Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 182325 AAA
AFDLBF

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
525 PM CST THU DEC 18 2014

.SYNOPSIS...
ISSUED AT 307 PM CST THU DEC 18 2014

H5 ANALYSIS FROM THIS MORNING REMAINED ACTIVE ACROSS THE
LOWER 48 STATES. A CLOSED LOW WAS PRESENT ALONG THE MAINE ATLANTIC
COAST. FURTHER WEST...A SHORTWAVE WAS NOTED OVER CENTRAL SOUTH
DAKOTA...WITH A SECOND SHORTWAVE OVER CENTRAL KS AND A THIRD SHORTWAVE
OVER SWRN AZ. HT FALLS OF 50 TO 80 METERS...IN ASSOCIATION WITH THE
DISTURBANCE IN KANSAS...WERE NOTED OVER MISSOURI AND NRN OK. SOUTH
OF THE KANSAS DISTURBANCE...A 50 TO 70 KT JET STREAK EXTENDED FROM
SERN NM INTO THE MID ATLANTIC AND CANADIAN MARITIMES. AT THE
SURFACE...FOG AND STRATUS DOMINATED CENTRAL AND EASTERN PORTIONS OF
THE FORECAST AREA TDY WITH SOME CLEARING NOTED IN THE EASTERN
NEBRASKA PANHANDLE...AS WELL AS THE WESTERN SANDHILLS AND FAR SWRN
NEBRASKA. TEMPERATURES AS OF 3 PM CST RANGED FROM 27 AT AINSWORTH
AND VALENTINE TO 30 AT THEDFORD.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 307 PM CST THU DEC 18 2014

THE MAIN FORECAST CONCERNS OVER THE SHORT TERM ARE THE TEMPERATURES
AND THE POTENTIAL FOR FOG FORMATION.

IN ASSOCIATION WITH THE MOIST RETURN FLOW FROM THE SURFACE HIGH
PRESSURE SITUATED OVER THE UPPER MIDWEST...LOW STRATUS WILL CONTINUE
MOVING SLOWLY EASTWARD THIS EVENING AND TONIGHT ACROSS THE FORECAST
AREA. RELATIVELY DRIER AIR ASSOCIATED WITH A WEST WIND MOVES INTO THE
PANHANDLE AND FAR WESTERN COUNTIES TONIGHT...KEEPING THE SKY
RELATIVELY CLOUD FREE. THE 18/12Z MODEL RUNS...ESPECIALLY THE NAM
AND RAP...AND CURRENT TRENDS IN THE VISIBLE SATELLITE IMAGES BRING
THE BACK EDGE OF THE STRATUS TO THE HIGHWAY 83 CORRIDOR BY 19/00Z.
LIGHT WINDS AND A CLEARING SKY WILL ALLOW THE ATMOSPHERE TO DECOUPLE
OVERNIGHT...AND WITH DEW POINT DEPRESSIONS GENERALLY THREE DEGREES
OR LESS...FOG FORMATION IS FAVORABLE ALONG THE EDGE OF THE STRATUS
DECK. MIN TEMPS HAVE BEEN ADJUSTED DOWNWARD FROM THE PREVIOUS
FORECAST WEST OF HIGHWAY 83 TO ACCOUNT FOR THE DECOUPLING AND AN
EXISTING SNOW PACK IN MANY LOCATIONS. OVER NORTH CENTRAL NEBRASKA...WHERE
STRATUS IS EXPECTED TO REMAIN THROUGH THE NIGHT...HAVE KEPT MIN
TEMPS A FEW DEGREES WARMER.

FRIDAY...ANY FOG SHOULD BURN OFF BY 19/15Z AND MAX TEMPS WILL REFLECT
THE AMOUNT OF CLOUD COVER. DESPITE MOSTLY CLEAR SKIES AND WEST WINDS
FOR THE WESTERN 2/3 OF THE FORECAST AREA...HIGHS WILL STILL BE IN
THE UPPER 30S TO LOWER 40S AS 850HPA TEMPS STRUGGLE TO REACH 5C.
MODELS ARE CONSISTENT WITH KEEPING THE STRATUS FARTHER EAST...AND
HIGHS WILL STAY IN THE LOWER TO MID 30S. NOT LOOKING AT A DRIZZLE
THREAT AS FORECAST SOUNDINGS INDICATE RELATIVELY DRIER AIR RIGHT AT
THE SURFACE...TOO THIN OF A MOISTURE BAND...AND NO LIFT IN THE
NEAR SURFACE CLOUD LAYER.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 307 PM CST THU DEC 18 2014

MID RANGE...FRIDAY NIGHT THROUGH SUNDAY...IN THE MID
RANGE PERIODS...THE MAIN FORECAST CHALLENGE IS TEMPERATURES. FOR
FRIDAY NIGHT...BOTH THE LATEST NAM AND GFS SOLNS POSITION THE
WESTERN EDGE OF THE STRATUS DECK FROM SARGENT UP TO NAPER AT 00Z
SATURDAY. BY 12Z SATURDAY...THIS LINE EXTENDS ROUGHLY ALONG THE FAR
NERN BORDER OF THE FORECAST AREA. AS HAS BEEN THE CASE OVER THE PAST
COUPLE OF NIGHTS...THE WESTERN FRINGES OF THE STRATUS DECK IS WHERE
FOG WAS MOST PREVALENT. WITH LIGHT WINDS EXPECTED FRIDAY
NIGHT...DECIDED TO INSERT SOME PATCHY FOG ACROSS OUR FAR
NORTHEASTERN 4 COUNTIES. ELSEWHERE...CLEAR SKIES AND COLD TEMPS ARE
EXPECTED. WITH THE LIGHT WEST NORTHWESTERLY WINDS FORECAST ACROSS
SWRN NEBRASKA...DECIDED TO GO WITH SLIGHTLY COLDER LOWS IN THE
PLATTE RIVER VALLEY. ON SATURDAY...A WEAK SURFACE TROUGH WILL PUSH
EAST INTO THE CENTRAL SANDHILLS AND NORTH CENTRAL NEBRASKA. WITH
MOSTLY CLEAR SKIES...LIGHT WESTERLY WINDS AND H85 TEMPS IN THE LOW
SINGLE DIGITS ABOVE ZERO...HIGHS WILL REACH THE LOWER 40S...WITH
SOME MID AND UPPER 30S IN THE FAR NORTHEAST...WHERE STRATUS AND FOG
WILL BE POSSIBLE SATURDAY MORNING. FOR SATURDAY NIGHT AND
SUNDAY...LIGHT WESTERLY WINDS AND MOSTLY CLEAR SKIES ARE EXPECTED.
WITH THE EXCEPTION OF THE VALLEYS...WESTERLY WINDS SHOULD KEEP THE
BL SOMEWHAT MIXED SAT NIGHT. THIS WILL RESULT IN LOWS IN THE LOWER
20S WITH SOME TEENS POSSIBLE IN THE PLATTE VALLEY. SUNDAY WILL BE
THE WARMEST DAY OF THE PERIOD. WESTERLY WINDS WILL INCREASE AHEAD OF
AN APPROACHING COLD FRONT. SOUTH OF THE FRONT...H85 TEMPS WILL
INCREASE TO 3 TO 7C SUNDAY AFTERNOON...EQUATING TO HIGHS IN THE 40S
AND LOWER 50S. DECIDED TO UNDER CUT THIS A TAD BASED ON EXPECTED
RESIDUAL SNOW COVER AND THE THREAT FOR MID AND HIGH LEVEL CLOUDINESS
AS INDICATED IN THE GFS AND NAM H700-H500 RH PROGS.

SUNDAY NIGHT THROUGH CHRISTMAS DAY...FOR THE EXTENDED
PERIODS...PRECIPITATION CHANCES MONDAY-MONDAY NIGHT...FOLLOWED BY
PRECIPITATION CHANCES CHRISTMAS EVE NIGHT AND CHRISTMAS DAY WILL
HIGHLIGHT THE EXTENDED PERIODS. FOR MONDAY-MONDAY NIGHT...AN UPPER
LEVEL TROUGH OF LOW PRESSURE WILL DROP SOUTH FROM THE EASTERN
DAKOTAS INTO THE UPPER MIDWEST. AT THE SAME TIME ANOTHER...SEPARATE
UPPER LEVEL DISTURBANCE WILL DROP SOUTH ACROSS THE NORTHERN AND
CENTRAL ROCKIES. WITH BOTH THE GFS AND ECMWF SOLNS...SUFFICIENT LIFT
AND MOISTURE EXISTS WITH BOTH SYSTEMS TO PRODUCE PRECIPITATION.
ATTM...FEEL MORE CONFIDENT IN PRECIP CHANCES IN NORTHERN AND
NORTHEASTERN NEBRASKA IN ASSOCIATION WITH THE FIRST DISTURBANCE
MENTIONED ABOVE. ATTM THERE ARE SOME SUBTLE DIFFERENCES WITH THE
UPPER LEVEL JET STRUCTURE WITH THE WESTERN DISTURBANCE. THE ECMWF IS SLIGHTLY
FURTHER WEST WITH THE JET COMPARED TO THE GFS SOLN MONDAY...WHICH
FAVORS PRECIPITATION OVER THE ROCKIES VS. THE NEBR PANHANDLE AND FAR
SWRN CWA. ON TUESDAY AND THE FIRST HALF OF WEDNESDAY...THE FORECAST
AREA WILL BE BETWEEN SYSTEMS WITH MAINLY DRY CONDS EXPECTED. BY
MIDWEEK...A STRONG UPPER LEVEL TROUGH WILL DROP SOUTH INTO
IDAHO...UTAH AND NEVADA. THIS FEATURE WILL MIGRATE TO THE EAST
SOUTHEAST ON CHRISTMAS DAY. INCREASED MID LEVEL FRONTOGENESIS WILL
DEVELOP BEHIND AN EXITING ARCTIC FRONT CHRISTMAS DAY...WHICH WILL
LEAD TO INCREASED CHANCES FOR SNOW ACROSS THE FORECAST AREA. WITH
GOOD MODEL AGREEMENT NEXT WEEK...CONFIDENCE CONTINUES TO INCREASE IN
PRECIP CHANCES FOR CHRISTMAS DAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 524 PM CST THU DEC 18 2014

THE NAM...RAP AND BOTH HRRR MODELS SHOW LIFR DEVELOPING THIS
EVENING AT KLBF WHILE JUST ONE MODEL SHOWS THE SAME AT KVTN. THE
FORECAST IS FOR CLEARING AT LBF THIS EVENING FOLLOWED BY FOG
DEVELOPMENT AND IFR. AS INDICATED BY THE 4 MODELS...IFR/LIFR
WOULD BECOME WIDESPREAD OVERNIGHT ALONG AND EAST OF HIGHWAY 83
INCLUDING AREAS NEAR KOGA. IMPROVEMENT TO VFR ACROSS ALL AREAS IS
EXPECTED AROUND 18Z. VFR IS GENERALLY EXPECTED WEST OF HIGHWAY 61
TONIGHT AND FRIDAY.

THERE IS A CHANCE THAT LIFR WILL SET IN AT KLBF THIS EVENING AND
REMAIN IN PLACE THROUGH 14Z-16Z FRIDAY AS SHOWN BY THE RAP...NAM
AND HRRR MODELS. FOR NOW THE FORECAST IS FOR BETTER CONDITIONS
GIVEN THAT THESE MODELS TEND TO OVERFORECAST VISIBILITY
RESTRICTIONS AND THERE ARE SOME MIDLEVEL CLOUDS FORECAST TO MOVE
OVERHEAD TONIGHT WHICH COULD AFFECT THE RADIATION CONDITION
NECESSARY FOR DENSE FOG AND LIFR.

&&

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

$$

SYNOPSIS...CLB
SHORT TERM...DS
LONG TERM...CLB
AVIATION...CDC






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