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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KOAX 072326
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
526 PM CST SAT DEC 7 2013

.AVIATION...
-- Changed Discussion --
00Z TAFS FOR KOMA...KLNK AND KOFK. VFR CONDITIONS
INITIALLY AS WE WAIT FOR THE ATMOSPHERE TO SATURATE DOWNWARD.
EXPECTING SNOW AND EVENTUALLY MVFR CONDITIONS TO DEVELOP AT ALL
SITES. OPTED TO DROP INTO IFR FOR A 6-8 HOUR PERIOD WHEN SNOW MAY
BE THE HEAVIEST. COULD SEE A FEW FLAKES AT KLNK BY 04-06Z...BUT
BECOMING PREVAILING AND WIDESPREAD BY 07-09Z. SOUTHEAST WINDS
THROUGH FIRST HALF OF THE PERIOD INCREASING TO AROUND 12 KNOTS...
THEN BECOMING LIGHT AND VARIABLE AND THEN NORTHWEST AS THE
SURFACE TROUGH MOVES THROUGH BY 08/21Z. SNOWFALL ACCUMULATIONS
AVERAGING AROUND 3 INCHES PLUS OR MINUS ONE HALF INCH.

DEWALD
-- End Changed Discussion --

&&

.PREV DISCUSSION... 
-- Changed Discussion --
/ISSUED 320 PM CST SAT DEC 7 2013/

SHORT TERM...TONIGHT THROUGH TUESDAY.
ACCUMULATING SNOW THROUGH SUNDAY AND COLD TEMPERATURES WILL
CONTINUE TO BE THE PRIMARY FORECAST CONCERNS IN THE SHORT TERM.
HOW LONG TO SATURATE AND HOW QUICKLY SYSTEM WILL MOVE OUT WILL
LEAD CONCERNS WITH FORECAST AMOUNTS.

WITH CLEAR SKIES OVERNIGHT AND LIGHTER WINDS...RESULTED IN
TEMPERATURES ACROSS THE ENTIRE CWA DROPPING BELOW ZERO. MOST
LOCATIONS WERE 2 TO 8 DEGREES BELOW ZERO...HOWEVER SNOWCOVERED
AREAS IN NORTHEAST NEBRASKA DROPPED TO AT LEAST 10 TO 22 DEGREES
BELOW ZERO.

THE 12Z RAOBS SHOWED THAT THE OAX PW WAS A PALTRY 0.09 OF AN INCH
WITH SUCH A COLD ATMOSPHERE. AT H3...A 130KT JET EXTENDED FROM THE
UPPER MISSISSIPPI VALLEY INTO THE NORTHEAST U.S. WITH ANOTHER
135KT JET MOVING INTO CENTRAL CALIFORNIA. THE H5 TROF EXTENDED
FROM THE NORTHERN PLAINS INTO OREGON WITH 110M HEIGHT FALLS AT
RENO NEVADA. HIGH CLOUDS DID OVERSPREAD MUCH OF THE AREA. THROUGH
THE MORNING...HIGH CLOUDS HAVE INCREASED WITH SOME MID CLOUDS AT
18Z REPORTED IN SOUTH CENTRAL NEBRASKA AND CIGS BELOW 5K FEET IN
SOUTHWEST NEBRASKA. BY 21Z...LBF HAD PICKED UP A DUSTING OF SNOW
AND THE WSR-88D WAS SHOWING MORE ACTIVITY OVER PARTS OF KANSAS.

THROUGH 00Z MONDAY...THE H3 JET WILL TRACK EAST INTO THE CENTRAL
PLAINS...STRENGTHENING TO 150KTS.  THERE WILL BE SOME COUPLING OF
THIS JET WITH THE JET OVER THE NORTHEAST U.S. ENHANCING THE UPPER
LEVEL DIVERGENCE OVER THE FORECAST AREA.  AT H5...THE HEIGHT FALLS
TRACK INTO THE FOUR CORNERS REGION WITH THE TROF DEEPENING OVER THE
ROCKIES AND THEN PROGRESSES ACROSS THE PLAINS THROUGH SUNDAY
EVENING. MEANWHILE....120M HT FALLS IN WESTERN CANADA LEAD TO THE H5
TROF RE-ESTABLISHING ITSELF ACROSS MONTANA AND THIS TROF WILL THEN
MOVE THROUGH THE PLAINS MONDAY.

BROAD MID LEVEL WARM AIR ADVECTION BEGINS IN EARNEST THIS AFTERNOON
AND CONTINUED THROUGH 18Z SUNDAY...SHIFTING INTO IOWA SUNDAY
AFTERNOON. INITIAL TOP DOWN SATURATION LOOKS TO OCCUR WESTERN AND
CENTRAL NEBRASKA LIFTING INTO PARTS OF NORTHEAST NEBRASKA BY AROUND
06Z. THE HRRR/RAP SEEMS TO HAVE A GOOD HANDLE ON THIS. NONE OF THE
MODELS SEEM TO PICK UP ON THE SNOW IN KANSAS...ALTHOUGH IT IS
LIGHT. THE H85 THETA-E ADVECTION INCREASES ACROSS KANSAS WITH
PRECIPITATION ECHOES INCREASING ACROSS THE REST OF THE CWA AS
ISENTROPIC LIFT/OMEGA ALSO INCREASE. THERE ARE STILL SOME
DIFFERENCES ON HOW QUICKLY THINGS WILL SATURATE AND THIS WILL
IMPACT SNOW ACCUMULATIONS. WILL LEAN TOWARD A BLEND OF THE DRIER
GFS AND THE FASTER NAM FOR SATURATION TIMING MORE LIKE THE
EC/HOPWRF/ARW-NAM. HAVE SETTLED ON QPF OF .15 TO .20 ACROSS THE
CWA FOR THE EVENT AND LIQUID TO SNOW RATIOS OF AROUND 17. THIS
WOULD GIVE MAINLY 2 TO 4 INCHES OF FLUFFY SNOWFALL FOR THE CWA.
DUE TO THE CONSISTENCY OVER THE LAST COUPLE OF DAYS...HAVE GONE
WITH A WINTER WEATHER ADVISORY FOR THE FORECAST AREA. FOR NOW LEFT
PAWNEE AND RICHARDSON OUT IN COORD WITH EAX. THE WESTERN COUNTIES
WILL START AT MIDNIGHT AND WILL START THE SOUTHEAST NEBRASKA AND
SOUTHWEST IOWA COUNTIES AT 3AM AND CONTINUE THE ADVISORY THROUGH
6PM. SOME ADDITIONAL LIGHT AMOUNTS COULD LINGER INTO SUNDAY
EVENING ESPECIALLY FOR WESTERN IOWA.

SURFACE HIGH PRESSURE WILL BUILD IN FOR MONDAY AND INITIALLY THERE
WILL BE SOME BRISK NORTHWEST WINDS. THESE WINDS WILL BECOME
SOUTHWEST DURING THE AFTERNOON AS THE SURFACE HIGHS DROPS
SOUTHWARD AND SURFACE LOW PRESSURE DEVELOPS ACROSS THE NORTHERN
PLAINS. HIGHS SUNDAY SHOULD BE IN THE TEENS WITH TEENS AND 20S
MONDAY. WESTERLY FLOW SHOULD HELP TEMPERATURES RISE INTO THE 20S
TUESDAY.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY.

A FAIRLY QUIET SENSIBLE WEATHER PERIOD IS EXPECTED IN THE EXTENDED.
THE LARGE-SCALE FLOW WILL BE PREDOMINATELY NORTHWEST THROUGH THE
PERIOD WITH ONLY MINOR SHORTWAVE TROUGHS AFFECTING THE LOCAL AREA
THAT WILL BE MOISTURE STARVED AND PROVIDE ONLY WEAK FORCING FOR
ASCENT. THUS WE HAVE LEFT THE FORECAST FOR THE EXTENDED DRY. THE
FIRST OF THESE SHORTWAVE TROUGHS WILL BE MOVING THROUGH ON TUESDAY
NIGHT AND ALLOW FOR A COLD FRONT TO CROSS THE FA BY WED AM. WE HAVE
LOWERED GOING HIGHS ON WED WITH THE EXPECTED CAA AND CONTINUED SNOW
COVER. THIS SURFACE HIGH WILL MOVE OFF TO THE EAST ON WED
NIGHT...BUT WE MAY SEE TEMPS QUICKLY DROP OFF IN THE EAST WED
EVENING SO WE ALSO SHAVED THE LOWS ON WED NIGHT PRIMARILY ACROSS WRN
IA WITH TEMPERATURES LIKELY WARMING AFTER MIDNIGHT. WARMER PACIFIC
AIR WILL START TO SPILL INTO THE REGION FOR THU AND FRI WITH
SOUTHWEST SURFACE WINDS AND THIS SHOULD LEAD TO A DECENT WARM
UP...BUT HIGHS ARE STILL LIKELY TO REMAIN BELOW NORMAL. THE SECOND
SHORTWAVE TROUGH WILL MOVE THROUGH ON FRIDAY AND ALLOW FOR A COLD
FRONT TO AGAIN MOVE THROUGH FRI NIGHT. THIS SYSTEM LOOKS GENERALLY
DRY BUT WILL ALLOW FOR MUCH COOLER AIR TO SPILL INTO THE FA TO START
THE NEXT WEEKEND.

AVIATION...
18Z TAFS FOR KOMA...KLNK...AND KOFK.

VFR CONDITIONS WILL CONTINUE THROUGH THIS AFTERNOON AND INTO THE
EVENING HOURS...WITH LIGHT WINDS BECOMING SOUTHEASTERLY BELOW
10KT...AND WITH A FEW MID-LEVEL CLOUDS. CEILINGS WILL DROP LATER
THIS EVENING...WITH SNOW DEVELOPING AT KOFK BY AROUND MIDNIGHT AND
KOMA/KLNK A FEW HOURS LATER. KEPT VISIBILITY DUE TO SNOW ON THE
LIGHT SIDE AS MAINLY LIGHT TO MODERATE SNOWFALL RATES ARE
EXPECTED. CEILINGS ARE MVFR INITIALLY...WITH THE POTENTIAL TO COME
DOWN TO IFR AS MORE MODERATE SNOWFALL OCCURS ON SUNDAY MORNING.
-- End Changed Discussion --

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM CST SUNDAY
     FOR NEZ011-012-015>018-030>034-042>045-050-051-065-066-078-
     088-089.

     WINTER WEATHER ADVISORY FROM 3 AM TO 6 PM CST SUNDAY FOR NEZ052-
     053-067-068-090-091.

IA...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM CST SUNDAY
     FOR IAZ043-055.

     WINTER WEATHER ADVISORY FROM 3 AM TO 6 PM CST SUNDAY FOR IAZ056-
     069-079-080-090-091.

&&

$$