Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 302309
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
609 PM CDT SAT AUG 30 2014

.SYNOPSIS...
ISSUED AT 345 PM CDT SAT AUG 30 2014

AT 20Z THE UPPER LEVEL PATTERN ACROSS THE CONUS WAS PROGRESSIVE WITH
A DEAMPLIFYING RIDGE OF HIGH PRESSURE ALONG THE EASTERN SEABOARD...A
TROUGH EJECTING INTO THE GREAT LAKES...SHORTWAVE RIDGING ACROSS THE
CENTRAL AND NORTHERN PLAINS...AND A BROAD UPPER TROUGH DIGGING INTO
THE PACIFIC NORTHWEST.

CLOSER TO THE SANDHILLS REGION SOUTHEASTERLY SURFACE FLOW AND LOW
LEVEL MOISTURE RETURN WAS STEADILY INCREASING IN RESPONSE TO A
DEEPENING SFC LOW PRESSURE JUST WEST OF THE BLACK HILLS. SKIES OVER
THE CWA WERE CLEAR WITH TEMPERATURES IN THE UPPER 70S TO
NEAR 90.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 345 PM CDT SAT AUG 30 2014

QUIET CONDITIONS WILL PREVAIL ACROSS THE CWA FOR THE REST OF THE
AFTERNOON AND EARLY EVENING WITH STRONG SUBSIDENCE IN PLACE OVER THE
CWA. HOWEVER H5 HEIGHTS WILL BEGIN TO FALL IN THE NEXT FEW HOURS IN
RESPONSE TO A TROUGH DIGGING INTO THE PAC NORTHWEST. A LEAD WAVE
WILL TRACK ACROSS SOUTHERN WY AND NORTHERN CO THIS EVENING...LEADING
TO STORM DEVELOPMENT ACROSS THE HIGHER TERRAIN OF EASTERN WY AND THE
PANHANDLE. ISOLATED ACTIVITY MAY MAKE IT OUT OF THE PANHANDLE AND
TRACK EAST INTO THE CWA TONIGHT...AIDED BY A STRENGTHENING LLJ AND
STEEPENING MID LEVEL LAPSE RATES. EXPECTING MORE WIDESPREAD COVERAGE
TO REMAIN NORTH OF THE AREA CLOSER TO THE MAIN SFC LOW AND NOSE OF
THE LLJ.

MAIN FORECAST CONCERN ON SUNDAY WILL BE THE POTENTIAL FOR SEVERE
WEATHER AS THE NORTHWEST CONUS TROUGH MOVES TOWARD THE CENTRAL
PLAINS. MODELS HAVE COME INTO A CONSENSUS ON THE POSITION OF A COLD
FRONT JUST EAST OF A LBF TO ANW LINE BY EARLY AFTERNOON. AREAS ALONG
AND EAST OF THE FRONT WILL BE AT RISK FOR SEVERE WEATHER GIVEN A
HIGHLY UNSTABLE AND STRONGLY SHEARED ENVIRONMENT CHARACTERIZED BY ML
CAPE IN EXCESS OF 2000 J/KG AND DEEP LAYER SHEAR BETWEEN 40-50 KTS.
STOUT EML WILL LIKELY KEEP THE ATMOSPHERE IN THE VICINITY OF THE
COLD FRONT CAPPED TO DEEP SURFACE BASED CONVECTION UNTIL AN UPPER
LEVEL JET STREAK AND DIFFLUENT FLOW ALOFT OVERSPREADS THE AREA
BETWEEN 21-00Z. GIVEN THE STRONG SHEAR AND STEEP MID LEVEL LAPSE
RATES OF 8 C/KM STORM MODE WILL LIKELY BE DISCRETE UPON INITIATION
WITH A FEW SUPERCELLS CAPABLE OF LARGE HAIL POSSIBLE. STORM UPDRAFTS
WILL LIKELY MERGE AS THEY MOVE EAST OF THE CWA.

WEST OF THE COLD FRONT STORMS WILL BE POSSIBLE BEGINNING MID TO LATE
MORNING IN THE PANHANDLE AND SPREADING EAST THROUGH THE DAY. STEEP
LAPSE RATES AND STRONG SHEAR WILL PROMOTE THE POTENTIAL FOR A FEW
STRONG STORMS...HOWEVER WIDESPREAD SEVERE WEATHER IS UNLIKELY SINCE
ALL CONVECTION SHOULD BE ELEVATED.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 345 PM CDT SAT AUG 30 2014

SUNDAY NIGHT THROUGH TUESDAY...

THE SURFACE FRONT IS FORECAST TO BE LOCATED JUST SOUTHEAST OF THE
FORECAST AREA EARLY SUNDAY EVENING ALONG WITH SURFACE BASED
STORMS. ACROSS WESTERN NEBRASKA...ELEVATED POST FRONTAL SHOWERS
AND THUNDERSTORMS ARE EXPECTED. EARLY EVENING CAPES FROM 1500-2500
J/KG AVBL ABOVE 700MB. GIVEN DEEP LAYER SHEAR AS HIGH AS 45-55
KTS...THIS SUPPORTIVE OF A FEW STRONG STORMS. PROGRESSIVE NATURE
OF THE SYSTEM SHOULD PUSH STORMS EAST OF FORECAST AREA BY 06Z.

ON MONDAY...UPPER FLOW WILL REMAIN NW AS A FAIRLY STRONG PV
ANOMALY THROUGH NERN WY INTO THE BLACK HILLS BY LATE AFTN. THIS
WILL BRING A CHANCE FOR AFTN SHOWERS AND THUNDERSTORMS TO MAINLY
SHERIDAN AND CHERRY COUNTY. THE 12Z GFS APPEARS TOO FAST AND
FAVOR THE SLOW NAM MODEL. SOMEWHAT DRIER AIR WILL WORK INTO WRN
NEBR AS DEWPOINTS RANGE FROM THE MID 40S TO LOW 50S WEST TO THE
LOWER TO MID 50S SOUTHEAST. GOING INTO MONDAY NIGHT...RUNNING 20
TO 30 POPS NORTHEAST FROM HAY SPRINGS THROUGH BROKEN BOW.

TUESDAY...A FAIRLY STRONG UPPER TROUGH WILL DROP INTO SRN BRITISH
COLUMBIA AND PAC NW. UPPER FLOW WILL BE ZONAL ACROSS THE CENTRAL
PLAINS. WARM AIR ADVECTION RETURNS AS H8 TEMPS WARM ABOVE 25C SW
AND SERN PNHDL. HIGHS NEAR 80 NCTRL TO NEAR 85 SOUTHWEST.


TUESDAY NIGHT THROUGH SATURDAY...

WARM AIR ADVECTION WILL CONTINUE INTO WEDNESDAY WITH H85 TEMPS
RANGE FROM 25 TO 30C AND HIGHS RESPOND REACHING NEAR 90. UPPER
FLOW ALSO BECOMES SOUTHWEST AS POSITIVELY TILTED TROUGH MOVES
ACROSS ALBERTA...SRN SASKATCHEWAN INTO THE PAC NW. THIS UPPER
TROUGH WILL EXPAND INTO HUDSON BAY CANADA AND ALSO THE WEST COAST
BY FRIDAY. THIS WILL BRING A COLD FRONT INTO WESTERN NEBRASKA BY
WEDNESDAY NIGHT OR THURSDAY NIGHT. THE ECMWF AND GEM ARE THE FAST
PUSHING THE FRONT THROUGH BY 12Z THU...WHILE THE GFS SLOWEST
MOVING THE FRONT THROUGH BY 12Z FRIDAY. THE GFS ENSEMBLE ALSO
SLOWER AND IN AGREEMENT WITH THE ECMWF AND GEM. THIS WILL BRING A
COOL DOWN THURSDAY TO THE UPPER 70S NW TO THE MID 80S
SOUTHWEST...WITH 70S FOR FRIDAY AND SATURDAY. SHOWERS AND
THUNDERSTORMS IN THE FORECAST THURSDAY NIGHT THROUGH SATURDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 606 PM CDT SAT AUG 30 2014

WITH A SURFACE FRONT STALLED ACROSS WESTERN AND SOUTHERN NEBRASKA
THIS EVENING AND AN UPPER SYSTEM COMING ACROSS THE ROCKIES AND INTO
NEBRASKA...THERE IS A POSSIBILITY THAT THUNDERSTORMS WILL DEVELOP
AFTER 06Z IN CENTRAL AND WESTERN NEBRASKA. MOISTURE ACROSS SOUTHERN
NEBRASKA IS LIMITED...BUT IT IS LIKELY TO INCREASE SOME THIS EVENING
WITH THE SOUTHERLY LOW LEVEL WIND. FOR NOW...THOUGH...IT APPEARS
THAT THE AREAL COVERAGE WILL BE LIMITED AND TS WILL NOT BE INCLUDED
IN THE FORECASTS FOR VTN AND LBF AT THIS TIME. OTHERWISE...CEILING
AND VISIBILITY WILL BE UNLIMITED THROUGHOUT THE AREA.

&&

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

$$

SYNOPSIS...MARTIN
SHORT TERM...MARTIN
LONG TERM...ROBERG
AVIATION...SPRINGER





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