Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 271806
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
106 PM CDT THU AUG 27 2015

.SYNOPSIS...
ISSUED AT 315 AM CDT THU AUG 27 2015

PERSISTENT HIGH PRESSURE ALOFT...WHICH WAS LOCATED OVER
THE CENTRAL AND SOUTHERN ROCKIES OVER THE PAST COUPLE OF DAYS...HAS
BEGUN TO BREAK DOWN AND IT IS BEING FORCED TO THE SOUTHEAST INTO NEW
MEXICO AND WEST TEXAS. A STRONG SHORTWAVE TROUGH OF LOW PRESSURE WAS
LOCATED OVER NERN UT...SWRN WY AND NWRN COLORADO AS OF 00Z FRIDAY.
WV IMAGERY OVERNIGHT HAS THIS FEATURE NOW INTO WYOMING. EAST OF THIS
APPG SHORTWAVE...A NICE COMPLEX OF THUNDERSTORMS HAS DEVELOPED
TONIGHT ACROSS SOUTH DAKOTA WITH THE MAIN AREA OF CONVECTION LOCATED
ALONG THE I90 CORRIDOR OF CENTRAL SOUTH DAKOTA. FURTHER
SOUTH...CONVECTION HAS TRIED TO DEVELOP OVERNIGHT ALONG AND NORTH OF
HIGHWAY 20 IN NORTHERN NEBRASKA...BUT HAS NOT BEEN ABLE TO INCREASE
IN INTENSITY AND COVERAGE OVERNIGHT. ACROSS THE REMAINDER OF THE
CONUS TONIGHT...UPPER LEVEL LOW PRESSURE WAS LOCATED OFF THE COAST
OF WASHINGTON STATE...WHILE A SECOND TROUGH OF LOW PRESSURE EXTENDED
SWD FROM WESTERN QUEBEC INTO THE CAROLINAS. AT THE SURFACE...LOW
PRESSURE HAS CONTINUED TO DEEPEN ACROSS THE FAR NWRN CWA OVER THE
PAST FEW HOURS AND WAS LOCATED ROUGHLY OVER SHERIDAN COUNTY AS OF 3
AM CDT. A WARM FRONT EXTENDED EAST NORTHEAST OF THE LOW INTO EAST
CENTRAL SOUTH DAKOTA...WITH A TROUGH OF LOW PRESSURE EXTENDING SW OF
THE LOW INTO NORTHERN COLORADO. EAST SOUTHEAST OF THE LOW...A
DRYLINE EXTENDED TO WEST OF NORTH PLATTE AND JUST EAST OF MCCOOK.
DEW POINTS WEST OF THE DRYLINE WERE IN THE 40S...WITH 60S DEW POINTS
NOTED EAST OF THIS FEATURE. SKIES WERE MOSTLY CLOUDY WITH A THICK
VEIL OF HIGH CLOUDS PRESENT ACROSS THE NORTHERN HALF OF THE FORECAST
AREA. TEMPERATURES AS OF 3 AM CDT RANGED FROM 67 AT NORTH PLATTE TO
74 AT VALENTINE.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 315 AM CDT THU AUG 27 2015

TODAY AND TONIGHT...THE MAIN FORECAST CHALLENGES ARE
TEMPERATURES TODAY...AND THE THREAT FOR THUNDERSTORMS LATER TODAY
AND TONIGHT. FOR TODAY...SURFACE LOW PRESSURE...CURRENTLY OVER THE
NERN PANHANDLE...WILL BEGIN TO PUSH EAST LATER THIS MORNING AS THE
UPPER LEVEL SHORTWAVE LIFTS FROM WYOMING INTO WESTERN SD AND THE
NEBR PANHANDLE. BY 21Z...THE LOW WILL BE LOCATED OVER NORTH CENTRAL
NEBRASKA WITH A COLD FRONT EXTENDING INTO THE SERN PANHANDLE. EAST
OF THE FRONT...H85 TEMPS WILL SURGE TO 25 TO 28C. THE LATEST
GUIDANCE CAME IN WARMER FOR THIS AFTERNOON AND TRENDED TEMPERATURES
UP FROM THE INHERITED FCST. HIGHS TDY WILL RANGE FROM THE UPPER 70S
IN THE PINE RIDGE...TO THE LOWER 90S IN FAR SOUTHWESTERN
NEBRASKA...WHERE DRIER AIR EXISTS. SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO DEVELOP INVOF THE FRONT AFTER MIDDAY AS THE MAIN TROUGH
OF LOW PRESSURE LIFTS EAST INTO WESTERN AND CENTRAL NEBRASKA. FOR
THE MOST PART...THE INHERITED FCST HAD THIS WELL IN HAND. THE ONLY
CHANGES THAT WERE MADE WERE TO TAKE OUT POPS THIS MORNING IN THE
CENTRAL AND EASTERN CWA AS WE WILL SEE A BRIEF REPREVE BETWEEN THE
ONGOING THREAT IN THE EAST AND THE APPROACHING MAIN SYSTEM THIS
AFTERNOON. AS FOR THE SEVERE THREAT THIS AFTERNOON...THINKING HERE
IS THAT THE MAIN THREAT WILL BE ALONG AND EAST OF AN AINSWORTH TO
BROKEN BOW LINE. SB CAPES IN THESE AREAS RANGE FROM 2500 ALONG THIS
LINE...TO 4000+ IN THE FAR NORTHEAST. DEEP LAYER SHEAR HOWEVER IS
FAIRLY WEEK ON THE ORDER OF 20 TO 30 KTS...SO THE SEVERE THREAT
APPEARS FAIRLY MARGINAL ATTM. FOR THIS EVENING...THUNDERSTORMS IN
ASSOCIATION WILL THE FRONT WILL BE MOST PREVALENT ACROSS THE
NORTHEAST INTO SERN SD WHERE UPPER LEVEL DYNAMICS WILL BE STRONGEST
THIS EVENING. CURRENT FORECAST HAS THE POP THREAT HANDLED WELL WITH
LIKELY POPS FCST IN THE NORTHEASTERN CWA. PWATS ACROSS NORTHEASTERN
NEBRASKA WILL BE ON THE ORDER OF 1.5 TO 2.0 INCHES THIS
EVENING...WHICH WOULD SUPPORT HEAVY RAIN. HOWEVER...THE UPPER LEVEL
TROUGH IS FAIRLY PROGRESSIVE WITH THIS SYSTEM...SO THE FLASH
FLOODING THREAT APPEARS MINIMAL ATTM. THE MAIN UPPER LEVEL TROUGH
WILL LIFT EAST OF THE FORECAST AREA OVERNIGHT...WITH DRY CONDITIONS
EXPECTED. LOWS WILL RANGE FROM THE MID 50S IN THE FAR NORTHWEST...TO
THE MID 60S IN THE EAST.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 315 AM CDT THU AUG 27 2015

FRIDAY THROUGH SATURDAY NIGHT...THE UPPER LEVEL LOW ACROSS THE NRN
ROCKIES SHOULD MOVE EAST THROUGH SOUTH DAKOTA TODAY AND THEN INTO
MINNESOTA BY FRIDAY MORNING. THE MODELS SUGGEST THE POTENTIAL FOR
SOME WRAP AROUND SHOWERS GENERALLY EAST OF AINSWORTH. THIS SHOULD
END BY NOON IF ANYTHING DEVELOPS. BY THEN THE UPPER LOW SHOULD BE
FAR ENOUGH EAST TO ALLOW A BATCH OF PACIFIC HIGH PRESSURE TO
INFILTRATE THE FCST AREA WITH COOLER DRIER AIR. FRIDAY SHOULD SUNNY
MOST AREAS.

THEREAFTER...THE FIRST OF A SERIES OF LOW PRESSURE SYSTEMS WILL MOVE
INTO NORTH CENTRAL CANADA. WINDS BECOME SOUTH SATURDAY AND THIS
SHOULD BEGIN THE PROCESS OF WARMING UP THE FCST AREA.

HIGHS FRIDAY RISE INTO THE UPPER 70S TO UPPER 80S. UPPER 80S TO
AROUND 90 ARE EXPECTED SATURDAY. H700MB TEMPERATURES WILL BE RISING
TOWARD 10C-12C EFFECTIVELY CAPPING THE ATMOSPHERE. THE FCST IS
TOTALLY DRY AFTER FRIDAY MORNING WITH NEAR CLEAR SKIES AS A BROAD
UPPER LEVEL RIDGE BUILDS EAST INTO THE CNTL PLAINS. THIS IS A RESULT
OF A DEEP UPPER LEVEL LOW DROPPING THROUGH ALASKA SETTING UP A LONG
WAVE TROF ACROSS THE WRN U.S.

THE LOW TEMPERATURE FORECAST REFLECTS FORECAST DEW POINTS IN THE 50S
TO NEAR 60. THE DEEPER MOISTURE AND HIGHER DEW POINTS ARE SHOWN WELL
EAST ACROSS THE MISSOURI BASIN. LOWS TO FALL INTO THE 50S SATURDAY.
SOUTH WINDS SATURDAY NIGHT WOULD HOLD LOWS IN THE UPPER 50S TO THE
LOWER 60S AND A CHECK ON THE VENERABLE NAM FORECAST
VISIBILITY...AKA...THE FOG PRODUCT...INDICATES NO FOG EITHER
SATURDAY OR SUNDAY MORNING.

SUNDAY THROUGH WEDNESDAY...THE UPPER LEVEL HEIGHT FIELD EVOLVES VERY
SLOWLY FEATURING AN UPPER LOW ACROSS WRN CANADA. THIS PLACES THE
FCST AREA IN A PROLONGED PERIOD OF SOUTHWESTERLIES ALOFT AND WARM
AIR ADVECTION FROM 700MB TO THE SFC. WINDS AT H850 MB BECOME SOUTH
SATURDAY AND REMAIN SO THROUGH WEDNESDAY.

MOISTURE SHOULD INCREASE AT THE LOWER LEVELS BUT WITH H700MB
TEMPERATURES RISING TOWARD 15C...ORGANIZED TSTM DEVELOPMENT APPEARS
UNLIKELY. NONETHELESS THE GFS AND ECM SUGGEST MOSTLY ISOLATED
DIURNALLY DRIVEN CONVECTION COULD FIRE ON A DRYLINE FORECAST TO
SETUP ACROSS WRN NEB. POPS ARE LIMITED TO ISOLATED FOR THIS PORTION
OF THE FCST. THE GFS ENSEMBLE SHOWS VERY LITTLE ACCUMULATED RAINFALL
THROUGH WEDNESDAY. THE MODELS DEVELOP A 30-40KT LOW LEVEL JET EACH
NIGHT...MONDAY THROUGH WEDNESDAY WHICH COULD PERHAPS SUPPORT STORM
DEVELOP.

THE TEMPERATURE FORECAST FOLLOWS A CONSERVATIVE APPROACH FOR HIGHS
IN THE UPPER 80S TO LOWER 90S. THIS APPROACH ASSUMES THE SOUTH WINDS
LIMIT VERTICAL MIXING. THE MEX AND ECM GUIDANCE INDICATES MOSTLY
90S. FORECAST LOWS IN THE UPPER 50S TO MID 60S IS A PLAY ON THE
NOCTURNAL LOW LEVEL JET KEEPING THE ATMOSPHERE MIXED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 105 PM CDT THU AUG 27 2015

LOW PRESSURE SYSTEM SPINNING ACROSS WESTERN NEBRASKA THIS
AFTERNOON. THE LOW WILL BE THE FOCUS FOR THUNDERSTORM DEVELOPMENT
THIS AFTERNOON AND EVENING...WHICH WILL LIKELY IMPACT KVTN AND
CONTINUED THE TEMPO GROUP. LESS CONFIDENCE OF DEVELOPMENT/IMPACT
ACROSS SOUTHWEST NEBRASKA...HOWEVER DID INCLUDE A VCTS FOR NOW.

ACTIVITY QUICKLY PUSHES EAST OVERNIGHT WITH WIDESPREAD VFR
CONDITIONS.

&&

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

&&

$$

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



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