Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 050900
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
400 AM CDT SAT SEP 5 2015

.SYNOPSIS...
ISSUED AT 400 AM CDT SAT SEP 5 2015

WEAK EMBEDDED SHORT WAVE MOVING QUICKLY ACROSS THE CENTRAL
ROCKIES AND ONTO THE HIGH PLAINS IN SWRLY FLOW ALOFT WORKING IN
CONCERT WITH LLJ TO GENERATE SHRA AND ISOLD TSRA ACROSS PORTIONS
OF WRN NEB EARLY THIS MORNING. MEANWHILE UPPER TROUGH AND
ASSOCIATED LOW OVER THE PAC NW STARTING TO MOVE EWD WHILE HEIGHTS
RISE ACROSS THE PLAINS. THESE TWO THINGS CONTRIBUTING TO
TIGHTEN/INCREASE THE UPPER FLOW AHEAD OF THE LOW IN THE NW.
MOISTURE AND ASSOCIATED CONVECTIVE ACTIVITY FROM TROPICAL STORM
KEVIN MOVING ONSHORE ON THE BAJA PENINSULA.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM CDT SAT SEP 5 2015

FORECAST ISSUES FOR EARLY THIS MORNING INVOLVES THE POTENTIAL FOR
ADDITIONAL CONVECTIVE DEVELOPMENT IN SRN/WRN NEB WHICH SEVERAL OF
THE CAMS SUGGEST WILL HAPPEN THROUGH THE MORNING. RADAR ECHOES
OVER THE LAST FEW HOURS HAVE INCREASED IN THE ERN PANHANDLE...BUT
NEW DEVELOPMENT AS PER THE OPERATIONAL HRRR HAS YET TO OCCUR
ASSOCIATED WITH THE NWD ADVANCING WARM FRONT OVER SRN NEB. SHORT
RANGE MODELS DO HAVE ELEVATED INSTABILITY PRESENT AND SPC
MESOANALYSIS BASED ON RAP SHOWS DEEP MOIST CONVERGENCE INCREASING
TO SUPPORT THIS IDEA. HAVE TRENDED THE HOURLY POP GRIDS TO
REFLECT THIS OCCURRING...DESPITE EXP HRRR AND NSSL WRF NOT
EVOLVING IN THIS MANNER.

ATTENTION THEN TURNS TO ADDITIONAL TSRA DEVELOPMENT THIS
AFTERNOON. AS PREVIOUSLY MENTIONED SHORT WAVE CONTINUES TO MOVE
NEWD INTO THE DAKOTAS TODAY...WEAK LARGE SCALE HEIGHT FALLS ALSO
MOVE OUT OF THE AREA. HOWEVER AS PAC NW UPPER LOW CONTINUES TO
MOVE EWD GOOD HEIGHT FALLS DEVELOP ACROSS WRN MT. THE INCREASED
SWRLY FLOW AHEAD OF THIS FEATURE ALLOWS THE SFC LOW TO REDEVELOP
OVER ERN WY THIS AFTERNOON. AS THIS OCCURS...DEEPER MIXING SOUTH
OF THE SFC LOW WILL DEVELOP THIS AFTERNOON SERVING TO LOWER DEW
POINTS ACROSS THE PANHANDLE. AT THIS SAME TIME...INCREASING SERLY
LOW LEVEL FLOW IN THE TIGHTENING SFC GRADIENT WILL INCREASE DEW
POINTS/LOW LEVEL MOISTURE FURTHER EAST OVER TIME. THE RESULT IS
TO TIGHTEN THE GRADIENT AND EVENTUALLY TO DEVELOP THUNDERSTORMS
ASSOCIATED WITH THIS BOUNDARY. SUITE OF MODELS CONTAIN A WIDE
VARIETY OF SOLUTIONS HOWEVER IN HOW EXTENSIVE THE QPF WILL
BE...IF AT ALL. NAM SUGGESTS A LARGE INCREASE IN PW BY AFTERNOON
/PRIOR TO CONVECTIVE DEVELOPMENT IN THE MODEL/ ASSOCIATED WITH
THE FETCH OF MID/UPPER LEVEL MOISTURE ORIGINATING FROM THE ERN
PAC TROPICS VIA THE SWRLY FLOW. IF DEEP MOIST CONVECTION CAN
DEVELOP...THE WARM MOIST MID LEVELS WOULD ALLOW FOR A CAPE
PROFILE MORE CONDUCIVE TO HEAVY RAIN PRODUCING STORMS AND SHEAR
OF 25-30KTS WOULD BE MARGINAL FOR DEVELOPING STRONG STORMS. AS
ALWAYS HOWEVER SMALL SCALE STORM INTERACTIONS MAY ALLOW FOR MORE
ROBUST DEVELOPMENT ON OCCASION.

TEMPERATURES TODAY WILL BE TRICKY DUE TO LEFT OVER CLOUD COVER
FROM ONGOING CONVECTION AS WELL AS NEW CLOUD COVER FROM
ADDITIONAL DEVELOPMENT THIS AFTERNOON. ASSUMING SRN AREAS WOULD
RECEIVE BEST INSOLATION FOR A LONGER PERIOD OF TIME AND THEREFORE
MAXES ARE HIGHER THERE...THOUGH 90S WILL AGAIN BE COMMON TODAY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 400 AM CDT SAT SEP 5 2015

SOUTHWEST FLOW TO START THE WEEK TRANSITIONS TO MORE ZONAL FLOW AS
AN UPPER LEVEL LOW LIFTS ACROSS THE NORTHERN ROCKIES INTO THE
CANADIAN PLAINS. A COUPLE OF COLD FRONTS WILL RESULT IN FALLING
TEMPS FOR THE WEEK. MAIN CONCERN IN THE EXTENDED WILL BE TIMING THE
COOL DOWNS AND LOW POP CHANCES THROUGHOUT THE PERIOD.

SUNDAY INTO MONDAY SW FLOW WILL TAP SOME PACIFIC MOISTURE. MODELS
SHOWING SOME MOISTURE FROM THE EASTERN PACIFIC TROPICAL SYSTEMS
GET DRAWN ACROSS THE 4 CORNERS AND TOWARDS THE HIGH PLAINS. THIS
MAY BE ENOUGH TO INCREASE THE MOISTURE IN THE MID/UPPER LEVELS THAT
CAN BE TAPPED BY WEAK DISTURBANCES RIDING ACROSS THE AREA. MODELS
HAVE INCREASE THE LIGHT QPF OVER THE CWA AND CAN NOT ARGUE
NEEDING LOW POPS WITH EACH PASSING WAVE.

MID WEEK A COLD FRONT WILL PUSH ACROSS THE AREA. TIMING OF THE
FRONT AND BETTER MOISTURE RESULTS IN BEST CHANCE FOR PRECIP TO BE
ACROSS THE EASTERN ZONES. BEHIND THE FRONT TEMPS COOL INTO THE
70S...WHICH WOULD BE BELOW NORMAL.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1127 PM CDT FRI SEP 4 2015

ISOLATED SHOWERS AND THUNDERSTORMS ARE EXPECTED THE REST OF
TONIGHT IN WESTERN NEBRASKA. CONFIDENCE IN SHOWERS/THUNDERSTORMS
OCCURRING BEFORE 15Z IS LOW. IN FACT...THE PROBABILITY OF
SHOWERS/THUNDERSTORMS THROUGH THE PERIOD IS 30 PERCENT OR LOWER
WHICH DOES NOT INSPIRE A LOT OF CONFIDENCE THAT THEY WILL OCCUR
AT LBF OR VTN. THE BEST CONSENSUS AMONG THE EVENING MODEL RUNS
WOULD BE THAT THE CHANCES OF PRECIPITATION WILL BE 18-01Z
SATURDAY. WE HAVE ACCOUNTED FOR THAT BY USING PROB30 IN THE
FORECASTS FOR LBF AND VTN 19-24Z.

&&

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

&&

$$

SYNOPSIS...JWS
SHORT TERM...JWS
LONG TERM...MASEK
AVIATION...SPRINGER


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