Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 220336
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
936 PM CST SUN DEC 21 2014

.UPDATE...
ISSUED AT 923 PM CST SUN DEC 21 2014

COMPLEX FORECAST OVER THE NEXT 36 HOURS AS A STRONG PAC SHRTWV
TROF/JET MAX EMERGES ONTO THE PLAINS AND CLOSES OFF A MID LVL
CIRCULATION. MODELS CONT TO TREND FARTHER SOUTH WITH THIS SYSTEM
AND SEEMS REASONABLE GIVEN THE OBSERVED JET ON THE 00Z UPPER AIR
ANALYSIS. GOING FORECAST HAS THIS HANDLED PRETTY WELL BUT WE DID
UPDATE FOR A COUPLE CHANGES. WE HAVE SEEN WIDESPREAD -DZ ACRS THE
FA THIS EVNG AS WAA HAS INCREASED OVER A NEARLY SATURATED LOWER
ATMOSPHERE. THE MAIN BAND OF RA HAS YET TO DEVELOP THOUGH AS BOTH
THE KOAX/KLBF SOUNDINGS STILL SHOW SOME DRY MID-LEVEL AIR. SHRT
RANGE MODELS INDICATE THAT WE STILL HAVE SOME TIME BEFORE THE
FORCING OVER-COMES THIS DRY AIR AND ALLOWS FOR RAIN TO DVLP. THUS
HAVE PUSHED BACK THE ONSET OF THE LIKELY/CAT POPS...AND SLOWED THE
EWD PROGRESS OF THIS BAND ACRS THE FA ON MON AS WELL. WE ALSO
INCREASED OVERNIGHT LOWS...MAINLY IN THE NW WHERE PRETTY GOOD
SOUTHERLY FLOW SHOULD KEEP TEMPS INTO THE UPPER 30S OVERNIGHT.

WE WILL WAIT TO SEE THE FULL SET OF MODEL GUIDANCE BEFORE MAKING
ANY CHANGES TO THE MON NIGHT/TUE TIME FRAME...BUT WITH THE FARTHER
SOUTH SOLUTION ON THE LATEST MODELS THE THREAT OF SOME
ACCUMULATING SN IS THERE FOR THE I-80 CORRIDOR. THIS IS SUPPORTED
BY THE 18Z GFS/NAM AND THE 00Z NAM AS WELL. POINT FORECAST
SOUNDINGS OFF THE 00Z NAM INDC THAT WE WILL REMAIN TO WARM FOR
FROZEN PRECIP UNTIL AT LEAST 03Z TUE IN EAST CNTRL NEB BUT AFTER
THAT SOUNDINGS DO SUPPORT SN WITH GOOD LIFT OVERNIGHT INTO EARLY
TUE MRNG. IF THESE SOLUTIONS PAN OUT IT WOULD RESULT IN LESS SN
OVER NE NEB AND MORE OVER E-CNTRL NEB AND SW IA.

&&

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY)
ISSUED AT 321 PM CST SUN DEC 21 2014

RAIN THEN SNOW CHANCES TONIGHT THROUGH TUESDAY REMAIN THE PRIMARY
FORECAST CONCERNS.

LOW CLOUDS CLEARED FOR A TIME OVERNIGHT...BUT HAVE RETURNED TODAY
WITH MOIST LOW LEVEL SOUTHERLY FLOW. HOWEVER FOG HAS NOT BEEN AS
THICK GIVEN STRONGER WINDS. OUR FAR NORTHWEST CWA IS SEEING A
LITTLE MORE SUN THIS AFTERNOON...BUT THAT WILL BE SHORT-LIVED AS
STRATUS FROM THE SOUTH OVERSPREADS THERE SHORTLY.

ATTENTION THEN TURNS TO MID LEVEL TROUGH OVERHEAD...WITH AXIS
STRETCHING FROM SASKATCHEWAN INTO TEXAS...CUTTING THROUGH CENTRAL
NEBRASKA THIS AFTERNOON. MID LEVEL LOW NOTED ON WATER VAPOR AND RAP
ANALYSIS IN CANADA IS FORECAST TO TRANSLATE SOUTH OVERNIGHT...WITH A
WEAK CIRCULATION CENTERED OVER EASTERN NEBRASKA BY MONDAY AFTERNOON.
SURFACE LOW SHOULD FORM IN EASTERN SOUTH DAKOTA LATE
TONIGHT...PROMPTING SOUTHERLY FLOW TO CONTINUE IN EASTERN NEBRASKA
AND WESTERN IOWA THROUGH 12Z. COLD FRONT SHOULD BE ENTERING OUR
WESTERN CWA SHORTLY THEREAFTER...SWINGING THROUGH ALL THE CWA BY 00Z
TUESDAY. ISENTROPIC UPGLIDE ENHANCED BY DEVELOPING UPPER LOW WILL
LEAD TO HIGH PRECIPITATION CHANCES AS WE GO THROUGH THE NIGHT. HAVE
LIKELY POPS FOR A GOOD PART OF OUR AREA FROM ABOUT 06Z THROUGH 12Z.
THIS PRECIP SHIELD SHOULD BE WORKING NORTHEAST OF OUR AREA BY LATE
MONDAY MORNING...HOWEVER SECONDARY AREA OF PRECIP WILL BE DROPPING
SOUTH ON BACK SIDE OF SURFACE LOW IN TROWAL REGION OF UPPER LOW.
FORECAST SOUNDINGS SHOW A RELATIVELY DEEP LAYER OF SURFACE-BASED
WARM AIR OVERNIGHT WILL BE COOLED TOP-DOWN FROM NORTHWEST TO
SOUTHEAST LATE TONIGHT AND MONDAY. THIS SUGGESTS RAIN IS THE
FAVORED PRECIP TYPE TONIGHT...WITH A TRANSITION OVER TO A MIX OF
SNOW LATE TONIGHT IN OUR FAR NORTHWEST...THEN TO SNOW DURING THE
DAY MONDAY. AM NOT EXPECTING SLEET OR FREEZING RAIN BASED ON
CONFIGURATION OF TEMPERATURE PROFILE ON GFS/NAM FORECAST
SOUNDINGS.

AS COLD AIR FILTERS SOUTH ON MONDAY AFTERNOON AND NIGHT...SNOW
CHANCES WILL CONTINUE ACROSS MUCH OF THE CWA...BUT NORTHEAST
NEBRASKA WILL REMAIN UNDER FAVORED MID LEVEL DEFORMATION ZONE
THROUGH THE DAY TUESDAY. CURRENTLY SNOW AMOUNTS LOOK TO TOP OUT
AROUND 2 INCHES THERE...BUT COULD SEE SOME HIGHER AMOUNTS IF SNOW
PERSISTS IN ANY ONE AREA LONGER THAN EXPECTED. PERHAPS A HALF INCH
OR SO LOOKS TO BE IT ALONG INTERSTATE 80...AND LOWER OR NO AMOUNTS
TO THE SOUTH.

WINDS WILL ALSO KICK UP TUESDAY AS SURFACE LOW BEGINS TO MOVE AWAY
FROM THE PLAINS. COULD BE A BLOWING SNOW CONCERN THEN.

TEMPERATURES TONIGHT MAY ACTUALLY RISE A FEW DEGREES AFTER A SLIGHT
DECLINE THIS EVENING. THEN WE MAY SNEAK A FEW MORE DEGREES ON MONDAY
BEFORE COOL ADVECTION REALLY KICKS IN DURING THE AFTERNOON.
NORTHEAST NEBRASKA MAY SEE NO WARMING AT ALL ON MONDAY. COOLER HIGHS
IN THE UPPER 20S TO MIDDLE 30S ARE FORECAST TUESDAY GIVEN COLDER
AIRMASS AND CLOUD COVER...ALONG WITH BRISK NORTHWEST WINDS. MORE
SUNSHINE WEDNESDAY AND A WESTERLY WIND COMPONENT SHOULD PUSH HIGHS
INTO THE 30S ONCE AGAIN...BUT MIGHT HOLD IN THE 20S IN NORTHEAST
NEBRASKA WHERE EXPECTED NEW SNOW COVER WILL LIMIT WARMING.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 321 PM CST SUN DEC 21 2014

POTENTIAL SNOW FOR CHRISTMAS IS THE MAIN CONCERN IN THE LONGER TERM
PERIOD.

UPPER TROUGH BRINGING POTENTIAL SNOWS MONDAY INTO TUESDAY WILL SLIDE
OFF TO OUR EAST BY WEDNESDAY...AND WILL LIFT THROUGH THE UPPER EAST
COAST ON CHRISTMAS. ANOTHER TROUGH TO OUR WEST WILL BE GATHERING AT
THE SAME TIME...PRODUCING SOUTHWEST FLOW ALOFT OVER THE PLAINS. THAT
TROUGH LOOKS MORE PROGRESSIVE TODAY THAN IN PREVIOUS MODEL
CYCLES...AND GFS/ECMWF ARE RELATIVELY SIMILAR IN STRENGTH AND TIMING
OF WAVE MOVING INTO THE PLAINS...BUT DIFFER BY A COUPLE OF STATES ON
LOCATION OF POTENTIAL SNOW. GFS PAINTS MOST OF ITS QPF ACROSS
SOUTHERN NORTH DAKOTA...WHILE ECMWF TARGETS NEBRASKA AND IOWA.

BOTH MODELS HAVE CONTINUED THE TREND OF A MORE PROGRESSIVE
TROUGH...THUS THE MOVE FROM THURSDAY NIGHT/FRIDAY CHANCE TO A
THURSDAY/THURSDAY NIGHT CHANCE IS MAINTAINED. AS WILL BE OUR CHANCE
POPS ALREADY GOING...WITH ENSEMBLE FORECASTS AND RUN-TO-RUN AND
MODEL-TO-MODEL CONSISTENCY OFFERING NO CLEAR SOLUTION. AT ANY
RATE...IF WE DO SEE SNOW...AMOUNTS SHOULD BE AN INCH OR TWO GIVEN
PROGRESSIVE NATURE OF THE SYSTEM.

TEMPERATURES COULD APPROACH 40 EARLY CHRISTMAS BEFORE COLDER AIR
SPILLS INTO THE REGION WITH POTENTIAL SNOW. THIS COOLER AIRMASS WILL
REMAIN OVER THE REGION THROUGH THE WEEKEND...WITH HIGHS IN THE 20S
AND 30S.

&&

.AVIATION...(00Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 923 PM CST SUN DEC 21 2014

VIFR TO IFR CONDS ARE EXPECTED THROUGH THE PERIOD. WE WILL SEE DZ
ACRS THE TAF SITES THIS EVNG...AND AS THE STORM SYSTEM GETS CLOSER
TO THE TERMINALS LATE TONIGHT...THIS SHOULD BECOME -RA INTO MON
MRNG. WE WILL SEE A CDFNT MOV FM NW TO SE ACRS THE TAF SITES
DURING THE PERIOD WITH WINDS BECOME NW ON MON AFTN.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.

&&

$$

UPDATE...BOUSTEAD
SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...BOUSTEAD


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