH MAY RESULT IN ICE PELLETS WITH
THE MORE VIGOROUS CONVECTIVE ELEMENTS. SURFACE OBSERVATIONS ALSO
REVEAL A WARMING TREND WITH THE PASSAGE OF THE MID LEVEL DRY
SLOT...WITH TEMPERATURES OVER WRN IL INCREASING TO AROUND FREEZING
IN ITS WAKE. THUS...THE SURFACE FREEZING LINE MAY TEND TO LIFT NWD
WITH TIME INTO PORTIONS OF CENTRAL-WRN IL AND ERN IA. OTHERWISE...AS
THE AFTERNOON PROGRESSES...THE S/W TROUGH IS FORECAST TO ENCOUNTER
AN UPPER RIDGE POSITIONED OVER THE GREAT LAKES REGION...AND LARGE
SCALE ASCENT IS EXPECTED TO DECREASE SUBSTANTIALLY...RESULTING IN
LOWERED PRECIPITATION/FREEZING RAINFALL RATES.

..GARNER.. 01/20/2010

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

...NOTICE...
SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.

ATTN...WFO...IND...LOT...ILX...MKX...DVN...ARX...MPX...DMX...

LAT...LON   41409060 40398824 40408749 41078729 42098770 43239019
            43539158 43509404 42889408 41409060

Mesoscale Discussions in Illinois, 2010Mesoscale Discussions in Iowa, 2010Mesoscale Discussions in Wisconsin, 2010Every mesoscale discussion in 2010

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.