Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000
FXUS63 KOAX 261148
AFDOAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
548 AM CST FRI DEC 26 2014

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 315 AM CST FRI DEC 26 2014

SNOW LATER TODAY AND TONIGHT IS THE PRIMARY FORECAST CONCERN.

WINTER WEATHER ADVISORY WILL BE IN EFFECT FOR A GOOD PART OF
NORTHEAST NEBRASKA THIS AFTERNOON AND TONIGHT. TOTAL SNOW AMOUNTS OF
2 TO 4 INCHES LOOK LIKELY IN THIS AREA...ALONG WITH WINDS UP TO 20
MPH.

AFTER A MOSTLY SUNNY HOLIDAY...LOW CLOUDS HAVE AGAIN INVADED EASTERN
NEBRASKA AND WESTERN IOWA THIS MORNING...SPREADING SOUTH BEHIND A
COLD FRONT WHICH SHOULD BE SOUTH OF NEBRASKA AND SOUTHWEST IOWA BY
OR SHORTLY AFTER SUNRISE. MEANWHILE...MID LEVEL RIPPLES IN SOUTHWEST
FLOW ALOFT EMANATING FROM BASE OF UPPER TROUGH IN ARIZONA WAS
PROVIDING WEAK LIFT FROM TIME TO TIME...CAUSING PATCHY DRIZZLE OR
FREEZING DRIZZLE FROM CENTRAL INTO NORTHEAST NEBRASKA. THIS
PHENOMENON APPEARS TO BE ISOLATED ENOUGH TO LIMIT IMPACTS THIS
MORNING.

ATTENTION THEN TURNS TO STRONGER WAVE EXPECTED TO EJECT INTO THE
PLAINS AND BEGIN TO AFFECT OUR AREA THIS AFTERNOON. GFS/NAM HAVE
SLOWED TIMING OF THIS FEATURE A TAD FROM EARLIER RUNS...AND APPEAR A
LITTLE MORE ROBUST WITH FORCING. AS WAVE MOVES INTO CENTRAL NEBRASKA
THIS AFTERNOON...ISENTROPIC UPGLIDE WILL INCREASE MARKEDLY ALONG
290K THETA SURFACE...MAGNIFYING FRONTOGENETICAL FORCING IN THE 600-
550MB LAYER OVER NORTHEAST NEBRASKA. BEST LIFT IS FORECAST NEAR OR
JUST AFTER 00Z...AND IS MAXIMIZED WITHIN DENDRITIC TEMPERATURE
REGIME OF FORECAST SOUNDINGS SUGGESTING EFFICIENT SNOW-MAKING.
NEGATIVE THETA-E LAPSE RATES AND EQUIVALENT POTENTIAL VORTICITY
SUGGEST AT LEAST CONDITIONAL INSTABILITY WILL LEAD TO BANDING OF
PRECIPITATION AS WELL. LESS FAVORABLE ENVIRONMENT IS FORECAST ACROSS
THE REST OF EASTERN NEBRASKA AND SOUTHWEST IOWA...BUT BROAD ASCENT IN
WARM ADVECTION REGIME WILL STILL BRING PRECIP TO THESE AREAS. AS
WAVE MOVES NORTHEAST OVERNIGHT...ASSOCIATED LIFT WILL TAPER AS WE
HEAD TOWARD 06Z. HOWEVER MOISTURE WILL REMAIN IN A DEEP DENDRITIC
TEMPERATURE LAYER ACROSS NORTHEAST NEBRASKA THROUGH OR PAST 12Z...SO
WE WILL LIKELY SEE PERSISTENT LIGHT SNOW THERE ADDING TO
ACCUMULATION.

AN ENSEMBLE APPROACH TO SNOWFALL AMOUNTS USING A VARIETY OF MODEL
OUTPUT POINTS TO SNOWFALL POTENTIAL IN THE 3 TO 4 INCH RANGE OVER A
GOOD CHUNK OF NORTHEAST NEBRASKA...WITH AMOUNTS TAPERING TO AN INCH
OR LESS ALONG AND SOUTHEAST OF INTERSTATE 80. SPECIFIC HUMIDITY
CALCULATIONS USING GARCIA METHOD SUGGEST SOME 5 INCH AMOUNTS ARE
ALSO POSSIBLE IN NORTHEAST NEBRASKA...MOST LIKELY NORTHWEST OF THE
NORFOLK AREA WHERE FRONTOGENESIS IS AT A MAXIMUM.

SNOWFALL MAY LINGER PAST 12Z IN PARTS OF NORTHEAST NEBRASKA AND WEST
CENTRAL IOWA...OTHERWISE EXPECT DECREASING CLOUDS AND COLD
TEMPERATURES. HIGHS WILL LIKELY HOLD IN THE 20S DESPITE SUNSHINE AND
LIGHT WESTERLY FLOW. MOSTLY CLEAR SKIES AND SNOWCOVER SHOULD PUSH
LOWS INTO SINGLE DIGITS SUNDAY MORNING IN NORTHEAST NEBRASKA...BUT
SOUTHWEST LOW LEVEL FLOW AHEAD OF AN APPROACHING COLD FRONT MAY HOLD
LOWS IN THE TEENS. THEN WE SHOULD REBOUND INTO THE 20S AND 30S
SUNDAY BEFORE CLOUDS THICKEN WITH ARRIVAL OF COLD FRONT LATER IN THE
DAY.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 315 AM CST FRI DEC 26 2014

BROAD TROUGH IS FORECAST TO SETTLE OVER MUCH OF THE CONUS TO START
THE WEEK...BRINGING COLD TEMPERATURES TO MUCH OF THE PLAINS. THE
LEADING EDGE OF THAT COLD AIR WILL BE SLIPPING THROUGH THE CWA
SUNDAY NIGHT WHEN 850 TEMPERATURES DROP FROM ABOUT 5 BELOW 00Z
MONDAY TO NEAR 15 BELOW BY 12Z TUESDAY. WEAK LIFT ACCOMPANYING THIS
COLD SURGE COULD SQUEEZE OUT SOME LIGHT SNOW MONDAY AND MONDAY
NIGHT...BUT AMOUNTS SHOULD BE LIGHT. THE MAIN WEATHER STORY AT THIS
TIME IS THE COLDER TEMPERATURES WITH MONDAY HIGHS IN THE TEENS NORTH
AND 20S SOUTH...DROPPING TO THE SINGLE DIGITS AND TEENS ON TUESDAY.
OVERNIGHT LOWS BOTH MONDAY NIGHT AND TUESDAY NIGHT WILL LIKELY DROP
BELOW ZERO IN MANY AREAS. A SLIGHT WARMING TREND IS FORECAST
WEDNESDAY AND THURSDAY AS THERMAL TROUGH SHIFTS TO THE EAST WITH
CORE OF MID LEVEL TROUGH.

&&

.AVIATION...(12Z TAFS FOR KOFK...KLNK AND KOMA.)
ISSUED AT 545 AM CST FRI DEC 26 2014

IFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH MUCH OF THE PERIOD
WITH INCREASING CHANCE OF LIGHT SNOW AT KOFK AFTER 18Z AND AFTER
01Z AT KLNK AND KOMA.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...WINTER WEATHER ADVISORY FROM 2 PM THIS AFTERNOON TO 4 AM CST
     SATURDAY FOR NEZ011-012-015>018-030>033-042-043.

IA...NONE.
&&

$$

SHORT TERM...DERGAN
LONG TERM...DERGAN
AVIATION...FOBERT


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