Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 251126 AAA
AFDLBF

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
526 AM CST THU DEC 25 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 404 AM CST THU DEC 25 2014

THERMAL AND MOISTURE PROFILES LOOK GOOD FOR SNOW ACROSS SHERIDAN
COUNTY. LIFT IS DEEP BUT JUST 5 MICROBARS SUPPORTING THE MODERATE
SNOW FORECAST TOTALS NEAR 5 INCHES BY FRIDAY MORNING...MAINLY
ALONG PINE RIDGE. THE FRONTOGENESIS IS MODEST IN THE NAM. FARTHER
EAST THERE IS EVIDENCE OF A 700MB DRY SLOT NEAR VALENTINE WHICH
WOULD GREATLY LIMIT SNOWFALL. THE FORECAST SHOWS A FAIRLY SHARP
CUTOFF ASSOCIATED WITH THIS DRY INTRUSION. THE SNOWFALL FORECAST
IS MARGINAL ALONG THE ERN FLANK OF THE WINTER WEATHER ADVISORY BUT
GIVEN IT WILL MOSTLY OCCUR AFTER NIGHTFALL THE ADVISORY WILL BE
ALLOWED TO STAND WITH NO CHANGES.

THE MODELS APPEAR TO HAVE TRENDED NORTH SOMEWHAT FAVORING SHERIDAN
COUNTY AND THE FORECAST CENTROID OF HIGHEST SNOWFALL IS NORTHWEST OF
THE HPC FORECAST.

MEANWHILE THE RAP13 AND THE 06Z NAM ARE TAKING THE
BETTER FOCUS ACROSS THE WRN CHEYENNE DIVIDE AND TOWARD THE HIGHER
TERRAIN NORTH OF SCOTTSBLUFF WHICH IS SOUND. THIS METEOROLOGICAL
WOBBLING WILL LIKELY CONTINUE TODAY. THE LATEST RADAR AND OBS ACROSS
WRN SD INDICATE SNOW IS NOW UNDERWAY...ABOUT 5 HOURS SOONER THAN
FORECAST WHICH SUPPORTS THE OFFICIAL FORECAST. THE NAM MODEL SHOWS
FORCING ACROSS NW NEB THIS EVENING AROUND 03Z WHICH LIFTS EAST INTO
ERN SD BY 06Z. THE RAP WEAKENS THIS DISTURBANCE VERY QUICKLY AND
RAPIDLY SETS UP A CLOSED H700MB LOW NEAR CHEYENNE. THERE IS WOBBLING
IN THE MODELS BUT THIS IS NORMAL AND THE FORECAST FOLLOWS THE MODEL
CONSENSUS.

SATELLITE WATER VAPOR SHOWS A VIGOROUS UPPER LOW DROPPING THROUGH
THE CNTL ROCKIES THIS MORNING. THIS STORM IS BEING FUELED BY A HIGH
QUALITY SUBTROPICAL RIVER OF MOISTURE OFF OF HAWAII SUGGESTING THERE
COULD BE ROOM FOR SURPRISE SNOWFALL AMOUNTS...SOMEWHERE. THE
NATIONAL WEATHER HAZARDS MAP SHOWS AN INCREASE IN WINTER STORM
WARNINGS ACROSS THE CNTL ROCKIES.

THE LATEST WIND FORECAST INDICATES NORTH WINDS AT 15 TO 20 MPH
GUSTING TO NEAR 30 MPH. THIS IS ABOUT 5 MPH LESS THAN THE PREVIOUS
FORECAST. THE 00Z ECM WAS THE ONLY MODEL INDICATING 25 MPH WIND
SPEEDS. BLOWING SNOW IS INCLUDED IN THE FORECAST TONIGHT WHICH IS
CONSISTENT WITH AND WIND SPEEDS APPROACHING 25 MPH.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 404 AM CST THU DEC 25 2014

THIS PORTION OF THE FORECAST BEGINS WITH ONGOING PRECIPITATION
ACROSS WESTERN AND NORTH CENTRAL NEBRASKA ASSOCIATED WITH THE
UPPER LEVEL TROUGH CURRENTLY WITH ITS BASE OVER CENTRAL CALIFORNIA
AND EXTENDING NORTH THROUGH IDAHO. BY 12Z FRIDAY...THE BASE OF THE
TROUGH IS EXPECTED TO HAVE MOVED EAST AND BE OVER ARIZONA.
MEANWHILE...ANOTHER SHORTWAVE TROUGH FROM THE NORTHERN STREAM
WOULD BE MOVING INTO MONTANA.

ON FRIDAY MORNING SNOW OVER NORTHWEST NEBRASKA SHOULD BE WINDING
DOWN AS THE LEAD SHORTWAVE TROUGH THAT WILL MOVE ACROSS THE AREA
TONIGHT MOVES EAST INTO THE UPPER MISSISSIPPI RIVER VALLEY. CROSS
SECTIONS SHOW THE AMOUNT OF LIFT ACROSS THIS AREA DIMINISHING FRIDAY
MORNING...WITH THE DEEP MOISTURE ALSO ON THE WAYSIDE BY 18Z AS DRY
AIR STARTS TO ADVECT INTO NORTHWEST NEBRASKA BEHIND THE SHORTWAVE.
ADDITIONAL SNOW AMOUNTS OVER THE AREAS IN THE WINTER WEATHER
ADVISORY WILL BE MINIMAL ON FRIDAY AND AS WINDS GO DOWN THROUGH THE
DAY...ENDING THE ADVISORY AT 18Z CONTINUES TO LOOK APPROPRIATE.

LOOKING FURTHER SOUTH AND EAST AT 12Z...THE COLUMN ISN/T COMPLETELY
SATURATED AS THE MODELS ARE SHOWING DRY AIR IN THE MID LEVELS...FROM
750MB TO 600MB. SATURATION IS SEEN THOUGH BELOW 750MB BUT THE DRY
LAYER LOOKS TOO DEEP TO PROVIDE A SEEDER/FEEDER PROCESS. THERE IS
INDICATION THAT LIFT IN THIS LAYER INCREASES LATE THURSDAY NIGHT AND
FRIDAY MORNING WHICH COULD INDICATE POTENTIAL FOR FREEZING DRIZZLE
AS NO ICE WOULD BE INTRODUCED INTO THAT LAYER. HOWEVER...THE
MOISTURE QUICKLY INCREASES AFTER 12Z AND WITH LITTLE CONFIDENCE ON
THIS HAVE NO MENTION IN THE FORECAST AT THIS TIME AND HAVE ONLY
SNOW.

THROUGH THE DAY FRIDAY AND SATURDAY...THE UPPER LEVEL TROUGH IS
EXPECTED TO BECOME ELONGATED AS A 120KT-130KT JET SHEARS IT INTO
SEVERAL PIECES. THE MODELS ARE IN GOOD AGREEMENT WITH THIS
OCCURRING....WITH THE FIRST PIECE OF ENERGY MOVING UP THROUGH KANSAS
AND INTO EASTERN NEBRASKA BY SATURDAY MORNING. THEN DURING THE DAY
SATURDAY...THIS SHORTWAVE TROUGH PHASES TOGETHER WITH THE SHORTWAVE
MOVING OUT OF MONTANA ACROSS CENTRAL AND EASTERN NEBRASKA.

SNOW IS EXPECTED TO INCREASE IN COVERAGE AND INTENSITY OVER THE
SOUTHERN PART OF THE FORECAST AREA LATE FRIDAY MORNING AND AFTERNOON
AS LIFT INCREASES DUE TO THE SHORTWAVE TROUGH MOVING THROUGH KANSAS
AND THE EASTERN PART OF NEBRASKA. CURRENT MODELS SHOW THE 8-12
UBAR/S OF OMEGA THROUGH THE DENDRITIC GROWTH ZONE ACROSS SOUTHERN
NEBRASKA WHICH COULD LEAD TO SLIGHTLY HIGHER THAN NORMAL SNOW TO
LIQUID RATIOS /16:1 TO 19:1/. SO...DESPITE QPF AMOUNTS NOT BEING
SIGNIFICANT FRIDAY AND FRIDAY NIGHT /0.10 TO 0.20 INCHES/ COULD GET
UP TO 3 INCHES IN SOME PARTS OF THE AREA BY SATURDAY MORNING. COLD
AIR ADVECTION WILL BE ONGOING THROUGH THE DAY FRIDAY AND WITH CLOUDS
AND SNOW DON/T EXPECT TEMPERATURES TO WARM MUCH. PRIOR FORECAST HAD
HIGHS IN THE UPPER TEENS TO MID 20S WHICH STILL LOOK GOOD AND ONLY
MINOR MODIFICATIONS WERE MADE.

AS THE MONTANA SHORTWAVE PUSHES THROUGH SUBSIDENCE WILL START TO DRY
THINGS OUT OVER NORTHWEST NEBRASKA BY SATURDAY MORNING. NOT ENTIRELY
CONFIDENT ON HOW MUCH CLOUDS WILL REMAIN BY 12Z...BUT IF SKIES DO
CLEAR...WITH A GOOD SNOWPACK ON THE GROUND TEMPERATURES COULD DROP
TO NEAR 0F. HIGH PRESSURE BUILDS INTO THE REGION ON SATURDAY WHICH
WILL BRING AN END TO ALL OF THE SNOW AND ALSO DIMINISH THE WINDS.
TEMPERATURES SHOULD BE A BIT WARMER BUT NOT BY MUCH...WITH HIGHS
LIKELY IN THE 20S.

QUIET CONDITIONS WILL BE SEEN FOR THE REMAINDER OF THE WEEKEND...BUT
ANOTHER STRONG SYSTEM WILL MOVE INTO THE PACIFIC NORTHWEST SATURDAY
NIGHT AND WILL DIG SOUTH INTO THE SOUTHWEST CONUS. THE MODELS ARE IN
DECENT AGREEMENT AND CONTINUE TO BRING SOME VERY COLD AIR DOWN INTO
THE PLAINS BEHIND A COLD FRONT PUSHED BY THIS SYSTEM. THE FRONT
LOOKS TO MOVE SOUTH ACROSS NEBRASKA LATE SUNDAY NIGHT AND MONDAY.
THIS ARCTIC FRONT WILL BRING AN AIRMASS WITH 850MB TEMPERATURES DOWN
AROUND -20C INTO THE AREA /COMPARED TO THE LATEST OBSERVATION AT
KLBF OF 2C/. HIGHS ON TUESDAY COULD BE QUITE COLD...ONLY IN THE
SINGLE DIGITS. THAT BEING SAID...DESPITE THE AGREEMENT IN THE
MODELS...THE GFS ENSEMBLES ARE SHOWING A LARGE DEGREE OF
SPREAD...WITH A STANDARD DEVIATION OF 9 FOR TUESDAY/S HIGHS...WITH A
RANGE FROM 0F TO 42F OVER THE NORTHWEST PART OF THE FORECAST AREA.
BELIEVE THE COLDER ROUTE IS THE WAY TO GO WITH THE AGREEMENT IN A
COLD AIRMASS MOVING IN AND WITH DEEP SNOWPACK TO HELP REDUCE
TEMPERATURE RISES. IN ADDITION...THERE WILL BE CHANCES FOR SNOW
AGAIN EARLY NEXT WEEK BEHIND THE PASSING OF THE ARCTIC FRONT.
NOTHING SIGNIFICANT FOR SNOW AMOUNTS IS EXPECTED AT THIS TIME BUT
WILL CONTINUE TO MONITOR FOR ANY CHANGES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 526 AM CST THU DEC 25 2014

IFR IN SNOW AND LOW CEILINGS WILL SPREAD SOUTH AND WEST TO NEAR
KVTN-KOGA TODAY. THE SAME FLIGHT RESTRICTIONS WILL CREEP SOUTH TO
NEAR KIML-KLBF-KONL BY 12Z FRIDAY MORNING. OTHERWISE VFR WILL
BECOME MVFR WITH THE PASSAGE OF A COLD FRONT TODAY AND TONIGHT.
THE FRONT IS CURRENTLY MOVING THRU SRN SD.

&&

.LBF WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM NOON CST /11 AM MST/ TODAY TO NOON
CST /11 AM MST/ FRIDAY FOR NEZ004-005-022>024-035-056-094.

&&

$$

SHORT TERM...CDC
LONG TERM...BROOKS
AVIATION...CDC





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