000
FXUS63 KILX 161726
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1226 PM CDT THU MAY 16 2013

.DISCUSSION...
ISSUED 937 AM CDT THU MAY 16 2013

DIFFUSE FRONTAL BOUNDARY WAS ROUGHLY CENTERED ALONG THE I-72
CORRIDOR THIS MORNING. HAVE MAINLY HAD SOME POP-UP TYPE SHOWERS
AND STORMS ALONG THE BOUNDARY OVER THE LAST COUPLE HOURS...WITH A
MORE ORGANIZED BAND OF SHOWERS ACROSS THE NORTHERN CWA
DISSIPATING. GREATEST ACTION HAS BEEN LIFTING OUT OF SOUTHERN
ILLINOIS AND SCRAPING THE FAR SOUTHEAST CWA.

NOT TOO MUCH CHANGE FROM EARLIER THINKING ABOUT PLACEMENT OF
SHOWERS AND STORMS TODAY. HAVE SENT SOME UPDATED GRIDS AND ZONES
TO ADJUST THE WINDS BASED ON THE LATEST LOCATION OF THE BOUNDARY.
LITTLE ADJUSTMENT NEEDED TO TEMPERATURES OR PRECIP CHANCES...
ALTHOUGH SOME CHANGES IN THE GRIDS WERE MADE IN THE FAR SOUTHEAST
TO BOOST POPS DUE TO ONGOING CONVECTION.

GEELHART


&&

.AVIATION...
ISSUED 1225 PM CDT THU MAY 16 2013

POP-UP NATURE OF SHOWERS/STORMS THIS AFTERNOON WILL BE A CHALLENGE
IN GOING WITH ANYTHING MORE THAN VCTS. ONE LINE OF STORMS WAS
LOCATED JUST SOUTH OF KSPI/KTAZ BUT REMAINING STATIONARY...SO WILL
NOT ADD A PREVAILING TSRA AT KSPI YET. MANY OF THE STORMS SHOULD
FADE WITH SUNSET...AND HAVE GONE WITH LARGELY DRY CONDITIONS AT
ALL TAF SITES MUCH OF THE NIGHT. LATEST HIGH- RESOLUTION GUIDANCE
SUGGESTING SOME LATE NIGHT DEVELOPMENT NEAR KPIA/KBMI...AND HAVE
PUT SOME VCTS BACK THERE...ALTHOUGH MAIN CONCERN LATE NIGHT WILL
BE WITH AREAS OF MVFR FOG. ON FRIDAY MORNING...POTENTIAL EXISTS
FOR ADDITIONAL SHOWERS/STORMS TO LIFT UP FROM THE SOUTH...AND HAVE
MENTIONED VCTS AT KSPI/KDEC AFTER 15Z.

GEELHART

&&

.PREV DISCUSSION...
ISSUED 319 AM CDT THU MAY 16 2013

SHORT TERM...TODAY THROUGH FRIDAY

QUASI-STATIONARY FRONT LIES WEST-EAST ACROSS CENTRAL IL EARLY
THIS MORNING BUT HAS BECOME ILL DEFINED DUE TO CONVECTION AND
RESULTING OUTFLOW BOUNDARIES. BEST COVERAGE OF THUNDERSTORMS FOR
PAST FEW HOURS HAS OCCURRED OVER THE NORTHERN THIRD OF THE CWA
WHERE A 30 KT WSW LOW LEVEL JET HAS PROVIDED ENHANCED CONVERGENCE
INTO THE LOW AND MID LEVEL BOUNDARIES. THIS ACTIVITY WILL CONTINUE
TO FADE TOWARDS SUNRISE AS THE LLJ WEAKENS. MAIN FORECAST
CHALLENGE TODAY WILL BE COVERAGE AND TIMING OF TSTMS WITH BOUNDARY
REMAINING IN THE AREA...AND A CLOSED UPPER LOW CURRENTLY OVER
OKLAHOMA WHICH WILL BE OPENING UP AND LIFTING NORTHEAST. MOISTURE
LEVELS INCREASE AHEAD OF THIS FEATURE SO EXPECT BETTER STORM
COVERAGE THAN YESTERDAY ESPECIALLY DURING PEAK AFTERNOON
INSTABILITY. LATEST HI-RES SHORT RANGE MODELS FOCUS THIS ACTIVITY
OVER THE CENTRAL AND SOUTHERN CWA AND HAVE PLACED HIGHEST CHANCE
POPS HERE.  FORECAST SOUNDINGS SHOW ENOUGH MID LEVEL COOLING TO
ERODE CAPPING...AND AFTERNOON/EARLY EVENING CAPES ON THE ORDER OF
1K J/KG. WINDS ALOFT ARE QUITE LIGHT NEAR 10 KTS SO STORMS WILL BE
SLOW MOVERS AND CAPABLE OF HEAVY RAIN RATES AS PRECIPITABLE WATER
RISES TO AROUND 1.25 INCHES. STORMS SHOULD DISSIPATE DURING THE
EVENING WITH LOSS OF DAYTIME HEATING AND NO LLJ SUPPORT.

THE BOUNDARY LIFTS NORTH OF THE CWA ON FRIDAY...BUT
MORE SCATTERED AFTERNOON CONVECTION EXPECTED AS THE UPPER TROF
SHIFTS ACROSS THE AREA. TEMPS WILL REMAIN SEVERAL DEGREES ABOVE
NORMAL FOR THE NEXT COUPLE DAYS WITH HIGHS IN THE LOWER 80S AND
LOWS IN THE LOWER 60S.

LONG TERM...SATURDAY THROUGH WEDNESDAY

LINGERING EFFECTS OF THE UPPER TROF COULD BRING SCATTERED
CONVECTION BACK TO PRIMARILY THE EASTERN CWA SATURDAY
AFTERNOON...CLOSER TO THE DEPARTING TROF. BY LATE SATURDAY INTO
SUNDAY UPPER RIDGING WILL BUILD ACROSS THE MISSISSIPPI VALLEY IN
RESPONSE TO THE NEXT SYSTEM DEVELOPING OVER THE ROCKIES. THIS
PROVIDES THE BEST SHOT AT A DRY PERIOD IN THE FORECAST AND HAVE
REMOVED ANY MENTIONABLE POPS SATURDAY NIGHT THROUGH SUNDAY
AFTERNOON. SUNDAY HAS THE POTENTIAL TO BE THE WARMEST OF THE NEXT
7 DAYS AS 850MB TEMPS WARM INTO THE UPPER TEENS AND AMPLE
SUNSHINE. HAVE BOOSTED HIGHS IN TO THE MID 80S.

A DEEP UPPER LOW IS FORECAST TO CLOSE OFF OVER THE NORTHERN PLAINS
BY THE END OF THE WEEKEND...AND SLOWLY MOVE TOWARDS THE WESTERN
GREAT LAKES BY WEDNESDAY ACCORDING TO THE GFS...OR OVER THE CWA
ACCORDING TO THE 00Z ECMWF. IN EITHER CASE THIS SETS UP A
PROLONGED PERIOD OF DIFFLUENT SOUTHWEST MID LEVEL OVER THE MIDWEST
FROM SUNDAY NIGHT...THROUGH AT LEAST TUESDAY. GULF MOISTURE WILL
HAVE OVERSPREAD THE MIDWEST BY THIS TIME...AND WITH SHORTWAVES
RIPPLING OVER THE AREA SCATTERED CONVECTION WILL BE AROUND FROM
TIME TO TIME. HAVE CHANCE POPS IN THE REMAINDER OF THE EXTENDED
AND WHILE CERTAINLY MANY HOURS WILL BE DRY...IMPOSSIBLE TO TIME AT
THIS POINT. STRONG OR SEVERE STORMS MAY BE POSSIBLE DEPENDING ON
INSTABILITY...BUT WITH A DEEPLY OCCLUDED SYSTEM THIS SCENARIO IS
NOT AS WELL DEFINED AS 24 HOURS AGO. TEMPERATURES WILL REMAIN WELL
ABOVE NORMAL UNTIL THE LONGWAVE TROF CAN SHIFT THROUGH WHICH MAY
NOT BE UNTIL THE END OF THE FORECAST PERIOD OR LATER.

25


&&

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

$$