FXUS64 KOUN 230558
AFDOUN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
1158 PM CST TUE DEC 22 2009
.AVIATION...
A PRONOUNCED DRY SLOT AT LOW LEVELS IS CAPTURED FAIRLY WELL BY
RUC 0.5 KM RH AND BY LOW LEVEL ISENTROPIC SURFACES...AS WELL AS
OBSERVATIONS. HOWEVER...TAF GUIDANCE WANTS TO START NEARLY EVERY
TERMINAL WITH AN IFR OR LIFR CEILING. THIS IS NOT REALITY...SO WE
WILL LEAN TOWARD THE OPTIMISTIC SIDE THROUGH SUNRISE OR SO...AT
WHICH TIME MODEL RH PROGS SHOW 90-100 PCT RH AT LOW LEVELS OVER
THE MAJORITY OF THE AREA. THIS IS A TRICKY WIND FORECAST AT
KOKC/KOUN/KSPS AS A WIND SHIFT ASSOCIATED WITH A SURFACE FRONT MAY
LINGER NEAR THESE SITES UNTIL THE FRONT ACCELERATES WED AFTERNOON.
TAYLOR
&&
.PREV DISCUSSION... /ISSUED 1048 PM CST TUE DEC 22 2009/
UPDATE...
UPDATING GRIDS TO EXPAND SNOW ACCUMULATIONS FARTHER SOUTH INTO
CENTRAL OKLAHOMA AND DOWN TOWARDS THE ARBUCKLES FOR CHRISTMAS EVE.
LATEST GFS COMING IN RELATIVELY CLOSE TO THE MORE SOUTHWARD TRACK
OF THE UPPER LOW AS WAS ALSO DEPICTED BY THE LATEST NAM. STILL
SOME QUESTION REMAINS ON AMOUNTS AS DRY SLOT WITH LEAD SHORT WAVE WILL
TEMPORARILY MOVE OUT MOISTURE. MOST OF THE SNOW WILL LIKELY OCCUR
ON THE BACK SIDE OF THE UPPER LOW WHICH WILL BE PROGRESSIVE. AT
THIS TIME... IT APPEARS THAT THE MOST LIKELY WINDOW FOR
SIGNIFICANT ACCUMULATIONS WILL BE FROM VERY LATE WEDNESDAY NIGHT
THROUGH ABOUT MIDDAY THURSDAY. STRONG NORTH WINDS COULD ALSO LEAD
TO CONSIDERABLE BLOWING AND DRIFTING.
PREV DISCUSSION... /ISSUED 931 PM CST TUE DEC 22 2009/
UPDATE...
LEAD SHORT WAVE IS CURRENTLY MOVING THROUGH WEST TEXAS THIS
EVENING WITH SCATTERED LIGHT PRECIPITATION... PROBABLY MOSTLY
VIRGA... CURRENTLY DEVELOPING OVER OKLAHOMA AND PARTS OF NORTH
TEXAS. AS THE DRY SLOT WORKS ASSOCIATED WITH THE WAVE MOVES NORTHEAST...
THE CHANCE FOR MEASURABLE PCPN IN THE SOUTHWEST PART OF THE CWA
WILL BE FALLING OFF. MEANWHILE... HAVE INCLUDED THE CHANCE FOR
FREEZING DRIZZLE IN THE FAR NORTHWEST OKLAHOMA FOR THE
OVERNIGHT HOURS. TEMPERATURES HAVE LIKELY SLIPPED JUST BELOW
FREEZING IN FAR WESTERN HARPER COUNTY... AND COULD SEE SUB-
FREEZING TEMPS SLIP A LITTLE FARTHER EAST AND SOUTH BY MORNING. AT
THIS POINT... IT LOOKS LIKE PCPN WILL REMAIN VERY LIGHT... BUT
WILL KEEP TABS ON IT AS THE NIGHT PROGRESSES.
QUICK LOOK AT NEW MODEL RUNS TAKE THE 500 MB LOW FARTHER TO THE
SOUTH AGAIN WHICH COULD INCREASE THE CHANCE FOR ACCUMULATING SNOW FARTHER
SOUTH IN OUR AREA. HOWEVER... AMOUNTS ARE MORE PROBLEMATIC AS THIS
EVENING'S SHORT WAVE IS FORECAST TO BRING A DRY SLOT INTO THE AREA
LATE TONIGHT AND WEDNESDAY. THE DRY SLOT THEN EVOLVES INTO A
'DONUT HOLE' OF LOWER RH'S ACROSS MUCH OF THE AREA AS MOISTURE
BEGINS TO WRAP AROUND THE PERIPHERY OF THE MID LEVEL LOW WEDNESDAY
NIGHT. THIS COULD REDUCE PRECIPITATION AMOUNTS BEFORE WE POSSIBLY
SEE A NARROW WINDOW OF SOMEWHAT HEAVIER SNOW ACROSS CENTRAL
OKLAHOMA THURSDAY MORNING AS THE BAND OF MOISTURE ON THE WESTERN
SIDE OF THE LOW MOVES EAST. WILL SEE HOW THE OTHER MODELS
SOLUTIONS EVOLVE BEFORE ADJUSTING THINGS TOO MUCH.
PREV DISCUSSION... /ISSUED 552 PM CST TUE DEC 22 2009/
AVIATION...
GENERALLY...THE IDEA OF CEILINGS LOWERING INTO THE IFR CATEGORY
LATER TONIGHT...THEN IMPROVING SOME TOWARD LATE MORNING WEDNESDAY
HAS BEEN FOLLOWED. LOW LEVEL RELATIVE HUMIDITY PLOTS/ISENTROPIC
CHARTS FROM SHORT TERM MODELS DEPICT A WEDGE OF DRY AIR OVER
SOUTHWEST OK/WESTERN NORTH TX THAT COULD KEEP KCSM/KHBR FREE OF
IFR OR EVEN MVFR CIGS FOR A GREATER PERIOD THAN FORECAST. THIS LOW
LEVEL DRYING IS EXPECTED TO ALLOW CIGS AT KOKC/KOUN TO BECOME VFR
AROUND MIDDAY TOMORROW...THOUGH TIMING IS UNCERTAIN.
TAYLOR
PREV DISCUSSION... /ISSUED 402 PM CST TUE DEC 22 2009/
DISCUSSION...
SURFACE FRONTAL BOUNDARY CURRENTLY EXTENDS FROM NORTH CENTRAL INTO
SOUTHWEST OKLAHOMA. ALTHOUGH AIR ON THE COOL SIDE OF THIS BOUNDARY
IS NOT TOO COLD YET... THE COLDER AIR IN THE NORTHERN PLAINS WILL
MOVE SOUTH TOWARD THIS BOUNDARY OVER THE COURSE TONIGHT AND EARLY
WEDNESDAY. UPSTAIRS... THE UPPER LOW MOVING INTO ARIZONA WILL
MOVE EAST TONIGHT WITH STRONGER LIFT THAN EARLIER ANTICIPATED
DEVELOPING ACROSS THE AREA AHEAD OF THIS WAVE. WITH THE MOIST LOW-
LEVEL ATMOSPHERE AND THE BOUNDARY ACROSS A PORTION OF THE AREA...
IT IS LOOKING LIKE HIGHER CHANCES OF MEASURABLE RAIN AS OPPOSED TO
JUST DRIZZLE AND HAVE THEREFORE INCREASED THE POPS.
THE 12Z MODELS ARE ON THE SAME PAGE WITH THE EVOLUTION OF THIS
SYSTEM ALTHOUGH IT IS SLIGHTLY DIFFERENT THAN PREVIOUS RUNS. AFTER
THE FIRST WAVE MOVES BY THE AREA... SURFACE CYCLOGENESIS DEVELOPS
ALONG THE BOUNDARY WITH THIS SURFACE LOW MOVING NORTHEAST
TOMORROW AFTERNOON ALLOWING COLDER AIR TO BEGIN SPREADING ACROSS
MUCH OF THE AREA. MEANWHILE THE UPPER TROF CURRENTLY DIVING SOUTH
FROM OREGON SWINGS EAST FROM THE SOUTHWEST UNITED STATES AND
PASSES OVER THE AREA THURSDAY. WHILE THE BEST MOISTURE SHIFTS EAST
AS THE FIRST WAVE MOVES EAST... LINGERING MOISTURE MAY BE
SUFFICIENT FOR PRECIPITATION TO PERSIST. ENOUGH COOL AIR FILTERS
INTO THE AREA TO SUPPORT THE CHANGE TO SNOW IN NORTHWEST OKLAHOMA
LATE WEDNESDAY AFTERNOON ACCORDING TO THE BUFR SOUNDINGS... WITH
THE COOL AIR SPREADING ACROSS THE AREA AND SUPPORTING A CHANGEOVER
TO SNOW FARTHER SOUTHEAST THURSDAY AS PRECIPITATION IS WANING.
THE OVERLAP BETWEEN THE SUFFICIENTLY COLD LOW-LEVEL AIR AND
PRECIPITATION MAY ALLOW SOME LIGHT ACCUMULATIONS /AN INCH OR SO/
ACROSS NORTHERN OKLAHOMA BUT STILL DO NOT EXPECT SIGNIFICANT
SNOWFALL. MORE LIKELY TO BE NOTICED WILL BE THE STRONG NORTH WINDS
/25 TO 35 MPH IN SOME AREAS/ ON CHRISTMAS EVE IN RESPONSE TO THE
DEEPENING LOW PRESSURE TO THE EAST AS THIS SECOND WAVE MOVES
THROUGH THE PLAINS. THE WIND IN CONJUNCTION WITH THE COLDER LOW-
LEVEL AIR WILL MAKE IT FEEL QUITE COLD. PRECIP MAY LINGER NORTH ON
THURSDAY NIGHT AND FRIDAY AS ANOTHER SHORTWAVE MOVES SOUTH THROUGH
THE PLAINS ON THE BACK SIDE OF THE SECOND LOW... BUT MOISTURE WILL
BE LIMITED.
IN THE EXTENDED... NO SIGNIFICANT UPDATES EXCEPT TO LOWER MAX
TEMPERATURES ON SUNDAY AND MONDAY.
&&
.PRELIMINARY POINT TEMPS/POPS...
OKLAHOMA CITY OK 48 59 32 38 / 30 70 50 30
HOBART OK 44 55 29 37 / 20 40 40 10
WICHITA FALLS TX 50 65 34 39 / 20 40 50 20
GAGE OK 31 39 21 30 / 40 60 50 20
PONCA CITY OK 43 50 30 36 / 70 90 60 50
DURANT OK 56 68 40 42 / 40 60 70 30
&&
.OUN WATCHES/WARNINGS/ADVISORIES...
OK...NONE.
TX...NONE.
&&
$$
32/03/03
