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000
FXUS63 KILX 100236
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
835 PM CST TUE FEB 9 2010

.DISCUSSION...
ISSUED 835 PM CST TUE FEB 9 2010

UPPER LOW HAS MOVED INTO SOUTHERN INDIANA AND THE ASSOCIATED SURFACE
LOW IS WELL EAST INTO OHIO. CLOUD TOPS ARE WARMING ON IR SATELLITE
IMAGERY...AND RADARS HAVE SHOWN A DECREASE IN BOTH COVERAGE AND
REFLECTIVITIES IN THE PAST COUPLE OF HOURS. PUDDLE OF COLD SURFACE
AIR HAS MOVED TO THE ILLINOIS/INDIANA BORDER...WITH TEMPERATURES TO
THE WEST BEGINNING TO RISE. MAIN FORECAST QUESTION WILL BE THE
MAGNITUDE OF BLOWING SNOW OVERNIGHT. A SURFACE TROUGH LIES WEST-EAST
OVER THE NORTHERN COUNTIES OF THE FORECAST AREA...AND OBSERVED WINDS
ARE RATHER GUSTY TO ITS NORTH. THIS FEATURE IS EXPECTED TO COME
SOUTHWARD TONIGHT...WITH THE 00Z NAM AND RUC MODELS BOTH SHOWING THE
SURFACE PRESSURE GRADIENT INCREASING WITH ITS PASSAGE. SO THE THREAT
FOR BLOWING SNOW WILL PROBABLY INCREASE OVERNIGHT...DESPITE SOME
AREAS NOT SEEING MUCH IN THE WAY OF REDUCED VISIBILITIES YET.

WILL UPDATE THE FORECASTS SHORTLY TO HAVE JUST FLURRIES INSTEAD OF
MEASURABLE SNOW...AND REPLACE THE SNOW/BLOWING SNOW ADVISORY IN THE
NORTH/EAST TO A BLOWING SNOW ADVISORY. WILL KEEP WATCHING THE WINDS
NORTH OF THE SURFACE TROUGH FOR THE POSSIBILITY OF DROPPING THE
ADVISORY IN THE SOUTHWEST...BUT WILL KEEP IT GOING FOR NOW.

04
&&

.AVIATION...
ISSUED 516 PM CST TUE FEB 9 2010

SFC TROF EXTDS WWD FM A LOW OVR OH THRU NRN IN AND NRN IL. UPR LOW
NOW NR EVV MOVG EWD. INITIAL WLY SFC WNDS 10-20 KT WL BCM NWLY AND
INCRS AS SFC TROF MOVS SEWD 02Z-06Z. SNOW WL DCRS WITH TIME AND
SHOULD BE E OF THE CNTL IL TERMINALS ARND 06Z...BUT VSBY
RESTRICTIONS WL CONT DUE TO BLSN. THE WNDS ARE FCST TO STAY UP THRU
AT LEAST 18Z WED...THEN DCRS. CIGS SHOULD 1K-2K FT RANGE...PERHAPS
BLO 1K FT AT TIMES 06Z-12Z WED. AS THE SFC PRES GRADIENT RELAXES AFT
18Z WED...CLDS SHOULD BEGIN BREAKING UP AS THE WNDS COME DOWN.

04
&&

.PREV DISCUSSION...
ISSUED 300 PM CST TUE FEB 9 2010

MODELS REMAIN SIMILAR WITH THE OVERALL PATTERN THROUGH 72HRS. THEN
DIFFERENCES SEEN WITH TIMING OF A CLIPPER SYSTEM FORECAST TO MOVE
INTO THE AREA ON FRIDAY. THE SAME SPEED DIFFERENCES ARE SEEN IN THE
LONG TERM WITH ANOTHER STRONGER CLIPPER SYSTEM FORECAST TO ARRIVE
OVER THE WEEKEND. WILL TAKE A BLEND OF THE MODELS THIS FORECAST
PACKAGE AND LET THEM WORK THINGS OUT LATER DOWN THE ROAD WITH THE
TWO CLIPPER SYSTEMS FOR THE WEEKEND.

SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT
MAIN CONCERN IN THE SHORT TERM IS THE BLOWING SNOW FOR TONIGHT AND
EARLY TOMORROW MORNING...ALONG WITH THE COLD TEMPS NEXT COUPLE OF
DAYS...FOLLOWED BY A CLIPPER SYSTEM FOR LATER IN THE WEEK. GRADIENT
IS BEGINNING TO TIGHTEN OVER WESTERN IL THIS AFTERNOON AND SHOULD
CONTINUE INTO TONIGHT AS THE COLD AIR AND SFC LOW CONTINUES TO LIFT
NORTHEAST INTO THE EASTERN GRT LKS REGION. SNOW WILL ALSO CONTINUE
OVER NORTHERN SECTIONS AS THE SFC TROUGH ROTATES AROUND THE
BACK-SIDE OF THE LOW. AN ADDITIONAL INCH IS POSSIBLE IN NORTHERN
AREAS...MAINLY ALONG AND NORTH OF I-74 THROUGH THE EVENING HOURS. AS
THIS OCCURS...WINDS WILL BECOME NORTHWESTERLY AND BE GUSTY WITH WIND
SPEEDS AROUND 30 MPH POSSIBLE. THESE WINDS WILL CONTINUE OVERNIGHT
AND INTO TOMORROW MORNING. BASED ON ALL THIS...WILL KEEP WINTER
WEATHER ADVISORY GOING FOR CURRENT LOCATIONS TIL TOMORROW AT NOON.

HIGH PRSS WILL THEN BUILD INTO THE REGION FOR TOMORROW NIGHT THROUGH
THURSDAY NIGHT. THIS WILL BRING BITTER COLD TEMPS AND CALM WINDS.
THEN AS NORTHWESTERLY FLOW RETURNS FOR LATER IN THE WEEK A CLIPPER
SYSTEM WILL DROP INTO THE REGION AND BRING ANOTHER CHANCE OF SNOW.
MOISTURE SHOULD BE LACKING WITH THIS SYSTEM AND MODELS DIFFER SOME
ON TIMING. SO FOR NOW WILL JUST GO WITH CHANCE POPS FOR LIGHT SNOW
FOR FRIDAY IN THE NORTH FOR NOW.

UNDERCUT GUIDANCE AS BITTER COLD AIR IS LOCATED OVER THE REGION FOR
TONIGHT. HOWEVER...COLDEST AIR WILL BE WED NIGHT AS CALM
WINDS...CLEAR SKIES AND FRESH SNOW COVER WILL ALLOW LOTS OF
RADIATIONAL COOLING. AGAIN, UNDERCUT GUIDANCE THROUGH THE PERIOD.

LONG TERM...SATURDAY THROUGH TUESDAY
NORTHWESTERLY FLOW WILL CONTINUE INTO THE WEEKEND IN ADDITION TO
ANOTHER...STRONGER...SHORT WAVE THAT WILL DROP INTO THE REGION.
ECMWF AND GFS DIFFER WITH TIMING OF THIS SYSTEM AS WELL AND TRIED TO
TAKE BLEND OF THE TWO SOLUTIONS. SO FOR NOW WILL HAVE CHANCE POPS
FOR SAT AND SAT NIGHT...WITH CHC IN THE EAST FOR SUNDAY. WILL LET
MODELS COME INTO BETTER AGREEMENT BEFORE INCREASING POPS BEYOND
CHANCE. BEYOND THIS SYSTEM...REMAINDER OF EXTENDED LOOKS DRY FOR NOW.

KEPT TEMPS AT OR JUST BELOW NORMAL THROUGH THE PERIOD AS ANOTHER HI
PRSS AREA BUILDS INTO THE REGION FOR THE BEGINNING OF NEXT WEEK.

AUTEN
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL NOON CST WEDNESDAY FOR ILZ040>042-
047>057-061.

WINTER WEATHER ADVISORY UNTIL NOON CST WEDNESDAY FOR ILZ027>031-
036>038-043>046.

&&

$$