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000
FXUS63 KILX 211808
AFDILX

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

.DISCUSSION...
ISSUED 1100 AM CDT TUE MAY 21 2013

MADE SOME MINOR ADJUSTMENTS TO LOWER TEMPS A BIT FOR THIS
AFTERNOON AND ADJUST THE MENTION OF SHOWERS AND T-STORMS MORE
TOWARD THE LATE AFTERNOON AND ESPECIALLY THIS EVENING AND
OVERNIGHT.

THE LATEST SURFACE ANALYSIS INDICATED THAT THE MAIN SYNOPTIC FRONT
WAS JUST APPROACHING THE MS RIVER...WITH VARIOUS OUTFLOW
BOUNDARIES MAINLY SOUTH OF THE OHIO RIVER VALLEY. THE BEST
INSTABILITY IS EXPECTED TO BE IN SOUTHERN AND SOUTHEAST IL THIS
AFTERNOON. A MAJORITY OF THE SHORT RANGE MODELS INCLUDING THE
HRRR...NAM 12...00Z WRF AND SPC SSEO ALL POINT TO THE BEST
POTENTIAL FOR CONVECTION AFTER 00Z...MAINLY EAST OF I-55 JUST
AHEAD OF THE ADVANCING COLD FRONT.

DUE TO THE CLUSTERS OF STORMS CURRENTLY TRACKING THROUGH THE LOWER
MS AND TN VALLEYS...AND ADDITIONAL DEVELOPMENT IN THOSE AREAS
LATER THIS AFTERNOON...THE BEST MOISTURE FLOW WILL PROBABLY BE
CUTOFF FROM CENTRAL AND SE IL. THIS SHOULD KEEP THE HIGHEST
INSTABILITY TO OUR SOUTH. HOWEVER...INCREASING WIND SHEAR MAY
PRODUCE SCATTERED HIGH WIND GUSTS WITH SOME OF THE STORMS THIS
EVENING.



&&

.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

&&

.PREV DISCUSSION...
ISSUED 330 AM CDT TUE MAY 21 2013

SHORT TERM...TODAY THROUGH FRIDAY

MCS THAT BROUGHT HEAVY RAINS...FREQUENT LIGHTNING AND SEVERAL
SEVERE WIND DAMAGE REPORTS TO CENTRAL/EASTERN IL DURING MONDAY
EVENING HAS WEAKENED EASTWARD ACROSS INDIANA WITH LINGERING
SHOWERS AND ISOLATED THUNDERSTORMS SE OF A CHAMPAIGN TO
SPRINGFIELD LINE AND TRACKING NE. 998 MB LOW PRESSURE OVER NE SD
WITH ITS WARM FRONT OVER NORTHERN WI/LOWER MI AND ITS COLD FRONT
OVER WESTERN IA...NW MO...SE KS AND CENTRAL OK. STRONG 555 DM 500
MB LOW WAS OVER NE SD AND HAS NOT MOVED MUCH PAST 24 HOURS. ONE
MORE VERY WARM AND HUMID DAY EXPECTED OVER CENTRAL AND SE IL WITH
HIGHS IN THE LOW TO MID 80S AS SOME SUNSHINE RETURNS DURING THE
MORNING AND EARLY AFTERNOON. SHOWERS AND ISOLATED THUNDERSTORMS TO
DIMINISH EAST OF I-55 DURING THE MORNING AND REFIRE UP LATER THIS
AFTERNOON AND EVENING.

SPC HAS SHIFTED SLIGHT RISK OF SEVERE STORMS A BIT FURTHER EAST
AND GENERALLY EAST OF THE IL RIVER VALLEY LATE THIS AFTERNOON AND
EVENING. PER SPC DAY1 OUTLOOK DISCUSSION...SW FLOW WILL BE IN
PLACE TODAY FROM THE MID MS VALLEY NE INTO THE GREAT LAKES REGION.
SURFACE LOW PRESSURE IS FORECAST TO MOVE EASTWARD ACROSS THE UPPER
MS VALLEY WITH A CORRIDOR OF LOW LEVEL MOISTURE EXTENDING NNE FROM
THE LOWER OH VALLEY INTO LOWER MI. SFC DEWPOINTS ACROSS
CENTRAL AND EASTERN IL SHOULD BE IN THE MID TO UPPER 60S
RESULTING IN MODERATE DESTABILIZATION. MODEL FORECASTS INITIATE
STORMS BY MID AFTERNOON ALONG THE INSTABILITY AXIS WITH STORMS
MOVING NEWD ACROSS THE REGION. FORECAST SOUNDINGS ALONG THE
INSTABILITY AXIS WEST OF DETROIT AND NORTH OF INDIANAPOLIS AT
21Z/4 PM SHOW MLCAPE VALUES IN THE 1000 TO 2000 J/KG RANGE WITH
STEEP LOW-LEVEL LAPSE RATES AND UNIDIRECTIONAL WIND PROFILES. THIS
ENVIRONMENT SHOULD BE FAVORABLE FOR WIND DAMAGE AS CELLS INCREASE
IN COVERAGE DURING THIS AFTERNOON. SEVERAL MODEL FORECASTS SHOW AN
ENHANCED SEVERE THREAT ACROSS SOUTHERN LOWER MI TO THE SOUTHEAST
OF THE SURFACE LOW AND ON THE NOSE OF THE LOW-LEVEL JET. FOR THIS
REASON...AN ENHANCED WIND DAMAGE THREAT (30%) WILL BE POSSIBLE
WITH BOWING LINE-SEGMENTS IN LOWER MI LATE THIS AFTERNOON. LARGE
HAIL AND A FEW TORNADOES (5%) MAY ALSO OCCUR WITH THE MORE INTENSE
CELLS. CENTRAL AND EASTERN IL HAS 15% RISK OF DAMAGING WIND GUSTS
AND LARGE HAIL AND 2% RISK OF A TORNADO LATE THIS AFTERNOON AND
EVENING.

STRONG CUTOFF LOW TO MOVE EAST AND BE 557 DM 500 LOW OVER NW IA BY
DAWN WED WITH 1004 MB SURFACE LOW MOVING EAST/WEAKENING INTO NE IA
AND NORTHERN IL. CONTINUE HIGH CHANCES OF SHOWERS AND THUNDERSTORMS
THRU TONIGHT WITH THE SLIGHT RISK OF SEVERE STORMS EAST OF THE IL
RIVER VALLEY THRU THE EVENING. COLD FRONT TO MOVE EAST THROUGH IL
WED MORNING AS SURFACE LOW MOVES INTO SE LOWER MI BY SUNSET WED.
THIS TO KEEP A GOOD CHANCE OF SHOWERS AND A FEW THUNDERSTORMS
AROUND ON WED WITH LIKELY CHANCES OVER EASTERN IL. SPC HAS 5% RISK
OF SEVERE STORMS NEAR THE WABASH RIVER WED WHILE SLIGHT CHANCE OF
SEVERE STORMS IS FROM OHIO EAST. HIGHS WED IN THE MID TO UPPER
70S WITH LAWRENCEVILLE NEAR 80F.

562 DM 500 MB LOW TO OVER INTO NORTHERN INDIANA THU MORNING AND
CONTINUE CHANCES OF SHOWERS AND MOSTLY CLOUDY SKIES WITH COOLER
TEMPS IN THE UPPER 60S AND LOWER 70S FOR HIGHS THU AND MILDEST
FROM SPRINGFIELD TO TERRE HAUTE SOUTH. UPPER LEVEL LOW/TROF PULLS
AWAY FROM IL THU NIGHT AND FRI AS 1031 MB CANADIAN HIGH PRESSURE
SETTLES INTO THE WESTERN GREAT LAKES AND IL. THIS TO BRING MORE
SUNSHINE BUT COOL TEMPS WITH HIGHS IN THE UPPER 60S TO AROUND 70F
AFTER LOWS THU NIGHT IN THE MID TO UPPER 40S OVER CENTRAL IL AND
LOWER 50S SE IL.

LONG TERM...FRIDAY NIGHT THROUGH MONDAY

UPPER LEVEL RIDGING INTO THE GREAT PLAINS LATE THIS WEEK AND MODELS
STILL SHOWING A DISTURBANCE RIDGING OVER THE UPPER LEVEL RIDGE WITH
QPF BUT DIFFER ON TIMING ON POSITION OF THIS DISTURBANCE. HAVE
SLIGHT CHANCE OF CONVECTION OVER THE IL RIVER VALLEY AFTER MIDNIGHT
FRI NIGHT. THEN 20-40% CHANCE OF CONVECTION OVER CENTRAL IL SAT
THRU MONDAY WHILE SE IL APPEARS TO STAY DRIER SAT AND SAT NIGHT AND
MONDAY. HIGH PRESSURE OVER THE GREAT LAKES REGION MEMORIAL DAY
WEEKEND WILL TEND TO KEEP AREAS NE OF CENTRAL IL DRIER AS WELL.
TEMPS TO GRADUALLY MODIFY FROM SAT THROUGH MONDAY WITH HIGHS IN THE
MID TO UPPER 70S MEMORIAL DAY.

07


&&

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

$$