Flash Flood Warning 18, NWS Tulsa, OK

EASTERN OKLAHOMA/NORTHWEST ARKANSAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TULSA OK
402 AM CDT SAT APR 24 1999

PROBLEM(S) OF THE DAY:
TEMPERATURES
POPS
WILL THERE BE CONVECTION?

OBSERVATIONS INDICATE A VERY GOOD BAROCLINIC ZONE ACROSS THE
FORECAST AREA WITH A STATIONARY SURFACE FRONT ALONG THE FAR
SOUTHEASTERN EDGE OF OKLAHOMA. THERE SHOULD BE ENOUGH LIFT ASSOCIATED
WITH A PROCESSION OF RELATIVELY WEAK VORTICITY CENTERS FORECAST TO
MOVE NORTHEASTWARD ACROSS THE AREA...TO PRODUCE AT LEAST A 50/50
CHANCE OF RAIN AND POSSIBLY A THUNDERSTORM OR TWO ACROSS THE ENTIRE
AREA PERIODICALLY THROUGHOUT THE DAY AND INTO THE TONIGHT PERIOD.
LATE TONIGHT THE NGM...ETA AND TO A LESSER EXTENT THE AVN INDICATE A
STRONGER VORTICITY CENTER SWEEPING JUST INTO THE WESTERN ZONES BY
12Z. THERE IS CONSIDERABLE LIFT ASSOCIATED WITH THIS FEATURE AND
ELEVATED CONVECTION SHOULD RESULT. THEREFORE...WILL GO WITH LIKELY
POPS FROM KBVO TO KMLC AND KEEP 50 POPS EVERYWHERE ELSE FOR REASONS
DISCUSSED ABOVE.

TEMPERATURES WILL DEPEND GREATLY ON HOW FAR SOUTH THE LOW CLOUDS
STAY THROUGH THE DAY. THE ETA LOW-LEVEL RH PROGS INDICATE THAT THE
LOW CLOUDS SHOULD REMAIN IN PLACE ACROSS ALL BUT FAR SOUTHEAST
OKLAHOMA AND POSSIBLY WEST CENTRAL ARKANSAS. PERSISTENCE OF DIURNAL
RANGES LOOKS TO BE A GOOD FORECAST FOR TODAYS TEMPERATURES.
THEREFORE...LOOK FOR HIGHS NOT TO REACH 60 AGAIN TODAY ACROSS
NORTHEAST OKLAHOMA WITH IDB AGAIN POSSIBLY REACHING INTO THE 80S.
LOWS TONIGHT WILL ONCE AGAIN REFLECT A TINY DIURNAL RANGE WITH
PLENTY OF EXPECTED CLOUD COVER AND A PERSISTENT EASTERLY BREEZE.
TEMPERATURES FOR THE FIRST TWO PERIODS ARE GENERALLY LOWER THAN
MOS...EXCEPT FOR KFSM AND KIDB.

ELEVATED CONVECTION IN ASSOCIATION WITH THE AFOREMENTIONED STRONGER
SHORT-WAVE TROUGH WILL SWEEP NORTHEASTWARD ACROSS MOST OF EASTERN
BY MIDDAY SUNDAY...BUT MAY LINGER ACROSS THE NORTHEAST CORNER OF
OKLAHOMA AND THE NORTHWEST CORNER OF ARKANSAS WELL INTO THE
AFTERNOON.  TO DEAL WITH THIS...LIKELY POPS WILL BE FORECAST FOR ALL
BUT EXTREME SOUTHEAST OKLAHOMA...WHERE GOOD CHANCE POPS SHOULD BE
SUFFICIENT.  THE AREA SHOULD SEE A BREAK IN THE PRECIPITATION LATE
SUNDAY AND SUNDAY EVENING...BEFORE THE MAIN SHORT-WAVE TROUGH SWEEPS
NORTHEAST ACROSS THE AREA.  THE AVN INDICATES AN IMPRESSIVE DRY PUNCH
WRAPPING INTO THIS SYSTEM...SO THERE MAY BE AN ABRUPT END TO THE
PRECIPITATION CHANCES FROM SOUTHWEST TO NORTHEAST ACROSS THE AREA
EITHER LATE SUNDAY NIGHT OR EARLY MONDAY.  LIKELY POPS WILL BE
EXTENDED THROUGH SUNDAY NIGHT WITH JUST 20S AND 30S FOR EARLY ON
MONDAY.

WITH SURFACE WINDS TURNING AROUND TO THE SOUTHEAST AND SOUTH SUNDAY
AND SUNDAY NIGHT THERE SHOULD BE A MODEST WARMING TREND...BUT SMALL
DIURNAL RANGES WILL STILL BE THE RULE THROUGH SUNDAY NIGHT.  LOOK FOR
GOOD WARM UP BEHIND THE SYSTEM ON MONDAY WHEN WEST SOUTHWESTERLY
LOW-LEVEL FLOW SHOULD RESULT IN TEMPERATURES ONCE AGAIN APPROACHING
80 DEGREES IN SOME AREAS.  UPPED HIGHS IN EXTENDED PERIODS TO BE
CONSISTENT WITH WARMUP ON MONDAY.  NO OTHER CHANGES WERE MADE TO
THE EXTENDED FORECAST.

FCSTID = 19
TUL   59  54  66  60 /  50  70  70  70
FSM   73  64  74  61 /  50  50  70  60
MLC   65  57  75  62 /  50  70  70  60
BVO   57  51  65  58 /  50  70  70  70
FYV   67  58  69  60 /  50  50  70  70
IDB   82  69  84  70 /  50  50  50  50
BYV   67  58  69  60 /  50  50  70  70
MIO   62  55  66  59 /  50  50  70  70
MKO   59  54  66  60 /  50  70  70  70
F10   59  54  66  60 /  50  70  70  70
HHW   82  69  84  70 /  50  50  50  50

.TUL...
AR...NONE.
OK...NONE.

--------------------
EXPERIMENTAL OUTPUT:

HAZARDOUS WEATHER EXPECTED NEXT 24 HOURS:  NONE
NGM fCONFIDENCE:  6 ON A SCALE OF 0 TO 10
ETA CONFIDENCE:  7 ON A SCALE OF 0 TO 10
AVN CONFIDENCE:  7 ON A SCALE OF 0 TO 10
FCST CONFIDENCE: 8 ON A SCALE OF 0 TO 10

ARZ001-002-010-011-019-020-029-OKZ049-053>076-251100-

EASTERN OKLAHOMA/NORTHWEST ARKANSAS HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TULSA OK
100 PM CDT SAT APR 24 1999

...FLASH FLOODING WILL BE POSSIBLE THIS AFTERNOON ACROSS SOUTHEAST
OKLAHOMA AND WESTCENTRAL ARKANSAS...
...ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS EASTERN OKLAHOMA
AND NORTHWEST ARKANSAS AFTER MIDNIGHT...
...MORE SEVERE WEATHER EXPECTED SUNDAY AND SUNDAY NIGHT...

.SYNOPSIS...
EARLY THIS AFTERNOON...A STATIONARY FRONT WAS LOCATED FROM SOUTHERN
ARKANSAS ACROSS THE SOUTHEAST CORNER OF OKLAHOMA TO CENTRAL TEXAS. SOUTH
OF THE FRONT...VERY HIGH AMOUNTS OF LOW LEVEL MOISTURE WERE PRESENT.
NORTH OF THE FRONT...SOUTHERLY WINDS ALOFT WERE LIFTING THE WARM HUMID
AIRMASS UP AND OVER THE COOLER AIR...ALLOWING FOR THE FORMATION OF
THUNDERSTORMS THIS MORNING...SOME OF THEM SEVERE WITH VERY HEAVY
RAINFALL. THESE STORMS ARE EXPECTED TO WEAKEN THROUGH THE AFTERNOON AND
DISSIPATE BY THIS EVENING. HOWEVER...REDEVELOPMENT OF THUNDERSTORMS ARE
EXPECTED AFTER MIDNIGHT TONIGHT...SOME OF WHICH COULD BE SEVERE WITH
LOCALLY HEAVY RAINFALL. AS A STRONG UPPER LEVEL DISTURBANCE MOVES OUT OF
THE WESTERN U.S. SUNDAY...SEVERE WEATHER IS AGAIN EXPECTED SUNDAY
AFTERNOON AND NIGHT...MOVING FROM WEST TO EAST ACROSS EASTERN OKLAHOMA
AND NORTHWEST ARKANSAS.

.DISCUSSION...
THUNDERSTORMS HAVE PERSISTED ACROSS SOUTHEAST OKLAHOMA SINCE EARLY THIS
MORNING AND WILL CONTINUE TO PRODUCE HEAVY RAINFALL AND SOME FLOODING
THIS AFTERNOON. RADAR ESTIMATES INDICATE UP TO 4 INCHES OF RAINFALL
ACROSS SOUTHWESTERN PITTSBURG COUNTY WITH OTHER BANDS OF 2 TO 3 INCHES
ACROSS LATIMER...HASKELL...LE FLORE...SEBASTIAN AND SOUTHERN FRANKLIN
COUNTIES. THE PERSISTENT STORMS HAVE STABILIZED THE ATMOSPHERE SOMEWHAT
SO STORMS THIS AFTERNOON ARE NOT LIKELY TO PRODUCE HAIL OR DAMAGING
WINDS. THE STORMS ARE EXPECTED TO DISSIPATE BY EARLY EVENING.

LATER TONIGHT...SOUTHERLY WINDS ALOFT WILL INCREASE AND BRING MOISTURE
INTO THE AREA AGAIN. ELEVATED INSTABILITY WILL INCREASE WITH CAPE VALUES
NEAR 1500 J/KG EXPECTED USING PARCELS LIFTED FROM 5000 FEET. THERE WILL
BE A THREAT OF SEVERE STORMS AFTER MIDNIGHT ACROSS ALL OF EASTERN
OKLAHOMA AND NORTHWEST ARKANSAS WITH LARGE HAIL UP TO 1 INCH IN DIAMETER
AND VERY HEAVY RAINFALL THE PRIMARY THREATS.

ANOTHER ROUND OF MORE SIGNIFICANT SEVERE STORMS WILL BE LIKELY LATE
SUNDAY AFTERNOON AND ESPECIALLY SUNDAY NIGHT. A STRONG UPPER LEVEL
DISTURBANCE WILL LIFT OUT OF THE SOUTHWESTERN U.S. EXPECTED INSTABILITY
AND VERTICAL WIND PROFILES INDICATE THAT SUPERCELL STORMS CAN BE
EXPECTED SUNDAY EVENING.

.EMERGENCY MANAGEMENT AGENCY AND SPOTTER ACTIVATION...
SPOTTER ACTIVATION IS NOT EXPECTED THROUGH TONIGHT HOWEVER...SPOTTERS
AND EMERGENCY MANAGEMENT AGENCIES SHOULD BE PREPARED FOR THE POSSIBILITY
OF SIGNIFICANT SEVERE WEATHER LATE SUNDAY AFTERNOON AND SUNDAY NIGHT.