FXUS64 KOUN 241211
AFDOUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
611 AM CST THU DEC 24 2009
.AVIATION...THE TAFS ARE NECESSARILY PESSIMISTIC ON CEILINGS AND
VISIBILITY...AS A MAJOR WINTER STORM TAKES SHAPE DURING THE DAY.
THE CHANGE TO SNOW HAD REACHED KCSM...AND A RAIN TO SNOW MIX WAS
REPORTED AROUND KHBR AND KLAW. MIXED PRECIPITATION WILL PERSIST
LONGEST IN CENTRAL AND NORTH CENTRAL OKLAHOMA BEFORE CHANGING TO
SNOW. WITH INTENSE MID AND UPPER LEVEL LIFT ARRIVING TODAY...SNOW
SHOULD BECOME HEAVY AT TIMES. EQUALLY AS IMPORTANT ARE THE
WINDS...WHICH WERE ALREADY GUSTING OVER 40 KNOTS. THIS WAS
INDICATIVE OF A DEEPENING...INTENSE CYCLONE...AND THE WINDS WILL
ONLY INCREASE FURTHER WITH THE ARRIVAL OF AN ARCTIC FRONT DURING
THE DAY. WHERE SNOW ACCUMULATE...BLOWING SNOW WILL FURTHER REDUCE
VISIBILITY. IMPROVEMENT WILL BE SLOW DURING THE EVENING...BUT BY
LATE IN THE PERIOD...THE STORM WILL EXIT TO THE EAST...AND WIND
SPEEDS WILL DECREASE SIGNIFICANTLY AFTER MIDNIGHT.
&&
.PREV DISCUSSION... /ISSUED 453 AM CST THU DEC 24 2009/
..MAJOR WINTER STORM TODAY AND THIS EVENING...
THE CHRISTMAS EVE STORM NOW UNFOLDING HAS BEHAVED LIKE A GIFT
WRAPPED IN MULTIPLE BOXES...IT IS FULL OF SURPRISES. ALL ALONG...THE
MODELS HAVE SHOWN AN UNUSUAL AMOUNT OF SPREAD REGARDING THE TRACK
AND INTENSITY OF THE CYCLONE.
..TRENDS...
SOME IMPORTANT TRENDS THAT SHOWED UP OVERNIGHT INCLUDE...THE MID AND
UPPER CYCLONE SHOWING MORE CLOSED HEIGHT CONTOURS AND TRACKING A
LITTLE FARTHER SOUTH. THIS MEANS MORE INTENSE LIFTING FOR A LONGER
DURATION FOR A FAIRLY BROAD AREA ALONG AND NORTH OF THE TRACK. THE
NAM...ECMWF...AND NOW RUC GENERALLY AGREE ON THE TRACK AND INTENSITY
OF THE SURFACE LOW...MAINTAINING ABOUT 989 MB ALONG A PATH THROUGH
EXTREME SOUTHEAST OKLAHOMA...AND CURVING TOWARD NORTHWEST ARKANSAS.
SURFACE AND SATELLITE OBSERVATIONS SEEM TO BE BEARING THIS OUT AS A
GOOD LIKELIHOOD. WE WERE ABLE THEN...TO USE THE 00Z AND 06Z NAM
FIELDS WITH SOME CONFIDENCE. INCREDIBLY...THIS MEANS THAT THE
CYCLONE IS VERIFYING SOMEWHERE TOWARD THE EXTREME SIDE OF WHAT WAS
THOUGHT TO BE POSSIBLE JUST ONE TO TWO DAYS AGO. THE DEVELOPING
TRACK AND INTENSITY SUGGESTS A MAJOR WINTER STORM HAS JUST BEGUN IN
OUR TEXAS COUNTIES AND WESTERN OKLAHOMA...AND WILL HAVE SEVERE
IMPACTS ACROSS THE REMAINDER OF NORTHERN...CENTRAL...AND SOUTHERN
OKLAHOMA THROUGH THIS EVENING.
..ICE POTENTIAL...
WHILE SNOW AND BLOWING SNOW ARE THE PRIMARY IMPACT...WE HAVE ALSO
INTRODUCED A PERIOD OF MIXED PRECIPITATION...INCLUDING FREEZING RAIN
AND SLEET...FOR CENTRAL AND NORTH CENTRAL OKLAHOMA...MAINLY THROUGH
NOON TODAY. OUR SPECIAL 06 UTC SOUNDING SHOWED A SUBSTANTIAL WARM
NOSE AT 800-700 MB. WITH THE MID LEVEL LOW CLOSING OFF NEAR THE RED
RIVER...EASTERLY WINDS WILL HOLD THE WARM AIR IN PLACE FROM THE OKC
METRO AREA NORTHWARD. AS COLD AIR SURGES IN AT THE SURFACE...THIS
CREATES A SETUP FOR ICE FROM MID MORNING TO MIDDAY. THE EFFECT IS
MORE PRONOUNCED IN THE RUC...AND THE NCEP PRECIP TYPE ALGORITHM
AVAILABLE PER THE SPC WEB SITE PAINTS A STRIPE OF ICE FROM OKC NORTH
ALONG INTERSTATE 35.
..HEAVY SNOW...
BY MIDDAY TO EARLY AFTERNOON...STRONG DYNAMIC LIFTING AND SOME COLD
ADVECTION SHOULD CHANGE ALL OF OUR FORECAST AREA OVER TO SNOW.
DESPITE THE LOSS OF A FEW SNOW HOURS DUE TO THE MORNING ICING...WE
STILL FEEL THERE WILL BE SIGNIFICANT SNOW ACCUMULATIONS FROM
OKLAHOMA CITY NORTH. THE SNOWFALL WILL BE GREATEST FARTHER
SOUTH...WHERE STRONG LIFTING WILL BEGIN MUCH EARLIER IN THE MORNING.
IN THE 06Z NAM...WE SEE STRONG VERTICAL MOTION THROUGH THE DENDRITIC
CRYSTAL GROWTH ZONE OVER NEARLY THE ENTIRE FORECAST AREA THIS
AFTERNOON. IT IS VERY DIFFICULT TO FORECAST HOW MUCH SNOW WILL
ACCUMULATE ON A GIVEN SURFACE...SINCE GROUND TEMPERATURES ARE ON THE
MILD SIDE...AND THE EVENT IS OCCURRING AT DAYTIME. IT IS
LIKELY...HOWEVER...THAT THERE WILL BE PERIODS OF HEAVY SNOW...WITH
ACCUMULATION OR 1 TO EVEN 2 INCHES PER HOUR...SOMEWHERE FROM CENTRAL
INTO SOUTH CENTRAL OKLAHOMA. THE 06Z NAM SNOW ACCUMULATION ALGORITHM
IS NOT TOO FAR OFF FROM OUR THINKING...AND WE RAISED SNOW TOTALS IN
THOSE AREAS.
..NEAR BLIZZARD...
AN ARCTIC FRONT WILL MOVE FROM WESTERN KANSAS THIS MORNING TO THE
INTERSTATE 44 CORRIDOR AT EARLY AFTERNOON. COLDER...DRIER AIR IN A
SHALLOW LAYER NEAR THE GROUND...ALONG WITH VERY GUSTY WINDS...WILL
INCREASE THE AMOUNT OF BLOWING SNOW AND LOWER WIND CHILL
TEMPERATURES TO AROUND 10 DEGREES ABOVE ZERO. IT IS EVEN POSSIBLE
THAT A BLIZZARD WARNING WOULD BE JUSTIFIED FOR A FEW HOURS THIS
AFTERNOON...SHOULD THE SNOW ACCUMULATION AND BLOWING SNOW OCCUR AS
FORECAST. THIS IS A LIFE THREATENING STORM.
..AFTER THE STORM...
WE USED THE COLDER NAM AND ECMWF TEMPERATURES IN THE DAYS TO
COME...GIVEN WIDESPREAD SNOW COVER. THE GFS DID NOT SEEM TO ACCOUNT
FOR THIS. WINDS ARE EXPECTED TO DECREASE RATHER QUICKLY IN THE
SECOND HALF OF THURSDAY NIGHT...SO THIS KEEPS WIND CHILLS JUST ABOVE
THE ADVISORY CRITERIA...AT LEAST IN THE CURRENT FORECAST. THIS
SHOULD BE REEVALUATED THIS EVENING. AFTER SEVERAL DAYS OF
COLD...THERE IS ANOTHER STORM SYSTEM SET TO BRING A CHANCE OF RAIN
OR SNOW BY NEXT TUESDAY AND WEDNESDAY.
..THANKS...
TO SURROUNDING NWS FORECAST OFFICES AND THE HPC AND SPC FOR THEIR
COLLABORATION THIS MORNING.
&&
.PRELIMINARY POINT TEMPS/POPS...
OKLAHOMA CITY OK 31 14 29 14 / 100 40 0 0
HOBART OK 30 11 31 12 / 100 20 10 0
WICHITA FALLS TX 34 12 34 14 / 100 20 0 0
GAGE OK 25 14 28 16 / 70 10 0 0
PONCA CITY OK 31 17 24 16 / 100 60 10 10
DURANT OK 45 20 33 19 / 100 50 0 10
&&
.OUN WATCHES/WARNINGS/ADVISORIES...
OK...WINTER STORM WARNING UNTIL 10 PM CST THIS EVENING FOR OKZ007-008-
012-013-018>020-024>032-039>043-045>048-050>052.
WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR
OKZ004>006-009>011-014-015.
WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR OKZ016-017-
021>023-033>038-044.
TX...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR TXZ083>090.
&&
$$
02/22/22
