AREAS AFFECTED...FAR NERN MO...FAR ERN IA...CNTRL/NRN IL
CONCERNING...BLIZZARD
VALID 201652Z - 202245Z
SUMMARY...BLIZZARD CONDITIONS WILL OVERSPREAD AREAS ALONG AND EAST
OF THE MS RIVER LATE THIS MORNING INTO THE AFTERNOON...AS A STRONG
SFC LOW DEEPENS AND SNOWFALL INTERACTS WITH VERY STRONG WINDS.
DISCUSSION...RECENT WATER VAPOR/IR SATELLITE LOOPS DEPICT A
WELL-DEFINED COMMA HEAD STRUCTURE WITH A COMPACT VORT CENTER
APPROACHING THE MS RIVER N OF ST. LOUIS. AN ASSOCIATED 985-MB SFC
LOW IS ANALYZED JUST NW OF PEORIA AT 16Z. ENHANCED CONVECTIVE
INSTABILITY AND WEAK WAA WITHIN THE BRANCH OF THE BIFURCATED WARM
CONVEYOR BELT THAT WRAPS AROUND THE CYCLONE WILL SUPPORT BANDS OF
MODERATE TO LOCALLY HEAVY SNOW W/SW OF THE SFC LOW...WHICH IS
FORECAST TO TRACK NEWD AND REACH CHICAGO BY MID/LATE AFTERNOON.
SNOWFALL RATES OF 0.5-1 IN/HR WILL BE COMMON WITH THIS ACTIVITY. AN
ISOLATED LIGHTNING STRIKE MAY OCCUR WITH THE MOST INTENSE SNOWFALL
RATES.
THE TIGHT SFC PRESSURE GRADIENT WITHIN THE WRN SEMICIRCLE OF THE LOW
WILL FURTHER TIGHTEN AS THE LOW DEEPENS AT A RATE OF 0.5 TO 1 MB PER
HOUR. THIS IS IN RESPONSE TO ITS INTERACTION WITH A SECONDARY SUBTLE
VORT MAX NEAR THE APEX OF THE DRY SLOT CURLING INTO THE COMMA HEAD
NEAR CHICAGO. FORECAST SOUNDINGS SUGGEST 45-60 KT OF 0-1-KM MEAN
FLOW EVOLVING WITHIN THE SWRN QUADRANT OF THE LOW...WHICH WILL
LIKELY BECOME MANIFESTED AT THE SFC AS WLY TO NWLY WINDS OF 35-50
MPH WITH GUSTS REACHING 60 MPH. HIGH-RESOLUTION GUIDANCE SUGGESTS
THAT THE SPATIOTEMPORAL PHASING OF THESE WINDS WITH THE SNOW FOR 2-4
HOURS WILL OCCUR...CREATING BLIZZARD CONDITIONS WITH NEAR-ZERO
VISIBILITIES.
BLIZZARD CONDITIONS WILL LIKELY MOVE ACROSS THE MS RIVER PRIOR TO
18Z...REACHING A LINE FROM NEAR ROCKFORD TO SPRINGFIELD BY 20Z...AND
A LINE EXTENDING FROM E OF ROCKFORD TO NEAR BLOOMINGTON/NORMAL BY
22Z. INITIALLY...RAIN/SLEET MAY BRIEFLY MIX WITH THE PRECIPITATION
BEFORE A QUICK PHASE CHANGE TO SNOW OCCURS AS THE LOWER TROPOSPHERE
COOLS.
..COHEN.. 12/20/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...LOT...ILX...LSX...DVN...
LAT...LON 42388998 42328872 41278834 39738847 39268919 38969009
39119109 39689159 40029154 40429147 40999125 41429092
42099043 42388998
