000
FXUS63 KILX 220434
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1134 PM CDT TUE MAY 21 2013

.DISCUSSION...
ISSUED 830 PM CDT TUE MAY 21 2013

LATEST SURFACE ANALYSIS INDICATES A WEAK COLD FRONT LOCATED OVER
PARTS OF WEST CENTRAL ILLINOIS EARLY THIS EVENING. HAD SOME
ISOLATED SHOWERS DEVELOP JUST TO THE EAST OF THE BOUNDARY WHICH
HAVE AFFECTED MAINLY OUR NORTHERN COUNTIES. MEANWHILE TO THE
SOUTH...SEVERAL LARGE THUNDERSTORM COMPLEXES WERE TRACKING EAST
ALONG AND SOUTH OF THE OHIO RIVER WITH THE NORTHERN FRINGES OF
THE STORMS EDGING INTO OUR SOUTHEAST COUNTIES.

A SHORTWAVE TROF NOTED ON THE WATER VAPO LOOP OVER OKLAHOMA THIS
EVENING IS FORECAST TO ROTATE NE TOWARDS OUR AREA BY WEDNESDAY
MORNING SPREADING SHOWERS AND ISOLATED THUNDERSTORMS NORTHWARD
INTO MOST OF OUR AREA. WONDERING HOW MUCH OF AN AFFECT...IF
ANY...THE MCS ACTIVITY TO OUR SOUTH WILL HOLD BACK THE MOISTURE
FEED NORTH INTO OUR AREA AHEAD OF THE SOUTHERN PLAINS UPPER WAVE.
LOOKS AS IF THE LAST FEW RUNS OF THE HI-RES RAPID REFRESH IS
PULLING BACK SOME FROM ITS PREVIOUS FORECASTS IN BRINGING IN A
LARGE AREA OF SHOWERS AND STORMS...AT LEAST UNTIL THE UPPER WAVE
MOVES INTO OUR AREA WEDNESDAY MORNING...ABOUT 6 HOURS SLOWER THAN
WHAT WE WERE SEEING EARLIER TODAY.

HAVE MADE SOME MINOR ADJUSTMENTS TO THE GRIDS WITH RESPECT TO THE
TWO AREAS OF RAIN CURRENTLY AFFECTING OUR NORTH AND SOUTH...BUT
OVERALL...THE FORECAST LOOKS ON TRACK FOR THE OVERNIGHT HOURS INTO
WEDNESDAY MORNING. SHOULD HAVE THE UPDATED ZONES OUT BY 900 PM.

&&

.AVIATION...
ISSUED 1120 PM CDT TUE MAY 21 2013

MAIN CONCERN THIS FORECAST PERIOD WILL BE THE COVERAGE OF SHOWERS
AND ISOLATED TSRA OVERNIGHT AND INTO THE DAY ON WEDNESDAY AS AN
UPPER LEVEL WAVE DRIFTS ACRS THE REGION. OTHER THAN SOME ISOLATED
SHOWERS THAT MOVED ACRS THE AREA OVER THE PAST FEW HOURS THAT HAS
BEEN ABOUT IT RAIN-WISE. VFR CONDITIONS CONTINUE AND ARE EXPECTED
TO HOLD INTO AT LEAST WEDNESDAY MORNING BEFORE A SLOW MOVING COLD
FRONT TRACKS THRU THE TAF SITES BRINGING SOME SCATTERED SHOWERS
AND CIGS AT OR JUST ABOVE MVFR CAT. SATELLITE AND SFC OBS TO THE
NORTHWEST OF THE SFC LOW CURRENTLY OVER IOWA AND WISCONSIN SHOWING
A LARGE AREA OF MVFR CIGS AND IT APPEARS AS THE LOW SHIFTS OFF TO
OUR EAST BY LATER TOMORROW...SOME OF THOSE LOWER CIGS WILL SHIFT
SE INTO OUR AREA...ESPECIALLY TOMORROW NIGHT. FOR NOW...WILL KEEP
THE CIGS AT OR JUST ABOVE MVFR FOR NOW BUT MOST SITES MAY SEE
THE LOWER CIGS MOVE IN AFTR 00Z THU. SFC WINDS WILL REMAIN LIGHT
SSW TONIGHT AT 10 KTS OR LESS...AND THEN VEER MORE INTO A WESTERLY
DIRECTION ON WEDNESDAY AT 10 TO 15 KTS.

SMITH
&&


.PREV 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.


&&

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

$$