000
FXUS63 KILX 171458
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
958 AM CDT FRI MAY 17 2013

.DISCUSSION...
ISSUED 958 AM CDT FRI MAY 17 2013

CLOUD COVER LIFTING NORTHWARD IN RESPONSE TO WEAKENING UPPER LOW
OVER SOUTHEAST MISSOURI. HAVE BEEN SEEING A FEW SPRINKLES EDGING
INTO THE FAR SOUTHEAST CWA WITH THE ALTOCUMULUS DECK. MAIN
QUESTION WILL BE WITH TIMING OF THE CONVECTION TODAY. VISIBLE
SATELLITE IMAGERY SHOWING SOME CELLULAR DEVELOPMENT IN AREAS WEST
OF FLORA AND OVER THE LOWER ILLINOIS RIVER VALLEY...WHERE LITTLE
IS LEFT OF THE CAP. MODEL GUIDANCE IS STRUGGLING WITH THE
INITIALIZATION LOCATION...BUT THE HIGHER RESOLUTION MODELS SEEM TO
BE FAVORING THE NORTHEAST HALF OF THE CWA EARLY THIS AFTERNOON AND
THE SOUTHEAST BY MID AFTERNOON. SURFACE OBS ARE NOT SHOWING ANY
OBVIOUS BOUNDARIES YET THAT COULD SERVE AS A SPECIFIC FOCUS. AS A
RESULT... HAVE NOT DONE MUCH WITH THE LOCATION OF THE HIGHEST POPS
EXCEPT FOR REFINING THE MORE LIKELY TIMES FOR THE HIGHEST VALUES.

UPDATED GRIDS HAVE BEEN SENT...BUT THE WORDED FORECASTS STILL LOOK
GOOD AT THIS TIME.

GEELHART

&&

.AVIATION...
ISSUED 622 AM CDT FRI MAY 17 2013

CONDITIONS AT ALL TAF SITES WILL BE VFR MOST OF THE PERIOD WITH
VCTS AT ALL SITES FROM LATER THIS MORNING UNTIL EARLY THIS
EVENING. CONVECTION WILL BE VERY DIURNAL SO IT SHOULD DIMINISH AND
END VERY QUICKLY. ONCE THE PRECIP ENDS AM EXPECTING FOG TO DEVELOP
AT ALL SITES TONIGHT AND CONTINUE UNTIL TOMORROW MORNING. FOG
SHOULD BRING CONDITIONS DOWN TO MVFR IN THE EVENING AND THEN IFR
AT ALL SITES AFTER MIDNIGHT. WINDS WILL BE SOUTHEAST AROUND 10KTS
TODAY AND THEN BECOME LIGHT AND VARIABLE REMAINDER OF THE TAF
PERIOD.

AUTEN
&&

.PREV DISCUSSION...
ISSUED 317 AM CDT FRI MAY 17 2013

SHORT TERM...TODAY THROUGH SUNDAY

SURFACE BOUNDARY WHICH HAS BROUGHT SCATTERED STORMS TO THE AREA THE
PAST COUPLE DAYS HAS MIGRATED BACK NORTH AND NOW LIES NEAR THE
NORTHERN FRINGE OF THE CWA. THIS FEATURE WILL SLOWLY EDGE NORTH
TODAY...AND SOUTHEAST FLOW WILL CONTINUE TO BRING IN SEASONABLE
WARMTH AND MODEST HUMIDITY WITH DEWPOINTS IN THE LOW 60S. A CLOSED
UPPER LOW NOW TRACKING INTO SOUTHEAST MO IS FORECAST TO OPEN UP
AND LIFT TOWARDS THE LOWER OHIO VALLEY BY 00Z/SAT. INCREASING
MOISTURE AND LIFT ASSOCIATED WITH THIS LOW WILL BRING SCATTERED
CONVECTION BACK TO THE AREA TODAY. FEEL HIGHEST COVERAGE WILL BE
TIED TO DIURNAL HEATING...AND FOCUSED LIKELY POPS DURING THE
AFTERNOON. FOLLOWED 4KM WRF FOR CONVECTIVE TRENDS AS THIS MODEL
HANDLED YESTERDAYS SITUATION WELL. IN AREAS THAT DO SEE RAIN...HEAVY
RAINFALL RATES WILL AGAIN BE POSSIBLE AS PW RISES TO 1.5 INCHES
AND WINDS ALOFT ARE UNDER 15 KTS. THIS ACTIVITY SHOULD QUICKLY DIE
OFF THIS EVENING AS THE ATMOSPHERE STABILIZES.

FOR SATURDAY...THE UPPER LOW WILL SLOWLY DRIFT UP THE OHIO VALLEY
WITH ENOUGH LIFT AND MOISTURE LINGERING BACK INTO EASTERN IL TO
KEEP A CHANCE OF SCATTERED STORMS GOING. FARTHER WEST...DRY
WEATHER IS EXPECTED AS BRIEF UPPER RIDGING BUILDS TOWARDS THE
MISSISSIPPI VALLEY BY 00Z/SUN. BY SATURDAY NIGHT...A DEEP UPPER
TROUGH DIGGING EAST OF THE ROCKIES SPINS UP A SURFACE LOW OVER THE
CENTRAL PLAINS. THIS SENDS A WARM FRONT NORTHEAST ACROSS MO...WITH
ELEVATED CONVECTION POSSIBLY GETTING AS FAR NORTHEAST AS THE
WESTERN CWA LATE AND HAVE ADDED SCHC POPS TO ACCOUNT FOR THIS.

00Z MODELS SHOW THE WARM FRONT LIFTING WELL NORTH OF THE AREA ON SUNDAY
AND WITH 850 MB TEMPS RISING TO NEAR +20C HIGHS IN THE MID OR
UPPER 80S ARE POSSIBLE. MUCH OF THE CWA SHOULD REMAIN DRY WITH
WEAK CAPPING IN PLACE. HOWEVER ACROSS THE WEST WILL CARRY A LOW
CHANCE FOR AFTERNOON TSTMS AS CINH IS NEGLIGIBLE AND LEAD SHORTWAVE
ENERGY LIFTING OUT OF THE WESTERN TROF COULD SPARK SOME ACTIVITY.

LONG TERM...MONDAY THROUGH THURSDAY

MUCH OF THE EXTENDED FORECAST WILL BE ACTIVE AS A HIGH AMPLITUDE SLOW
MOVING UPPER TROF SHIFTS FROM THE NORTHERN PLAINS INTO THE GREAT
LAKES BY MID-WEEK. THIS WILL REQUIRE A PROLONGED PERIOD OF CHANCE
TO LIKELY POPS INTO WEDNESDAY. SUSTAINED SOUTHERLY FLOW AHEAD OF
THE PLAINS SURFACE LOW BRINGS GULF MOISTURE AND ASSOCIATED UPPER
60S TO AROUND 70F DEW POINT POOL INTO THE MIDWEST. MODERATE TO HIGH
INSTABILITY WILL BE IN PLACE FOR MONDAY AND TUESDAY...AND AS
SEVERAL SHORTWAVES LIFT ACROSS THE CWA IN DIFLUENT SOUTHWEST
FLOW...ROUNDS OF STRONG TO SEVERE CONVECTION ARE POSSIBLE. LATEST
00Z MEDIUM RANGE MODEL RUNS SHOW THE ACTUAL COLD FRONT NOT
ARRIVING UNTIL LATE TUESDAY OR EARLY WEDNESDAY. SO IN ADDITION TO
POSSIBLE SEVERE WEATHER HEAVY RAIN ALSO MAY BE REALIZED IF THE CURRENTLY
ADVERTISED TRENDS OF A STRONG SLOW MOVING SYNOPTIC SYSTEM AND HIGH
PW AIRMASS MATERIALIZE. TEMPERATURES WILL REMAIN SEVERAL DEGREES
ABOVE NORMAL UNTIL THE FRONT EVENTUALLY PASSES. POST- FRONTAL
AIRMASS WILL BRING TEMPS BACK TO NEAR OR SLIGHTLY BELOW NORMAL FOR
THE END OF NEXT WEEK.

25

&&

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

$$