Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 152329 AAA
AFDLBF

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
529 PM CST MON DEC 15 2014

.SYNOPSIS...
ISSUED AT 315 PM CST MON DEC 15 2014

H5 ANALYSIS FROM EARLIER THIS MORNING HAD AN UPPER LEVEL
LOW OVER CENTRAL KS IN THE VICINITY OF SALINA WITH A TROUGH
EXTENDING SWD INTO THE ARKLATEX. DOWNSTREAM RIDGING WAS PRESENT
ACROSS THE EASTERN GREAT LAKES AND MID ATLANTIC STATES. NORTHWEST OF
THE CLOSED LOW...HIGH PRESSURE WAS PRESENT OVER NWRN ALBERTA...WHILE
A TROUGH OF LOW PRESSURE EXTENDED FROM THE GULF OF ALASKA SOUTH TO
JUST OFF THE COAST OF NRN CALIFORNIA. AS OF 2 PM CST...THE UPPER
LEVEL LOW HAD TRACKED FROM CENTRAL KS TO JUST NORTH OF CHILLICOTHE
MO. AT THE SURFACE...LOW PRESSURE WAS IN THE VICINITY OF LAMONI IOWA
WITH A COLD FRONT EXTENDING SSE INTO SOUTH CENTRAL MO. HIGH PRESSURE
WAS NOTED OVER EASTERN MT. ACROSS WESTERN AND NORTH CENTRAL
NEBRASKA...STRONG NORTHERLY WINDS WERE PRESENT...ALONG WITH LIGHT
SNOW...WHICH AS REDUCED VISIBILITIES DOWN TO 1/2SM TO 2SM AS OF 2 PM
CST. UNDER CLOUDY SKIES...TEMPERATURES AS OF 2 PM CST RANGED
FROM...25 AT VALENTINE...TO 29 AT NORTH PLATTE...BROKEN BOW AND
OGALLALA.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 315 PM CST MON DEC 15 2014

FOR THE NEXT 36 HOURS...MAIN FORECAST CONCERNS REVOLVE
AROUND THE EXIT OF THE UPPER LEVEL SYSTEM THAT IS BRINGING
WIDESPREAD ACCUMULATING SNOW TO THE REGION.  TEMPERATURE FORECAST
TONIGHT AND TOMORROW ALSO DESERVES CONSIDERATION.

FORECAST GUIDANCE INDICATES THE UPPER LOW WILL CONTINUE TO THE EAST
OVER THE UPPER MISSISSIPPI VALLEY...AND GET CAUGHT UP IN A NORTHERN
STREAM SHORTWAVE/UPPER LOW OVER THE NEXT 24 HOURS.   LOW AMPLITUDE
TRANSITORY RIDGING WILL THEN TAKE HOLD ACROSS THE CENTRAL PLAINS AS
THE NEXT UPPER LEVEL TROUGH DEEPENS OVER THE WESTERN COAST.  AT THE
SURFACE...CANADIAN HIGH PRESSURE WILL FILL SOUTH BEHIND THE
DEPARTING SURFACE LOW PROVIDING FOR DRIER CONDITIONS AND COOLER
TEMPERATURES.  WITH CAA FILTERING SOUTH ACROSS THE
PLAINS...OVERNIGHT LOWS WILL BE CHILLY...GENERALLY IN THE SINGLE
DIGITS AND LOWER TEENS FROM WEST TO EAST ACROSS THE FORECAST AREA.
THE OVERNIGHT TEMPERATURE FORECAST IS A PRODUCT OF NUMERICAL
GUIDANCE WITH THE PREVIOUS FORECAST...WHICH ASSUMES SOME CLEARING.
IF SUBSTANTIAL CLEARING WERE TO OCCUR...TEMPERATURES MAY PLUMMET
ACROSS OUR WESTERN ZONES AS A FRESH SNOWPACK COMBINES WITH LIGHT
WINDS.  HIGHS REBOUND SOME TUESDAY...BUT WITH CANADIAN HIGH PRESSURE
OVERHEAD...AND WEAK COLD AIR ADVECTION CONTINUING...HIGHS SHOULD
ONLY TOP OUT IN THE 20S FOR LOCATIONS ALONG AND NORTH OF
I80...POSSIBLY A FEW LOWER 30S COULD BE ACHIEVED ACROSS OUR SOUTH AS
THE WINDS BEGIN TO VEER TO THE SOUTH LATE IN THE DAY BEHIND THE HIGH.

CONCERNING PRECIPITATION...NEAR TERM GUIDANCE HAS ACCUMULATING
SNOWFALL OUT OF THE CWA...SAVE FOR THE NORTHEASTERN SANDHILLS AND
NORTH CENTRAL NEBRASKA BY 00Z THIS EVENING...WITH SNOW ENDING
GENERALLY AT 03Z FOR OUR FAR NORTHEAST.  THE FORECAST USED A BLEND
OF THE 15.12Z NAM12 WITH THE LATEST RAP WHICH SEEMS TO PROVIDE A
PLAUSIBLE NORTHWEST TO EAST DEMISE OF THE SNOWFALL.  IR
SATELLITE/RADAR TRENDS OVER THE PAST FEW HOURS EARLY AFTERNOON
SUPPORT THE IDEA AS CLOUD TOPS ARE WARMING AND REFLECTIVITY IS
BECOMING LESS DEFINED.  SUPPOSE ANOTHER INCH OR TWO OF SNOW IS STILL
POSSIBLE ACROSS OUR NORTHERN ZONES LATE THIS AFTERNOON AS THE MODELS
SUGGEST QPF RATES OF UP TO FIVE HUNDREDTHS OF AN INCH PER HOUR
CONTINUING UNTIL 03Z.  IMPACTS FROM ANY ADDITIONAL SNOW HOWEVER WILL
CONTINUE TO COMPOUND VISIBILITY ISSUES WITH BLOWING SNOW FROM THE
30-40 MPH GUSTS OCCURRING...WINDS WILL WEAKEN THOUGH AS THE PRESSURE
GRADIENT RELAXES THIS EVENING.

THE CURRENT WINTER STORM WARNING AND WINTER WEATHER ADVISORY WILL
EXPIRE AT 00Z THIS EVENING...BUT A FEW SMALL CHANGES MAYBE/ARE
NEEDED.  ACROSS NORTH CENTRAL NEBRASKA...A EXTENSION OF THE
ADVISORY/WARNING IS NEEDED THROUGH 03Z TO ACCOUNT FOR THE LATER
ENDING TIME OF SNOW AND GUSTY NORTHWEST WIND.  COUNTIES MAY BE
DROPPED ACROSS OUR FAR SOUTH EARLY..BUT THE RECENT OB FROM KMCK
SUGGEST LIGHT TO OCCASIONAL MODERATE SNOW...WILL RE-EVALUATE IN THE
NEXT COUPLE HORUS. ELSEWHERE THE HEADLINES ARE ANTICIPATED TO BE
ALLOWED TO EXPIRE ON TIME.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 315 PM CST MON DEC 15 2014

MID RANGE...TUESDAY NIGHT THROUGH THURSDAY...IN THE MID
RANGE PERIODS...TEMPERATURES AND PRECIPITATION CHANCES ON WEDNESDAY
NIGHT ARE THE MAIN FORECASTING CHALLENGES IN THE MID RANGE PERIODS.
FOR TUESDAY NIGHT...A TROUGH OF LOW PRESSURE ALOFT WILL PUSH INTO
SRN CALIFORNIA RESULTING IN ANOTHER SOAKER FOR THE SWRN CONUS.
DOWNSTREAM OF THE TROUGH...LOW AMPLITUDE RIDGING WILL EXTEND ACROSS
THE SRN PLAINS INTO NEBRASKA. SURFACE HIGH PRESSURE WILL DOMINATE
THE PLAINS STATES AND OZARKS TUESDAY NIGHT. WITH FRESH
SNOWCOVER...LIGHT WINDS AND PARTLY CLOUDY SKIES...LOWS WILL BE COLD
IN THE SINGLE DIGITS AND LOWS WERE TRENDED DOWNWARD FROM THE
INHERITED FORECAST. FOR WEDNESDAY AND WEDNESDAY NIGHT...THE UPPER
LEVEL TROUGH WILL MIGRATE EAST INTO THE DESERT SOUTHWEST. SOME MODEL
DIFFERENCES WERE NOTED WITH THE FORWARD SPEED AND TRACK OF THIS
SYSTEM MIDWEEK. THE LATEST NAM AND ECMWF SOLNS FROM 12Z THIS MORNING
ACTUALLY DEVELOP A CLOSED LOW ALONG THE AZ/NM AND MEXICAN BORDER AT
00Z FRIDAY. THE GFS IS FASTER AND OPEN WITH THIS SYSTEM...MIGRATING
IT INTO NM AND WEST TX BY 00Z FRIDAY. WHAT ALL THREE MODELS DO
INDICATE IS A LEAD DISTURBANCE WHICH CROSSES THE SRN PLAINS INTO THE
OZARKS WEDNESDAY NIGHT. BOTH THE GFS AND ECMWF SOLNS LIFT INCREASED
LOW LEVEL MOISTURE INTO SRN NEBRASKA WEDNESDAY NIGHT IN ASSOCIATION
WITH THE LEAD DISTURBANCE. LIFT HOWEVER REMAINS WEAK PER CROSS
SECTIONS...AND WITH A FAIRLY DRY LAYER AROUND H7...AM NOT TOO
EXCITED ABOUT PCPN IN OUR AREA WEDS NIGHT. INHERITED FCST HAD A
SLIGHT CHANCE MENTION IN THE SOUTH AND SERN CWA DURING THE PERIOD
AND GIVEN THE LOW LEVEL MOISTURE AND SOME MODEL AGREEMENT BETWEEN
THE GFS AND ECMWF SOLNS...WILL LEAVE POP MENTION UNCHANGED FOR NOW.
AS FOR PTYPE WEDNESDAY NIGHT...LOOKING AT FCST SOUNDINGS...WAS
INITIALLY A LITTLE CONCERNED ABOUT THE THREAT FOR FREEZING DRIZZLE
IN THE SERN CWA. LOOKING AT BUFKIT SOUNDINGS...THE THREAT FOR FZDZ
SHOULD BE OFF TO THE SOUTHEAST OF THE FORECAST AREA AND WILL LEAVE
PRECIP MENTION AS ALL SNOW.

THURSDAY NIGHT THROUGH MONDAY...A TANDEM OF SRN STREAM WAVES WILL
TRACK ACROSS THE SRN TIER OF STATES FRIDAY...AND THEN AGAIN SUNDAY
NIGHT INTO MONDAY. ATTM...FAVORABLE FORCING FOR PRECIPITATION SHOULD
REMAIN SOUTH OF THE FORECAST AREA SO WILL FORECAST DRY CONDS ATTM.
HOWEVER...THE LATEST GFS SOLN BEGINS TO DIVERGE TOWARD A MORE ACTIVE
NRN STREAM NEXT WEEK...FORCING A CLIPPER SYSTEM THROUGH THE NRN
PLAINS EARLY NEXT WEEK...FOLLOWED BY SECOND...MUCH STRONGER NRN
STREAM SYSTEM AROUND CHRISTMAS EVE. IF THIS WOULD VERIFY...WE COULD
SEE COLD TEMPERATURES AND A POSSIBLE THREAT FOR SNOW. IN THE
MEANTIME...DECIDED TO KEEP CONDS DRY THROUGH THE WEEKEND AND INTO
NEXT WEEK...GIVEN THE ACTIVE SRN STREAM...WITH PCPN EXPECTED WELL
SOUTH OF THE FCST AREA.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 528 PM CST MON DEC 15 2014

THE SNOW AND BLOWING SNOW ACROSS NCNTL NEB SHOULD EXIT THE FCST
AREA 03Z-06Z THIS EVENING. FROM 06Z-15Z...FOG IS EXPECTED TO
DEVELOP...MAINLY ALONG AND WEST OF HIGHWAY 61 WITH POTENTIAL FOR
LIFR. MVFR CIGS ARE EXPECTED DURING THE SAME TIME ALONG AND EAST
OF HIGHWAY 183. VFR IS EXPECTED ALL AREAS FROM 15Z TUESDAY ONWARD.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 PM CST /5 PM MST/ THIS EVENING FOR
NEZ004-022>024-035-036-056>058-069-094.

WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR NEZ037-
038-059-070-071.

WINTER STORM WARNING UNTIL 9 PM CST THIS EVENING FOR NEZ005>010-
025-026.

WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR
NEZ027>029.

&&

$$

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





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