FXUS63 KILX 090545
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1145 PM CST WED FEB 8 2012

.DISCUSSION...
ISSUED 851 PM CST WED FEB 8 2012

THE WESTERN AND NORTHERN EDGE OF THE CLOUDS IS BEGINNING TO MAKE
SOME PROGRESS INTO CENTRAL ILLINOIS. HOW SOON THE CLOUDS CLEAR OUT
AND IF THE CLEARING CONTINUES THROUGH MORNING WILL PLAY A MAJOR
ROLL IN LOW TEMPS FOR TONIGHT. SUBSIDENCE INVERSIONS UNDER HIGH
PRESSURE CAN TRAP LOW MOISTURE THAT FORM STRATUS CLOUDS WHICH FILL
IN AGAIN OR RETROGRADE BACK TO THE N-NE. THERE APPEARS TO BE
ENOUGH OF A CLEARING AREA ACROSS N MO/IOWA TO KEEP OUR CLEARING
TRENDS GOING. HAVE TRENDED SLOWER WITH THE CLEARING BASED ON
SATELLITE TRENDS AND THE LATEST HRRR MODEL OUTPUT.

THE SURFACE RIDGE APPEARS TO BE MAINLY SETTLING TO THE SOUTH
INSTEAD OF SLIDING EAST INTO ILLINOIS...SO THAT GIVES MORE
CONFIDENCE TO THE CLEARING SCENARIO. KEPT THE FORECAST LOWS SLIGHTLY
BELOW GUIDANCE...AND WE MAY NOT BE COLD ENOUGH. SURFACE DEWPOINTS
ARE QUITE DRY JUST TO OUR N AND W. WOULD NOT BE SURPRISED TO SEE
SOME MID TEENS REPORTED IN OUR NW COUNTIES IN THE MORNING. FOR
NOW...KEPT UPPER TEENS AND LOW 20S IN PLACE.

NO OTHER CHANGES WERE NEEDED TO THE CURRENT FORECAST/GRIDS.
UPDATED INFO IS ALREADY AVAILABLE.

SHIMON

&&

.AVIATION...
ISSUED 1145 PM CST WED FEB 8 2012...FOR THE 06Z TAFS

CLEARING OF MVFR CLOUDS IS FINALLY MAKING BETTER PROGRESS FROM THE
WEST AND NORTH. PIA AND BMI HAVE BECOME SCT...BUT PIA IS STILL
CLOSE TO A BKN DECK WITH A BAND OF CLOUDS JUST TO THE WEST OF THE
AIRPORT. EVEN WITH THAT...PIA SHOULD BECOME VFR SHORTLY AFTER 07Z
AFTER THOSE CLOUDS SLIDE SE. WILL CLEAR OUT THE REMAINING TAF
SITES BY 08Z-09Z...WITH SOME MVFR FOG POSSIBLE AS TEMPS FALL UNDER
CLEAR SKIES AND LIGHT WINDS. WE KEPT THE TEMPO GOING FM 11Z-14Z
TIME FRAME FOR ALL TERMINALS.

THE MAIN CHANGE TO THE TAFS WAS TO INCREASE VFR CLOUD COVER THUR
AFTERNOON AS WAA FLOWS INCREASE AHEAD OF THE NEXT SYSTEM. SW WINDS
WILL INCREASE TO 10-12KT ON THUR AS WELL.

CLOUDS WILL LIKELY CONTINUE THROUGH THE REMAINDER OF THE TAF
PERIOD...AND POSSIBLY DROP TO MVFR LEVELS AFTER SUNSET ON THURSDAY.


SHIMON
&&

.PREV DISCUSSION...
ISSUED 305 PM CST WED FEB 8 2012

SHORT TERM...TONIGHT THROUGH SATURDAY...
LARGE AREA OF HIGH PRESSURE OVER THE PLAINS WILL MOVE SOUTHEAST AND
DOMINATE THE WEATHER OVER IL TONIGHT THROUGH THURSDAY NIGHT.
EXTENSIVE CLOUD COVER OVER THE AREA WILL MOVE SLOWLY SOUTH WITH MOST
AREAS SEEING CLEAR SKIES BY SUNRISE. THE MAIN WEATHER FEATURE FOR
THE SHORT TERM WILL BE A STRONG COLD FRONT THAT WILL MOVE THROUGH
THE AREA ON FRIDAY. BY MIDDAY...THE FRONT SHOULD BE ABOUT MIDWAY
THROUGH THE FORECAST AREA...THEN INTO THE OHIO VALLEY BY 00Z SAT.
WITH THE CURRENT HIGH PRESSURE HAVING PUSHED MUCH OF THE QUALITY
MOISTURE FAR TO THE SOUTH...IT WILL TAKE SOME TIME FOR IT TO MAKE A
RETURN AND MAY NOT MAKE IT TO CENTRAL IL IN TIME TO INTERACT WITH
THE FRONT. SOME OF THE SHORT RANGE MODELS ARE PAINTING SOME QPF OVER
EASTERN IL WITH THE FRONT...SO WILL CONTINUE WITH SOME SLIGHT CHANCE
POPS THERE. AFTER THAT...THE LARGE CANADIAN AIRMASS IN THE WAKE OF
THE FRONT WILL SPREAD OVER THE CENTRAL/EASTERN CONUS BRINGING
TEMPERATURES BACK TO WINTER-TIME LEVELS STARTING FRIDAY NIGHT AND
LASTING INTO THE EXTENDED PERIOD. FOR NOW...IT APPEARS THAT FRIDAY
NIGHT INTO SATURDAY WILL BE THE COLDEST WITH LOWS 10-20 AND HIGHS IN
THE 20S.

LONG TERM...SUNDAY THROUGH WEDNESDAY...
THE GFS AND ECMWF ARE IN AGREEMENT THAT AN UPPER SHORTWAVE WILL COME
OUT OF THE SOUTHERN ROCKIES AND INTO THE PLAINS EARLY NEXT WEEK. BY
THEN...THE CANADIAN HIGH WILL BE OFF THE EAST COAST AND MOISTURE
FROM THE GULF WILL STREAM NORTHWARD THROUGH THE MS VALLEY. POPS WILL
BEGIN RISING ON MONDAY AS LIGHT SNOW...PERHAPS MIXED WITH LIGHT RAIN
AT THE START...MOVES INTO THE WESTERN HALF OF IL. HIGHEST CHANCE OF
PRECIPITATION WILL BE MONDAY NIGHT WITH THE PASSAGE OF THE UPPER
WAVE. ANY SURFACE REFLECTION OF THIS SYSTEM WILL BE SUBTLE/WEAK AND
THEREFORE THE QPF FORECASTS ARE ON THE LOW SIDE DUE TO THE LACK OF
LOW LEVEL FOCUS.

MODEL AGREEMENT ENDS THERE AS THE NEXT STORM SYSTEM/UPPER LOW COMES
INTO THE SOUTHERN ROCKIES BY TUESDAY. THE GFS SIMPLY KEEPS THE LOW
CHUGGING INTO THE PLAINS AND THROUGH THE MIDWEST ON WEDNESDAY...
WHILE THE ECMWF HOLDS IT BACK WELL TO THE WEST THROUGH THIS PERIOD.
SOME OF THE AUTOMATED POP GUIDANCE IS OBVIOUSLY WEIGHTED TOWARD THE
GFS...WITH LIKELY POPS ON WEDNESDAY. USUALLY...SLOWER IS BETTER WITH
SOUTHWESTERN UPPER LOWS...SO WILL KNOCK DOWN POPS INTO THE CHANCE
RANGE. POPS MAY BE DELAYED EVEN FURTHER IF THE ECMWF ENDS UP BEING
THE WINNING MODEL.

04


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$