Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 252114
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
314 PM CST THU DEC 25 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 312 PM CST THU DEC 25 2014

MAIN FORECAST CONCERNS IN THE SHORT TERM CENTER ON TWO DISTINCT
BANDS OF ACCUMULATING SNOWFALL.  MULTIPLE WINTER WEATHER ADVISORIES
ARE CURRENTLY IN EFFECT FOR THE SNOW.  PLEASE SEE THE APPROPRIATE
ADVISORY FOR YOUR AREA OF CONCERN.

THROUGH THE OVERNIGHT...PROXIMITY SOUNDINGS ACROSS NORTHWEST
NEBRASKA EAST THROUGH OUR NORTHERN ZONES REVEAL A FAVORABLE PROFILE
FOR ACCUMULATING SNOW.  THE NAM...GFS...RAP...AND OTHERS ALL AGREE
IN SUFFICIENT LIFT OPERATING ON A SATURATED DGZ TO PRODUCE
WIDESPREAD LIGHT SNOW.  MID-LEVEL FRONTOGENETIC FORCING IS NOT
OVERLY IMPRESSIVE...BUT FAVORABLE NONETHELESS FOR A MESOSCALE BAND
OF MODERATE SNOW GENERALLY FAVORING GARDEN AND SHERIDAN COUNTIES
NORTHEAST THROUGH CENTRAL CHERRY COUNTY.  SNOW AMOUNTS WILL
GENERALLY RANGE IN THE 1-3 INCH RANGE ACROSS NORTHWEST
NEBRASKA...EXCEPT UNDER THE HEAVIER BAND WHERE A GENERAL 3-5 INCHES
WILL BE POSSIBLE.  THE UPDATED FORECAST FALLS IN LINE WITH THE
PREVIOUS...THUS NO CHANGES ARE NEEDED.  WILL NEED TO WATCH THE END
TIME OF THE WINTER WEATHER ADVISORY FOR NORTHWEST NEBRASKA HOWEVER
AS DRY AIR WILL QUICKLY FILL SOUTH EARLY ON FRIDAY...SHUTTING DOWN
THE SNOW MACHINE.  THIS NW WINTER WEATHER ADVISORY EXPIRES FRIDAY AT
18Z.

FREEZING DRIZZLE HAS BEEN NOTED ON NEDOT WEBCAMS THIS AFTERNOON
ACROSS THE CENTRAL SANDHILLS /GENERALLY NEAR THE LEADING EDGE OF THE
STRATUS/...AND AFTER ANALYSIS OF PROXIMITY SOUNDINGS FROM THE
REGION...FELT IT WAS BEST TO INCLUDE A PATCHY FZDZ MENTION GOING
THROUGH THIS EVENING FOR PORTIONS OF SOUTHWEST NEBRASKA NORTHEAST
THROUGH THE CENTRAL SANDHILLS.

FRIDAY...THE MODELS CONTINUE TO CONVERGE ON A SOLUTION WHERE A PIECE
OF ENERGY /PV ANOMALY/ FROM A DESERT SOUTHWEST TROUGH ROTATES
NORTHEAST ACROSS THE CENTRAL PLAINS...SPREADING SNOW FOR THE CENTRAL
SANDHILLS AND POINTS SOUTHEAST.  ANALYSIS OF THE PV15 FIELD SUGGEST
THE MODELS HAVE A GOOD HANDLE ON THE CURRENT LOCATION OF THE
ANOMALY...WHICH YIELDS BETTER CONFIDENCE.  SNOW IS EXPECTED TO
INCREASE IN COVERAGE AND INTENSITY FIRST ACROSS SOUTHWEST NEBRASKA
EARLY FRIDAY AFTERNOON...THEN SPREAD NORTHEAST ACROSS EASTERN
PORTIONS OF THE FORECAST AREA THROUGH TOMORROW AFTERNOON.  FORCING
AND QPF WITH THIS SYSTEM IS NOT OVERLY IMPRESSIVE...BUT FAVORABLE
SLR/S WILL YIELD SOME ACCUMULATIONS.  HAVE ISSUED A WINTER WEATHER
ADVISORY FOR LOCATIONS ALONG AND SOUTHEAST OF A OGALLALA TO BURWELL
LINE.   THE BEST FRONTOGENETIC FORCING WILL FAVOR THE HEAVIEST
ACCUMULATIONS...WHICH IS ANTICIPATED ALONG AND EAST OF A NORTH
PLATTE TO BURWELL LINE.  SNOW ACCUMULATIONS MAY AMOUNT TO 2-4 INCHES
THERE...WITH LOCALLY HIGHER AMOUNTS POSSIBLE. ELSEWHERE 1-3 INCHES
ARE POSSIBLE IN THE ADVISORY AREA...BUT GIVEN THE HOLIDAY
TRAVEL...IT/S BEST TO LET THE TRAVELING PUBLIC KNOW OF THE POTENTIAL
IMPACTS WITH AN ADVISORY.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 312 PM CST THU DEC 25 2014

SYSTEM RELATIVE ISENTROPIC LIFT CONTINUES INTO LATE FRIDAY EVENING
AS MANIFEST IN THE LOCAL PRESSURE DERIVATIVE IN THE 280-295K LAYER
AND IN A CROSS-SECTION OF AGEOSTROPHIC VERTICAL CIRCULATION.
SATURATION DEFICITS ARE 5-15MB BUT MIXING RATIO IS 1-2G/KG...SO
ADDITIONAL MOISTURE WILL NOT BE REAL HIGH. SINCE A LARGE PART OF THE
SATURATED LAYER IS IN THE DENDRITIC GROWTH ZONE...THE SNOW TO LIQUID
RATIO WILL BE WELL ABOVE THE SEASONAL AVERAGE...POSSIBLY EXCEEDING
20/1 FROM THE NAM. HOWEVER...WE ARE LEANING TOWARD THE GFS GUIDANCE
WHICH WOULD GIVE STORM TOTAL PRECIPITATION AMOUNTS OF 0.10-0.25 INCH
SOUTH AND EAST OF AN ANW-OGA LINE WITH THE MAXIMUM ALONG AN ONL-BBW
AXIS. THIS SEEMS TO BE MORE IN LINE WITH THE 1-2G/KG MIXING RATIO.
THE GFS ALSO SHOWS A SLIGHTLY WARMER SATURATED LAYER AT -12C IN THE
LIFT AND ACCRETION LAYERS AND THUS WE WOULD EXPECT A LOWER SNOW TO
LIQUID RATIO MORE ON THE ORDER OF 17-19/1. MOST OF THE PRECIPITATION
IS LIKELY TO BE BEFORE 00Z FRIDAY EVENING AND THE ADDITIONAL AMOUNTS
IN THE EVENING WILL BE ONE TO TWO INCHES. WIND WILL DECREASE TO 10
TO 20 MPH BY 06Z.

THE NEXT SYSTEM OF CONCERN IS AN ARCTIC FRONT PIVOTING THROUGH
NEBRASKA MONDAY AND MONDAY NIGHT. SYSTEM RELATIVE LIFT AND
FRONTOGENESIS IN THE 280-290K LAYER PRODUCE DECENT UPWARD
MOTION...ESPECIALLY IN SOUTHWEST NEBRASKA. THE AIR IS NEARLY
SATURATED WITH SPECIFIC HUMIDITY OF 1-1.5G/KG AND PRECIPITABLE WATER
OF 0.20-0.25 INCH. FORECAST SOUNDINGS SHOW A FAIRLY DEEP SATURATED
ISOTHERMAL AREA THROUGH THE DENDRITIC LAYER (900-650MB) AND BEYOND.
AGAIN THIS WOULD POINT TO A HIGH SNOW TO LIQUID RATIO...SO SNOWFALL
COULD BE SIGNIFICANT. TEMPERATURES WILL BE A MAJOR ISSUE AS WELL.
WITH THE SOURCE OF THE AIR MASS BEING ABOVE THE ARCTIC CIRCLE AND
EXPECTED WIDESPREAD SNOW COVER...VERY COLD WEATHER IS LIKELY MONDAY
THROUGH WEDNESDAY NIGHT. HIGHS MONDAY MAY BE ONLY 5 TO 10 IN THE
SANDHILLS AND THE PANHANDLE AND 10-15 IN CENTRAL AND SOUTHWEST
NEBRASKA. LOWS MONDAY NIGHT AND TUESDAY NIGHT ARE LIKELY TO BE BELOW
ZERO. ANY WIND AT ALL WILL PRODUCE DANGEROUS WIND CHILL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1149 AM CST THU DEC 25 2014

COMPLICATED AVIATION FORECAST AS THE MODELS DEVELOP TWO SEPARATE
BANDS OF SNOW DURING THE 18Z AVIATION FORECAST PERIOD...EACH OF
WHICH WILL BRING SNOW...LOWERED CEILINGS AND REDUCED VISIBILITIES
TO PORTIONS OF THE FORECAST AREA. RIGHT NOW...SNOW AND FZFG IS
SPREADING EAST ACROSS NORTHWESTERN NEBRASKA. KVTN HAS LOWERED BELOW
1SM AS FZFG IMPACTS THE SITE...THE PERIOD OF FOG SHOULD BE BRIEF
HOWEVER...AS SNOW WILL BECOME THE PRIMARY IMPACT LATE THIS
AFTERNOON. SNOW WILL CONTINUE ACROSS NORTHERN NEBRASKA AND THE
WESTERN SANDHILLS INTO THE OVERNIGHT. FRIDAY...THE SECOND BAND
WILL DEVELOP ACROSS SOUTHWEST NEBRASKA DURING THE 12-15Z
TIME FRAME...AND THEN SPREAD NORTHEAST ACROSS KLBF AND KBBW BY
EARLY AFTERNOON /RIGHT AT OR JUST BEFORE 18Z/. SNOW...REDUCED
VISIBILITY AND LOWERED CEILINGS ARE ANTICIPATED ONCE AGAIN. A
PERIOD OF FZDZ MAY BE A CONCERN AS WELL...BUT CONFIDENCE WAS NOT
SUFFICIENT ENOUGH FOR A MENTION IN THE FORECAST. ALL IN ALL FORECAST
UPDATES ARE ANTICIPATED.


&&

.LBF WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 9 AM CST /8 AM MST/ FRIDAY TO
MIDNIGHT CST /11 PM MST/ FRIDAY NIGHT FOR NEZ025>029-036>038-
057>059-069>071.

WINTER WEATHER ADVISORY UNTIL NOON CST /11 AM MST/ FRIDAY FOR
NEZ004-005-022>024-035-056-094.

&&

$$

SHORT TERM...JACOBS
LONG TERM...SPRINGER
AVIATION...JACOBS






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