432 
FXUS63 KILX 212002
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
302 PM CDT TUE MAY 21 2013

.DISCUSSION...
ISSUED 300 PM CDT TUE MAY 21 2013

AFTER SEVERAL WARM AND HUMID DAYS...WE ARE HEADED TOWARD AN
EXTENDED PERIOD OF AT OR BELOW NORMAL TEMPS AS THE OCCLUDED LOW
OVER THE MN/SD BORDER FINALLY BECOMES PROGRESSIVE AND DEPARTS
EASTWARD THROUGH THE GREAT LAKES IN THE NEXT COUPLE DAYS.

SHORT TERM...TONIGHT THROUGH FRIDAY.

THE LATEST SURFACE ANALYSIS SHOWS THE SYNOPTIC COLD FRONT ENTERING
WESTERN IL AT 19Z. SATELLITE LOOPS SHOW A TRAIN OF 3 STORM
COMPLEXES FROM OKLAHOMA TO TENNESSEE MOVING EAST. OUR AREA WILL
SEE ONE MORE ROUND OF SHOWERS AND STORMS TONIGHT...BUT NO SEVERE
STORMS ARE EXPECTED. THE NOON UPDATE TO THE DAY ONE OUTLOOK FROM
SPC PUSHED THE NORTHERN EDGE OF THE SLIGHT RISK AREA SOUTH INTO
THE OHIO RIVER VALLEY. THAT SEEMS TO BE IN RESPONSE TO MARGINAL
INSTABILITY AND WIND SHEAR NORTH OF THE STORM COMPLEXES TO THE
SOUTH. ALSO...THOSE SYSTEMS WILL LIKELY CUT LIMIT OUR SUPPLY OF
MOISTURE ON THE SOUTHERLY LLJ. 

WE STILL KEPT CATEGORICAL POPS IN THE MAJORITY OF OUR COUNTIES
TONIGHT AS A WAVE OF LOW PRESSURE LIFTS NORTHEAST ALONG THE COLD
FRONT OVERNIGHT...WITH ITS PATH SET TO BE ROUGHLY UP THE I-55
CORRIDOR. EAST OF THAT TRACK WE MAY SEE SOME STORMS DEVELOP...WITH
GUSTY WINDS, SMALL HAIL AND LOCALLY HEAVY DOWNPOURS. THE 4KM HRRR
SHOWS STEADY RAINS MAINLY SOUTHEAST OF I-55 TONIGHT...WHILE THE
NCEP 4KM-WRF-NMM SHOWS WIDESPREAD RAINS DEVELOPING BY 06Z ALL
ACROSS OUR COUNTIES AND LINGERING THROUGH WED MORNING IN THE EAST.
OUR REGULAR DETERMINISTIC MODELS WERE GENERALLY IN AGREEMENT WITH
THAT PROGRESSION AS WELL.

AS THE COLD FRONT FINALLY DEPARTS INTO INDIANA ON
WEDNESDAY...SHOWERS WILL STILL LINGER IN CENTRAL IL. AN ISOLATED
THUNDERSTORM MAY DEVELOP IN THE EAST...BUT DRY AND STABLE AIR
SHOULD BEGIN TO SHUT DOWN CONVECTIVE UPDRAFTS IN THE SW HALF OF
OUR AREA BY WEDNESDAY EVENING. SHOWER CHANCES WILL CONTINUE ON
THURSDAY AS THE UPPER COLD POOL SLIDES ACROSS IL. STEEP LAPSE
RATES WILL HELP FUEL SOME DIURNAL SHOWERS...WITH HELP FROM A 500
MB SHORTWAVE ROUNDING THE BASE OF THE UPPER TROUGH.

DRY AND COOL CONDITIONS SHOULD RETURN TO THE AREA FOR THURSDAY
NIGHT AND FRIDAY. LOWS FRIDAY MORNING WILL DIP INTO THE LOW 40S IN
MUCH OF THE AREA...WITH AFTERNOON HIGHS IN THE UPPER 60S. 

LONG TERM...SATURDAY THROUGH TUESDAY.

SATURDAYS TEMPS WILL REMAIN BELOW NORMAL IN THE UPPER 60S TO
AROUND 70...AS CLOUDS AND SHOWERS RETURN TO CENTRAL IL...ACCORDING
TO THE ECMWF. THE GFS KEEPS THE HOLIDAY WEEKEND DRY UNTIL LATE
SATURDAY NIGHT INTO SUNDAY MORNING THEN KEEPS RAIN THROUGH
MEMORIAL DAY. THE ECMWF ON THE OTHER HAND SHOWS THE OPPOSITE
TREND. IT HAS WET CONDITIONS FRIDAY NIGHT THROUGH SATURDAY
NIGHT...THEN DRY SUNDAY THROUGH MONDAY AS IT PUSHES THE COLD FRONT
SOUTH OF IL. THE ALLBLEND HAS BEEN INFLUENCED BY BOTH
SOLUTIONS...SO THE EXTENDED IS FULL OF CHANCE POPS. THE CANADIAN
IS MORE CLOSELY FOLLOWING THE GFS SOLUTION...SO THERE APPEARS TO
BE MORE MOMENTUM TOWARD A WET END TO THE HOLIDAY WEEKEND.

SHIMON
&&

.AVIATION...
ISSUED 108 PM CDT TUE MAY 21 2013

ONLY MADE A FEW CHANGES TO THE TAFS FOR CENTRAL AND EASTERN
ILLINOIS WITH THE EARLY AFTERNOON UPDATE.

GUSTY SOUTHWEST WINDS WILL BE THE RULE THIS AFTERNOON AS PLENTY OF
DOWNWARD MOMENTUM AHEAD OF A COLD FRONT IS PRESENT. THIS WILL ALSO
DRY OUT THE LOWER ATMOSPHERE A BIT THIS AFTERNOON...KEEPING THE
BEST INSTABILITY IN SOUTHERN IL AND SOUTH OF THE OHIO RIVER
VALLEY. CONVECTION CURRENTLY FROM THE OHIO VALLEY BACK INTO THE
SOUTHERN PLAINS IS ALSO EXPECTED TO TRAP THE BEST LOW LEVEL RETURN
FLOW WELL TO OUR SOUTH. THIS MEANS THAT THE PRIMARY WINDOW FOR
CONVECTIVE DEVELOPMENT WILL BE THIS EVENING AND OVERNIGHT AHEAD OF
A SLOWLY ADVANCING COLD FRONT.

THERE IS SOME UNCERTAINTY AS TO HOW LOW THE CEILINGS ARE EXPECTED
TO DROP TO LATE TONIGHT AND INTO WEDNESDAY MORNING. THE NAM IS
VERY BULLISH WITH THE IFR AND LIFR CEILINGS BEHIND THE COLD FRONT
PASSAGE. HOWEVER...LOWER CEILINGS IN THIS RANGE TYPICALLY OCCUR
CLOSER TO THE LOW TRACK...WHICH THE NAM AND GFS BOTH TAKE NORTH OF
THE CENTRAL AND EASTERN IL TAF SITES. THUS...WILL GO WITH MVFR
CEILINGS IN THE 1-2 KFT RANGE TOWARD EARLY MORNING IN CENTRAL IL
AND AFTER DAYBREAK INTO THE EARLY AFTERNOON IN EASTERN IL.

MILLER 
&&

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

$$