Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 282353
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
553 PM CST SUN DEC 28 2014

.SYNOPSIS...
ISSUED AT 320 PM CST SUN DEC 28 2014

HIGHLY AMPLIFIED PATTERN REMAINS ACROSS MUCH OF NORTH AMERICA WITH
SEVERAL SIGNIFICANT PV ANOMALIES SHOWN IN WATER VAPOR IMAGERY THIS
AFTERNOON. STILL HAVE SOME CONCERNS THAT MODELS MAY NOT BE HANDLING
THE INITIALIZATION OF THE INDIVIDUAL PV ANOMALIES CORRECTLY...BUT
SEEM TO NOT BE TOO FAR OFF ON THERMAL FIELDS BASED ON UA ANALYSIS.
MID CLOUDS ADVANCING ACROSS NEBRASKA THIS AFTERNOON WITH ANOTHER
AREA OF COOLING CLOUD TOPS IDENTIFIED ACROSS WY IN ASSOCIATION WITH
NEXT PIECE OF ENERGY MOVING QUICKLY SEWD. ARCTIC COLD FRONT LOCATED
ACROSS SRN SD AND IS BACKING SLOWLY SWWD ACCOMPANIED BY STRATUS. KLNX
88D INDICATING INCREASING ECHOES ACROSS THE SANDHILLS AND A FEW
SITES IN THE PANHANDLE REPORTING -SN.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 320 PM CST SUN DEC 28 2014

LEAD SHORTWAVE WAVE/PV ANOMALY IS CURRENTLY PROGRESSING INTO WESTERN
WYOMING PER WATER VAPOR IMAGERY. MODELS CONTINUE TO BRING THIS WAVE
EAST ACROSS NEBRASKA TONIGHT AND MONDAY. THE OVERALL TREND IN THE
MODELS TODAY HAS BEEN FOR THE WYOMING SHORTWAVE TO BE A BIT WEAKER
AS IT MOVES ACROSS. MODEL SOUNDINGS AND CROSS SECTIONS STILL
INDICATE THAT SNOW WILL FALL...BUT THE UPWARD VERTICAL MOTION ISN/T
QUITE AS ROBUST AS IN PREVIOUS MODEL RUNS. WILL ONLY SLIGHTLY
DECREASE CURRENTLY FORECASTED SNOW AMOUNTS BASED ON THE LATEST MODEL
TRENDS...AS MODELS ARE NOTORIOUS FOR NOT HANDLING THESE NORTHERN
ROCKIES SYSTEM WELL. STILL THINKING THAT A 17:1 OR 18:1 SNOW TO
LIQUID RATIO LOOKS GOOD FOR TONIGHT...AND ABOUT 19:1 OR SO FOR
MONDAY. DGZ IS DEEP...AND DESPITE WEAK LIFT...SNOW PRODUCTION LOOKS
FAVORABLE...SO A WIDESPREAD 1 TO 3 INCHES WITH LOCAL AMOUNTS TO 4
INCHES IS LIKELY. WINDS WILL INCREASE SOMEWHAT LATER TONIGHT...AS
THE PRESSURE GRADIENT TIGHTENS DUE TO HIGH PRESSURE BUILDING SOUTH
INTO THE REGION. 500 METER WIND SPEEDS DO INCREASE TO AROUND 20
KTS BY LATE MONDAY AFTERNOON...WHICH WILL SUPPORT 15 TO 20 MPH
SUSTAINED WINDS AT THE SURFACE. SO WHILE NOT EXPECTED TO BE A HUGE
DEAL...THERE WILL BE ENOUGH WIND TO CAUSE SOME BLOWING AND
DRIFTING SNOW.

TEMPERATURE WISE...ARCTIC AIR WILL BE SPILLING INTO THE AREA BY
AFTERNOON MONDAY. EXPECT FALLING TEMPERATURES AND BITTER COLD WIND
CHILLS. TEMPERATURES FALL TO NEAR ZERO BY LATE AFTERNOON ACROSS
NORTHERN NEBRASKA...WITH SINGLE DIGITS FARTHER SOUTH.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 320 PM CST SUN DEC 28 2014

SURFACE HIGH PRESSURE AND ASSOCIATED ARCTIC AIR CONTINUES TO SETTLE
OVER THE NRN ROCKIES AND INTO THE HIGH PLAINS REGION THROUGH TUESDAY
INTO TUESDAY NIGHT. AS THIS HAPPENS BEST FRONTOGENESIS AND LARGE
SCALE UPWARD VERTICAL MOTION ENDS ACROSS WESTERN NEBRASKA LATE
MONDAY NIGHT INTO TUESDAY MORNING. WEAK UPSLOPE FLOW WILL ALSO
WEAKEN AS MUCH DRIER AIR FILTERS INTO THE REGION IN THE LOW LEVELS.
THIS WILL GRADUALLY BRING AN END TO THE SNOW FIRST ACROSS THE NORTH
AND THEN SOUTHWEST BY TUESDAY NIGHT. SKIES WILL ALSO GRADUALLY CLEAR
FROM NORTH TO SOUTH BY SUNRISE WED MORNING. THIS WILL MEAN WITH
FRESH SNOW COVER TEMPS WILL FALL QUICKLY. DESPITE VERY COLD AIR IT
LOOKS AS THO RECORDS ARE OUT OF REACH. THE MAIN CONCERN WILL BE WIND
CHILL VALUES MONDAY EVENING THROUGH WEDNESDAY AND HEADLINES LOOK LIKE
THEY WOULD BE NEEDED IN THAT TIME FRAME AND SUBSEQUENT FORECASTS
WILL STRIVE TO REFINE THE SPECIFIC DETAILS CONCERNING THAT. FOR NOW
WILL BE FOCUSING ON SPREADING THE MESSAGE OF IMPACTS RELATED TO VERY
COLD WIND CHILLS.

AS THE NRN PLAINS BECOMES MORE UNDER THE INFLUENCE OF THE NRN STREAM
UPPER FLOW ALL THE MODELS ARE SIMILAR IN DEVELOPING AN UPPER LOW
OVER THE SOUTHWEST. HOWEVER...THE MODELS DIFFER IN THEIR HANDLING OF
THE CUT OFF SYSTEM WHICH RESULTS EVENTUALLY IN SIGNIFICANT
DIFFERENCES IN SENSIBLE WEATHER BY THE WEEKEND. THE GFS NOW APPEARS
TO BE A NRN OUTLIER WITH THE SRN STATES UPPER LOW AS IT MOVES IT
ACROSS THE SRN PLAINS QUICKER THAN GEM/EC AND EVENTUALLY SHEARS IT
OUT OVER THE MID MISSISSIPPI VALLEY. THE EC IS MUCH SLOWER WHICH
ALLOWS THE WRN STATES RIDGE THAT DEVELOPS BY LATE SATURDAY TO BUILD
FURTHER NORTH AND INLAND...WHILE THE GFS PHASES THE NRN AND SRN
STREAM AGAIN TO FORM A LARGE BROAD TROUGH OVER THE CONUS. THOUGH IT
IS HARD TO PIN DOWN A SINGLE PORTION OF THE MODEL RUNS THAT
INSTIGATE THE DRASTIC DIFFS...IT APPEARS AS THOUGH THE HANDLING OF A
REX BLOCK OVER THE PACIFIC AROUND 160W...AND ESPECIALLY THE AMOUNT
OF JET STREAM ENERGY TOPPING THE ANOMALOUS UPPER HIGH OVER THE NRN
AK INTO THE ARCTIC OCEAN THAT EVENTUALLY TRANSLATES TO WHETHER AN
UPPER RIDGE BUILDS IN TO THE WRN THIRD OF THE COUNTRY THROUGH THE
WEEKEND.

AS MENTIONED THIS RESULTS IN DRASTIC DIFFERENCES NOT ONLY TEMPS
BUT ALSO WHERE JET STREAM ENERGY RESIDES ACROSS THE PLAINS AND
ULTIMATELY PRECIPITATION. WITH SUCH DRASTIC DIFFERENCES IN MID
RANGE SOLUTIONS CONFIDENCE IS LOW IN FCST DETAILS FROM FRIDAY THRU
SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 552 PM CST SUN DEC 28 2014

FOR THE KLBF TERMINAL...EXPECT OVERCAST SKIES RANGING FROM 5000 TO
8000 FT AGL OVERNIGHT. CIGS WILL FALL TO 1500 FT AGL MONDAY
MORNING AS LIGHT SNOW DEVELOPS ACROSS SOUTHWESTERN NEBRASKA.
VISIBILITIES MAY DROP AS LOW AS 3SM WITH THE LIGHT SNOW. FOR THE
KVTN TERMINAL...LOOK FOR LIGHT SNOW TO DEVELOP BY MID EVENING
ACROSS NORTHERN NEBRASKA WITH CIGS AROUND 1500 FT AGL. VISBYS MAY
DROP AS LOW AS 2SM WITH THE SNOW. SNOW WILL END BY MID AFTERNOON
MONDAY...WITH CIGS REMAINING IN THE 1500 TO 2000 FT RANGE.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...JWS
SHORT TERM...TAYLOR
LONG TERM...JWS
AVIATION...CLB





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