Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 221741
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1141 AM CST MON DEC 22 2014

.SYNOPSIS...
ISSUED AT 349 AM CST MON DEC 22 2014

THE MAIN AREA OF SURFACE LOW PRESSURE EXTENDS FROM SWRN NORTH DAKOTA
INTO CENTRAL SOUTH DAKOTA IN RESPONSE TO A STRONG DISTURBANCE
ENTERING THE REGION. NORTHWEST WINDS HAVE INCREASED TO 15 TO 25 MPH
IN SOME AREAS OF WESTERN NEBRASKA. WHERE MIXING IS
OCCURRING...TEMPERATURES HOLDING IN THE UPPER 30S...EXCEPT AT LBF
WHERE WINDS REMAIN DECOUPLED AND TEMPERATURES COLDEST AT NEAR 30
DEGREES. THERE REMAIN SCATTERED LIGHT RAIN SHOWERS ACROSS THE
AINSWORTH AND ONEILL AREAS WITH ADDITIONAL SHOWERS MOVING FROM THE
BLACK HILLS REGION INTO THE PINE RIDGE AREA OF THE NRN PNHDL.

&&

.UPDATE...
ISSUED AT 1140 AM CST MON DEC 22 2014

FORECAST FOR TODAY INTO THIS EVENING WAS UPDATED PRIMARILY FOR
TEMPERATURES AND PRECIPITATION TRENDS. THE SURFACE LOW ASSOCIATED
WITH THE SYSTEM TO IMPACT THE AREA OVER THE NEXT 24-36 HOURS IS
CURRENTLY OVER THE NORTHEASTERN QUADRANT OF SOUTH DAKOTA...BETWEEN
KABR/KATY/KHON. THIS IS NEAR 200 MILES NORTH OF WHERE MODELS HAD
IT LOCATED 24 HOURS AGO WHICH EXPLAINS WHY PRECIPITATION IS
GENERALLY OVER SOUTH DAKOTA INTO EASTERN NEBRASKA RATHER THAN
ACROSS NEBRASKA TODAY. THE SLOWER TREND FROM THE MODELS WITH THE
PROGRESSION OF THIS SYSTEM CONTINUES SO THE FORECAST HAS BEEN
MODIFIED TO SLOW THE PRECIPITATION CHANCES INTO THE AREA UNTIL
LATER THIS AFTERNOON AND TONIGHT AS THE SURFACE LOW SLOWLY MOVES
SOUTH. THERE WILL BE SOME VERY LIGHT AND PERIODIC PRECIPITATION
SEEN OVER NORTH CENTRAL NEBRASKA THROUGH THE AFTERNOON AS RADAR
HAS BEEN INDICATING PRECIPITATION OVER THAT AREA THIS MORNING AND
LAPS SOUNDINGS SHOW THE COLUMN IS NEAR SATURATION. AUTOMATED
OBSERVATIONS HAVE NOT REPORTED ANY RAIN WITH THIS ACTIVITY...BUT
DID GET REPORT OF LIGHT RAIN...WHILE LOCATIONS UPSTREAM
/KICR/K9V9/KPIR ARE INDICATING LIGHT RAIN AND DRIZZLE CURRENTLY.
SO LEFT IN LOW PRECIPITATION CHANCES FOR THE REMAINDER OF THE DAY.
STILL LOOKING LIKE ENOUGH MOISTURE WILL BE PULLED AROUND THE
SYSTEM TO GET PRECIPITATION OVER INTO THE PANHANDLE AND WESTERN
SANDHILLS TONIGHT AND TUESDAY. AMOUNTS ARE STILL IN
QUESTION...WITH HIGHEST AMOUNTS LIKELY OVER THE PINE RIDGE OF 4
INCHES OR BETTER. WINDS HAVE STARTED TO INCREASE THIS
MORNING...BUT WILL SEE THE STRONGEST WINDS INTO TUESDAY AS THE
PRESSURE GRADIENT TIGHTENS OVER THE NEXT 24 HOURS AND VERTICAL
MIXING IS ABLE TO MIX STRONGER WINDS TO THE SURFACE. EVEN WITH THE
LIGHT SNOW...THESE WINDS SHOULD BE ENOUGH TO KEEP SNOW BLOWING
AROUND TO CREATE HAZARDOUS WINTER CONDITIONS TONIGHT AND TUESDAY
SO NO PLANS ON CHANGES TO THE CURRENT WINTER WEATHER ADVISORY.
TEMPERATURES HAVE WARMED MORE THAN THE PREVIOUS FORECAST HAD
INDICATED AS THE SYSTEM IS SLOWER TO BRING IN THE COOLER AIR AND
MUCH OF THE WESTERN PART OF THE AREA HAS SEEN SUNSHINE. THIS WILL
HAVE AN IMPACT ON TIMING OF CHANGEOVER TO SNOW AND THE UPDATED
FORECAST HAS DELAYED THIS TO LATER THIS AFTERNOON OVER THE
PANHANDLE...AND INTO THE EVENING FOR THE REMAINDER OF THE AREA.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 349 AM CST MON DEC 22 2014

A FAIRLY STRONG DISTURBANCE WITH A CENTER CURRENTLY MOVING INTO FAR
NORTHEAST MONTANA WILL DIG SOUTHEAST TODAY AND CLOSE OFF NEAR
CHAMBERLAIN SOUTH DAKOTA BY LATE AFTERNOON. THIS POSITION IS ABOUT
12 HOURS SLOWER THAN MODEL FORECASTS WERE SHOWING 24 HOURS AGO. DUE
TO THE SLOWING OF THE SYSTEM...A DELAY IN IMPACTS CONCERNING SNOW
AND BLOWING SNOW IS FORECAST TO BEGIN TONIGHT. THERE IS A LEAD
DISTURBANCE CURRENTLY LOCATED NEAR MOBRIDGE SD...WHICH WILL BRING AN
AREA OF RAIN CURRENTLY ACROSS THE BLACK HILLS REGION INTO NORTH
CENTRAL NEBRASKA TODAY. DUE TO LIMITED COVERAGE...HAVE HELD POPS IN
THE NCTRL TO AROUND 30 PERCENT...WHILE WEST CENTRAL AND SOUTHWEST
NEBRASKA FORECAST TO REMAIN DRY. ACROSS THE NCTRL...TEMPERATURES
ALOFT WILL GRADUALLY COOL TODAY WITH A CHANCE FOR RAIN OR SNOW.
TEMPERATURES WILL REACH TO AROUND 35 DEGREES IN THE NCTRL TO NEAR 40
IN THE SOUTHWEST. NW WINDS TO INCREASE TO 20 TO 30 MPH BY THIS
AFTERNOON WITH GOOD MIXING. SKIES TO ALSO REMAIN MOSTLY CLOUDY.

FOR TONIGHT...THE CLOSED LOW WILL DROP SOUTHEAST THROUGH EASTERN
NEBRASKA AND BECOME ELONGATED...EXTENDING FROM NEAR MANHATTAN KS TO
DUBUQUE IOWA. A VORTICITY LOBE ON THE WESTERN PERIPHERY OF THIS LOW
WILL BRING INCREASED CHANCES FOR SNOW TO WESTERN NEBRASKA OVERNIGHT.
A DEFORMATION BAND OF SNOW WILL DEVELOP FROM WESTERN SOUTH DAKOTA
INTO WESTERN NEBRASKA. AS H85 WINDS BACK FROM THE NW TO THE NORTH
TONIGHT...UPSLOPE CONDITIONS WILL STRENGTHEN IN THE PINE RIDGE
REGION. HIGHEST SNOWFALL AMOUNTS OF 2 TO 4 INCHES IN NORTHERN
SHERIDAN COUNTY. ACROSS THE REMAINDER OF THE ADVISORY AREA...1 TO 2
INCH AMOUNTS POSSIBLE. NORTHWEST WINDS AT H85 INCREASE CONSIDERABLY
AFTER MIDNIGHT TO 45 TO 50 KTS IN THE ADVISORY AREA. AS THESE WINDS
MIX DOWN...SURFACE WIND OF 25 TO 35 MPH WITH GUSTS UP TO 40 MPH ARE
LIKELY. THIS WILL CAUSE AREAS OF BLOWING SNOW AND REDUCED VISIBILITY
AFTER MIDNIGHT. THE BEGIN TIME FOR THE CURRENT WINTER WEATHER
ADVISORY WAS DELAYED UNTIL 00Z THIS EVENING AND EXTENDED THROUGH
TUESDAY ENDING 00Z WEDNESDAY. ADDITIONALLY BLAINE...BROWN AND KEYA
PAHA COUNTIES WERE ADDED TO THE ADVISORY.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 349 AM CST MON DEC 22 2014

MODELS ARE ABOUT 12 HOURS SLOWER WITH THE STORM SYSTEM COMPARED TO
THIS TIME YESTERDAY. ALL IN ALL THIS IS A RATHER COMPLEX
SYSTEM...WITH SEVERAL VORTICITY MAXIMA ROTATING AROUND A CLOSED H500
MB CENTER THAT SHOULD BE LOCATED ACROSS SOUTH CENTRAL SOUTH
DAKOTA...NEAR OR JUST SOUTH OF CHAMBERLAIN EARLY THIS EVENING. ONE
OF THOSE MAXIMUMS WILL ROTATE SOUTH INTO THE NORTH CENTRAL NEBRASKA
THIS EVENING...WITH THE H700 MB FLOW BACKING FROM NORTHWEST TO MORE
NORTH OR NORTHEAST. THIS SHOULD ALLOW FOR DEEPER MOISTURE TO WRAP
SOUTH INTO THE AREA...ALONG WITH AT LEAST WEAK LIFT THROUGH A NEARLY
SATURATED DGZ. THE RESULT SHOULD BE LIGHT TO PERHAPS MODERATE SNOW
DEVELOPING ACROSS NORTH CENTRAL NEBRASKA/SANDHILLS EARLY THIS
EVENING...THEN SPREADING SOUTH AND EAST ACROSS THE REST OF THE AREA.
THE MOST LIKELY AREA FOR MODERATE INTENSITY SNOWFALL WILL BE IN THE
UPSLOPE AREA OF THE PINE RIDGE. THIS AREA WILL HAVE TO BE WATCHED
CLOSELY...AS THE MID LEVEL FLOW TRAJECTORY IS IDEAL FOR HEAVIER SNOW
ACCUMULATIONS IN THAT AREA. FOR NOW...THINKING AROUND 4 TO 5 INCHES
WILL ACCUMULATE BY THE TIME THE SNOW ENDS TUESDAY IN THE PINE
RIDGE...WITH A WIDESPREAD 1 TO LOCALLY 4 INCHES ACROSS THE REST OF
NORTH CENTRAL NEBRASKA...AND AROUND ONE INCH OR SO ACROSS THE
CENTRAL INTO SOUTHWEST PORTIONS OF NEBRASKA. SO NOT EXPECTING A LOT
OF SNOW ACCUMULATION FOR THE MOST PART...BUT WIND WILL BECOME A
PROBLEM LATE TONIGHT INTO AT LEAST THE FIRST HALF OF TUESDAY ON THE
WEST SIDE OF STORM SYSTEM SYSTEM...WHICH SHOULD BE CENTERED ACROSS
WESTERN IOWA OR FAR EASTERN NEBRASKA BY TUESDAY MORNING. MODELS
GENERALLY INDICATE THE H850 MB FLOW INCREASING TO AROUND 50 KTS
AFTER MIDNIGHT TONIGHT...THEN DECREASING SLOWLY THROUGH THE DAY
TUESDAY. 500 METER AGL WIND SPEEDS INCREASE TO AROUND 30 TO 35
KTS...AND LOCAL SUSTAINED WINDS AROUND 30 MPH AT THE SURFACE ARE NOT
OUT OF THE QUESTION. THIS COULD CAUSE SOME PROBLEMS WITH LOW
VISIBILITY IN BLOWING SNOW...AND A WINTER WEATHER ADVISORY IS IN
EFFECT TO COVER THIS WHERE THE MOST SNOW ACCUMULATION AND WIND WILL
COMBINE.

WINDS WILL QUICKLY DIMINISH TUESDAY NIGHT...ALONG WITH CLEARING
SKIES AS RIDGING BUILDS INTO THE AREA AHEAD OF THE NEXT SYSTEM
SLATED TO ARRIVE LATER CHRISTMAS DAY INTO FRIDAY. MODELS CONTINUE TO
STRUGGLE WITH THIS SYSTEM...WITH THE PARALLEL GFS AND GEM THE TWO
STRONGEST SOLUTIONS...AND THE ECMWF AND ESPECIALLY THE OPERATIONAL
GFS WEAKER. WITH THE SPREAD IN THE MODELS...WILL CONTINUE TO KEEP
POPS IN THE CHANCE CATEGORY...AND ONLY ADJUST THE TIMING A BIT WITH
THIS FORECAST ISSUANCE. MODELS NOT REALLY IN AGREEMENT ON TIMING
EITHER...BUT IT DOES APPEAR THAT MOST OF WHAT SNOW FALLS SHOULD HOLD
OFF UNTIL AFTER CHRISTMAS DAY...SO TRIED TO ADJUST FOR
THAT.

IN THE WAKE OF THIS SYSTEM...SHOULD BE QUIET DURING THE WEEKEND.
TEMPERATURES WILL REMAIN CHILLY HOWEVER...AS MOST OF THE AREA SHOULD
HAVE AT LEAST SOME SNOW ON THE GROUND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1140 AM CST MON DEC 22 2014

DETERIORATING CONDITIONS ARE LIKELY ACROSS NEBRASKA OVER THE NEXT
24 HOURS. WINDS WILL CONTINUE TO INCREASE THROUGH THE
AFTERNOON...AND WILL BE STRONGEST DURING THE DAY TUESDAY WITH
SUSTAINED WINDS OUT OF THE NORTHWEST AT 20-30KTS AND GUSTS UP TO
40KTS. WINDS WILL DIMINISH TUESDAY EVENING. PRECIPITATION CHANCES
HAVE BEEN DELAYED FOR THE AREA...WITH CHANCES FOR SNOW INCLUDED IN
THE FORECAST THIS EVENING AND OVERNIGHT. IT IS POSSIBLE TO SEE
SOME LIGHT RAIN OVER NORTHERN NEBRASKA THIS AFTERNOON...BUT IT
WILL MOST LIKELY STAY EAST OF KVTN WITH NO IMPACTS TO VISIBILITY.
CEILINGS WILL DROP AS WELL WITH CONDITIONS EXPECTED TO DROP TO
IFR LATE TONIGHT AT KVTN AND TUESDAY MORNING AT KLBF. SNOW SHOULD
LOOSE INTENSITY BY LATE TUESDAY MORNING...BUT STRONG WINDS COULD
CREATE SOME BLOWING SNOW TO FURTHER CAUSE REDUCED VISIBILITIES.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 6 PM CST /5 PM MST/ THIS EVENING TO
6 PM CST /5 PM MST/ TUESDAY FOR NEZ004>006-008-023>026-035>037-
094.

&&

$$

UPDATE...BROOKS
SYNOPSIS...ROBERG
SHORT TERM...ROBERG
LONG TERM...TAYLOR
AVIATION...BROOKS








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