Flash Flood Warning 26, NWS Norman, OK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
630 PM CDT MON AUG 17 2009

.AVIATION...
OUTFLOW BOUNDARY EXTENDS FROM NEAR KOKC TO SOUTH OF KGAG.
SCATTERED THUNDERSTORMS ARE EXPECTED MAINLY NORTH OF THIS BOUNDARY
ALTHOUGH THE SPECIFIC TIMING FOR AFFECTING SPECIFIC TAF SITES IS
QUITE UNCERTAIN GIVEN THE SCATTERED NATURE OF THE CONVECTION. THE
OUTFLOW BOUNDARY WILL ALSO GIVE SOME VARIABLE WIND DIRECTION OVER
TIME AT THE NORTHERN AND CENTRAL OKLAHOMA TAF SITES.

&&

.PREV DISCUSSION... /ISSUED 259 PM/

DISCUSSION...TODAY OUR FOCUS IS ON THE SHORT TERM POTENTIAL FOR
HEAVY RAINFALL. THERE ARE NUMEROUS INGREDIENTS IN PLACE...INCLUDING
A STATIONARY FRONT BENEATH PARALLEL UPPER FLOW...AND ABUNDANT
MOISTURE. ACTIVITY IS EXPECTED INITIALLY ALONG AN OUTFLOW BOUNDARY
FROM THE OKLAHOMA CITY AREA...WESTWARD TO NEAR ARNETT. STEEP LAPSE
RATES SUPPORT THE THREATS OF DAMAGING WINDS AND SOME LARGE
HAIL...ESPECIALLY DURING THE EVENING. THESE LAPSE RATES WOULD TEND
TO FAVOR COLD POOLS TO KEEP STORMS MOVING...BUT THE COLD POOLS WILL
MEET RESISTANCE FROM AN EASTERLY TO SOUTHERLY LOW LEVEL JET.
THIS...ALONG WITH SLOW MOTION OF INDIVIDUAL CELLS...AND INCREASING
SYNOPTIC SCALE LIFT OVER NORTHERN OKLAHOMA...SUGGESTS REPEATED HEAVY
RAIN MAY OCCUR ALONG AND NORTH OF THE INITIAL LINE OF THUNDERSTORMS.

THIS REASONING LED TO THE FLASH FLOOD WATCH FOR COUNTIES ALONG AND
NORTH OF INTERSTATE 40. THE LARGE SCALE PATTERN WILL REMAIN IN PLACE
THROUGH TUESDAY NIGHT...AND THE FLOOD WATCH WILL NEED TO BE
REVISITED AND POSSIBLY EXTENDED IN TIME AFTER SEEING THE OUTCOME OF
THE MONDAY NIGHT CONVECTION.

WE ADJUSTED GFS GUIDANCE POPS UPWARD IN DAYS 1-3...BUT MOST
SIGNIFICANTLY FOR TONIGHT...WHERE THE NAM AND LOCAL WRF HAD A BETTER
HANDLE ON THE OUTFLOW BOUNDARY AND MORE SOUTHERLY SWATH OF
PRECIPITATION. MUCH LIKE TODAY...THERE SHOULD BE A THUNDERSTORM
COMPLEX ONGOING IN NORTHERN OKLAHOMA TUESDAY MORNING. MODELS HAVE A
CONSISTENT SIGNAL FOR STRONG LIFT AND ANOTHER ASSOCIATED COMPLEX IN
NORTHWEST OKLAHOMA WEDNESDAY MORNING. THE GFS GUIDANCE FOR HIGH
TEMPERATURES DID NOT REFLECT THE CONVECTION WELL...SO WE ADJUSTED
TEMPERATURES DOWNWARD ALONG A GRADIENT FROM INTERSTATE 40 NORTHWARD.

A COLD FRONT WILL SWEEP THROUGH LATE WEDNESDAY INTO THURSDAY...WITH
A CONTINUED CHANCE FOR STORMS ALONG THE FRONT...AND DRIER...MORE
STABLE AIR BEHIND IT.

&&

.PRELIMINARY POINT TEMPS/POPS...
OKLAHOMA CITY OK  72  90  74  95 /  40  20  20  20
HOBART OK         75  94  75 100 /  20  20  30  10
WICHITA FALLS TX  75 100  77 102 /  10  10  10  10
GAGE OK           66  82  68  93 /  70  30  60  20
PONCA CITY OK     72  81  76  92 /  70  50  40  30
DURANT OK         74  99  75  95 /  10  10  10  20

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...FLASH FLOOD WATCH THROUGH TUESDAY MORNING FOR OKZ004>020-024>026.

TX...NONE.
&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NORMAN OK
1200 PM CDT MON AUG 17 2009

OKZ004>048-050>052-TXZ083>090-181000-
HARPER-WOODS-ALFALFA-GRANT-KAY-ELLIS-WOODWARD-MAJOR-GARFIELD-NOBLE-
ROGER MILLS-DEWEY-CUSTER-BLAINE-KINGFISHER-LOGAN-PAYNE-BECKHAM-
WASHITA-CADDO-CANADIAN-OKLAHOMA-LINCOLN-GRADY-MCCLAIN-CLEVELAND-
POTTAWATOMIE-SEMINOLE-HUGHES-HARMON-GREER-KIOWA-JACKSON-TILLMAN-
COMANCHE-STEPHENS-GARVIN-MURRAY-PONTOTOC-COAL-COTTON-JEFFERSON-
CARTER-JOHNSTON-ATOKA-LOVE-MARSHALL-BRYAN-HARDEMAN-FOARD-WILBARGER-
WICHITA-KNOX-BAYLOR-ARCHER-CLAY-
1200 PM CDT MON AUG 17 2009

THIS HAZARDOUS WEATHER OUTLOOK COVERS NORTHERN...WESTERN...
CENTRAL...AND SOUTHERN OKLAHOMA...AND WESTERN NORTH TEXAS.

.DAY ONE...THIS AFTERNOON AND TONIGHT...

THUNDERSTORM OUTLOOK...
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
ACROSS PORTIONS OF OKLAHOMA.

LOCATION...
THE SLIGHT RISK AREA IS NORTH OF INTERSTATE 40.

TIMING...
THE MOST LIKELY TIME FOR SEVERE THUNDERSTORMS WILL BE FROM LATE
AFTERNOON THROUGH EARLY TUESDAY MORNING.

RECOMMENDED ACTIONS...
STORM SPOTTER GROUPS AND EMERGENCY MANAGEMENT PERSONNEL ACROSS THE
RISK AREA SHOULD PLAN FOR SEVERE WEATHER OPERATIONS FROM THIS
AFTERNOON UNTIL EARLY TUESDAY MORNING.

DISCUSSION...
MODERATE INSTABILITY... COMBINED WITH SURFACE BOUNDARIES... AN UPPER
LEVEL TROUGH... AND MODERATE VERTICAL WIND SHEAR... WILL BRING A
CHANCE OF SEVERE THUNDERSTORMS TO NORTHERN OKLAHOMA LATER TODAY. INSOLATION
AND AN OUTFLOW BOUNDARY ACROSS CENTRAL OKLAHOMA WILL PROVIDE
SUFFICIENT LIFT FOR THUNDERSTORMS LATER THIS AFTERNOON.
THUNDERSTORMS WILL BE CAPABLE OF PRODUCING VERY HEAVY RAIN AND
LOCALIZED FLOODING. A FEW THUNDERSTORMS MAY ALSO MAKE LARGE HAIL AND
DAMAGING WINDS.

PROBABILITY TABLE...
VALID THROUGH 700 AM CDT TUESDAY AUG 18.
PROBABILITY OF THUNDERSTORMS OCCURRING IN THE
              NWS NORMAN COUNTY WARNING AREA...100 PERCENT.
PROBABILITY OF SEVERE STORMS IF STORMS OCCUR...70 PERCENT.

OTHER HAZARDOUS WEATHER...
A FLOOD WATCH IS EFFECTIVE FOR THE NORTHERN HALF OF OKLAHOMA FROM
LATE THIS AFTERNOON THROUGH MID-DAY TUESDAY.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY...

THUNDERSTORM OUTLOOK...
SEVERE THUNDERSTORMS ARE POSSIBLE TUESDAY AND TUESDAY NIGHT.
THUNDERSTORM CHANCES RECEDE BEYOND WEDNESDAY MORNING.

OTHER HAZARDOUS WEATHER...
A FLOOD WATCH IS EFFECTIVE FOR THE NORTHERN HALF OF OKLAHOMA UNTIL
MID-DAY TUESDAY. THUNDERSTORMS TUESDAY MORNING WILL LIKELY GENERATE
VERY HEAVY RAINFALL.

THE NEXT SCHEDULED HAZARDOUS WEATHER OUTLOOK WILL BE ISSUED AT 7 AM
TUESDAY.

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