Severe Thunderstorm Warning 294, NWS Kansas City, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
638 PM CDT FRI SEP 10 2010

...UPDATED AVIATION DISCUSSION...

.MESOSCALE DISCUSSION...
/554 PM CDT FRI SEP 10 2010/
CONVECTION MOVING OUT OF WEST CENTRAL MO REMAINS ELEVATED AND HAS
NOT BEEN ABLE TO ROOT INTO THE BOUNDARY LAYER. WILL CONTINUE TO
MONITOR THIS ACTIVITY AS IT MOVES INTO CENTRAL MO. HOWEVER...PRIMARY
ATTENTION IS NOW BEING FOCUSED TO THE WEST OVER NORTHEAST AND EAST
CENTRAL KS. A COLD FRONT EXTENDING FROM A SURFACE LOW NR KMHK
THROUGH NORTH CENTRAL KS IS TRACKING EAST INTO EASTERN KS WHILE A
WARM FRONT EXTENDS ESE FROM THE LOW THROUGH SOUTHERN KANSAS CITY TO
BETWEEN SEDALIA AND CLINTON. THE WARM FRONT WILL LIKELY HOLD IN
PLACE WITH THE SURFACE LOW SLIDING ESE ALONG THIS BOUNDARY PER THE
21Z RUC. THE AIRMASS WITHIN THE WARM SECTOR HAS BECOME INCREASINGLY
UNSTABLE WITH MUCAPES NOW IN THE 3500-4000 J/KG RANGE. 0-6KM BULK
SHEAR IS CURRENTLY BETWEEN 30-40KTS OVER NORTHEAST KS AND IS PROGGED
TO INCREASE TO 40KTS INTO EAST CENTRAL KS. THE CUMULUS FIELD WITH
THE WARM SECTOR HAS THICKENED OVER THE PAST 2 HOURS WITH A FEW
TOWERS GOING UP ALONG THE COLD FRONT. EXPECT TO SEE STRONG TO SEVERE
THUNDERSTORMS FORM ALONG THE COLD FRONT OVER THE NEXT 1-2 HOURS.

INSPECTION OF THE LATEST KEAX HODOGRAPH SHOWS A FAVORABLE CW
ROTATION WITHIN THE LOWEST 3 KM. THE 0-3KM SRH IS AROUND 400 M2/S2
FAVORING ROTATING STORMS AND TORNADIC POTENTIAL. PROJECTED STORM
MOTION IS 240/25KTS.

MJ

&&

.PREV DISCUSSION...
/239 PM CDT FRI SEP 10 2010/
SHORT TERM/MESOSCALE (THROUGH THIS EVENING)...

AS NOTED IN 1247 PM UPDATED DISCUSSION...WE ARE WATCHING THE
APPROACHING ACCAS FIELD AND NORTHWARD MOVING WARM FRONT CLOSELY FOR
SURFACE BASED CONVECTION. MESONET DATA INDICATES THE WARM FRONT LIES
NEAR A KMHK...LOUISBURG KS...CLINTON LINE. STABILITY PARAMETERS
INDICATE A VERY TIGHT BAROCLINIC ZONE INVOF THE WARM FRONT WITH
MODERATE TO HIGH INSTABILITY WITH SURFACE BASED LIS FROM -6 TO -10.
WHILE THE 0-6KM SHEAR OF 20-25KTS IS MARGINAL FOR SEVERE STORMS
CLOSER INSPECTION OF THE LOWER LEVELS IS MORE IMPRESSIVE. 12Z NAM
HODOGRAPH SHOWS A VERY FAVORABLE CW TURNING PROFILE BELOW 1.7 KM.
LATEST RUC RUN PROGS 0-1KM BULK SHEAR AROUND 20KTS ALONG THE WARM
FRONT. RUC ALSO FORECASTS ENERGY HELICITY VALUES...EHI...OF 3-5
M2/S2 NEAR THE WARM FRONT AT 21Z. ANYTHING OVER .725 M2/S2 FAVORS
TORNADIC STORMS VS SUPERCELLS. 0-3KM CAPE IN THE 100-150 J/KG AND
LCL HEIGHTS AROUND 1700 FT ALSO SUPPORT TORNADO POTENTIAL. THE
FREEZING LEVEL REMAINS RATHER HIGH AT AROUND 15K FT AGL REQUIRING
50DBZ ECHOES TO 40-42KT TO PRODUCE 1 INCH HAIL. PER PROGGED
SOUNDINGS WITHIN THE WARM SECTOR SURFACE TEMPERATURES NEED TO BE
AROUND 87F FOR BOUNDARY LAYER BASED CONVECTION. CURRENTLY
TEMPERATURES JUST SOUTH OF THE WARM FRONT ARE JUST ABOUT THERE.

INITIAL STORM MOTION WILL BE AROUND 260/15KTS WHICH WOULD ENHANCE
HEAVY RAIN POTENTIAL WITH ANY ORGANIZED CLUSTERS.

AS NOTED BELOW VIRGA FROM THE APPROACHING ACCAS FIELD COULD COOL OFF
THE ELEVATED MIXED LAYER FASTER THAN THE MODELS PREDICT AND ALLOW
FOR SURFACE BASED STORMS TO FORM BY MID AFTERNOON. RADAR ECHOES OVER
EAST CENTRAL KS ARE VERY NEAR THE WARM FRONT...BUT STILL
ELEVATED...AND WE ARE WATCHING THESE ECHOES CLOSELY FOR ANY SIGNS OF
BECOMING ROOTED WITH THE LOWER LEVEL BOUNDARY LAYER.

MJ

SHORT TERM (THROUGH SATURDAY NIGHT)...

LATER THIS EVENING AND THROUGH THE OVERNIGHT HOURS...SFC FRONT
STRETCHING FROM SE SD SE THROUGH CENTRAL KANSAS WILL BECOME A BIGGER
PLAYER. ONCE STRONGER COOLING ARRIVES FROM NORTHERN ROCKIES UPR
TROUGH THIS FRONT SHOULD SHOW RENEWED CONVECTION...WITH THIS
CONVECTION LIKELY TAKING A LINEAR FORM AS IT MOVES THROUGH. FEEL THAT
THIS FRONT MAY PUSH SE A LITTLE SLOWER THAN GFS/EC INDICATE AND WILL
CONTINUE TO HOLD POPS A LITTLE HIGHER IN THE SE AFTER MIDNIGHT. THE
HEAVY RAIN THREAT WILL CONTINUE AS THE FRONT MOVES THROUGH...LIKELY
ENDING IN MOST AREAS BY MIDNIGHT AS ANY TSRA LINE WOULD BE
PROGRESSIVE.  THE POST FRONTAL ENVIRONMENT SHOULD FEATURE A BIT OF A
LAG IN COOLER TEMPS ALONG WITH A LINEAR BAND OF STRATUS...CLOUDS
SHOULD CLEAR BY SAT MORNING.

SATURDAY IS EXPECTED TO BE A PERFECT SEPTEMBER DAY AS SFC HIGH
PRESSURE SURGES IN FROM THE NORTHWEST. LOW HUMIDITY AND A MOSTLY
SUNNY SKY SHOULD ALLOW TEMPS TO CLIMB INTO THE UPR 70S TO LOWER 80S.
A COOL NIGHT WILL BE ON TAP FOR SAT NIGHT AS THE CENTER OF THE SFC
HIGH DRIFTS OVERHEAD. OVERNIGHT LOWS SHOULD FALL INTO THE LOWER TO
MIDDLE 50S IN MOST AREAS...WITH THE TYPICAL LOW SPOTS DROPPING A
DEGREE OR TWO COOLER GIVEN DECENT RADIATIONAL COOLING.

DUX

MEDIUM RANGE (SUNDAY THROUGH FRIDAY)...

CONSIDERABLE UNCERTAINTY THROUGHOUT THE MEDIUM RANGE PERIOD
REGARDING SPECIFIC SENSIBLE WEATHER FEATURES...DESPITE CONTINUED
GOOD AGREEMENT AMONG MODELS FEATURING SEVERAL LOW AMPLITUDE WAVES
PROGRESSING THROUGH FAST WNWLY FLOW ALOFT. TRANQUIL WEATHER DURING
THE FIRST PARTS OF THIS PERIOD WILL GRADUALLY BECOME MORE UNSETTLED
AS HIGHER THETA-E AIRMASS IS ADVECTED NORTHEAST ON THE WRN PERIPHERY
OF A SPRAWLING SFC HIGH PRESSURE SYSTEM EXTENDING FROM THE GREAT
LAKES THROUGH THE MIDDLE OHIO RIVER VALLEY. AS A RESULT...HAVE
INCREASED POPS TO CHANCE CATEGORY FOR SEVERAL PERIODS IN THE
TUESDAY-THURSDAY TIME FRAME...EXPECTING THE COMBINATION HIGHER
MOISTURE INTERACTING WITH DEEPER DYNAMIC AND ISENTROPIC LIFT TO
PERIODICALLY FORCE DEEP CONVECTION AT TIMES. WHILE NOT EXPECTING
RAINFALL THROUGH THE ENTIRE MIDWEEK PERIOD...CERTAINLY SEVERAL
CHANCES FOR SHOWERS AND THUNDERSTORMS ARE SUPPORTED BY BOTH
OPERATIONAL AND ENSEMBLE MEMBERS. BETTER CHANCES FOR DRIER AND MORE
TEMPERATE WEATHER APPEARS MORE LIKELY AT THE END OF THE
PERIOD...THOUGH UNCERTAINTY IS QUITE LARGE FOR THE AFOREMENTIONED
REASONS REGARDING FAST FLOW ALOFT. WITH SEVERAL CHANCES OF RAINFALL
AND ASSUMING EXTENSIVE CLOUD COVER THROUGH THE MAJORITY OF THE
PERIOD...HAVE HEDGED TEMPERATURES BETWEEN THE WARMEST ENSEMBLE
MEMBER (IN MOST CASES THE OPERATIONAL MEX GUIDANCE) AND THE ENSEMBLE
MEAN.

21

&&

.AVIATION...

FOR THE 00Z TAFS...WARM FRONT WILL BE NEAR THE KANSAS CITY SITES
EARLY THIS EVENING AND SHOULD BE ONE FOCUS FOR THUNDERSTORM
DEVELOPMENT...WITH SURFACE WAVE CURRENTLY NORTH OF WICHITA EXPECTED
TO SLIDE EAST TO NEAR THE STATE LINE BY 03Z. THUS LOOKING LIKE THE
MAIN TIME FRAME FOR STORMS IN THE KANSAS CITY AREA WILL BE THROUGH
ABOUT 04Z ONCE THE INVERTED SURFACE TROUGH EXTENDING NORTH FROM THE
SURFACE WAVE MOVES EAST OF THE REGION. COLD FRONT MAY NOT ARRIVE
UNTIL AFTER MIDNIGHT...SO WILL KEEP THE VARIABLE WIND GROUP THAT
PREVIOUS TERMINALS HAD TO INDICATE THE DIFFERENCE BETWEEN THE
SURFACE TROUGH AND THE COLD FRONT. FOR THE KSTJ SITE...IT WILL
REMAIN WELL NORTH OF THE WARM FRONT...BUT MAY STILL SEE CONVECTION
WITH THE INVERTED SURFACE TROUGH THROUGH MID EVENING. INSTABILITY
NOT AT GOOD IN THAT REGION...SO WILL BACK DOWN ON THUNDERSTORM
INTENSITY AND THE WIND POTENTIAL AT THAT SITE.

EXPECT WILL HAVE TO AMEND SOME AS STORMS BECOME MORE ORGANIZED AND
TIMING CAN BE BETTER DETERMINED.

LOOKING FOR A PERIOD OF FOG AND LOW CLOUDS IN THE POST FRONTAL ZONE
LATER TONIGHT...CLEARING PRETTY QUICKLY IN THE MORNING AS THE WINDS
PICK UP.

PC

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...FLASH FLOOD WATCH THROUGH SATURDAY MORNING FOR MOZ039-044>046-
     053-054.

     FLASH FLOOD WATCH UNTIL 1 AM CDT SATURDAY FOR
     MOZ028-029-037-038-043.

KS...FLASH FLOOD WATCH THROUGH SATURDAY MORNING FOR KSZ060.

     FLASH FLOOD WATCH UNTIL 1 AM CDT SATURDAY FOR
     KSZ025-057-103>105.

&&

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