Severe Thunderstorm Warning 209, NWS Topeka, KS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TOPEKA KS
1204 AM CDT MON AUG 17 2009

.UPDATE...
UPDATED FOR 06Z TAF PACKAGE.

&&

.DISCUSSION...
SEE PREVIOUS DISCUSSION ATTACHED.

&&

.AVIATION...
THUNDERSTORMS ARE PREDOMINANT AVIATION CONCERN THROUGH THE TAF
PERIOD. ONGOING CONVECTION WILL LIKELY CONTINUE TO BE SCATTERED
AND INTERMITTENTLY IMPACT TAF SITES THROUGH 08Z. EXPECT INCREASE
IN TSTORM COVERAGE FROM 09Z ON OUT...AND HAVE KEPT A PREDOMINANT
TS GROUP IN THE TAFS FOR THIS TIME AS A DISTURBANCE COMES OUT OF THE
ROCKIES. CONDITIONS WILL RAPIDLY DETERIORATE WITHIN TSTORMS AS
VERY HEAVY RAIN AND FREQUENT LIGHTNING ARE LIKELY WITH SOME SMALL
HAIL POSSIBLE. EMBEDDED MICROBURSTS ARE ALSO POSSIBLE WITH SOME OF
THESE STORMS. GRADUALLY BACKED OFF TO VCTS AND CB GROUPS TO INDICATE
LESSER CHANCES OF THUNDERSTORMS AFTER SUNRISE. HOWEVER...PRECIP
COULD HOLD IN INTO THE MID MORNING HOURS. WINDS SHOULD REMAIN
LARGELY FROM THE NORTHEAST WITH VARIABLE GUSTY WINDS NEAR STORMS.

&&

.PREV DISCUSSION... /ISSUED 639 PM CDT SUN AUG 16 2009/

DISCUSSION...

FRONTAL BOUNDARY DRAPED NE SW ACROSS THE FORECAST AREA...WITH FINE
LINE DRIFTING TOWARD THE RADAR ATTM.  WEST SOUTHWESTERLY FLOW ALOFT
MAKING FOR SLOW PROGRESS. AREA AHEAD OF THE FRONT IS NEARLY UNCAPPED
AND AROUND CONVECTIVE TEMPERATURES...AND CU FIELD APPEARS TO BE
INCREASING IN DEPTH WITH TIME.

THIS AFTERNOON...ONLY FORCING FOR LIFT THIS AFTERNOON IS FRONT
ITSELF. THERE IS GOOD INSTABILITY ALOFT WITH MORNING SOUNDING AROUND
2800 J/KG...AND 0-6KM SHEAR 30-40KTS WOULD BE SUFFICIENT TO SUPPORT
AN UPDRAFT...BUT FRONT MAY NOT BE STRONG ENOUGH TO OVERCOME LAST BIT
OF THE AFTERNOON CAP. WILL CARRY SLT CHANCE/CHANCE ACROSS THE
SE...BUT IF CELLS DONT GO IN THE NEXT FEW HOURS IT WILL PROBABLY BE
LATER TONIGHT BEFORE ACTIVITY COMES IN.

TONIGHT/MONDAY...SOME DIFFERENCES IN THE MODELS AS TO
TIMING/PLACEMENT OF OVERNIGHT CONVECTION.  STRONG SHORTWAVE TROF
VISIBLE OVER THE ROCKIES EXPECTED TO MOVE INTO OUR AREA
OVERNIGHT...INITIALLY INCREASING THE LLJ OVER THE 850 BOUNDARY THEN
MOVING OVER THE AREA MONDAY MORNING.  GFS DEVELOPS MCS IN NORTH
CENTRAL KANSAS AFTER MIDNIGHT AND PROPAGATES CONVECTION EASTWARD
WITH FOCUS ALONG AND NORTH OF I70 THEN SOUTHEAST IN THE LATE
AFTERNOON. SIMILAR INITIAL DEVELOPMENT IN THE NAM SLIGHTLY
SOUTH...WITH EC SHOWING A SLIGHTLY FARTHER SOUTHWARD SHIFT. WITH
MESOSCALE INFLUENCES ON DEVELOPMENT AND PROPAGATION HAVE GONE WITH
HIGHER POPS FROM 06 TO 18Z...WITH FIRST 6 HRS HIGHER POPS IN NC KS
AND LATER 6 HIGHER POPS EAST CENTRAL AS FOCUS SHIFTS EAST WITH TIME.
PW VALUES AROUND 2 INCHES IN THE COLUMN WILL MAKE HEAVY RAIN A
CONCERN...AND GOOD INSTABILITY AND LAPSE RATES ALOFT WILL MAKE HAIL
A THREAT AS WELL. NO FLOOD WATCH AT THIS TIME AS AREA WIDE GUIDANCE
VALUES ARE GENERALLY 2-3 INCHES. RAIN CONTINUING INTO THE MORNING
COUPLED WITH COOL CONVECTIVE OUTFLOWS AND CLOUDS WOULD LEAD TO
COOLER HIGHS AND HAVE GRIDS AS SUCH.

67

EXTENDED FORECAST...THE EXTENDED IS CHARACTERIZED BY AN ACTIVE UPPER
AIR PATTERN FORECAST TO PERSIST ACROSS THE CENTRAL CONUS THROUGH MID
WEEK. AN INITIAL SHORTWAVE TROUGH WILL BE IN THE PROCESS OF EJECTING
NORTHEASTWARD INTO THE NORTHERN GREAT LAKES MONDAY NIGHT. A
SECONDARY AND WEAKER SHORTWAVE TROUGH WILL DROP INTO NORTHERN UTAH
ON TUESDAY AND BEGIN TO DEAMPLIFY IN RESPONSE TO A LARGER UPPER
DISTURBANCE ON ITS HEELS. THIS SYSTEM WILL ENTER THE CENTRAL PLAINS
WEDNESDAY INTO THURSDAY AND SLOWLY EXIT THE REGION THEREAFTER.

AT THE SURFACE...A FRONTAL BOUNDARY WILL PERSIST ACROSS/NEAR THE
TOPEKA COUNTY WARNING AREA MONDAY NIGHT THROUGH THURSDAY THANKS TO A
PERSISTENT UPPER PATTERN DESCRIBED ABOVE. WITH FAVORABLE PERIODS OF
LARGE SCALE ASCENT AND ABUNDANT MOISTURE PRESENT...PERIODS OF SHOWERS
AND THUNDERSTORMS CAN BE EXPECTED ACROSS MOST OF THE AREA MONDAY
NIGHT THROUGH THURSDAY. THE EXACT TIMING AND LOCATION OF
PRECIPITATION WILL BE BETTER REFINED WITH SUBSEQUENT FORECASTS AS
MODEL CONSENSUS IMPROVES AND MESOSCALE DETAILS BECOME RESOLVED. WILL
NEED TO MONITOR FLASH FLOOD POTENTIAL AS THE WEEK PROGRESSES WITH
ANTICIPATED POSSIBILITY OF SEVERAL PRECIPITATION EVENTS ACROSS THE
AREA WITH TIME.

A COLD FRONT ASSOCIATED WITH THE MID WEEK UPPER DISTURBANCE WILL
MOVE THROUGH THE AREA ON THURSDAY...EFFECTIVELY ENDING PRECIPITATION
CHANCES FOR THE REMAINDER OF THE FORECAST AS DRIER AND COOLER AIR
ADVECT INTO THE REGION. TEMPERATURES DURING THE EXTENDED PERIOD WILL
BE AT OR SLIGHTLY BELOW NORMAL...AND WILL BE STRONGLY TIED TO BOTH
THE FRONTAL POSITION AND CLOUD COVER FROM CONVECTION.

BLAIR

&&

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

&&

BARJENBRUCH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TOPEKA KS
327 PM CDT SUN AUG 16 2009

KSZ008>012-020>024-026-034>040-054>056-058-059-172030-
REPUBLIC-WASHINGTON-MARSHALL-NEMAHA-BROWN-CLOUD-CLAY-RILEY-
POTTAWATOMIE-JACKSON-JEFFERSON-OTTAWA-DICKINSON-GEARY-MORRIS-
WABAUNSEE-SHAWNEE-DOUGLAS-LYON-OSAGE-FRANKLIN-COFFEY-ANDERSON-
327 PM CDT SUN AUG 16 2009

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A CHANCE FOR THUNDERSTORMS THIS AFTERNOON AND EVENING
ACROSS PORTIONS OF EAST CENTRAL KANSAS. A FEW OF THESE STORMS
COULD BE SEVERE...WITH HAIL AND HEAVY RAIN THE PRIMARY THREAT.

THUNDERSTORMS ARE EXPECTED TO DEVELOP AFTER MIDNIGHT TONIGHT ACROSS
NORTH CENTRAL KANSAS...AND MOVE EAST INTO NORTHEAST AND EAST
CENTRAL KANSAS. THE PRIMARY THREAT FROM THESE STORMS WILL BE HEAVY
RAIN AND HAIL.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THERE WILL BE A CONTINUED CHANCE FOR THUNDERSTORMS MONDAY THROUGH
THURSDAY ACROSS THE AREA. SOME OF THE THUNDERSTORMS MAY PRODUCE HEAVY
RAINFALL.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS SHOULD NOT BE NEEDED THIS AFTERNOON OR TONIGHT...BUT ARE
ENCOURAGED TO REPORT ANY SIGNIFICANT RAINFALL AMOUNTS THAT MAY
OCCUR TONIGHT.

67/BLAIR

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