Special Weather Statement, NWS St. Louis, MO

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1155 AM CDT SAT JUL 11 2015

.SHORT TERM:  (THROUGH LATE THIS AFTERNOON)
ISSUED AT 330 AM CDT SAT JUL 11 2015

CLUSTER OF ELEVATED THUNDERSTORMS EXTENDING FROM SOUTHEAST IA INTO
NORTH CENTRAL MO ARE OCCURING IN ASSOCIATION WITH GOOD MOISTURE
CONVERGENCE ASSOCIATED WITH THE SOUTHWESTERLY LLJ. BOTH THE
DETERMINISTIC AND CAMS ARE IN RELATIVELY GOOD AGREEMENT SPREADING
THIS ACTIVITY EASTWARD THIS MORNING IN CONJUCTION WITH THE STEERING
FLOW ALOFT AND GRADUALLY VEERING LLJ. THERE IS SOME QUESTION ON
THE SOUTHERN EXTENT OF ANY STORM POTENTIAL. GIVEN THE CURRENT MID
CLOUD EXTENT AND VEERING LLJ, I THINK THE POTENTIAL FOR ISOLATED-
WIDELY SCATTERED STORMS EXISTS THIS MORNING AT LEAST DOWN TO THE
I-70 CORRIDOR WHICH IS JUST NORTH OF THE LIFTING WARM FRONT. IN
THE WAKE OF THE CLOUDS, CONVECTION AND LIFTING WARM FRONT, WARMING
LOW AND MID LEVELS SHOULD RESULT IN MUCH WARMER TEMPERATURES TODAY
AND MORE SEASONABLE FOR THIS TIME IN JULY.

GLASS

.LONG TERM:  (TONIGHT THROUGH FRIDAY)
ISSUED AT 330 AM CDT SAT JUL 11 2015

THERE ARE LOTS OF QUESTIONS AND FORECAST CAVEATS TONIGHT INTO
TUESDAY. THE GENERAL PATTERN OF AN EXPANSIVE UPPER HIGH ANCHORED
ACROSS THE SOUTHERN PLAINS AND OUR LOCATION ON THE PERIPHERAL
NORTHWEST FLOW ALOFT POINTS TO BOTH BIG HEAT AND HUMIDITY AND
POTENTIAL THUNDERSTORM CHANCES. TO THIS END THE MODELS ARE QUITE
VARIED ON THE STRENGTH OF LOW-MID LEVEL WARMING AND EASTERN EDGE
OF THE STRONGER CAPPING AND PLACEMENT OF QPF. THE ECMWF SEEMS MOST
AGRESSIVE WITH THE EXTENT OF QPF INTO OUR CWA DURING MOST OF THE
FORECAST PERIODS. THE GENERAL THOUGHT IS THIS THAT THE VEERING
SOUTHWESTERLY LLJ AND ONLY MODERATELY WARM MID LEVEL TEMPS
TONIGHT ARE SUFFICIENT TO MERIT THUNDERSTORM CHANCES TONIGHT INTO
EARLY SUNDAY MORNING ACROSS PRIMARILY NORTHERN MO INTO CENTRAL IL.
BY SUNDAY AFTERNOON, STRONG WARMING IN THE LOW-MID LEVELS SHOULD
RESULT IN A FORMIDABLE CAP TO SURFACE BASED CONVECTION. A
RELATIVELY HOT AFTERNOON IS ON TAP WITH HIGHS IN THE 90S AND
AFTERNOON HEAT INDICES OF 100-103. THESE HI VALUES ARE LARGELY
BASED ON THE BELIEF THE MODELS ARE A BIT AGRESSIVE IN THE
MAGNITUDE OF THE SURFACE DEW POINTS. IF THE TDS ARE HIGHER THEN
WE MIGHT HAVE SOME 105 HIS. SUNDAY NIGHT INTO EARLY MONDAY A SHORT
WAVE TROF DIGGING FROM THE UPPER MS INTO THE LOWER GREAT LAKES
SHOULD LEAD TO HEIGHT FALLS ALOFT AND COOLING AND WESTWARD RETREAT
OF THE EDGE OF CAPPING, ALLOWING FOR A THREAT OF THUNDERSTORMS
PRIMARILY FOCUSED FROM FAR EASTERN MO INTO IL. THIS COULD BE A
COMBINATION OF SOUTHEAST MOVING CONVECTIVE COMPLEXES/CLUSTERS AND
NEW DEVELOPMENT.

MONDAY LOOKS TO BE THE HOTTEST DAY OVER THE NEXT 3 WITH CONTINUED
WARMING OF THE LOW-MID LEVELS - H85 TEMPS AOA +24 DEGC AND H7
TEMPS OF +12 TO +14 DEGC BY 00Z TUES. THIS LOOKS LIKE A DAY THAT
A HEAT ADVISORY WILL PROBABLY BE NEEDED PROVIDED THE OVERNIGHT
CONVECTION FROM SUNDAY SOMEHOW DOESN'T HAMPER IT. HEAT INDICES IN
MANY LOCATIONS SHOULD BE 105+. I DON'T ANTICIPATE MUCH CONVECTION
BEYOND THE MORNING RESIDUAL AND THE AFTERNOON CAP SHOULD BECOME
STOUT. MONDAY NIGHT HOWEVER IT APPEARS THAT A SIGNIFICANT SEVERE
WEATHER EVENT COULD DEVELOP WITH ANOTHER SHORT WAVE TROF DIGGING
FROM THE UPPER MS VALLEY INTO THE LOWER GREAT LAKES AND OH VALLEY
PROVIDING FORCING AND WEAKENING THE CAP. STRONG INSTABILITY WILL
BE IN PLACE AND DEEP LAYER SHEAR IS RATHER STOUT AT 35-40 KTS. ALL
THE PARAMETERS ARE SUGGESTIVE OF A POTENTIAL DERECHO SWEEPING FROM
EASTERN IA/NORTHWEST IL SOUTHEASTWARD AND IMPACTING FAR EASTERN MO
INTO IL.

A FRONTAL BOUNDARY FINALLY SINKS INTO THE AREA TUESDAY AND THEN
WAVERS NORTH AND SOUTH DURING THE WEEK RESULTING IN PROLONGED
THUNDERSTORM CHANCES IN THE VICINITY OF THE BOUNDARY AND
SEASONABLY HOT TEMPERATURES TO THE SOUTH OF IT.

GLASS

&&

.AVIATION:  (FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1120 AM CDT SAT JUL 11 2015

A WARM FRONT EXTENDS FROM NEAR IRK SOUTHEAST THROUGH THE ST LOUIS
METRO AREA. CONVECTION WILL CONTINUE TO DEVELOP ALONG AND NORTH OF
THIS FRONT THIS AFTERNOON AND TONIGHT IMPACTING UIN AT TIMES. IT
IS ALSO POSSIBLE THAT CONVECTION WILL MAKE IT AS FAR SOUTH AS THE
ST LOUIS METRO AREA. FOR NOW WILL JUST INCLUDE VCTS IN UIN OR A
TEMPO GROUP FOR TSRA AND LEAVE THE OTHER TAFS DRY. THIS FRONT
SHOULD SHIFT NORTH NORTHEAST OF THE AREA SUNDAY MORNING.
PREVAILING VFR CONDITIONS EXPECTED THROUGH THE PERIOD OUTSIDE OF
THE SHOWERS/STORMS. MAINLY S-SWLY SURFACE WINDS THIS PERIOD.

SPECIFICS FOR KSTL: COULD NOT RULE OUT CONVECTION MAKING IT AS
FAR SOUTH AS STL TONIGHT, BUT FOR NOW WILL KEEP THE STL TAF VFR
AND DRY THROUGH THE PERIOD WITH JUST SCATTERED DIURNAL CUMULUS
CLOUDS ALONG WITH SOME MID-HIGH LEVEL CLOUDINESS. SELY SURFACE
WIND WILL VEER AROUND TO A S-SWLY DIRECTION THIS AFTERNOON, THEN
BECOME MORE DUE SWLY LATE TONIGHT.

GKS

&&

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

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
147 PM CDT SAT JUL 11 2015

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-121200-
GREENE IL-MACOUPIN IL-MONTGOMERY IL-BOND IL-FAYETTE IL-CLINTON IL-
MARION IL-WASHINGTON IL-RANDOLPH IL-ADAMS IL-BROWN IL-PIKE IL-
CALHOUN IL-JERSEY IL-MADISON IL-ST. CLAIR IL-MONROE IL-KNOX MO-
LEWIS MO-SHELBY MO-MARION MO-MONROE MO-RALLS MO-PIKE MO-BOONE MO-
AUDRAIN MO-MONITEAU MO-COLE MO-OSAGE MO-CALLAWAY MO-MONTGOMERY MO-
LINCOLN MO-GASCONADE MO-WARREN MO-ST. CHARLES MO-FRANKLIN MO-
ST. LOUIS MO-ST. LOUIS CITY MO-JEFFERSON MO-CRAWFORD MO-
WASHINGTON MO-ST. FRANCOIS MO-STE. GENEVIEVE MO-IRON MO-
MADISON MO-REYNOLDS MO-
147 PM CDT SAT JUL 11 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN AND
CENTRAL MISSOURI AS WELL AS WEST CENTRAL AND SOUTHWEST ILLINOIS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A CHANCE FOR THUNDERSTORMS...PRIMARILY IN SOUTHWESTERN
ILLINOIS...EAST OF THE MISSISSIPPI RIVER. SEVERE STORMS WILL ALSO
BE POSSIBLE FOR SECTIONS OF SOUTHWEST ILLINOIS. FOR FURTHER
INFORMATION ON CONVECTIVE WATCHES...PLEASE REFER TO THE LATEST
STORM PREDICTION CENTER WATCH PRODUCTS.

MAJOR FLOODING WILL CONTINUE ON ALL POINTS ALONG THE ILLINOIS
RIVER FROM LA GRANGE TO THE CONFLUENCE OF THE MISSISSIPPI RIVER.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THERE IS A CHANCE FOR THUNDERSTORMS FOR MUCH OF THE AREA SUNDAY
THROUGH MONDAY NIGHT. SOME OF THE STORMS MAY BE SEVERE ACROSS
EASTERN MISSOURI AND WESTERN ILLINOIS ON SUNDAY NIGHT AND AGAIN
MONDAY AFTERNOON AND MONDAY NIGHT.

THE CHANCE FOR THUNDERSTORMS WILL CONTINUE FOR MUCH OF THE AREA
TUESDAY THROUGH FRIDAY.

HEAT INDICES MAY REACH DANGEROUS LEVELS OF 105 DEGREES AND
GREATER ON MONDAY AFTERNOON.

MAJOR FLOODING WILL CONTINUE ALONG THE ILLINOIS RIVER INTO EARLY
NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE ACROSS SECTIONS OF SOUTHWESTERN
ILLINOIS THROUGH EARLY THIS EVENING.

TES

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
1247 PM CDT SAT JUL 11 2015

ILZ095-096-111830-
BROWN IL-ADAMS IL-
1247 PM CDT SAT JUL 11 2015

...SIGNIFICANT WEATHER ADVISORY FOR ADAMS AND BROWN COUNTIES UNTIL
130 PM CDT...

AT 1246 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM
NEAR MENDON...MOVING EAST AT 35 MPH.

DIME SIZE HAIL AND WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH THIS
STORM.

LOCATIONS IMPACTED INCLUDE...
QUINCY...MOUNT STERLING...CAMP POINT...MENDON...CLAYTON...GOLDEN...
BUCKHORN...URSA...LIBERTY...VERSAILLES...LORAINE...WOODVILLE...
COATSBURG...MOUND STATION...COLUMBUS...RIPLEY...LA PRAIRIE...
KELLERVILLE...FOWLER AND CHATTON.

THIS INCLUDES INTERSTATE 172 BETWEEN EXITS 14 AND 19.

THIS WARNING ALSO INCLUDES SILOAM SPRINGS STATE PARK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD
TO FLASH FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

&&

LAT...LON 4019 9091 4011 9091 4010 9070 4009 9070
      4008 9067 4005 9068 4003 9061 3990 9056
      3988 9058 3985 9058 3992 9142 3995 9144
      4014 9143 4020 9128
TIME...MOT...LOC 1746Z 268DEG 30KT 4002 9134

GKS

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
208 PM CDT SAT JUL 11 2015

ILZ096-097-112000-
BROWN IL-PIKE IL-
208 PM CDT SAT JUL 11 2015

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN PIKE AND SOUTHERN
BROWN COUNTIES IN WEST CENTRAL ILLINOIS UNTIL 300 PM CDT...

AT 207 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 7
MILES SOUTH OF BUCKHORN...MOVING EAST AT 35 MPH.

DIME SIZE HAIL AND WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH THIS
STORM.

LOCATIONS IMPACTED INCLUDE...
BUCKHORN...LA GRANGE...VERSAILLES...PERRY...CHAMBERSBURG...FISHHOOK
AND COOPERTOWN.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD
TO FLASH FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

&&

A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 800 PM CDT FOR
WEST CENTRAL ILLINOIS.

LAT...LON 4002 9061 4002 9062 4000 9060 3998 9060
      3998 9051 3997 9051 3995 9053 3992 9054
      3988 9058 3983 9057 3979 9060 3976 9061
      3971 9064 3974 9092 3992 9091 4003 9061
TIME...MOT...LOC 1907Z 272DEG 33KT 3983 9082

GKS