Severe Thunderstorm Warning 157, NWS Kansas City, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
724 PM CDT FRI JUN 18 2010

.UPDATE...

EVENING ADJUSTMENT TO THE FORECAST...MOSTLY TO TRIM POP COVERAGE FOR
THE FIRST SIX HOURS...AND LIMIT POPS TO LESS THAN 40% AFTER MIDNIGHT.
EVENING ACTIVITY NEAR THE IOWA BORDER IS NOT HAVING ANY SUCCESS
CONGEALING INTO A LINER SYSTEM THAT WILL PUSH SOUTH DEEPER INTO
MISSOURI. LACK OF LOW LEVEL CONVERGENCE...OR ANY SEMBLANCE OF A
SHORTWAVE ALOFT...SEEMS TO HAVE LIMITED THE STORMS TO MOSTLY BEING
NORTH OF THE MISSOURI BORDER...WERE THE CAP IS A LITTLE WEAKER AND
SHEAR IS BETTER. LATE TONIGHT STORM ACTIVITY MIGHT GET GOING BACK
AGAIN IN THE WARM AIR ADVECTION ZONE...WHERE THE NOSE OF THE LOW
LEVEL JET AND LINGERING COLD FRONT INTERSECT IN NORTH CENTRAL
KANSAS/SOUTH CENTRAL NEBRASKA. IF THAT CONVECTION GETS GOING...
THOUGHTS ARE IT WOULD MOVE EAST DURING THE MORNING HOURS OF SATURDAY.
SO HAVE KEPT CHANCE POPS THROUGH THE EARLY MORNING HOURS FOR NOW.

CUTTER

&&

.DISCUSSION...

/411 PM CDT FRI JUN 18 2010/

SHORT TERM (TONIGHT THROUGH SATURDAY)...

EARLY MORNING CONVECTIVE COMPLEX...THAT MOVED EAST THROUGH IOWA
TODAY...PUT OUT A NICE BOUNDARY ACROSS THE FAR NORTHERN REACHES OF
MISSOURI THIS MORNING. HOWEVER...CONTINUED DEEP LAYER SOUTHERLY WINDS
AHEAD OF A COLD FRONT...CURRENTLY RESIDING JUST OFF THE FAR NORTHWEST
TIP OF MISSOURI FROM SOUTHWEST TO NORTHEAST...HAS PUSHED THAT
BOUNDARY UP INTO IOWA. VISIBLE SATELLITE IMAGERY INDICATES THAT THE
OUTFLOW BOUNDARY NOW TAILS BACK...AND IS INTERSECTING THE
FRONT...SOMEWHERE JUST TO THE SOUTH OF OMAHA. AGITATED CUMULUS CLOUDS
ACROSS SOUTHEAST NEBRASKA INDICATE THAT THE VERY WARM AND MOIST AIR
IN THE WARM SECTOR IS TRYING TO BREAK WHAT LITTLE CAP WAS SHOWN TO BE
IN PLACE BY THE 18Z SOUNDINGS FROM TOPEKA AND OMAHA. GIVEN LATEST RUC
ANALYSIS FROM SPC...MLCAPE VALUES ARE TIPPING THE SCALES AT AROUND
4000 J/KG. AFTERNOON WATER VAPOR IMAGERY SHOWS A RATHER LARGE FETCH
OF DRY AIR ALOFT ADVECTING INTO THE LOWER MISSOURI RIVER VALLEY
THANKS TO THE PERSISTENT SOUTHWEST FLOW AND DRY DESERT SOUTHWEST.

MODEL PREFERENCE IS NON-EXISTENT AS ALL THE MODELS HAVE BEEN HAVING
A DIFFICULT TIME PINNING DOWN ANY OF THE CONVECTIVE DETAILS OVER
RECENT DAYS. THEREFORE...FORECAST METHODOLOGY FOR TODAY THROUGH SATURDAY
IS BASED ON WHERE THE BOUNDARIES ARE...AND ARE EXPECTED TO BE...AND
GENERAL SYNOPTIC FEATURES. THIS RESULTS IN A RATHER LOW CONFIDENCE
FORECAST AFTER ABOUT THE FIRST 6 HOURS.

FOR THE REMAINDER OF THE AFTERNOON AND INTO THE EARLY
EVENING...CONVECTION MIGHT START FIRING IN SOUTHEAST NEBRASKA NEAR
THE INTERSECTION OF THE FRONT AND OLD OUTFLOW BOUNDARY. WITH AMPLE
INSTABILITY TO TAP...THUNDERSTORMS SHOULD BE ABLE TO RAMP UP TO
SEVERE LEVELS RATHER QUICKLY...WITH SUFFICIENT SHEAR NORTH OF THE IOWA
BORDER TO ALREADY JUSTIFY A TORNADO WATCH...NORTH OF OUR FORECAST
AREA. BIG ISSUES WITH THIS IDEA THOUGH IS THE LACK OF GOOD LOW LEVEL
CONVERGENCE...AS SURFACE WINDS AND LOW LEVEL SHEAR ARE RATHER WEAK
GIVEN FLOW AROUND A WEAK SURFACE LOW IN NORTHEAST KANSAS/ SOUTHEAST
NEBRASKA...AND NO INITIATING UPPER LEVEL SHORTWAVE TO BE SEEN ON WATER
VAPOR. SO...WHILE ITS NOT A SURE THING...HAVE STILL LEANED THE
FORECAST TOWARDS EXPECTATION OF A LINE OF THUNDERSTORMS MOVING INTO
THE NORTHWEST CORNER FROM NEBRASKA...AND SPREADING EAST AND SOUTH
AFTER 00Z TONIGHT. EXPECT ANY STORMS THAT DEVELOP TO HAVE A HARD
TIME LASTING...OR MAKING IT...SOUTH OF THE MISSOURI RIVER AS SHEAR
SOUTH OF THE IOWA BORDER IS VERY POOR...AND AN EML SHOULD CAP THIS
REGION OFF. ANY STORMS THAT DO MAKE IT INTO OUR FORECAST AREA SHOULD
BE ACCOMPANIED BY A THREAT OF DAMAGING WINDS...GIVEN DRY AIR
ALOFT...AND HEAVY RAIN AS PRECIPITABLE WATER VALUES ARE ABOVE 1.5
INCHES.

FOR SATURDAY...IF ANYTHING CAN GET GOING TONIGHT...THERE MIGHT BE
LINGERING ACTIVITY ACROSS THE REGION DURING THE MORNING HOURS OF
SATURDAY. HOWEVER...THE CHANCE POPS ACROSS THE AREA FOR SATURDAY ARE
MOSTLY BASED ON THE IDEA OF ANY RESIDUAL OUTFLOW BOUNDARY THAT
MIGHT HAVE SETTLED ACROSS THE REGION OVERNIGHT THANKS TO ANY
CONVECTION OR THE FRONT. ANOTHER HOT AND HUMID DAY WILL PREVAIL
SATURDAY PROVIDING PLENTY OF FUEL FOR THUNDERSTORMS IF THEY CAN GET
GOING.

CUTTER

MEDIUM RANGE (SUNDAY THROUGH FRIDAY)...

BY SUN MORNING...AN AREA OF LOW PRESSURE WILL STILL BE SITUATED OVER
WESTERN KS...WITH A WARM FRONT EXTENDING EASTWARD OVER THE IA/MO
BORDER. CAN EXPECT PRECIP TO FORM NORTH OF THIS BOUNDARY THROUGH THE
EVENING HOURS. STILL SOME UNCERTAINTY REGARDING THE LOCATION OF THIS
FRONT. GFS AND NAM PUTTING THE FRONT OVER SOUTHERN IA...WHILE THE
ECMWF AND GEM SHOW THE FRONT SAGGING FURTHER SOUTHWARD OVER NORTHERN
MO. IF THE PATTERN PANS OUT LIKE THE ECMWF/GEM...COULD SEE SOME
SCATTERED PRECIP MOVING ACROSS EXTREME NORTHERN MO...AND THE PRECIP
COULD LINGER INTO MON. THIS PATTERN WILL REMAIN FAIRLY CONSISTENT
THROUGH TUES...BEFORE A MORE ZONAL-LIKE FLOW SETS UP WITH A WEAK
RIDGE DEVELOPING OVER THE CENTRAL CONUS. FOR THE REMAINDER OF THE
EXTENDED...MODELS ARE PICKING UP ON A FEW WAVES OVER THE NORTHERN
AND CENTRAL PLAINS...WITH SOME POTENTIALLY CLIPPING THE NORTHERN
CWA. HOWEVER...BETWEEN THE UNCERTAINTY AMONGST THE MODELS AND THE
INCONSISTENCY BETWEEN CONSECUTIVE MODEL RUNS...HAVE KEPT POPS AT
ONLY SLIGHT CHANCES FOR EXTREME NORTHERN MO DURING THE LATTER HALF
OF THE PERIOD.

TEMPERATURES WILL BE A MAIN FOCUS FOR THE EXTENDED PERIOD.
CURRENTLY EXPECTING TEMPS TO REACH INTO THE UPPER 80S AND LOW/MID
90S FOR MUCH OF THE WEEK...WITH HEAT INDICES NEAR 100 DEGREES
POSSIBLE FOR THE SOUTHERN HALF OF THE CWA.

ACH

&&

.AVIATION...

FOR THE 00Z TAFS...EARLIER THOUGHTS ON CONVECTIVE INITIATION IN
SOUTHEAST NEBRASKA DID NOT WORK OUT SO WELL. INITIATION IS GOING ON A
TOUCH FARTHER EAST...AND AS A RESULT CONVECTION IS NO LONGER EXPECTED
TO REACH THE KANSAS CITY TERMINALS OVERNIGHT. HAVE LEFT VICINITY
THUNDER IN THE KSTJ TERMINAL FARTHER NORTH...BUT EVEN THAT ACTIVITY
LOOKS LIKE IT WILL SHIFT EAST QUICKLY THIS EVENING. OTHERWISE...
WITHOUT THE CONVECTION TO PUSH A SURFACE BOUNDARY SOUTH HAVE STEERED
WINDS BACK TO A PREVAILING SOUTHERLY DIRECTION OVERNIGHT WITH
SOUTHEAST WINDS DURING THE DAY SATURDAY. DO HAVE SOME THOUGHTS THAT
CONVECTION MIGHT TRY TO DEVELOP ACROSS THE TERMINALS TOMORROW IN THE
HEAT OF THE AFTERNOON...BUT AT THIS TIME BELIEVE WE HAVE NO SKILL IN
ACTUALLY FORECASTING THAT...SO WILL LEAVE FORECAST DRY FOR NOW.

CUTTER

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&

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