FXUS64 KOUN 290500
AFDOUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
1100 PM CST SAT NOV 28 2009
.AVIATION...
MODEL GUIDANCE HAS BACKED OFF ON DEVELOPMENT OF LOWER CIGS/VSBYS AT
TAF SITES AHEAD OF FRONT TONIGHT. THIS LOOKS LIKE A GOOD THING SINCE
THERE AREN'T ANY. STILL THINK THERE WILL BE A SHORT WINDOW OF
OPPORTUNITY FOR SOME ST/SC OR LIGHT FOG AS WINDS GO LIGHT FOR A
COUPLE HRS IN THE FRONTAL CONVERGENCE ZONE AND COOLER AIR HITS
INCREASING-BUT-SHALLOW LOW LEVEL MOISTURE. WINDS THEN WILL KICK UP
FROM THE N WITHIN A FEW HRS AFTER INITIAL WIND SHIFT. CIGS NOW
APPEAR MOST LIKELY WILL REMAIN AT MID/UPPER LEVELS BASED ON MODEL RH
FIELDS... BUT THERE MAY BE SOME COLD-ADVECTION SC DURING THE DAY.
&&
.PREV DISCUSSION... /ISSUED 901 PM CST SAT NOV 28 2009/
UPDATE...
COLD FRONT ACROSS THE TX PANHANDLE INTO FAR NORTHWEST OK WILL MOVE
ACROSS THE FA OVERNIGHT INTO SUNDAY. MEANWHILE... LOW LVL MOISTURE
WILL CONTINUE TO SPREAD NORTHWARD INTO THE FA AHEAD OF THE FRONT.
CLOUDS WILL ALSO CONTINUE TO INCREASE OVERNIGHT. SOME FOG MAY
DEVELOP LATER TONIGHT. HOWEVER... WINDS AHEAD OF THE FRONT WILL
LIKELY KEEP THE AIRMASS MIXED ENOUGH TO PREVENT FOG DEVELOPMENT
BEFORE THE CLOUDS MOVE IN THEN THE CLOUDS WILL PROBABLY KEEP TEMPS
HIGH ENOUGH IN THOSE AREAS WHERE THE WINDS TURN LIGHT AND DESPITE
THE MOISTURE ADVECTION TO ALSO PREVENT FOG DEVELOPMENT. BUT THERE
MAY BE SLIM WINDOW OF OPPORTUNITY FOR SOME PATCHY FOG TO DEVELOP
AHEAD OF THE FRONT FOR A FEW HOURS BEFORE THE FRONT AND DRIER AIR
MOVES THROUGH. WILL LEAVE MENTION OF FOG OUT OF THE GRIDS FOR NOW
AND CONTINUE TO MONITOR. ADJUSTED SKY COVER AND HOURLY GRIDS TO
CURRENT TRENDS.
PREV DISCUSSION... /ISSUED 546 PM CST SAT NOV 28 2009/
AVIATION...
CONDITIONS LIKELY TO DETERIORATE TO MVFR OVERNIGHT AS LOW-LEVEL
MOISTURE INCREASES AHEAD OF FRONT NOW NEAR KGAG/KWWR. LOW CLOUDS
MAY FILL IN QUICKLY AS COLDER AIR HITS THE HIGHER DEWPOINTS LATE
TONIGHT. N WINDS WILL INCREASE TO 15-20 G20-30 KT A FEW HRS AFTER
INITIAL WIND SHIFT AND WILL STAY UP THROUGH MOST OF SUNDAY BEFORE
DECREASING LATE.
PREV DISCUSSION... /ISSUED 240 PM CST SAT NOV 28 2009/
DISCUSSION...
THE NAM EXHIBITS GOOD RUN-TO-RUN CONSISTENCY WITH ITS TIMING
OF THE COLD FRONT FOR TONIGHT AND EARLY SUNDAY AND THE PROGRESSION
OF THE CUTOFF LOW ACROSS NORTHERN MEXICO THROUGH EARLY TUESDAY.
THE COLD FRONT SHOULD MOVE INTO NORTHWEST OKLAHOMA THIS EVENING
AND EXIT THE SOUTHEAST PART OF THE CWA SUNDAY MORNING. ALTHOUGH
HIGH TEMPERATURES WILL FALL NEARLY 20 DEGREES OVER A GOOD PART OF
THE AREA ON SUNDAY... THEY WILL STILL ONLY BE SLIGHTLY BELOW
NORMAL AS THE AIRMASS IS PRIMARILY PACIFIC IN ORIGIN.
MID-LEVEL WEAK ISENTROPIC LIFT ON SUNDAY COMBINED WITH AN INCREASE IN
HUMIDITIES AT THAT LEVEL... ALONG WITH SURFACE COLD FRONT MOVING
THROUGH THE AREA... SHOULD PROVIDE ENOUGH SUPPORT FOR SCATTERED
SHOWERS. HOWEVER... WE WILL SHIFT THE HIGHEST POPS INTO THE
AFTERNOON HOURS AS THE MID-LEVEL MOISTURE WILL STILL BE SOMEWHAT
LACKING DURING THE MORNING. RAINFALL AMOUNTS ARE EXPECTED TO BE
RELATIVELY LIGHT. BY SUNDAY AFTERNOON... THE 850 TO 700 MB
THICKNESSES ALONG WITH LOW-LEVEL WET BULB TEMPERATURES NEAR FREEZING
SUGGEST A SLIM POSSIBILITY OF A MIX OF LIGHT RAIN/SNOW ACROSS
NORTHWEST OKLAHOMA. HOWEVER... THE BOUNDARY LAYER TEMPERATURES ARE
FORECAST TO REMAIN RELATIVELY WARM... AND WITH ONLY LIGHT PCPN
EXPECTED... DOUBT THERE WILL BE SUFFICIENT EVAPORATIVE COOLING TO
LOWER THE SURFACE WET BULB TEMPERATURES TO FREEZING.
IN THE LATER FORECAST PERIODS... THE NAM CONTINUES TO BE A LITTLE
SLOWER AND FARTHER SOUTH WITH THE POSITION OF THE UPPER LOW TUESDAY
COMPARED TO THE GFS AND ECMWF. ATTM... WILL TREND TOWARDS THE GFS
AND SPREAD POPS A LITTLE FARTHER NORTH INTO CENTRAL OKLAHOMA FOR
TUESDAY NIGHT BUT WILL STAY LOWER THAN THE MORE BULLISH ECMWF.
IN THE 7 TO 9 DAY PERIODS... THE 12Z RUN OF THE GFS IS
SIGNIFICANTLY COLDER THAN THE PRIOR COUPLE OF RUNS AS IT PLUNGES
CANADIAN AIR SOUTHWARD THROUGH THE PLAINS. SINCE MOST OF THE
CHANGE OCCURS JUST BEYOND THE CURRENT FORECAST PERIOD THERE WILL
BE A COUPLE MORE MODEL RUNS TO EXAMINE BEFORE IT MOVES VERY FAR
INTO THE FORECAST PERIOD.
&&
.PRELIMINARY POINT TEMPS/POPS...
OKLAHOMA CITY OK 46 50 34 58 / 0 40 20 0
HOBART OK 42 48 31 53 / 0 30 10 0
WICHITA FALLS TX 51 54 35 57 / 10 40 20 10
GAGE OK 37 46 24 56 / 0 30 0 0
PONCA CITY OK 43 50 30 57 / 0 30 10 0
DURANT OK 56 57 42 58 / 10 50 40 10
&&
.OUN WATCHES/WARNINGS/ADVISORIES...
OK...NONE.
TX...NONE.
&&
$$
25/24/24
