Area Forecast Discussion
Issued by NWS North Platte, NE

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FXUS63 KLBF 010426 AAB
AFDLBF

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1126 PM CDT THU APR 30 2015

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 347 PM CDT THU APR 30 2015

A COLD FRONT IS VERY SLOWLY MOVING SOUTHEAST ACROSS THE PANHANDLE
INTO WESTERN SOUTH DAKOTA LATE THIS AFTERNOON. THIS FRONT WILL
CONTINUE TO SLOWLY MOVE SOUTHEAST TONIGHT...AND ROUGHLY EXTEND FROM
MCCOOK TO BROKEN BOW ON NORTHEASTWARD BY EARLY FRIDAY MORNING.
MOISTURE IS LIMITED...HOWEVER WHAT MOISTURE THERE IS WILL POOL IN
THE VICINITY OF THE FRONT. A SOUTHERLY LOW LEVEL JET WILL INCREASE
BY MID EVENING ACROSS WESTERN KANSAS...WITH THE NOSE POINTED AT
SOUTHWEST NEBRASKA AND THE SANDHILLS WHERE THE FRONT WILL BE SLOWLY
MOVING SOUTHEAST. FRONTOGENESIS WILL INCREASE DRAMATICALLY IN THE
850-700 MB LAYER DURING THIS TIME...WITH BETWEEN 500-1000 J/KG MID
LEVEL CAPE. EXPECT THAT AT LEAST SCATTERING OF SHOWERS AND
THUNDERSTORMS WILL RESULT. WILL KEEP POPS FAIRLY LOW DUE TO THE
LIMITED MOISTURE...BUT A SMALL CONCENTRATED AREA OF PRECIPITATION
COULD RESULT NEAR THE NOSE OF THE LOW LEVEL JET WITHIN AREA OF
INCREASING MID LEVEL FRONTOGENESIS.

FRONT SETTLES TO THE SOUTH ACROSS NORTHERN KANSAS THROUGH SOUTHEAST
NEBRASKA FRIDAY. A PERSISTENT AREA OF MID LEVEL FRONTOGENESIS
REMAINS JUST NORTH OF THE FRONT ACROSS CENTRAL AND SOUTHWEST
NEBRASKA...AND WILL CONTINUE AT LEAST A SLIGHT CHANCE FOR SHOWERS
AND THUNDERSTORMS FOR THESE AREAS. OTHERWISE AIRMASS MILD BEHIND THE
FRONT...AND 850 MB TEMPERATURES SUPPORT HIGHS IN THE LOW TO MID
70S.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 347 PM CDT THU APR 30 2015

A FAIRLY ACTIVE PERIOD IS EXPECTED AS THE UPPER RIDGE BUILDS OVER
THE SOUTHWEST U.S. DRIVING WEAK UPPER WAVES THROUGH THE CENTRAL AND
NORTHERN PLAINS. THIS PATTERN WILL RESULT IN AT LEAST A SLIGHT
CHANCE OF THUNDERSTORMS EACH DAY.

FRIDAY EVENING...A BOUNDARY MAKES ITS WAY INTO NORTHERN AND
WESTERN NEBRASKA. THE 0-6KM BULK SHEAR IS EXPECTED TO BE 30-50KT
WITH CONVECTIVE POTENTIAL ENERGY OF 800-1000J/KG IN CENTRAL...SOUTH
CENTRAL AND SOUTHWEST NEBRASKA. AS A RESULT...WE WOULD EXPECT
THUNDERSTORMS TO BE CONFINED TO AREAS SOUTH AND EAST OF A BROKEN
BOW-NORTH PLATTE-OGALLALA LINE.

ON SATURDAY...A LOW LEVEL TRAJECTORY DEVELOPS FROM THE TEXAS GULF
COAST AND FROM THE PACIFIC SOUTHWEST TO THE HIGH PLAINS. THIS WILL
RESULT IN A SLIGHT INCREASE IN PRECIPITABLE WATER TO ABOUT 0.75
INCH. THEN...ANOTHER FRONT COMES THROUGH AND CREATES ENOUGH LIFT TO
INITIATE SOME CONVECTION SATURDAY AFTERNOON AND EARLY EVENING IN THE
NEBRASKA SANDHILLS AND INTO SOUTHWEST NEBRASKA. THE CHANCES FOR AT
LEAST MARGINALLY LARGE HAIL ARE A LITTLE HIGHER WITH SURFACE-BASED
CONVECTIVE POTENTIAL ENERGY 1500-2000J/KG AND 0-6KM BULK SHEAR OF
35-40KT.

PATTERN TRANSITIONS FROM A BROAD ZONAL FLOW OVER THE WEEKEND TO A
HIGHER AMPLITUDE PATTERN OF DEVELOPING LONG WAVE TROUGH OVER THE
WEST COAST WITH A RIDGE OVER THE SOUTHEAST. TWO MAIN AREAS OF LOW
PRESSURE AND ASSOCIATED PV ANOMALIES EVOLVE OVER THE WEST...THE
STRONGER OF WHICH APPROACHES THE PAC NW BY MONDAY EVENING...THOUGH
THE SECOND UPPER LEVEL LOW MOVES ONSHORE OVER BAJA AND SO CAL SUNDAY
NIGHT INTO MONDAY IS SLIGHTLY MORE ANOMALOUS FOR THIS PERIOD OF
TIME...AND BECAUSE OF THE MORE SOUTHERN LATITUDE. EVENTUAL EVOLUTION
OF THE TWO INDIVIDUAL SYSTEMS BECOMES QUITE DIFFERENT IN THE MAIN
MID RANGE DETERMINISTIC MODELS THROUGH THE MIDDLE OF NEXT WEEK.
WITHING THE GFS ENSEMBLE MEMBERS THERE BECOMES MUCH GREATER
UNCERTAINTY BY THE END OF THE PERIOD. DESPITE THIS...BOTH GFS AND
ECMWF ARE FAIRLY WET FOR THE EASTERN TWO-THIRDS OF NEBRASKA. THIS IS
A RESULT OF A REASONABLY LONG PERIOD OF MOIST...SERLY FLOW AHEAD OF
THE NEGATIVELY TILTED UPPER LOW MOVING NORTHEAST FROM THE
SOUTHWESTERN U.S. AND A LARGE NEGATIVELY TILTED UPPER RIDGE
DOWNSTREAM...LEADING TO ANOMALOUSLY HIGH PRECIPITABLE WATER VALUES
TUE THROUGH THUR.

FORECAST WILL REMAIN A BLEND OF MODELS IN THE OUTER PERIODS...THOUGH
CONFIDENCE IN A LONG DURATION WIDESPREAD RAIN EVENTS ARE BELOW
AVERAGE AT THIS TIME. THIS IS BECAUSE IN A CONVECTIVE ENVIRONMENT
SUCH AS THIS AND WITH A SIGNIFICANT UPPER LOW EJECTING ONTO THE
PLAINS...VIGOROUS CONVECTION WOULD LIKELY BE FAVORED ALONG MORE
SIGNIFICANT BOUNDARIES...SUCH AS THE STRONG DRYLINE THAT DEVELOPS IN
THE TUESDAY INTO WED TIME FRAME FROM TX INTO OK. BY THURSDAY THE
DRYLINE DEVELOPS NWD DUE TO THE MORE NWD MOVEMENT OF THE UPPER LOW.
HOWEVER...AS MENTIONED EARLIER WITH THE ANOMALOUS PRECIPITABLE WATER
VALUES /EXCEEDING ONE INCH/ AND ALSO WITH EARLY FLOW NORTH OF A
STALLED FRONT ON THE NORTHERN SIDE OF THE SYSTEM...RAIN SHOWERS WITH
AT LEAST ISOLATED THUNDER SEEMS PLAUSIBLE THROUGH MID WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1125 PM CDT THU APR 30 2015

A POST FRONTAL DISTURBANCE HAS SPAWNED SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS SD/WRN NEB. THE FORECAST MODELS ARE HAVING
DIFFICULT TIME WITH THIS DEVELOPMENT BUT TIMING TOOLS SUGGEST IT
COULD EXIT HOLT COUNTY AROUND 13Z. FARTHER SOUTH...IT WOULD EXIT
THE AREA PERHAPS AROUND 15Z. VFR IS GENERALLY EXPECTED ALL AREAS
NORTH OF INTERSTATE 80 THEREAFTER. THE NAM MODEL SUGGESTS
ISOLATED TSTM DEVELOP SOUTH OF INTERSTATE 80...21Z-03Z FRIDAY
AFTN.

&&

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

$$

SHORT TERM...TAYLOR
LONG TERM...SPRINGER/JWS
AVIATION...CDC





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