622 
FXUS63 KILX 132356
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
556 PM CST MON FEB 13 2012

.DISCUSSION...
ISSUED 251 PM CST MON FEB 13 2012

CONCERNS THIS PACKAGE INCLUDE THE WINTER SYSTEM CURRENTLY MOVING
THROUGH THE AREA AND THE POTENTIAL OF FREEZING DRIZZLE ON THE BACK
END OF THE PCPN SHIELD OVERNIGHT. THE OTHER CONCERN INVOLVES THE
NEXT SYSTEM BRINGING THE RETURN OF WARMER TEMPERATURES AND RAIN TO
THE AREA FOR WED THROUGH THUR MORNING. 

MODELS REMAIN IN VERY GOOD AGREEMENT WITH THE FIRST SYSTEM
CURRENTLY COMING THROUGH THE AREA TONIGHT. FAIRLY GOOD AGREEMENT
IS SEEN IN THE MODELS WITH THE NEXT SYSTEM AS WELL AS THE SFC LOW
TRACKS ACROSS IL WEDNESDAY NIGHT. NAM IS SLOWER THAN
GFS/ECMWF/SREF...BUT THIS WILL NOT MAKE MUCH DIFFERENCE IN
RESULTING WEATHER OVER THE AREA. 

SHORT TERM...TONIGHT THROUGH THURSDAY

CURRENT WINTER SYSTEM CONTINUES TO MOVE ACROSS THE AREA WITH LIGHT
SNOW FALLING OVER WESTERN PORTIONS OF THE AREA. ONE WAVE OF SNOW
WENT THROUGH THE AREA EARLIER THIS MORNING...BUT IT DID NOT
PRODUCE MUCH SNOW AND MAINLY MOISTENED THE LOWER LAYERS OF THE
ATMOSPHERE. SINCE THEN...THE AREA HAS SEEN A BREAK IN THE PCPN AND
NOW ANOTHER WAVE OF LIGHT SNOW IS MOVING ACROSS THE AREA. UNLIKE
THE FIRST WAVE...THIS WAVE SHOULD PRODUCE MORE SNOW AND GET
FURTHER ACROSS THE CWA BEFORE WEAKENING. THIS WAVE SHOULD ALSO
LAST LITTLE LONGER BASED ON SATELLITE AND RADAR LOOPS SHOWING
MORE AND HIGHER RETURNS MOVING NORTHEAST OUT OF SOUTHWEST AND
SOUTH-CENTRAL MO TOWARD THE REGION. MODELS CONTINUE TO SHOW SOME
SMALL AMOUNTS OF ELEVATED INSTABILITY THIS EVENING MOVING NEAR AN
I-70 CORRIDOR...WHICH CAN ALSO BE SEEN IN THE FORECAST SOUNDINGS.
IN ADDITION...BASED ON WATER VAPOR & IR SATELLITE LOOPS...THE VORT
MAX IN KS LOOKS STRONGER THAN WHAT THE MODELS INITIALIZED WITH. SO
THINK PCPN WILL CONTINUE OVERNIGHT ACROSS THE SOUTHERN HALF OF THE
CWA. MODEL SOUNDING ALSO SNOW MID LEVELS DRYING OUT SOME THIS
EVENING AND MAINLY OVERNIGHT. WITH THE CONTINUED MID LEVEL VORT
MAX AND A SMALL WAA PROFILE...BELIEVE PATCHY FREEZING DRIZZLE
WILL BE POSSIBLE MAINLY OVERNIGHT ACROSS MOST OF THE AREA. THIS
ALREADY IN FORECAST SO HAVE DECIDED SUPPORT STILL THERE AND WILL
LEAVE IN FOR THIS FORECAST. MIX OF PATCHY FREEZING DRIZZLE AND
LIGHT SNOW COULD BE POSSIBLE EARLY TOMORROW MORNING IN THE EAST SO
WILL KEEP THOSE SMALL CHANCES GOING. 

CONSIDERING THERE IS NO REAL SFC REFLECTION OF THIS CURRENT
SYSTEM...AS IT MOVES EAST THE LARGE HIGH PRSS THAT GAVE US THE
COLD AND DRY CONDITIONS OVER THIS PAST WEEKEND WILL REMAIN OVER
THE SOUTHEASTERN US INTO THE MIDDLE OF THE WEEK. THIS WILL ALLOW
FOR TEMPS TO WARM BACK TO NORMAL AND ABOVE NORMAL LEVELS FOR TUE
THROUGH THUR. 

THE NEXT SYSTEM WILL APPROACH THE AREA FROM THE SOUTHWEST AND
BRING A CHANCE OF RAIN FOR WED AFTERNOON. ALL MODELS AGREE THAT IT
WILL BE WARM ENOUGH FOR ALL RAIN AND MOST OF IT WILL BE WED
NIGHT...WITH A SMALL CHANCE THURSDAY MORNING. DEPENDING ON AMOUNT
OF WAA AND MOISTURE ADVECTION AHEAD OF THIS SYSTEM...THERE COULD
BE SOME ISOLATED THUNDER WED NIGHT. HOWEVER...TOO MANY LIMITING
FACTORS RIGHT NOW TO INCLUDE IN THIS FORECAST PACKAGE.

TEMPS WILL BE WARMER AFTER THIS SYSTEM AND EXPECTING NORMAL TO
ABOVE NORMAL TEMPS THROUGH THE PERIOD. BELIEVE GUIDANCE LOOKS OK
AND TRIED TO STAY ON THE WARMER SIDE...ESPECIALLY GIVEN HIGH TEMP
FORECAST HAS BEEN TOO LOW PAST SEVERAL DAYS.

LONG TERM...THURSDAY NIGHT THROUGH MONDAY

AFTER THE SECOND SYSTEM...HIGH PRSS BUILDS IN AND SITS OVER THE
REGION THROUGH THE REST OF THE WEEK AND INTO THE WEEKEND.
ECMWF/GFS AGREE WITH A CONTINUED SPLIT/MESSY FLOW THROUGH THE
PERIOD. COULD BE ANOTHER SYSTEM MOVING INTO THE AREA FOR FIRST
PART OF NEXT WEEK...BUT THIS LOOKS TO OCCUR BEYOND THE FORECAST
PERIOD. 

TEMPS SHOULD REMAIN ABOVE NORMAL THROUGH THE PERIOD AND CURRENTLY
GUIDANCE INDICATES THIS.

AUTEN

&&

.AVIATION...
ISSUED 556 PM CST MON FEB 13 2012...FOR THE 00Z TAFS

A COUPLE OF BANDS OF SNOW WILL CONTINUE TO PUSH ACROSS THE
TERMINALS FOR THE NEXT 2-3 HOURS. ONE BAND OF HEAVY SNOW WENT
ACROSS SPI AND DROPPED VIS TO 3/4 SM FOR A SHORT TIME. THAT BAND
WILL BE HITTING DEC AROUND 00Z, BMI BTWN 00Z-01Z AND CMI TOWARD
01Z. PIA SHOULD BE JUST NORTH OF THE BAND. AFTER THAT BAND MOVES
THROUGH...DEC AND CMI MAY BE ON THE NORTHERN PERIPHERY OF THE
REMAINING SNOWFALL AREA. OTHERWISE...LIGHT SNOW WILL EVENTUALLY
CHANGE TO FREEZING DRIZZLE AS WE LOSE OUR SOURCE OF ICE CRYSTALS
ALOFT. WITHOUT THE SEEDING OF ICE FROM ABOVE THE LOWER CLOUD
LAYERS...THE SUPER COOLED WATER WILL REMAIN AS LIQUID AND FALL TO
THE GROUND AS FZDZ. THE TURBULENT LIFT NEEDED TO CREATE FZDZ WILL
BE CREATED BY ONE REMAINING 500 MB SHORTWAVE THAT WILL MOVE ACROSS
IL OVERNIGHT. THAT WAVE IS SHOWING UP VERY WELL ON WATER VAPOR
SATELLITE IMAGES...AND SHOULD AFFECT ILLINOIS TONIGHT THROUGH TUES
MID-MORNING.

THE LOW LEVEL MOISTURE WILL REMAIN IN PLACE THAT WHOLE TIME...SO
WE DECIDED TO USE AN EXTENDED PERIOD OF FZDZ IN THE TAFS. THE
GROUND CONTINUES TO REMAIN WARM...SO MOST OF THE ICING WILL BE ON
ELEVATED SURFACES. SOME SLIPPERY SPOTS MAY DEVELOP ON BRIDGES,
OVERPASSES, AND LESS TRAVELED AREAS. BUT THE OVERALL IMPACT SHOULD
REMAIN ON THE LOW SIDE. WE WILL WATCH CLOSELY FOR THAT TO BE THE
CASE...OTHERWISE A FREEZING RAIN ADVISORY MAY BE NEEDED FOR LATER
TONIGHT INTO TUES MORNING.

IFR CONDITIONS WILL BE LIKELY FOR ALL TERMINALS AFTER THE MAIN
AREAS OF SNOWFALL THIS EVENING. UPSTREAM OBSERVATIONS SHOW CLOUD
HEIGHTS OF 600-900 FT COMMON WELL BACK TO THE WEST INTO NEB/KS. 

MVFR CONDITIONS SHOULD DEVELOP TUESDAY MORNING AS MIXING OF DRY
AIR FROM ALOFT HELPS TO LIFT CIGS INTO THE 015-025 RANGE.

SHIMON
&&

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

$$