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000
FXUS63 KILX 201746
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1246 PM CDT MON MAY 20 2013

.DISCUSSION...
ISSUED 1041 AM CDT MON MAY 20 2013

AIRMASS HAS TEMPORARILY STABILIZED ACROSS CENTRAL ILLINOIS THIS
MORNING...THANKS TO OVERNIGHT CONVECTION THAT HAS PUSHED THE MAIN
OUTFLOW BOUNDARY TO A LAFAYETTE INDIANA TO FLORA ILLINOIS LINE.
15Z/10AM LAPS DATA SHOWS SBCAPE VALUES OF LESS THAN 500J/KG
BEHIND THE BOUNDARY...WITH VALUES IN EXCESS OF 2000J/KG AHEAD OF
THE BOUNDARY ACROSS THE FAR SE KILX CWA. FORECAST SOUNDINGS SHOW
AIRMASS GRADUALLY DESTABILIZING BY THIS AFTERNOON...HOWEVER
HIGHEST DEWPOINTS AND SUBSEQUENT CAPE VALUES WILL BE FOCUSED
FURTHER SOUTHEAST OVER THE OHIO RIVER VALLEY. NEVERTHELESS...CAPES
OF 1500 TO 2500J/KG SHOULD BE REALIZED ACROSS MUCH OF THE AREA
LATER TODAY. IN ADDITION...STRONG LOW-LEVEL SHEAR WILL BE IN
PLACE ACROSS THE WESTERN HALF OF THE CWA...WITH 0-6KM BULK SHEAR
VALUES RANGING FROM 45 TO 55KT. COMBINATION OF MODEST INSTABILITY
AND STRONG SHEAR WILL BE ENOUGH TO SUPPORT THE DEVELOPMENT OF
STRONG TO SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO THE
EVENING. HIGH-RES MODELS SUCH AS THE NAM12 AND 4KM HRRR SUGGEST
CONVECTION WILL FIRE ALONG ANOTHER BOUNDARY STRETCHING FROM
EASTERN KANSAS INTO WEST-CENTRAL ILLINOIS AFTER 19Z/2PM. INITIAL
CONVECTIVE MODE WILL BE SUPPORTIVE OF SUPERCELLS THIS AFTERNOON/EARLY
EVENING...BEFORE STORMS BECOME MORE LINEAR BY MID EVENING AS THEY
TRACK FROM SW TO NE ACROSS THE AREA. HAVE MODIFIED POPS/TEMPS JUST
A BIT FOR THE REMAINDER OF THE DAY...BUT CHANGES DO NOT
SIGNIFICANTLY IMPACT GOING FORECAST. CHANCE SHOWERS/STORMS THIS
MORNING...WITH LIKELY POPS ARRIVING ALONG/WEST OF I-55 BY MID TO
LATE AFTERNOON.



&&

.AVIATION...
ISSUED 1246 PM CDT MON MAY 20 2013

CLUSTER OF THUNDERSTORMS CURRENTLY CROSSING THE MISSISSIPPI RIVER
JUST SOUTH OF QUINCY WILL TRACK E/NE INTO THE AREA EARLY THIS
AFTERNOON. AIRMASS IS BEGINNING TO DESTABILIZE IN ADVANCE OF THIS
CONVECTION...SO CONFIDENCE IS GROWING THAT IT WILL HOLD TOGETHER
AND ARRIVE AT KSPI BETWEEN 19Z AND 21Z. ITS EVOLUTION BEYOND THAT
STILL REMAINS IN QUESTION...SO WILL ONLY CARRY VCTS AFTER 21Z AT
THE REMAINING TERMINALS. OUTSIDE OF ANY CONVECTION THAT DEVELOPS
THIS AFTERNOON...STRONG SOUTHERLY WINDS WILL GUST TO BETWEEN 25
AND 30KT. MODELS DISAGREE ABOUT THE TIMING/PLACEMENT OF ADDITIONAL
CONVECTION LATER TODAY AND TONIGHT...HOWEVER THE HRRR CONTINUES TO
FOCUS THE MOST WIDESPREAD STORMS DURING THE EVENING INTO THE
OVERNIGHT HOURS. WILL THEREFORE KEEP TEMPO GROUPS FOR THUNDER
BETWEEN 02Z AND 06Z AT KPIA AND BETWEEN 04Z AND 08Z FURTHER EAST
AT KCMI. AFTER THAT...MID-LEVEL DRYING IN THE WAKE OF THE
OVERNIGHT CONVECTION WILL LEAD TO A DRY TUESDAY MORNING.

BARNES
&&

.PREV DISCUSSION...
ISSUED 330 AM CDT MON MAY 20 2013

SHORT TERM...TODAY THROUGH THURSDAY

UNSETTLED WEATHER PATTERN EXPECTED THROUGH MID WEEK AS LARGE UPPER
LEVEL LOW OVER NE/SD GRADUALLY WEAKENS AS IT MOVES EASTWARD INTO
THE GREAT LAKES. SPC CONTINUES A SLIGHT RISK OF SEVERE STORMS
ACROSS MUCH OF IL FROM THIS AFTERNOON INTO TUE NIGHT. MODELS HAVE
TRENDED A BIT FASTER WITH WX SYSTEM AND SPC RISK OF SEVERE STORMS
ON WED IS EAST OF IL.

LEADING EDGE OF SHOWERS AND A FEW THUNDERSTORMS AS FAR EAST AS
PEORIA AND JACKSONVILLE WHILE STRONG TO SEVERE STORMS HEADING
TOWARD ST LOUIS METRO AREA EARLY THIS MORNING. MORE NUMEROUS
THUNDERSTORMS WERE OVER CENTRAL AND SW MO INTO SE KS WITH MCS
COMPLEX. ANOTHER AREA OF CONVECTION WAS OVER NE WI WITH ANOTHER
WEAKENING MCS. SURFACE MAP SHOWS DEEPENING 998 MB LOW PRESSURE
OVER CENTRAL SD WITH ITS WARM FRONT OVER NORTHERN WI WHILE ITS
COLD FRONT WAS OVER EASTERN NEBRASKA INTO CENTRAL KS/OK. IL WAS IN
WARM SECTOR WITH MOIST DEWPOINTS IN THE 60S AND EVEN 70F AT OLNEY
AND FAIRFIELD IN SE IL. TEMPS AT 3 AM WERE IN THE LOWER TO MIDDLE
70S EXCEPT RAIN COOLED MID 60S OVER WEST CENTRAL IL.

559 DM 500 MB LOW TO SLOWLY MOVE EAST INTO EASTERN SD BY SUNSET
WITH 998 MB SURFACE LOW MOVING INTO WEST CENTRAL MN. ANOTHER ROUND
OF SEVERE STORMS EXPECTED TO FIRE UP DURING MID/LATE AFTERNOON AND
CONTINUE INTO TONIGHT OVER THE CENTRAL PLAINS AND BE FURTHER EAST
INTO IL LATE THIS AFTERNOON AND TONIGHT. VERY UNSTABLE AIR MASS
WITH CAPES OF 2500-3500 J/KG AND GOOD WIND SHEAR TO AID IN THE
DEVELOPMENT OF SEVERE STORMS INCLUDING SOME SUPERCELLS. SPC HAS
15% RISK OF LARGE HAIL AND DAMAGING WIND GUSTS OVER IL WITH 30%
RISK OF LARGE HAIL FROM I-55 WEST AND 30% RISK OF DAMAGING WINDS
GUSTS FROM I-57 WEST. ALSO HAVE AT LEAST A 5% RISK OF TORNADOS
OVER MUCH OF IL EXCEPT FAR SE IL. HIGHS THIS AFTERNOON AGAIN IN
THE UPPER 80S TO NEAR 90F WITH DEWPOINTS IN THE UPPER 60S AND
LOWER 70S SO WILL FEEL LIKE A MID SUMMER DAY IN JULY.

UPPER LEVEL LOW STAYS IN PLACE NEAR SE SD TUE AND THEN WEAKENS A
BIT TO 562 DM AS IT TRACKS EASTWARD INTO EASTERN IA BY SUNSET WED
WHILE SURFACE LOW MOVES INTO SOUTHERN LAKE MI. ANOTHER SLIGHT RISK
OF SEVERE STORMS OVER MUCH OF IL TUE AFTERNOON/EVENING THOUGH NOT
QUITE AS UNSTABLE AS THIS AFTERNOON...AND SYSTEM IS STARTING TO
WEAKEN SO COVERAGE OF SEVERE STORMS APPEARS LESS. SPC HAS AT LEAST
15% RISK OF DAMAGING WINDS AND LARGE HAIL WITH THE 30% RISK SW IL SW
OF CLAY COUNTY. HIGHS TUE IN THE LOW TO MID 80S. SHOWERS STILL
LIKELY WED WITH A FEW THUNDERSTORMS ESPECIALLY OVER EASTERN IL.
RAINFALL AMOUNTS OF 1 TO 2 INCHES POSSIBLE TODAY THROUGH WED.
WEAKENING UPPER LEVEL TROF MOVES INTO IL THU KEEPING A CHANCE OF
SHOWERS AND ISOLATED THUNDERSTORMS ALONG WITH COOLER TEMPS WITH
HIGHS AROUND 70F FROM I-74 NORTH AND MID 70S IN SE IL.

LONG TERM...THURSDAY NIGHT THROUGH SUNDAY NIGHT

DRY WEATHER FINALLY RETURNS TO CENTRAL/SE IL THU NIGHT THROUGH FRI
NIGHT AS HIGHS PRESSURE SETTLES INTO THE GREAT LAKES REGIONS.
CARRIED 20-40% CHANCE OF SHOWERS AND THUNDERSTORMS FROM SAT
AFTERNOON THROUGH SUNDAY NIGHT OVER CENTRAL AND SE IL WITH SOME
MODELS SHOWING SHORT WAVE RIDGING OVER TOP OF UPPER LEVEL RIDGE INTO
PARTS OF IL THIS WEEKEND. THOUGH CONFIDENCE OF THIS HAPPENING IS LOW.
TEMPS SHOULD MODIFY EARLY NEXT WEEK WITH SOME UPPER LEVEL RIDGING
INTO IL.

07


&&

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

$$