Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 230522 AAA
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1122 PM CST SAT NOV 22 2014

.SYNOPSIS...
ISSUED AT 351 PM CST SAT NOV 22 2014

AT 20Z WATER VAPOR IMAGERY SHOWED TWO MAIN AREAS OF FOCUS. THE FIRST
WAS AN AREA OF LOW PRESSURE OVER WESTERN TEXAS WHICH WAS DRIVING
THUNDERSTORMS ACROSS MUCH OF TEXAS. SOUTHERLY MOIST FLOW AHEAD OF
THIS SYSTEM CARRIED 40 AND 50 DEGREE DEWPOINTS...HIGH CLOUD COVER
AND RAIN SHOWERS NORTH THROUGH EASTERN KANSAS AND INTO SOUTHERN IOWA
AND ILLINOIS. THE SECOND SYSTEM WAS A BROAD TROUGH OVER THE
NORTHWEST CONUS. THERE WERE SEVERAL EMBEDDED STRONGER SHORTWAVE
TROUGHS EMBEDDED IN THIS SYSTEM...ONE OVER NORTHERN MONTANA AND
ANOTHER AT THE BASE OF THE TROUGH ACROSS NORTHERN CALIFORNIA AND
NEVADA. INTERMITTENT THUNDERSTORMS WERE ALSO OBSERVED ASSOCIATED
WITH THIS SYSTEM. LOW PRESSURE AT THE SURFACE AHEAD OF THE NORTHWEST
SYSTEM WAS CENTERED OVER SOUTHERN SASKATCHEWAN AT 20Z WITH SEVERAL
FRONTAL SYSTEMS BRANCHING OUT ACROSS THE NORTHERN PART OF THE
COUNTRY. THE PRIMARY COLD FRONT EXTENDED FROM THE SURFACE LOW DOWN
ACROSS CENTRAL MONTANA AND INTO IDAHO. LOCALLY...DEEP MIXING UP TO
750MB IN SOME AREAS ACCORDING TO LAPS SOUNDINGS ALLOWED TEMPERATURES
TO RISE INTO THE 60S WITH KMCK REACHING 70 DEGREES. IN
ADDITION...BREEZY WINDS ALOFT WERE ABLE TO MIX DOWN TO THE SURFACE
WHICH BROUGH PERIODS OF WIND GUSTS UP TO 30KTS IN PLACES. THERE WAS
A WEAK TROUGH ALOFT THAT MOVED INTO WESTERN NEBRASKA THIS AFTERNOON
WHICH DID DIMINISH THE WINDS DESPITE THE DEEP MIXING...ESPECIALLY
OVER SOUTHWEST NEBRASKA. IN ADDITION...THERE WAS A WEAK SURFACE
TROUGH THAT DROPPED INTO NORTHWEST NEBRASKA THIS ATERNOON WHICH
LIMITED TEMPERATURE RISES OVER THE FAR NORTHERN AREAS OF SHERIDAN
COUNTY THIS AFTERNOON WHERE HIGHS TOPPED OUT IN THE LOW TO MID 50S.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 351 PM CST SAT NOV 22 2014

THE PRIMARY FORECAST CONCERNS THROUGH SUNDAY DEAL WITH THE FRONTAL
PASSAGE TONIGHT WHICH PLAYS A PART IN THE WIND...TEMPERATURE AND
PRECIPITATION FORECAST.

THE SHORTWAVE TROUGH OVER MONTANA AND ASSOCIATED COLD FRONT PUSHES
ACROSS THE FORECAST AREA BY 09Z TONIGHT. MODELS ARE IN GOOD
AGREEMENT WITH THE TIMING AND ALSO BRING IN QUITE STRONG NORTHWEST
WINDS BEHIND IT. THINKING THERE WILL BE AN INITIAL BURST OF WINDS
RIGHT BEHIND THE FRONT...THEN AFTER A BIT OF A LULL THEY WILL
INCREASE AFTER 12Z AS THE BOUNDARY LAYER STARTS TO MIX A BIT MORE.
FORECAST SOUNDINGS SHOW MIXING UP TO 850-800MB DURING THE DAY SUNDAY
AND WITH MODELS SHOWING WINDS AT 850MB AT 35-45 KTS SHOULD BE A
WINDY DAY.

AS FOR PRECIPITATION CHANCES...THE MODELS ARE SHOWING A RATHER THIN
BAND OF MOISTURE AND LIFT MOVING ACROSS THE AREA BEHIND THE FRONT.
THINKING IT WILL ONLY LAST 3-4 HOURS AND WITH SOUNDINGS SHOWING TOP
DOWN SATURATION AND SIGNIFICANT COOLING BEHIND THE FRONT THERE WILL
BE A SHORT PERIOD OF RAIN WITH A CHANGE-OVER TO SNOW BEFORE THE
PRECIPITATION ENDS. DON/T EXPECT AMOUNTS TO BE MUCH WITH ONLY A FEW
HUNDREDTHS OF QPF LIKELY. HOWEVER...THERE IS ENOUGH AGREEMENT
BETWEEN THE MODELS TO LEAD TO HIGHER CONFIDENCE ON GETTING SOME
LIGHT PRECIPITATION SO DID RAISE CHANCES TONIGHT.

INCREASED LOWS SLIGHTLY TONIGHT FOR SEVERAL REASONS. FIRST...AS THE
BOUNDARY LAYER SHOULDN/T DECOUPLE IN MOST PLACES OR IF IT DOES IT
WILL BE BRIEFLY SO NOT ALLOWING MUCH TIME TO SEE SIGNIFICANT DROPS
IN TEMPERATURES. SECOND...HIGH AMOUNTS OF CLOUD COVER WILL KEEP THE
SURFACE INSULATED SO ANOTHER STRIKE AGAINST RADIATIONAL COOLING. AND
THIRD...WITH THE WARM TEMPERATURES CURRENTLY EVEN AREAS THAT START
TO DROP OFF AHEAD OF THE FRONT WON/T HAVE ALL NIGHT TO COOL SO WENT
UP A FEW DEGREES.

FOR HIGHS ON SUNDAY COLD AIR ADVECTION WILL BE ONGOING THROUGH THE
DAY WITH 850MB TEMPERATURES COOLING TO NEAR 0C ACROSS MUCH OF
NEBRASKA BY THE END OF THE DAY SUNDAY. DROPPED HIGHS A FEW DEGREES
ESPECIALLY IN NORTHWEST NEBRASKA AS A SECOND SHORTWAVE TROUGH WILL
MOVE INTO THE AREA BRINGING INCREASED CLOUDS AND CHANCES FOR SOME
LIGHT SNOW SHOWERS IN THE AFTERNOON. THIS SHOULD LIMIT WARMING IN
THE AFTERNOON SO FELT HIGHS AROUND 40 WERE A BIT TOO WARM.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 351 PM CST SAT NOV 22 2014

MID RANGE...SUNDAY NIGHT THROUGH TUESDAY...IN THE MID
RANGE...THE MAIN FORECAST CHALLENGES ARE PRECIPITATION CHANCES
SUNDAY NIGHT FOLLOWED BY TEMPERATURES. ON SUNDAY NIGHT...AN UPPER
LEVEL LOW WILL TRACK FROM SRN MANITOBA INTO NORTHERN MINNESOTA. THIS
FEATURE WILL FORCE A BACK DOOR COLD FRONT INTO THE FORECAST AREA
SUNDAY NIGHT. CROSS SECTIONS TAKEN ACROSS NORTHERN NEBRASKA
INDICATE SOME MEAGER LIFT IN THE MOIST LAYER FROM 00Z TO 09Z SUNDAY
NIGHT. PRECIP TYPE WAS AN INITIAL CONCERN DURING THE EARLY EVENING
HOURS SUNDAY. HOWEVER...ENOUGH LOW LEVEL DRY AIR EXISTS IN THE LOWER
LEVELS TO SUPPORT SNOW OVER RAIN AND WILL KEEP PTYPES AS ALL SNOW.
ON MONDAY...THE BACK DOOR COLD FRONT WILL REMAIN ENTRENCHED ACROSS
NORTHEASTERN NEBRASKA...RUNNING PARALLEL TO THE MID LEVEL FLOW. WITH
THE FRONT ANCHORED ACROSS THE FORECAST AREA...TEMPERATURES WILL
VARY WIDELY MONDAY WITH UPPER 20S IN THE NORTHEAST...TO LOWER MID
40S IN THE FAR SOUTHWEST. ON MONDAY NIGHT...A WEAK REINFORCING SHOT
OF ARCTIC AIR WILL PUSH INTO THE NORTHEASTERN CWA THANKS TO A WEAK
UPPER LEVEL DISTURBANCE...WHICH WILL TRACK THROUGH THE UPPER MIDWEST
OVERNIGHT. NOT EXPECTING MUCH IN THE WAY OF PCPN WITH THIS FEATURE.
HOWEVER...I DID INCLUDE SOME POPS IN THE NORTHWESTERN CWA FOR
TUESDAY AFTERNOON AS WARMER AIR BEGINS TO PUSH INTO EASTERN WYOMING
AND WESTERN NEBRASKA...ALONG WITH SOME MID LEVEL WAA NOTED IN
THE MID LAYERS. AFTER LOWS IN THE TEENS MONDAY NIGHT...HIGHS WILL
REACH THE UPPER 30S TO UPPER 40S ON TUESDAY.

LONG RANGE...TUESDAY NIGHT THROUGH SATURDAY...THE LONG RANGE MODELS
THIS MORNING HAD DIVERGENT SOLUTIONS...PARTICULARLY IN RESPECT TO AN
ARCTIC COLD FRONT AND ITS LOCATION DURING THE MIDDLE TO END OF NEXT
WEEK...AS WELL AS THE OVERALL PATTERN BEYOND DAY 7. THE LATEST
MODELS...IE. ECMWF AND GFS SOLNS FROM THIS MORNING NO LONGER HAVE
180 DEGREE DIFFERING SOLNS BEYOND DAY 7. HOWEVER...WITH THE NEWEST
RUNS...THE MODEL DIFFERENCES ARE MOST PRONOUNCED ON WEDNESDAY AS THE
GFS HOLDS ONTO WARM AIR ACROSS THE REGION WITH THE ARCTIC FRONT
LOCKED IN ACROSS THE DAKOTAS. THE ECMWF IS MORE AGGRESSIVE WITH THIS
FEATURE...PUSHING THE FRONT INTO THE FORECAST AREA TUESDAY NIGHT. NO
SURPRISE...THE LATEST GUIDANCE FOR NORTH PLATTE WEDNESDAY RANGES FROM
A HIGH OF 59 IN THE MEX...TO 33 WITH THE ECE. EVEN THE GFS ENSEMBLE
GUIDANCE FROM LAST NIGHT HAS A RANGE IN HIGHS FROM 39 TO 60 WITH THE
MEAN AT 50. ATTM DECIDED TO INCORPORATE THE PREVIOUS FORECAST AND A
BLEND OF THE MEAN MEN GUIDANCE FROM LAST NIGHT. THIS YIELDED A HIGH
WEDNESDAY OF 49 FOR NORTH PLATTE. NO DOUBT THIS WILL CHANGE OVER THE
NEXT COUPLE OF DAYS AS THE MID RANGE PATTERN SORTS ITSELF OUT. BEYOND
WEDNESDAY...THERE IS MUCH HIGHER FORECAST CONFIDENCE IN AN ARCTIC
SURGE OF COLD AIR THURSDAY INTO FRIDAY...WHICH WILL RESULT IN HIGHS
MAINLY IN THE 30S. BEYOND FRIDAY...THE MODELS ARE HINTING AT THE
DEVELOPMENT OF A ZONAL PATTERN ACROSS THE LOWER 48 NEXT
WEEKEND...WHICH WILL LEAD TO MUCH WARMER TEMPS ACROSS THE CWA BEYOND
SATURDAY INTO THE FIRST WEEK OF DECEMBER. AS FOR PCPN
CHANCES...MAINLY DRY CONDS ARE EXPECTED IN THE LONG RANGE AS FORCING
IS FAIRLY WEEK. THE EXCEPTION MAY BE ON WEDNESDAY NIGHT IN
ASSOCIATION WITH THE ARCTIC FRONT. SINCE FRONTAL TIMING IS UP IN THE
AIR ATTM...WILL KEEP ANY POPS IN THE SLIGHT CHANCE
RANGE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1122PM CST SAT NOV 22 2014

A STRONG PACIFIC COLD FRONT SWEEPS THE FCST AREA OVERNIGHT
PRODUCING A BRIEF PERIOD OF MVFR CIGS IN SCATTERED RAIN AND SNOW
SHOWERS.

WINDS INCREASE TO 32026G39KT SUNDAY. A REINFORCING COLD FRONT
MOVES INTO NRN NEB AFTER 21Z SUNDAY PRODUCING MVFR CIGS AND
SCATTERED SNOW SHOWERS WHICH LAST THROUGH 06Z SUNDAY EVENING. MOST
OF THE MVFR IS EXPECTED NORTH OF NEBRASKA HIGHWAY 2.

&&

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

$$

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






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