Hail and Damaging Winds in Kansas, August 9, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
317 PM CDT SUN AUG 9 2009

.DISCUSSION...

SHORT TERM (THROUGH MONDAY EVENING)...

MAIN CHALLENGE FOR TONIGHT AND MONDAY IS THUNDERSTORM CHANCES.

SOUTHWEST FLOW CONTINUES ALOFT WITH UPPER TROF OVER THE NORTHERN
ROCKIES AND HIGH TO THE SOUTHEAST. SUBTROPICAL PLUME REMAINS BETWEEN
THESE AREAS OVER WESTERN AND CENTRAL PORTIONS OF KANSAS. AT
12Z...850MB FRONT WAS BISECTING NEBRASKA FROM SOUTHWEST TO NORTHEAST
WITH MOISTURE POOLING ALONG IT. 18Z OBJECTIVE ANALYSIS PUT COLD
FRONT FROM SOUTHEAST NEBRASKA TO SOUTHWEST KANSAS WITH MIDDLE 60 TO
LOWER 70 DEWPOINTS IN THE LOCAL AREA. RECENT PRECIPITATION REMAINS
MOSTLY JUST BEHIND THE SURFACE FRONT IN THE MID/UPPER MOISTURE
PLUME...WITH MORE ISOLATED ACTIVITY NEAR THE BOUNDARY. 18Z UPPER AIR
SOUNDING FROM TOP SHOWS AROUND 100 J/KG OF SURFACE CINH.

EXPECT FRONT TO CONTINUE TO SINK SOUTH AND SOUTHEAST TONIGHT AS THE
NORTHERN UPPER TROF PUSHES EAST ACROSS THE NORTHERN PLAINS.
DEWPOINTS SLOWLY FALLING AS DAYTIME MIXING CONTINUES...AND 18Z
SOUNDING SHOWING SOME COOLING ALOFT...BUT WARMING AROUND 800MB.
SOUTHWEST WINDS AROUND THIS LEVEL BRINGING IN WARMER AIR PER 12Z
DODGE CITY DATA...AND QUESTIONS REMAIN REGARDING SURFACE BASED
CONVECTION. DECENT LOW LEVEL DEWPOINT SPREADS AND FAIRLY
UNIDIRECTIONAL WINDS THROUGH THE TROPOSPHERE WOULD SUGGEST A WIND
THREAT AS WELL AS HAIL. RECENT RUC ANALYSIS AND MODEL FORECASTS SHOW
PRECIPITABLE WATER VALUES HIGHEST IN NORTHERN AREAS...PEAKING AROUND
2 INCHES OVERNIGHT WITH UPPER LEVEL JET CORE TO THE NORTHEAST. AS
THE LOW LEVEL JET VEERS IN RESPONSE TO THE EASTWARD MOVING
WAVE...LOW LEVEL FORCING FOR A FOCUSED PERSISTENT THUNDERSTORM
THREAT IS NOT OBVIOUS...BUT THE ABOVE SUGGEST AT LEAST SOME
POTENTIAL FOR TRAINING CELLS. SHOULD SEE PRECIPITATION CHANCES
SLOWLY DIMINISH AS DAWN APPROACHES AS A RESULT OF THE LLJ
ORIENTATION. SYNOPTIC BOUNDARY WILL LIKELY REMAIN IN THE CENTRAL AND
SOUTHERN COUNTIES MONDAY AND BRING A CONTINUED CHANCE FOR STORMS TO
THE AREA WITH PW VALUES REMAINING AROUND 1.75 INCHES. LITTLE
CONFIDENCE IN JUST WHERE THE BETTER CHANCES WILL BE AT THIS TIME.
HOW MUCH COOLING OCCURS FOR MONDAY IS AS WELL IN QUESTION...BUT WENT
BELOW GUIDANCE GIVEN PRECIP POTENTIAL.

65

LONG TERM (MONDAY NIGHT THROUGH SUNDAY)...

MAIN FORECAST CONCERNS DURING THIS PERIOD INCLUDE POTENTIAL STORM
SYSTEMS MONDAY NIGHT...AND AGAIN BY LATE NEXT WEEKEND.

SHORT WAVE TROUGH ENERGY LOOKS TO AMPLIFY AS SOME PHASING OF
NORTHERN AND SOUTHERN STREAMS OCCURS OVER THE HIGH PLAINS LATE ON
SUNDAY. TROUGH WILL THEN DROP SOUTHEAST ACROSS THE PLAINS BY
MONDAY NIGHT...COUPLING WITH A FAVORABLE ZONE OF JET DIVERGENCE
AND A REMNANT SURFACE FRONTAL BOUNDARY TO DEVELOP ONE OR MORE
CONVECTIVE SYSTEMS. THESE SYSTEMS WILL TRACK ACROSS THE PLAINS AND
INTO THE MISSISSIPPI VALLEY BY TUESDAY. PRECIPITATION WILL LIKELY
BE PROGRESSIVE AND WIDESPREAD WITH BETTER CHANCES ACROSS THE
SOUTHERN TWO THIRDS OF THE CWA. THIS SYSTEM WILL USHER IN SLIGHTLY
COOLER AND DRIER AIR WITH HIGH TEMPS FORECAST TO REMAIN AROUND 90
ON TUESDAY AND WEDNESDAY.

WILL LIKELY SEE A SLIGHT WARMING TREND FROM MID TO LATE WEEK AS
UPPER LEVEL RIDGE BUILDS BACK IN AND 850 TEMPS AGAIN APPROACH 25C
ACROSS WESTERN ZONES. THERE WILL BE A GRADIENT FROM WEST TO EAST
THOUGH AND HAVE KEPT EASTERN ZONES A BIT COOLER. LONG RANGE MODELS
THEN ISSUE ANOTHER LONG WAVE TROUGH THROUGH THE NORTHERN TIER BY
LATE WEEKEND. THIS MAY BRING CHANCES FOR PRECIP BACK INTO THE
FORECAST AS EARLY AS SUNDAY. CONFIDENCE IS RELATIVELY LOW IN JUST
HOW THIS WILL PLAY OUT AT THIS TIME DUE TO CONSIDERABLE MODEL
DIFFERENCES IN THE OVERALL LONG WAVE PATTERN AT 6 DAYS OUT.

BARJENBRUCH

&&

AVIATION...

MAIN CHANGES TO TAFS WERE TO MENTION CONVECTIVE CONCERNS EARLIER.
SCATTERED CONVECTIVE UNDERWAY FROM SOUTHWEST TO CENTRAL
KANSAS...WITH BOUNDARY LIKELY TO PUSH SOUTHEAST THROUGH THE LATE
AFTERNOON. THOUGH BOUNDARY MAY NOT PASS THROUGH THE TERMINALS
UNTIL LATE TONIGHT OR EARLY MONDAY...MAY SEE SOME STORMS MOVE IN
FROM THE SOUTHWEST...AND FORM OFF OF CONVECTIVE OUTFLOWS. NOT
CONFIDENT ENOUGH FOR MORE THAN CB MENTION YET HOWEVER. VEERING LOW
LEVEL WINDS SHOULD BRING AN END TO THE GREATER THREAT BY DAWN
MONDAY.

65

&&

.TOP WATCHES/WARNINGS/ADVISORIES...NONE.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TOPEKA KS
325 PM CDT SUN AUG 9 2009

KSZ008>012-020>024-026-034>040-054>056-058-059-102030-
REPUBLIC-WASHINGTON-MARSHALL-NEMAHA-BROWN-CLOUD-CLAY-RILEY-
POTTAWATOMIE-JACKSON-JEFFERSON-OTTAWA-DICKINSON-GEARY-MORRIS-
WABAUNSEE-SHAWNEE-DOUGLAS-LYON-OSAGE-FRANKLIN-COFFEY-ANDERSON-
325 PM CDT SUN AUG 9 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL...NORTH
CENTRAL AND NORTHEAST KANSAS.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS WILL CONTINUE TO DEVELOP ALONG AND BEHIND
A SLOW MOVING COLD FRONT THIS AFTERNOON AND GRADUALLY PUSH
EAST...GENERALLY ALONG AND NORTH OF INTERSTATE 70...DURING THE
EVENING HOURS. THE STRONGEST THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING LARGE HAIL TO THE SIZE OF HALF DOLLARS AND DAMAGING
WINDS UP TO 60 MPH. HEAVY RAIN WILL ALSO BE POSSIBLE AS
THUNDERSTORMS MAY REPEATEDLY TRACK OVER THE SAME AREAS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

ADDITIONAL STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE FROM
MONDAY INTO MONDAY NIGHT AS THE SLOW MOVING COLD FRONT GRADUALLY
MOVES THROUGH THE AREA. DAMAGING WINDS AND LARGE HAIL WILL BE THE
PRIMARY SEVERE WEATHER THREATS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON INTO TONIGHT.