Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 272120
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
320 PM CST SAT DEC 27 2014

.SYNOPSIS...
ISSUED AT 320 PM CST SAT DEC 27 2014

HIGHLY AMPLIFIED PATTERN ACROSS NORTH AMERICA WITH A TROUGH OF LOW
PRESSURE ACROSS THE PLAINS WITH HIGH PRESSURE DEVELOPING ACROSS THE
ERN PACIFIC. MUCH OF NEBRASKA HAS FRESH SNOW COVER...DEEPEST IN PARTS OF
THE PANHANDLE. SUNSHINE WARMING TEMPS MOST PLACES INTO THE 20S WITH
LIGHT WINDS OVER MUCH OF WESTERN AND NORTH CENTRAL NEBRASKA. THE
FRESH SNOW COVER WILL HAVE AN EFFECT ON LOW TEMPERATURES TONIGHT AS
MENTIONED IN THE SHORT TERM DISCUSSION. MODELS DO HAVE SOME ISSUES
IN THEIR INITIALIZATION OF THE MORE SIGNICIANT PV ANOMALIES AND
ASSOCIATED UPPER LEVEL COLD AIR COMPARED TO THIS MORNINGS SATELLITE
AND UPPER AIR SOUNDINGS...GENERALLY INITIALIZED A TAD TOO FAR NORTH
THAN SAT PICS SUGGEST.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 320 PM CST SAT DEC 27 2014

HIGH PRESSURE BOTH AT THE SURFACE AND ALOFT IS IN CONTROL ACROSS THE
CENTRAL PLAINS...WITH A CLEAR CALM NIGHT IN STORE FOR WESTERN AND
NORTH CENTRAL NEBRASKA. HAVE GONE BELOW GUIDANCE FOR LOWS...AS SET
UP IDEAL FOR GOOD RADIATIONAL COOLING WITH THE FRESH SNOW COVER AND
LIGHT WINDS. HAVE WENT BELOW ZERO IN BOTH THE PLATTE AND PORTIONS OF
THE NIOBRARA RIVER VALLEYS.

NEXT SYSTEM...CURRENTLY OFF THE BRITISH COLUMBIA COAST...WILL BEGIN
TO INFLUENCE OUR WEATHER SUNDAY. WINDS WILL BECOME EAST TO SOUTHEAST
DURING THE AFTERNOON AS LOW PRESSURE DEEPENS IN THE LEE OF THE
ROCKIES. CLOUDS WILL BE ON THE INCREASE...AS MID LEVEL MOISTURE
INCREASES. HAVE LEFT SNOW CHANCES OUT DURING THE DAY FOR ALL AREAS
EXCEPT THE FAR NORTHERN PANHANDLE...WHERE THE ATMOSPHERE WILL
SATURATE ENOUGH BY LATE AFTERNOON TO SUPPORT SOME LIGHT SNOW OR
FLURRIES.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 320 PM CST SAT DEC 27 2014

AS RIDGING CONTINUES TO DEVELOP IN THE EASTERN PACIFIC NORTHWARD
INTO ALASKA THROUGH THE NEXT FEW DAYS THE RESULTING FLOW DOWNSTREAM
OF THIS RIDGE WILL BE FROM THE NORTH AND WILL BRING SIGNIFICANTLY
COLDER AIR INTO THE REGION DURING THE PERIOD. AS THE RIDGE THEN
CONTINUES TO BUILD INTO THE ARCTIC CIRCLE BY LATE NEXT WEEK...A
BIFURCATED POLAR LOW WILL DEVELOP WHICH WILL RESEMBLE THE
ANOMALOUSLY COLD MID NOVEMBER PERIOD...AND ALSO SIMILAR TO LAST
WINTER. THE RESULT FOR THE PLAINS WILL EVENTUALLY BE ANOMALOUSLY
COLD TEMPERATURES EARLY THIS WEEK...THEN AGAIN BY NEXT WEEKEND.

LOOKING A LITTLE CLOSER AT DETAILS...SHORT WAVE CURRENTLY OFF THE
COAST OF BRITISH COLUMBIA WILL CARVE OUT A LARGE UPPER TROUGH OVER
THE CONUS. AS IS TYPICALLY THE CASE IN THESE HIGHLY SHEARED
ENVIRONMENTS...WHILE THE MODELS ARE FAIRLY SIMILAR IN THEIR
DEVELOPMENT OF THE LARGE SCALE TROUGH...INDIVIDUAL PV ANOMALIES
/SHORT WAVE ENERGY/ IS HANDLED DIFFERENTLY IN THE MODELS WHICH MAKES
TIMING AND LOCATION OF RESULTING PRECIPITATION DIFFICULT. THE FIRST
PV ANOMALY SHOULD APPROACH THE WRN PORTION OF NEBRASKA SUNDAY NIGHT
INTO MONDAY MORNING. THE COLD AIR ALOFT ASSOCIATED WITH THE SYSTEM
WILL ALSO MOVE SOUTHEASTWARD INTO THE WESTERN HIGH PLAINS. THE
RESULTANT ZONAL FLOW ALOFT THAT DEVELOPS AS THE LARGE SCALE TROUGH
DEVELOPS WILL CREATE LOW PRESSURE IN THE LEE OF THE ROCKIES LATE
SUNDAY NIGHT. THE NAM GENERATES MORE SIGNIFICANT SOUTHERLY FLOW
BRIEFLY AHEAD OF THE ADVANCING COLD FRONT SUNDAY NIGHT. THE END
RESULT OF THIS IS STRONGER FRONTOGENESIS IN THE NAM MONDAY MORNING
WHICH COMES FROM A MORE SIGNIFICANT CONTRIBUTION FROM THE
ROTATIONAL COMPONENT OF THE THERMAL FIELD...IN ADDITION TO THE
FLOW NORMAL TO THE ISOTHERMS. THEREFORE THE NAM GENERATES A MORE
SIGNIFICANT BAND OF SNOW ACROSS NORTH CENTRAL NEBRASKA. AS THIS
OCCURS...THE LIFT IN RESPONSE TO THE MID LEVEL FORCING TAKES
PLACES IN A SATURATED DGZ WHICH EXTENDS FROM JUST BELOW 700MB TO
NEAR THE SURFACE IN THE KVTN FORECAST SOUNDING...LEADING TO SNOW
TO LIQUID RATIOS OF 20-25 TO 1. SIMPLY PUT THIS MEANS IT WON/T
TAKE MUCH LIFT IN THIS INCREASINGLY COLDER REGIME TO PRODUCE
ACCUMULATING SNOWFALL DESPITE A MOISTURE PROFILE BEING AVERAGE.
ALSO WINDS SPEEDS WILL CREATE WIND CHILLS EVENTUALLY EXCEEDING
ADVISORY CRITERIA BY MONDAY NIGHT AND INTO TUESDAY WHICH IS
MENTIONED IN THE HWO. WILL HAVE TO WATCH THE DEVELOPMENT OF THIS
INITIAL WAVE SUNDAY NIGHT AND MONDAY BECAUSE THESE QUICK MOVING
SYSTEMS HAVE THE POTENTIAL TO PRODUCE SIGNIFICANT SNOWFALL IF
TIMING IS RIGHT.

BEYOND MONDAY...VERY COLD AIR WILL CONTINUE TO FILTER INTO THE
PLAINS. THE UPPER LOW THAT DEVELOPS ACROSS THE SOUTHWEST AND THE
RESULTANT SPLIT FLOW WILL KEEP THE NORTHERN PLAINS UNDER THE
INFLUENCE OF THE NORTHERN STREAM. AS THE UPPER LOW MOVES INTO THE
SOUTHERN PLAINS...THE NORTHERN PLAINS TEMPERATURES WILL MODERATE
SOMEWHAT THOUGH SNOW COVER MAY TRUMP THE TYPICAL EFFECTS OF ZONAL
FLOW ALOFT. THEN THE UPPER LOW IN THE SOUTH WILL PULL INTO THE MID
MISSISSIPPI VALLEY. THE PRECIPITATION ASSOCIATED WITH THIS SYSTEM
TOWARD THE END OF THE PERIOD SHOULD PASS SOUTH OF THE AREA. SO A
MAINLY DRY FORECAST IS IN PLACE THROUGH THE END OF THE WORK WEEK
AS TEMPERATURES REMAIN BELOW AVERAGE FOR THIS TIME OF YEAR.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1201 PM CST SAT DEC 27 2014

VFR AND CLEAR SKIES ARE EXPECTED TODAY AND TONIGHT WITH HIGH
PRESSURE REMAINS IN CONTROL. INCREASING MID LEVEL CLOUDS AROUND
10000 FT AGL WILL OCCUR SUNDAY MORNING AS THE NEXT WEATHER SYSTEM
APPROACHES THE AREA. WIND SPEEDS THE NEXT 24 HRS WILL BE
GENERALLY 10 KTS OR LESS.


&&

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

$$

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





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