Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 141813
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
113 PM CDT SUN SEP 14 2014

.UPDATE...
ISSUED AT 652 AM CDT SUN SEP 14 2014

DESPITE MID LEVEL CLOUDINESS IN AN AREA OF WEAK FRONTOGENESIS AND
DECENT ELEVATED INSTABILITY...ECHOES HAVE DECREASED ACROSS CHERRY
COUNTY THIS MORNING AND HAVE THEREFORE PULLED THEM FROM THE FCST.
OTHERWISE NO MAJOR CHANGES.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 342 AM CDT SUN SEP 14 2014

MAIN UPPER PV ANOMALY LOCATED ACROSS NRN ND WILL CONTINUE ITS QUICK
EWD PROGRESSION TO THE NRN GREAT LAKES REGION THROUGH THE DAY WHILE
ASSOCIATED FRONT LOSES SWD MOMENTUM AND IS PROGGED BY THE MODELS TO
STALL ACROSS NRN NEB. THIS IS IN LINE WITH CURRENT PRESSURE FIELDS
EARLY THIS MORNING AS BEST FALLS ARE OVER NRN MN AND WEAK RISES
BEHIND THE FRONT AS IT ENTERS THE NRN PORTION OF THE STATE. UNDULAR
BORE EVIDENT WITH THE FRONT CURRENTLY ON KLNX 88D INDICATING STABLE
LOW LEVELS...HOWEVER RAP ANALYSIS AND IR IMAGERY SUGGEST SMALL AREA
OF WEAK MID LEVEL FRONTOGENESIS INDICATIVE OF DEVELOPING WARM AIR
ADVECTION ACROSS NWRN FCST AREA CURRENTLY AND LIKELY TAPPING WEAK
INSTABILITY BASED ON CONVECTIVE NATURE TO CLOUDS...AND ECHOES
SHOWING UP ALOFT ON KLNX 88D. FOR THE REST OF THE AREA...VERY LITTLE
IN THE WAY OF CLOUDS ASSOCIATED WITH THE FRONT WHICH IS EVIDENCE OF
ITS KATABATIC NATURE WITH 0.5KM/1KM AND 700 MB VWP WINDS FROM AREA
RADARS AND RAP SHORT TERM FCST SOUNDINGS SHOWING NWRLY WINDS AHEAD
OF THE FRONT. HAVE INCLUDED SPRINKLES EARLY THIS MORNING BASED ON
RADAR TRENDS MENTIONED ABOVE.

AS UPPER PV ANOMALY AND ASSOCIATED UPPER LOW MOVES INTO NRN MN THIS
MORNING...MID AND UPPER FLOW BECOMES ZONAL ACROSS THE CENTRAL
ROCKIES AND HIGH PLAINS. IN RESPONSE...MID LEVEL WINDS BECOME SWRLY
WHICH WILL ADVECT THE EML EWD OVER THE EWD ADVANCING DRYLINE ACROSS
ERN CO...AS LOWER LEVEL WINDS BACK AND BECOME S/SERLY DURING THE
AFTERNOON. NAM PROGS SFC DEW POINTS INTO THE MID 50S ACROSS SWRN
NEB...HOWEVER THE AFOREMENTIONED EML DEVELOPS A SIGNIFICANT CAP EAST
OF THE DRYLINE IN SWRN NEB DURING THE AFTERNOON HOURS. SCT/BKN CLOUD
COVER IS EXPECTED EAST OF THE DRYLINE AS WELL WHICH WILL BE EVIDENCE
OF THE HIGHER LOW LEVEL THETA E AND HIGHER CAPE. HOWEVER...DESPITE
THE NEXT APPROACHING UPPER PV ANOMALY AND STALLED SFC BOUNDARY
ACROSS THE NRN PORTION OF THE STATE...AND THE PREVIOUSLY MENTION
HIGHER CAPE AND DECENT SHEAR...THE CAP IS EXPECTED TO BE TOO STRONG
TO ALLOW CONVECTIVE INITIATION DURING THE AFTERNOON IN WRN NEB.
HOWEVER...CONVECTION ALLOWING MODELS /CAMS/ ARE QUICKER TO DEVELOP
STORMS ACROSS NRN NEB INTO SERN SD BY EVENING WHICH WILL BE CLOSER
TO MAIN UPPER LEVEL SUPPORT AND SFC WARM FRONT SO PRECIP CHANCES
WILL BE RETAINED IN THE NERN PORTION OF THE FCST AREA...THOUGH MAY
BE PUSHED BACK IN TIME A LITTLE.

NEXT SIGNIFICANT UPPER PV ANOMALY AND ASSOCIATED UPPER LOW WILL MOVE
INTO THE NRN PLAINS THIS EVENING AND SUNDAY NIGHT. THIS WILL GIVE A
NUDGE TO THE STALLED SFC BOUNDARY AND WILL MOVE IT SWD
SOMEWHAT...BUT THE HIGH PLAINS NOCTURNAL LOW LEVEL JET WILL DEVELOP
AS DRIER AIR ACROSS THE HIGHER ELEVATIONS FURTHER WEST COOLS RAPIDLY
AFTER SUNSET...BUT ALSO PARTLY IN RESPONSE TO THE LOWERING HEIGHTS
ACROSS THE NRN PLAINS. THIS LIFT WILL BE ABLE TO TAP THE ELEVATED
INSTABILITY STILL RESIDING ACROSS SWRN NEBR TO DEVELOP THUNDERSTORMS
OVERNIGHT SUNDAY NIGHT AS THE FRONT SLOWLY CONTINUES TO SAG ACROSS
THE REMAINDER OF THE STATE. THOUGH THE NAM SUPPORTS PRECIP IN THE
SWRN PORTION OF THE STATE OVERNIGHT...CAMS FOCUS MOST OF THE PRECIP
ALONG THE COLD FRONT IN NRN NEB.

AS FOR TEMPERATURES...DESPITE DEVELOPING CLOUD COVER DURING THE
AFTERNOON IN THE SW...TEMPS WILL BE MUCH WARMER WITH INCREASING SRLY
WINDS BUT WILL BE SLIGHTLY COOLER ACROSS THE NORTH AS WINDS BECOME
ERLY NORTH OF THE WARM FRONT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 342 AM CDT SUN SEP 14 2014

QUASI-ZONAL UPPER TROPOSPHERIC FLOW TO PREVAIL BEHIND A PASSING
NORTHERN PLAINS WAVE EARLY IN THE EXTENDED...BUT WILL EVENTUALLY
GIVE WAY TO NORTHWESTERLY AS A WESTERN CONUS RIDGE BUILDS EAST. AS
A RESULT A GENERAL LACK OF OMEGA IS ANTICIPATED ATOP MUCH OF THE
FORECAST AREA THROUGH TUESDAY AFTERNOON...WITH THE MODELS
PROJECTING NO ATMOSPHERIC DISTURBANCES IMPACTING THE REGION.
TUESDAY EVENING INTO WEDNESDAY...THE OPERATIONAL MODELS /GFS
INITIALLY...THEN ECMWF WEDNESDAY MORNING/ GENERATES MEASURABLE QPF
ACROSS SOUTHEASTERN PORTIONS OF THE CWA...THE MODELS ARE KEYING ON
SUFFICIENT THERMAL ADVECTION/UPGLIDE IN THE 305-310K SFC FOR
PRECIPITATION PRODUCTION. DESPITE THIS...DECIDED TO LEAVE QPF OUT
OF THE FORECAST AS PROXIMITY AND BUFR SOUNDINGS SUGGEST A MOISTURE
CHALLENGED ATMOSPHERE ABOVE THE BOUNDARY LAYER WITH THE GFS
SHOWING SIGNIFICANT DRY MID LEVELS. WITH THIS IN MIND...FELT THAT
POPS WILL BE ISOLATED AT BEST IN COVERAGE WITH QPF AMOUNTS LIGHT.
IF SHOWERS/STORMS ARE TO GO...SOUTHEASTERN PORTIONS OF THE CWA
OVERNIGHT TUESDAY INTO EARLY WEDNESDAY WOULD BE THE MOST LIKELY OF
LOCATIONS. ADDITIONAL THERMAL ADVECTION INDUCED STORMS ARE SHOWN
WEDNESDAY NIGHT INTO THURSDAY...BUT MOSTLY REMOVED /SOUTH AND
EAST/ FROM OUR CWA. CR ALLBLEND PULLED ALL MENTION OF QPF OUT OF
OUR CWA DURING THIS TIME PERIOD...WHICH IS FINE FOR NOW. UPPER
PATTERN UNDERGOES A CHANGE LATE IN THE WEEK WITH THE APPROACH OF A
WESTERN CONUS TROUGH AND ATTENDANT COLD FRONT PASSAGE. THE
TROUGH/COLD FRONT WILL SUPPRESS THE RIDGE EAST OF THE FORECAST
AREA LATE WEEK AND PROVIDE FOR PRECIPITATION. THE GFS IN
COMPARISON TO THE EC REMAINS MUCH STRONGER WITH THIS LATE WEEK
TROUGH AND MORE FAVORABLE FOR WIDESPREAD SHOWERS/STORMS. THE CR
ALLBLEND PROCEDURE RAMPS UP POPS STARTING FRIDAY...WITH POPS
MAXIMIZED NEAR 40 PERCENT FOR SATURDAY AND INTO EARLY SUNDAY. TO
BE HONEST...REALLY NOT TOO KEEN ON 4 PERIODS OF QPF THAT IS
ASSOCIATED WITH THE PASSAGE OF THIS DISTURBANCE/FRONT...ESPECIALLY
IN A SOMEWHAT PROGRESSIVE PATTERN...BUT WILL LEAVE THE PROCEDURE
UNCHANGED DUE TO THE USUAL TIMING/STRENGTH DIFFERENCES SEEN THIS
FAR OUT.

DRIZZLE REPLACED THE SLIGHT CHANCE MENTION OF QPF FROM 12-15Z THIS
MONDAY AS PROXIMITY SOUNDINGS REVEAL DRYING ALOFT...BUT A SATURATED
BL WITH WEAK LIFT.  THIS DRIZZLE SHOULD NOT LAST LONG AS PROXIMITY
SOUNDINGS REVEAL RAPID BL DRYING BEHIND THE FRONT.  WILL ALSO NEED
TO MONITOR THE RETURN OF LOW LEVEL MOISTURE EARLY TUESDAY AS SURFACE
HIGH PRESSURE BUILDS EAST OF THE MISSOURI VALLEY.  NAM12 0.5AGL RH
WOULD INDICATE A SIGHT POTENTIAL OF FOG ACROSS SOUTHWEST
NEBRASKA...BUT CONFIDENCE WAS NOT SUFFICIENT TO INCLUDE THE MENTION
WITH THIS FORECAST.

RETURN SOUTHERLY FLOW AND RESULTANT THERMAL ADVECTION WILL PROMOTE A
WARMING TREND MONDAY THROUGH MID-LATE WEEK...WIDESPREAD HIGHS IN THE
80S BY THURSDAY ARE ANTICIPATED.  WARMEST READINGS WILL BE ACROSS
OUR WEST EACH DAY WITH A GREATER INFLUENCE FROM THE UPPER TROPOSPHERIC
RIDGE.  OVERNIGHT LOWS WILL BENEFIT AS WELL...RISING FROM THE 40S
MONDAY MORNING...TO POSSIBLY THE 50S TO 60S BY WEEKS END.
TEMPERATURES COOL LATE WEEK BEHIND THE FRONT...BUT AT THAT...NOT
ANTICIPATING WHAT WE SAW A FEW DAYS AGO...NO FROST OR FREEZE
ISSUES ARE EXPECTED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 112 PM CDT SUN SEP 14 2014

TROUGH MOVING ACROSS THE AREA THIS EVENING LIKELY TO SPARK SOME
THUNDERSTORMS. FAVORABLE MODEL SOUNDINGS SUPPORT IMPACT OVERNIGHT
TO KLBF HOWEVER STILL HAVE SOME UNCERTAINTY FOR KVTN. WILL
CONTINUE THE PROB30 FOR KLBF...WITH NO MENTION YET FOR KVTN...AND
WILL MONITOR FOR POSSIBLE AMENDMENT. LATER TONIGHT...BEHIND
THUNDERSTORM ACTIVITY...EXPECT SOME STRATUS TO DEVELOP WITH MVFR
CIGS...POSSIBLY IFR. ACTIVITY WILL BE ERODE FROM THE NW AS HIGH
PRESSURE BUILDS SOUTH.

&&

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

&&

$$

UPDATE...JWS
SHORT TERM...JWS
LONG TERM...JACOBS
AVIATION...MASEK




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