Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 040000
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
700 PM CDT THU SEP 3 2015

.SYNOPSIS...
ISSUED AT 326 PM CDT THU SEP 3 2015

ANOMALOUS UPPER TROUGH OVER THE PAC NW CONTINUING TO DIG FURTHER
SOUTH AS EVIDENCED BY WATER VAPOR IMAGERY AND 50M HEIGHT FALLS AT H5
AT MEDFORD OR. DOWNSTREAM RIDGE OVER THE PLAINS ALSO CONTINUING TO
BUILD INTO SRN CANADA WITH WEAK HEIGHT RISES THERE...HOWEVER MORE
SUBTLE H5 HEIGHT FALLS IN ASSSOCIATION WITH A PV ANOMALY MOVING IN
SWRLY FLOW ALOFT ACROSS WRN CO. SOME LIGHTNING ASSOCIATED WITH THIS
FEATURE AS IT INTERACTS WITH HIGHER TERRAIN AND NEW LIGHTNING
DEVELOPING INTO THE NERN CO HIGH PLAINS EARLY THIS AFTERNOON. TEMPS
HAVE CLIMBED QUICKLY WHERE STRONG INSOLATION IS PREVALENT...WITH MID
TO UPPER 90S ALREADY IN NC NEB.

&&

.UPDATE...
ISSUED AT 657 PM CDT THU SEP 3 2015

RADAR AND THE RAPID REFRESH SHORT RANGE MODELS INDICATE THAT THERE
WILL PROBABLY BE TWO DISTINCT CONVECTIVE SYSTEM DEVELOPING
TONIGHT...ONE IN THE CENTRAL AND NORTHERN SANDHILLS AND THE OTHER
IN SOUTHWEST NEBRASKA. THE FORECAST HAS BEEN UPDATED TO REFLECT
THAT SCENARIO BY BLENDING THE CURRENT FORECAST WITH THE RAPID
REFRESH OUTPUT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 326 PM CDT THU SEP 3 2015

PRIMARY FCST ISSUE WILL BE COVERAGE OF SHRA/TSRA AS THE
AFOREMENTIONED PV ANOMALY MOVES NEWD INTO SRN WY AND WRN NEBR THIS
EVENING. WEAK HEIGHT FALLS ASSOCIATED WITH THE PV ANOMALY WILL
OVERSPREAD THE WESTERN PORTION OF NEB THIS AFTERNOON. AS THIS
OCCURS...PRESSURE FALLS IN THE HIGH PLAINS WILL INCREASE SERLY FLOW
AT LOW LEVELS AND SERVE TO TIGHTEN THE DEW POINT GRADIENT ACROSS THE
WRN PORTION OF THE AREA...AS DEEPER MIXING LOWERS DEW POINTS IN THE
WEST AND MORE MOIST AIR WORKS IN FROM THE SE. IN ADDITION...SWRLY
FLOW ALOFT IS CONTRIBUTING TO THE DEEPER MOISTURE AS EVIDENCED BY
THE INCREASE IN MIXING RATIO AT 320K. AS A RESULT THE 1.11 INCH PW
ON THIS MORNINGS LBF SOUNDING IS NEAR THE 90TH PERCENTILE AND WELL
ABOVE THE MEAN AMOUNT FOR THIS TIME OF YEAR. HOWEVER...THE STRONGEST
UPPER FORCING REMAINS FURTHER WEST OF THE AREA AND AS A RESULT
EFFECTIVE SHEAR LAGS INITIAL DEVELOPMENT THIS AFTERNOON. THEREFORE
EXPECTING ISOLATED TSRA TO DEVELOP ALONG/NEAR THE CONVERGENCE LINE
FROM SW NEB INTO THE WESTERN SANDHILLS...AND MUCH LIKE THE LAST
COUPLE DAYS WILL STRUGGLE INITIALLY AS THE CONVECTIVE TOWERS FIGHT
DRY AIR ENTRAINMENT...BUT SINCE BETTER CAPE IS AVAILABLE ABOVE THE
LFC TODAY...AND WITH THE ARRIVAL OF BETTER EFFECTIVE SHEAR AS THE
UPPER FORCING PROGRESSES...ISOLD TO SCT TSRA SHOULD SUSTAIN AND MOVE
NEWD. AS THE LLJ DEVELOPS IN RESPONSE TO THE UPPER FORCING...AND
THEN IS LATER ENHANCED AS IS TYPICAL ON THE HIGH PLAINS AS THE DRIER
AIR TO THE WEST COOLS QUICKER TAN THE MOIST AIR TO THE
EAST...UPSCALE DEVELOPMENT SHOULD OCCUR THIS EVENING AND ALLOW TSRA
TO INCREASE IN COVERAGE ACROSS WRN NEB...WHERE RAINFALL HAS BEEN
SCARCE THE LAST TWO WEEKS. DESPITE BETTER DYNAMICS EVENTUALLY...SVR
TSRA NOT EXPECTED BECAUSE OF INSUFFICIENT SHEAR...THOUGH WOULDN/T BE
SURPRISED IF SMALL SCALE STORM INTERACTIONS CAUSE A COUPLE TO BECOME
STRONG.

AS THE PV ANOMALY PROGRESSES NEWD OVERNIGHT...PRECIP SHOULD DECREASE
IN COVERAGE AND INTENSITY THROUGH THE NIGHT AND ESPECIALLY AS LLJ
WANES TWD 12Z SAT. DECENT SUNSHINE SHOULD OCCUR BY LATE MORNING MOST
LOCATIONS AND ALLOW TEMPS TO CLIMB TO ABOVE AVE AGAIN
FRIDAY...THOUGH NOT AS WARM AS THE LAST COUPLE OF DAYS. NEXT SHORT
WAVE TROUGH EMBEDDED WITHIN SWRLY FLOW WILL WORK INTO THE CENTRAL
ROCKIES AND OUT ONTO THE HIGH PLAINS LATE FRIDAY.. THERE IS SOME
DISAGREEMENT AMONG THE MODELS AS TO THE FORCING ASSOCIATED WITH IT
BUT REGARDLESS ANY PRECIP CHANCES WOULD COME BEYOND 00Z SAT.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 326 PM CDT THU SEP 3 2015

MID AND LONG TERM MODELS IN FAIR AGREEMENT. TROUGH AXIS WILL LIE
OVER WESTERN NEBRASKA FRIDAY NIGHT AND INTO THE DAY SATURDAY AND
SATURDAY NIGHT WITH 40KT LLJ. SLIGHT CHANCES FOR TRW RETAINED
FRIDAY NIGHT INTO SATURDAY MORNING AND THEN INCREASING THROUGH THE
DAY SATURDAY AS THE NEGATIVELY TILTED UPPER LOW MOVES INTO THE
NORTHERN PLAINS. WITH THE ATMOSPHERE MIXED AND INCREASING WAA AND
MOISTURE ADVECTION AHEAD OF THE COLD FRONT SUNDAY MORNING HAVE
INCREASED TO CHANCE POPS ALONG THE FRONTAL BOUNDARY SATURDAY
MORNING AND THEN SHIFTING EAST THROUGH THE DAY. LOWS FRIDAY AND
SATURDAY NIGHT IN THE 60S AND 70S WITH THE FAIRLY STRONG LOW LEVEL
JET. HIGHS ON SATURDAY IN THE LOW 90S. COOLER ON SUNDAY WITH THE
PASSAGE OF THE COOL FRONT AND PRECIPITATION ENDING OVER NORTH
CENTRAL NEBRASKA. STRONG NORTHWEST FLOW THROUGH THE DAY ON SUNDAY.
LOWS IN THE 40S AND 50S SUNDAY NIGHT. FRONTAL BOUNDARY LIFTS NORTH
BACK INTO WESTERN NEBRASKA AND BECOMES THE FOCUS FOR THUNDERSTORMS
THROUGH THE DAY MAINLY OVER THE EASTERN NHALF OF THE FORECAST
AREA. HIGHS IN THE 80S MONDAY. CLOUDY AND COOL THROUGH THE
REMAINDER OF THE FORECAST PERIOD WITH HIGHS IN THE 70S AS THE
UPPER LOW MOVES SLOWLY EAST OUT OF SOUTH CENTRAL CANADA. SLIGHT
CHANCES FOR PRECIPITATION TUESDAY WITH WEAK WAVES MOVING THROUGH
ZONAL FLOW ALOFT PUSHES A WEAK COLD FRONT ACROSS THE AREA.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 623 PM CDT THU SEP 3 2015

WIDELY SCATTERED THUNDERSTORMS IN WESTERN AND NORTHWEST NEBRASKA
WILL CONTINUE. OTHER STORMS ARE EXPECTED TO DEVELOP ON THE OUTFLOW
LATER TONIGHT. AT THIS TIME...IT STILL APPEARS THAT THE COVERAGE
WILL BE 40 PERCENT OR LESS AND THE MOST LIKELY TIME IS 04Z OR LATER
FOR VTN AND LBF. CURRENT INDICATIONS ARE THAT TWO SYSTEMS WILL
DEVELOP...ONE IN THE NORTHWEST AND ONE IN THE SOUTHWEST.


&&

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

$$

UPDATE...SPRINGER
SYNOPSIS...JWS
SHORT TERM...JWS
LONG TERM...POWER
AVIATION...SPRINGER


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