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| Mesoscale Discussion 17 |
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MESOSCALE DISCUSSION 0017
NWS STORM PREDICTION CENTER NORMAN OK
0617 PM CST SAT JAN 12 2013
AREAS AFFECTED...NWRN INDIANA...NRN/CNTRL/W-CNTRL IL...PARTS OF
E-CNTRL/SERN/S-CNTRL MO
CONCERNING...WINTER MIXED PRECIPITATION
VALID 130017Z - 130615Z
SUMMARY...WINTER MIXED PRECIPITATION WILL INCREASE IN COVERAGE AND
INTENSITY THIS EVENING. THIS WILL INCLUDE THE THREAT FOR FREEZING
RAIN WITH RATES OF 0.05 TO 0.10 IN/HR...WITH LOCALLY HIGHER RATES
ALSO POSSIBLE. FREEZING RAIN WILL BECOME INCREASINGLY LIKELY IN THE
CHICAGO AND ST. LOUIS AREAS AFTER 04Z.
DISCUSSION...A LARGE SHIELD OF CONVECTIVE-DEBRIS-RELATED
PRECIPITATION WITHIN A WARM CONVEYOR BELT WILL CONTINUE TO
OVERSPREAD THE AREA THIS EVENING. THIS ACTIVITY SHOULD PERSIST THE
OVERNIGHT HOURS AS ELEVATED WARM ADVECTION OCCURS THROUGH THE
NIGHT...WITH A TENDENCY FOR HIGHER PRECIPITATION RATES TO SHIFT NEWD
IN TANDEM WITH THE STRONGER ASCENT.
AS SUBFREEZING SFC-LAYER TEMPERATURES UNDERCUT THE ELEVATED WARM
ADVECTION...THE LEADING EDGE OF WINTER MIXED PRECIPITATION WILL
ADVANCE ESEWD ACROSS THE REGION. IMMEDIATELY BEHIND THIS LEADING
EDGE...A 40-70-MILE WIDE CORRIDOR OF POTENTIAL FREEZING RAIN WILL BE
ASSOCIATED WITH LIQUID-EQUIVALENT RATES OF 0.05-0.10 IN/HR. LOCALLY
HIGHER RATES MAY OCCUR OWING TO A MODEST CONVECTIVE ENHANCEMENT
ASSOCIATED WITH NARROW ELEVATED CAPE PROFILES. THE FREEZING-RAIN
CORRIDOR WILL LIKELY MOVE INTO NWRN INDIANA BY 07Z.
SENSIBLE HEAT FLUXES ASSOCIATED WITH PREVIOUSLY FALLEN LIQUID MAY
INITIALLY DELAY THE ONSET OF ICING ON MANY SURFACES...ASIDE FROM
ELEVATED/METAL SURFACES. REGARDLESS...OBSERVATIONS UPSTREAM ACROSS
CNTRL MO INTO NERN OK INDICATE PERSISTENT FREEZING RAIN
OCCURRING...AND SFC ICING WILL BE LIKELY.
TO THE WNW OF THE FREEZING-RAIN CORRIDOR...DEEPER COLD AIR WILL
LIMIT/PRECLUDE MELTING OF DESCENDING HYDROMETERS AND SUPPORT SLEET
AND LIGHT TO OCCASIONALLY MODERATE SNOW. REMAINING PRECIPITATION
WILL PROGRESSIVELY TRANSITION TO SLEET/SNOW FROM WNW TO ESE DURING
THE OVERNIGHT HOURS...ESPECIALLY ACROSS NRN IL. PRECIPITATION RATES
ARE EXPECTED TO DECREASE AREA-WIDE BY 09Z AS STRONGER FORCING FOR
ASCENT SHIFTS NE OF THE AREA.
PLEASE REFERENCE MCD 16 FOR ADDITIONAL DETAILS REGARDING ONGOING
WINTER MIXED PRECIPITATION ACROSS NERN OK...SERN KS...CNTRL MO...AND
W-CNTRL IL.
..COHEN.. 01/13/2013
ATTN...WFO...PAH...LOT...ILX...LSX...DVN...SGF...
LAT...LON 42428783 41838762 41628732 41668710 41638697 41398697
41168716 40538755 39478833 38798905 37649004 36759171
36519342 36659386 36919364 37599270 38429166 39459025
40098976 40779025 41449012 41868981 42368904 42428783
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