Forecast Update/Freeze Warning

000FXUS64 KOUN 091741AFDOUN

AREA FORECAST DISCUSSIONNATIONAL WEATHER SERVICE NORMAN OK1130 AM CST SUN DEC 9 2007

SUN DEC 9 2007CONVECTION OVERNIGHT AND THIS MORNING HAS BEEN MORE WIDESPREAD AND VIGOROUS THAT WAS ANTICIPATED...WITH THE CONVECTIVE ELEMENTS OFTEN ACCOMPANIED BY SLEET AND HOURLY ACCUMULATIONS OF ICE NEAR ONE QUARTER INCH. A VERY TIGHT BAROCLINIC ZONE REMAINS OVER THE AREATHIS MORNING WITH ASSOCIATED FRONTOGENESIS CONTINUING DUE TO THE VEERED FLOW ACCOMPANYING THE PASSAGE OF A SHORTWAVE TROUGH OVERKANSAS...AND THE BACKED FLOW OVER WEST TEXAS ACCOMPANYING THEAPPROACH OF THE LONGER-WAVE TROUGH WITH A CONTINUED AND NEARLYSTEADY-STATE ATMOSPHERIC LIFTING RESPONSE RESULTING OVER THE MUCH OFTHE AREA.CURRENT RADAR/PROFILER TRENDS COMBINED WITH THE LATEST 12Z NAMSUGGESTS THAT PRECIPITATION MAY NOT END TEMPORARILY AS WAS ONCETHOUGHT. RATHER...AREAS OF FREEZING RAIN MIXED WITH FREEZING RAINSHOWERS AND SLEET SHOWERS ARE EXPECTED TO PERSIST THROUGH THISAFTERNOON AND EVENING MAINLY ALONG AND JUST SOUTH OF INTERSTATE 44AS THE LONGER-WAVE APPROACHES...WITH PERHAPS NORTHWESTERN OKLAHOMARECEIVING A BRIEF LULL IN DEVELOPMENT DURING THIS TIME.THE ICE STORM WARNING AREA AND FREEZING RAIN ADVISORY AREA WEREALREADY MODIFIED EARLIER AND WE EXPECT THAT WE ALREADY NEED TOEXPAND THE ICE STORM WARNING INTO TONIGHT FOR THE AREA DESCRIBEDABOVE WITH MONDAY AND MONDAY NIGHT STILL APPEARING AS THE MAINPERIODS TO BE CONCERNED WITH IN REGARDS TO MORE SIGNIFICANTACCUMULATIONS OF ICE SPREADING OVER NORTHERN OKLAHOMA.REGARDING TOTAL ICE ACCUMULATIONS...LOCAL MAXIMA IN ICE THATACCOMPANIED OVERNIGHT/MORNING CONVECTION HAVE ALREADY EXCEEDED ICESTORM WARNING CRITERIA (1/4" OF ICE) IN SOME AREAS. ASIDE FROM THESERECENT AMOUNTS...TOTAL ICE STORM AMOUNTS ISSUED OVERNIGHT ARE STILLLOOKING GOOD. ALTHOUGH WE ARE CONCERNED ABOUT AREAS NEAR AND JUSTSOUTH OF INTERSTATE 44 RECEIVING PERHAPS A BIT MORE THAN ONE QUARTERINCH BEFORE TEMPERATURES HOPEFULLY CLIMB ABOVE FREEZING ON MONDAY.JAMES------------------------647 AM CST SUN DEC 9 2007.UPDATE...WE HAVE EXPANDED THE ICE STORM WARNING INTO PORTIONS OF WESTERNAND NORTHERN OKLAHOMA TO ACCOUNT FOR THE LARGE AREA OF RAIN ANDTHUNDERSTORMS THAT HAVE SPREAD INTO THOSE AREAS. WE EXPECT THISACTIVITY TO TEMPORARILY DIMINISH THIS AFTERNOON... WITHREDEVELOPMENT POSSIBLE LATE TONIGHT.&&.PREV DISCUSSION... /ISSUED 503 AM CST SUN DEC 9 2007/DISCUSSION...SUBFREEZING TEMPERATURES HAVE MOVED THROUGH MUCH OF SOUTHWEST ANDCENTRAL OKLAHOMA INTO PARTS OF WESTERN NORTH TEXAS. THE ACTIVEBAND OF SHOWERS AND EMBEDDED THUNDERSTORMS HAS SHIFTED NORTH INTOTHE COLDER AIR ACROSS PORTIONS OF CENTRAL OKLAHOMA RESULTING INSIGNIFICANT ICING ON EXPOSED SURFACES EXTENDING FROM AROUNDNORMAN... THROUGH SE OKC AND CONTINUING ALONG THE I44 CORRIDORTHROUGH LINCOLN COUNTY. WHILE RELATIVELY WARM GROUND TEMPERATURESHAVE TENDED TO LIMIT THE FORMATION OF ICE ON ROADWAYS... AIRTEMPERATURES HAVE COOLED SUFFICIENTLY FOR ICE ACCUMULATIONS ONEXPOSED SURFACES. DUE TO THE TRAINING OF SHOWERS AND THUNDERSTORMSACROSS THIS AREA... WE ISSUED AN ICE STORM WARNING FOR TODAY FORPARTS OF CENTRAL OKLAHOMA.THE MODELS INDICATE THAT PRECIP INTENSITY OVER THE AREA SHOULDDECREASE BY AFTERNOON AS THE CURRENT STRONG WARM ADVECTION NEARTHE 850 MB LEVEL WEAKENS. THE WINDS AT THIS LEVEL ARE FORECAST TOVEER WITH SOME COLD ADVECTION OCCURRING OVER ALL BUT THESOUTHEAST. HAVING SAID THAT... WE CONTINUE TO SEE PRECIPITATIONFORM OVER WESTERN OKLAHOMA INTO THE TEXAS PANHANDLE... THUSACTIVITY MAY PERSIST LONGER THAN EXPECTED TODAY. WE WILL ALSOEXTEND THE FREEZING RAIN ADVISORY THAT IS IN EFFECT FOR A LARGEPART OF THE CWA INTO THE DAY. GIVEN THE UNCERTAINTY ON EXACTLYWHEN PCPN SHOULD DIMINISH TODAY AND IN AN EFFORT TO SIMPLIFYWINTER WEATHER HEADLINES... WE HAVE OPTED TO RUN BOTH THE ADVISORYAND WARNING FOR TODAY... ALTHOUGH WE EXPECT BY AFTERNOON WE SHOULDSEE MUCH OF THE FREEZING RAIN BE REPLACED BY FREEZING DRIZZLE.WARM TEMPERATURES ALOFT SHOULD SEVERELY LIMIT THE LIKELIHOOD OFSNOW... BUT OCCASIONAL SLEET WILL BE POSSIBLE OVER THE NORTHWEST.MOVING ON LATER IN THE FORECAST THINGS GET EVEN MORE COMPLICATED.WE BELIEVE THAT PRECIPITATION WILL INCREASE OVER THE AREA AGAINLATE TONIGHT INTO MONDAY AS WARM ADVECTION INCREASES AGAIN ASWINDS BACK IN RESPONSE TO THE APPROACH OF THE LARGE SW UPPER LOW.THIS ACTIVITY WILL LIKELY CONTINUE INTO TUESDAY. WHILE CONFIDENCEIS HIGH ON THE LIKELIHOOD OF PCPN... THE DISTRIBUTION OF LIQUIDVS. FREEZING/FROZEN TYPES CONTINUES TO REMAIN THE BIG QUESTIONESPECIALLY ACROSS THE CENTRAL AND SOUTHERN PORTIONS OF THE AREA.THE LOW LEVEL COLD AIR IS EXPECTED TO CONTINUE TO ADVANCE SOUTHTHROUGH TONIGHT. THE GFS HAS BEEN THE WARMER MODEL IN THE LOWERLEVELS WHILE THE NAM HAS BEEN CONSIDERABLY COOLER AND THUS WOULDGENERATE FROZEN PRECIPITATION FARTHER SOUTH. WE WILL BIAS THEFORECAST IN THE DIRECTION OF THE NAM FOR THE TEMPS. HOWEVER... THE MODELSSTART WARMING THE BOUNDARY LAYER UP BY LATE MONDAY AND INTOTUESDAY. WHILE THEY MAY BE A LITTLE QUICK TO SCOUR OUT THE COLDAIR... THE PRECIPITATION TYPE THAT WILL OCCUR OVER THE CENTRAL ANDSOUTHERN ZONES BECOMES PROBLEMATIC BY TUESDAY AFTERNOON ANDBEYOND. WE WILL CONTINUE THE WINTER STORM WATCH FOR TONIGHT... ANDMOST LIKELY THAT WOULD BE FOR INCREASING PRECIP INTENSITIESSTARTING LATE TONIGHT... AND CONTINUE IT INTO EARLY TUESDAY.HOWEVER... IF MODEL TRENDS CONTINUE... THE THREAT OF SIGNIFICANTICING WILL DECREASE AFTER TUESDAY MORNING OVER AT LEAST THE SOUTH.GIVEN THE STRONG WARM ADVECTION... AND DEEP WARM LAYER ALOFT... ITMAY BE HARD TO KEEP FREEZING RAIN GOING IN AREAS THAT ARE ONLY AFEW DEGREES BELOW FREEZING. ANOTHER REINFORCING SHOT OF COLD AIRCOMES DOWN LATE TUESDAY NIGHT INTO WEDNESDAY... WHICH COULD SHIFTTHE FREEZING PRECIP LINE FARTHER SOUTH ONCE AGAIN AS THE UPPERTROUGH TO OUR WEST FINALLY MOVES OUT.&&.PRELIMINARY POINT TEMPS/POPS...OKLAHOMA CITY OK 31 26 34 32 / 80 40 70 70HOBART OK 30 25 33 29 / 60 40 70 70WICHITA FALLS TX 35 29 36 33 / 70 60 70 70GAGE OK 25 21 29 26 / 60 10 70 70PONCA CITY OK 27 22 34 30 / 70 10 70 70DURANT OK 44 31 44 38 / 80 70 70 70&&.OUN WATCHES/WARNINGS/ADVISORIES...OK...ICE STORM WARNING UNTIL 6 PM CST THIS AFTERNOON FOR OKZ006>008- 011>031-040. WINTER STORM WATCH FROM 6 PM CST THIS EVENING THROUGH LATE MONDAY NIGHT FOR OKZ004>047-050-051. FREEZING RAIN ADVISORY UNTIL 6 PM CST THIS AFTERNOON FOR OKZ004- 005-009-010-032>039-042-044.TX...WINTER STORM WATCH FROM 6 PM CST THIS EVENING THROUGH LATE MONDAY NIGHT FOR TXZ083>090. FREEZING RAIN ADVISORY UNTIL 6 PM CST THIS AFTERNOON FOR TXZ083>088.&&$$30/32