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000
FXUS63 KLSX 260456
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1156 PM CDT SAT MAY 25 2013

.UPDATE...
ISSUED AT 919 PM CDT SAT MAY 25 2013

AREA HAS BEEN MAINLY FREE OF RAIN THIS EVENING. RECENT RUNS OF THE
RAP HAVE BEEN CONSISTENT WITH AN INCREASE IN LOW LEVEL MOISTURE
CONVERGENCE ACROSS NORTHERN MISSOURI INTO WEST CENTRAL ILLINOIS
TOWARD MIDNIGHT. PROPAGATION VECTORS SUGGEST ANY ORGANIZED CONVECTION
WILL MOVE SOUTH AND SOUTHEASTWARD. WILL LOWER POPS FOR THE REST OF
THE EVENING...BUT THEN LEAVE LIKELY POPS GOING OVER THE NORTHERN
CWA AFTER MIDNIGHT.

HAVE ALSO TWEAKED TEMPERATURES DOWN A BIT OVER THE NORTHERN CWA
WHERE CURRENT OBSERVATIONS ARE CLOSE TO GOING LOWS.

BRITT

&&

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 323 PM CDT SAT MAY 25 2013

AN MCS REMNANT WILL CONTINUE TO WEAKEN THIS AFTN AS IT MOVES ACROSS
THE AREA. SCHC-CHC POPS LOOK REASONABLE FOR THE LATE AFTN PD BASED
ON RADAR TRENDS.

ATTN THEN TURNS TO THE OVERNIGHT PD. LATE AFTN SFC OBS REVEALED A
SHARP WMFNT STRETCHING ACROSS WRN MO AND SWRN IA INTO THE NRN
PLAINS. THIS BDRY IS EXPECTED TO PROVIDE THE FOCUS FOR ADDITIONAL
AREAS OF PCPN TONIGHT HOWEVER IT IS NOT YET CLEAR WHETHER PCPN WILL
TAKE THE FORM OF ANOTHER MCS /POSSIBLY MORE THAN ONE/...A BROAD AREA
OF PCPN ANCHORED NEAR THE H85 WMFNT...OR SOME COMBINATION OF THE
TWO. THESE SCENARIOS SEEM EQUALLY PLAUSIBLE GIVEN THE CURRENT BDRY
LOCATION...FCST LLJ STRENGTH AND ORIENTATION...INSTABILITY
PROGS...AND OBSERVED TRENDS OVER THE PREVIOUS 18 HOURS. ATTM THE
BEST PCPN CHCS APPEAR TO BE OVER THE NRN AND NERN CWA...BUT IT IS
EQUALLY POSSIBLE THAT A BROAD AREA OF PCPN COULD REMAIN NORTH AND
EAST OF THE CWA FOR MOST OF THE NIGHT OR THAT AN MCS COULD FORM AND
BRING WIDESPREAD RAIN TO A LARGE PORTION OF THE CWA. IN
SHORT...UNSETTLED WEATHER WILL CONTINUE THROUGH TONIGHT.

KANOFSKY

.LONG TERM...(SUNDAY THROUGH NEXT SATURDAY)
ISSUED AT 323 PM CDT SAT MAY 25 2013

(TONIGHT-TUESDAY)

GIVEN HOW DIFFICULT DETERMINING TODAYS CONVECTIVE TREND HAS
BEEN...PINNING DOWN THIS THREAT OVER THE REMAINDER OF THE HOLIDAY
WEEKEND WILL CERTAINLY REMAIN VERY CHALLENGING SINCE THERE IS
ESSENTIALLY NO CHANGE IN THE OVERALL SYNOPTIC PATTERN.
SYNOPTIC AND HI-RES EXPICIT THUNDERSTORM MODELS ARE IN AGREEMENT IN
A VERY BROAD SENSE THAT AN ELEVATED THUNDERSTORM THREAT WILL PERSIST
ACROSS THE REGION AS WEAK SHORTWAVES PROPAGATE THROUGH THE MID LEVEL
RIDGING...INTERACTING WITH AND OCCAIONALLY INTENSIFYING BROAD ZONE
OF LOW LEVEL WARM ADVECTION ALONG 850MB BAROCLINIC ZONE THAT IS
PROGGED FROM THE MID MO VALLEY INTO IL.  HOWEVER...THERE IS ALMOST
NO AGREEMENT ON WHERE AND WHEN STORM INITIATION WILL OCCUR SINCE LOW
LEVEL JET AND FORCING SEEMS MUCH LESS FOCUSED THAN WHAT OCCURRED
LAST NIGHT AND TODAY.

FOR NOW WILL MAINTAIN A BROAD BRUSH APPROACH TO FORECAST THROUGH
MONDAY...AND FINE TUNING BOTH POPS AND TEMPERATURES WILL BECOME A
NOWCAST ISSUE ONCE CONVECTIVE TRENDS BECOME BETTER DEFINED.  HIGHEST
POPS WILL REMAIN OVER OUR N/NE COUNTIES NEAR THE 850MB THERMAL
GRADIENT WHERE LIFT SHOULD BE MAXIMIZED AND/OR SE PROPAGATION OF MCS
CLUSTERS WILL BE MOST LIKELY.  HOWEVER...AS WAS PROVEN TODAY
CERTAINLY CANNOT RULE OUT THUNDERSTORM CHANCES FURTHER S DUE TO WEAK
SHORTWAVE ENERGY...A MORE UNSTABLE AIRMASS IN THE WARM SECTOR...AND
POSSIBLE BOUNDARY INTERACTIONS...SO WILL MAINTAIN CHANCE POPS
ELSEWHERE.

IN THE MONDAY NIGHT-TUESDAY TIME FRAME UPPER RIDGE WILL PUSH EAST
AND SW FLOW WILL BECOME ESTABLISHED OVER AREA AS UPPER TROF DEEPENDS
OVER THE WESTERN U.S.   WITH TIME THIS SHOULD PUSH THE 850 MB
THERMAL GRADIENT AND MCS THREAT FURTHER N AND E...WITH A
CORRESPONDING DROP IN POPS FROM S TO N ACROSS THE CWA DURING THIS
TIME.

(WEDNESDAY-SATURDAY)

SW FLOW ALOFT WILL DOMINATE THE MID MISSISSIPPI VALLEY FOR THE
END OF THE WEEK AS UPPER LEVEL LOW SLOWLY FORMS OVER THE NORTHERN
ROCKIES. PRIMARY QUESTION IS HOW MUCH UPPER LEVEL DYNAMICS WILL BE
ABLE TO WORK E INTO OUR CWA AS LARGE BLOCKING RIDGE WILL ALSO BE
FORMING OVER THE SOUTHEAST CONUS. CONSENSUS OF MEDIUM RANGE
GUIDANCE SUGGESTS LEAD TROF INITIALLY OVER THE SW U.S. SHOULD LIFT
INTO THE PLAINS WEDNESDAY NIGHT AND CLIP OUR AREA ON
THURSDAY...FOLLOWED BY SEVERAL ADDITIONAL SHORTWAVES ROTATING
AROUND THE UPPER LOW. THROUGHOUT THE PERIOD...IT APPEARS THAT MAIN
DYNAMICS WILL STRETCH FROM PLAINS INTO UPPER MISSISSIPPI
VALLEY...SUGGESTING THAT MAIN THUNDERSTORM THREAT WILL BE OVER W/N
SECTIONS OF OUR FA...WITH THE STORMS STRUGGLING TO WORK INTO SE MO
AND S IL.

SINCE REGION WILL BE WELL ENTRENCHED IN THE WARM SECTOR...
TEMPERATURES SHOULD BE ABOVE AVERAGE WITH DAYTIME HIGHS PRIMARILY IN
THE 80S.

TRUETT

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1142 PM CDT SAT MAY 25 2013

THUNDERSTORMS CONTINUE TO BE THE PRIMARY FOCUS FOR THIS CYCLE. NOW
WATCHING SOME LIGHT SHOWERS DEVELOP ACROSS WEST CENTRAL ILLINOIS
STRETCHING SOUTHEAST INTO PARTS OF SOUTH CENTRAL ILLINOIS. EXPECT
THIS DEVELOPMENT TO CONTINUE AND BUILD SOUTHWARD OVERNIGHT. SHORT
RANGE MODEL GUIDANCE NEVER REALLY DEVELOPS ANYTHING PARTICULARLY
HEAVY OR ORGANIZED...SO HAVE NOT REALLY CHANGED THE VCTS FORECAST
IN MOST OF THE TAFS. EXPECT VFR FLIGHT CONDITIONS TO PREVAIL
OUTSIDE OF ANY SHOWERS OR STORMS.

GUIDANCE IS PRETTY INSISTENT THAT THERE WILL BE ANOTHER ROUND OF
THUNDERSTORMS ON SUNDAY AFTERNOON/EVENING. NOT SURE HOW STRONG
THIS ROUND OF STORMS WILL BE. SOME MODELS SUGGEST ONLY SCATTERED
AFTERNOON THUNDERSTORMS...WHILE OTHER MODELS HAVE WIDESPREAD
STORMS WITH HEAVY RAIN AND POSSIBLY STRONG WIND GUSTS. IF THE
SECOND SCENARIO IS MORE ACCURATE...THUNDERSTORMS WILL LAST WELL
INTO THE EVENING...POTENTIALLY PAST 06Z SUNDAY NIGHT.

SPECIFICS FOR KSTL...

THUNDERSTORMS CONTINUE TO BE THE PRIMARY FOCUS FOR THIS CYCLE.
EXPECT LIGHT SHOWERS NOW DEVELOPING OVER WEST CENTRAL INTO SOUTH
CENTRAL ILLINOIS TO BECOME MORE WIDESPREAD. SHORT RANGE MODEL
GUIDANCE NEVER REALLY DEVELOPS ANYTHING PARTICULARLY HEAVY OR
ORGANIZED...SO HAVE NOT REALLY CHANGED THE VCTS FORECAST. EXPECT
VFR FLIGHT CONDITIONS TO PREVAIL OUTSIDE OF ANY SHOWERS OR
STORMS.

GUIDANCE IS PRETTY INSISTENT THAT THERE WILL BE ANOTHER ROUND OF
THUNDERSTORMS ON SUNDAY AFTERNOON/EVENING. NOT SURE HOW STRONG
THIS ROUND OF STORMS WILL BE. SOME MODELS SUGGEST ONLY SCATTERED
AFTERNOON THUNDERSTORMS...WHILE OTHER MODELS HAVE WIDESPREAD
STORMS WITH HEAVY RAIN AND POSSIBLY STRONG WIND GUSTS. IF THE
SECOND SCENARIO IS MORE ACCURATE...THUNDERSTORMS WILL LAST WELL
INTO THE EVENING...POTENTIALLY PAST 06Z SUNDAY NIGHT.

CARNEY

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$

WFO LSX