Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 051156
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
656 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 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 655 AM CDT SAT SEP 5 2015

FCST DIFFICULTIES TODAY INVOLVE THE PRECIP FCST AND ASSOCIATED
CLOUD COVER. ONGOING SHRA OVER NC NEB HAS HAD A COUPLE OF
LIGHTNING FLASHES BUT OVERALL INTENSITY NOT TOO IMPRESSIVE.
OPERATIONAL HRRR HAS HAD POOR RUN TO RUN CONSISTENCY AND EARLIER
DEVELOPED TSRA OVER THE SW NEAR THE WARM FRONT WITH ELEVATED
INSTABILITY BUT PRECIP NEVER MATERIALIZED THOUGH MID LEVEL
CLOUDINESS DID. AGAIN SEVERAL POTENTIAL SOLUTIONS IN THE
CONVECTIVE INITIATION ENVELOPE FOR LATER THIS MORNING AS WELL AS
THIS AFTERNOON WHEN LL FLOW INCREASES IN RESPSONE TO DEVELOPING
LOW PRESSURE IN ERN WY. NAM HAS BEEN TOO AGGRESSIVE WITH DRY LOWER
LAYERS PRESENT UP THROUGH 12Z THIS MORNING. END RESULT IS LITTLE
CONFIDENCE IN ANY ONE SOLUTION. IN ADDITION...BASED ON LATEST SFC OBS
AND RADAR VWP THERE DOES EXISTS SOME LOW LEVEL DIRECTIONAL AND
SPEED SHEAR...BUT AT THIS TIME THE DIFFERENCE IS BELOW CRITERIA.

AS SFC LOW DEVELPS LATER...THERE STILL APPEARS TO BE SOME
TIGHTENING OF THE LOW LEVEL MOISTURE GRAIENT SO HAVE INCLUDED SOME
GUSTS IN TAFS AND...LIKE HAS BEEN THE CASE WITH THE LAST WEEK OR
SO...POTENTIAL CONVECTIVE DEVELOPMENT LOOKS POSSIBLE BUT LACK OF
SHEAR AND LARGE CAPE SHOULD KEEP COVERAGE AND INTENSITY TO A
MINIMUM. FCST CONFIDENCE IS BELOW AVERAGE ON TIMING OF CONVECTION
AT KLBF AND KVTN FOR LATER TODAY.

&&

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

$$

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



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