Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 170438
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
1138 PM CDT TUE SEP 16 2014

.SYNOPSIS...
ISSUED AT 305 PM CDT TUE SEP 16 2014

H5 ANALYSIS FROM THIS MORNING HAD A CLOSED LOW OVER
NORTHERN PORTIONS OF HUDSON BAY WITH A TROUGH EXTENDING SWD INTO
QUEBEC AND NEW ENGLAND. FURTHER WEST...BROAD NORTHWESTERLY FLOW
EXTENDED FROM THE MIDWEST...TO THE INTER MOUNTAIN WEST. RIDGING
EXTENDED FROM UTAH...NWD INTO BRITISH COLUMBIA. WEST OF THE
RIDGE...A TROUGH WAS PRESENT OFF THE WEST COAST OF THE CONUS. HIGH
PRESSURE WAS LOCATED ACROSS THE NRN GULF INTO SRN TX...WHILE TS
ODILE WAS LOCATED OVER CENTRAL PORTIONS OF THE BAJA PENINSULA. CLOUD
COVER IN ASSOCIATION WITH ODILE HAS ALREADY PUSHED INTO THE SRN HALF
OF AZ AND NEW MEXICO THIS AFTERNOON. ACROSS WESTERN AND NORTH CENTRAL
NEBRASKA...LOW CLOUDS...WHICH WERE LOCATED BEHIND A COLD FRONT...HAD
PUSHED INTO PORTIONS OF SOUTHWEST AND CENTRAL NEBRASKA THIS MORNING.
AS OF 3 PM CDT...THE CLOUDS HAVE ERODED ON THEIR WESTERN FLANK AND
WERE LOCATED OVER CUSTER...GARFIELD...WHEELER AND SOUTHERN HOLT
COUNTIES. AT THE SURFACE...HIGH PRESSURE WAS LOCATED OVER SRN IA/NRN
MO CURRENTLY. A SURFACE TROUGH WAS PRESENT OVER THE HIGH PLAINS OF
EASTERN WYOMING...THE NEBRASKA PANHANDLE AND EASTERN COLORADO.
BETWEEN THESE TWO FEATURES...SRLY WINDS HAVE INCREASED THIS
AFTERNOON AND HAVE BEEN BREEZY AT TIMES. AS OF 2 PM
CDT...TEMPERATURES RANGED FROM 66 AT BROKEN BOW UNDER CLOUDY
SKIES...TO 79 AT IMPERIAL AND OGALLALA UNDER CLEAR SKIES.

&&

.UPDATE...
ISSUED AT 955 PM CDT TUE SEP 16 2014

THE BOUNDAY LAYER RELATIVE HUMIDITY FROM THE CURRENT RAPID REFRESH
MODELS INDICATES FOG WILL BE A LITTLE MORE EXTENSIVE THAN
PREVIOUSLY INDICATED. WE HAVE UPDATED THE FORECAST TO REFLECT THAT
THINKING.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 305 PM CDT TUE SEP 16 2014

DEW POINTS CONTINUE TO SLOWLY RISE ACROSS THE AREA LATE THIS
AFTERNOON...AND WILL CONTINUE TO DO SO TONIGHT AS SOUTHERLY LOW
LEVEL FLOW DRAWS GULF MOISTURE NORTHWARD. SOME CHANCE OF FOG TONIGHT
AS THE MOISTURE SPREADS NORTH...BUT A CLOSE INSPECTION OF BUFKIT DATA
INDICATES THAT SATURATED LAYER IS VERY SHALLOW...EXTENDING FROM THE
SURFACE TO ABOUT 300 FEET AGL. WITH THE SHALLOW MOIST LAYER NOT
ANTICIPATING MUCH STRATUS...BUT SOME FOG WILL BE
POSSIBLE...ESPECIALLY ALONG AND SOUTH OF INTERSTATE 80.

WARM AIR ALOFT WILL NOSE INTO WESTERN AND SOUTHWEST NEBRASKA
WEDNESDAY...WITH NAM MODEL INDICATING H850 MB TEMPS NEARING 27C BY
AFTERNOON. LOOKS AS IF THIS WARMER AIR WILL EASILY MIX TO THE
SURFACE...SO WILL BOOST HIGHS 3 TO 5 DEGREES INTO THE MID AND UPPER
80S WEST AND SOUTHWEST NEBRASKA...WITH UPPER 70S AND LOWER 80S
ELSEWHERE.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 305 PM CDT TUE SEP 16 2014

WEDNESDAY NIGHT THROUGH SATURDAY...THE MAIN FORECAST CHALLENGES ARE
TEMPERATURES...ALONG WITH PRECIPITATION CHANCES FOR WEDNESDAY
NIGHT. FOR WEDNESDAY NIGHT INTO THURSDAY...SURFACE LOW PRESSURE
LOCATED OVER EASTERN COLORADO...WILL LEAD TO SERLY AND EASTERLY
LOW LEVEL WINDS WEDNESDAY NIGHT. LOW LEVEL MOISTURE WILL INCREASE
OVERNIGHT THANKS TO THE SERLY AND EASTERLY UPSLOPING WINDS. THIS
UPSLOPING WILL LEAD TO THE DEVELOPMENT OF LOW CLOUDS OVERNIGHT. IN
ADDITION TO LOW CLOUDS...THE MODEL SOLNS CONTINUE TO ADVERTISE
ELEVATED INSTABILITY WEDNESDAY NIGHT INTO EARLY THURSDAY ACROSS
THE CENTRAL AND EASTERN CWA. A 700 MB FRONTAL BOUNDARY WILL PUSH
EAST THURSDAY NIGHT AS RIDGING BUILDS IN FROM THE WEST. CALCULATED
LI`S FROM THE 800MB LEVEL RANGE FROM -4 TO -6C OVERNIGHT SO PLENTY
OF ELEVATED INSTABILITY WILL BE PRESENT IN THE CENTRAL AND EAST.
INHERITED FCST CONTINUES TO MENTION SLIGHT CHANCES FOR TSRAS IN
THE CENTRAL AND EASTERN CWA FOR WEDNESDAY NIGHT. MADE SOME MINOR
ADJUSTMENTS TO SHIFT THIS ACTIVITY EAST THURSDAY MORNING BASED ON
THE LATEST MODEL TRENDS. ON THURSDAY...WE SHOULD SEE A FAIRLY WIDE
RANGE IN TEMPERATURES. WITH CLOUDS ANTICIPATED IN THE EAST INVOF A
WARM FRONT...HIGHS WILL STRUGGLE TO GET OUT OF MIDDLE 70S. FURTHER
WEST BEHIND THE WARM FRONT...SOME HIGHS AROUND 90 ARE
POSSIBLE...ESPECIALLY IN THE EASTERN PANHANDLE. ON THURSDAY
NIGHT...THE WARM FRONT WILL CLEAR THE REMAINDER OF THE FORECAST
AREA. SURFACE LOW PRESSURE OVER SWRN SD WILL DEEPEN RESULTING IN
INCREASED SRLY WINDS OVERNIGHT THURSDAY NIGHT. WITH DECENT MIXING
EXPECTED...LOW TEMPS WILL BE MILD WITH READINGS IN THE UPPER 50S
TO AROUND 60 FORECAST. ON FRIDAY...A FRONTAL BOUNDARY WILL BE
ORIENTED FROM EASTERN SOUTH DAKOTA INTO THE NRN NEBRASKA
PANHANDLE. SOUTH OF THE FRONT ACROSS MOST OF WESTERN AND NORTH
CENTRAL NEBRASKA...HIGHS WILL REACH THE 80S TO NEAR 90. INHERITED
FORECAST HAD SOME MENTION OF THUNDERSTORMS INVOF THE FRONT OVER
NORTH CENTRAL NEBRASKA FRIDAY AFTERNOON. DECIDED TO STRIP THESE
FROM THE FORECAST...BASED ON A SLOWER PROGRESSION OF THE
FRONT...AND THE DEGREE OF CAPPING FRIDAY AFTERNOON. BY FRIDAY
NIGHT...A TROUGH OF LOW PRESSURE ALOFT WILL TRAVERSE THE
DAKOTAS...FORCING THE FRONT SOUTH THROUGH THE FORECAST AREA...AS
WELL AS LEADING TO COOLER TEMPERATURES ALOFT AND INCREASED
INSTABILITY. INHERITED FORECAST REMAINS ON TRACK WITH THE HIGHEST
POPS FRIDAY NIGHT. I DID GO AHEAD AND LINGER POPS IN THE EAST
SATURDAY MORNING BASED ON THE SLOWER PROGRESSION OF THE FRONT AND
UPPER LEVEL SUPPORT.

SATURDAY NIGHT THROUGH TUESDAY...COOLER...BUT SEASONAL TEMPERATURES
WILL SET IN BEHIND THE FRONT FOR SUNDAY THROUGH TUESDAY AS THE
PATTERN TRANSITIONS TO MORE NORTHERLY FLOW ALOFT. WITH THE FRONTAL
BOUNDARY WELL SOUTH AND WEST OF THE AREA...THE FOCUS FOR
THUNDERSTORMS WILL SHIFT SOUTH OF THE AREA INTO KANSAS AND OKLAHOMA.
ON MONDAY...AN UPPER LEVEL TROUGH WILL LIFT FROM THE SWRN CONUS INTO
THE CENTRAL AND SRN ROCKIES. THIS WILL LEAD TO INCREASED CHANCES FOR
PCPN OVER COLORADO AND NEW MEXICO. SOME OF THIS ACTIVITY WILL
EVENTUALLY MAKE ITS WAY INTO FAR SOUTHWESTERN NEBRASKA AND WRN KS BY
TUESDAY AND HAVE INCLUDED A SLIGHT CHANCE FOR TSRAS IN THE FAR SWRN
CWA. HIGHS SUNDAY...MONDAY AND TUESDAY WILL BE SEASONAL WITH
READINGS IN THE 70S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1137 PM CDT TUE SEP 16 2014

UNLIMITED CEILING AND VISIBILITY IS LIKELY TONIGHT UNTIL SOMETIME
AFTER 08Z. THEN...WITH LIGHT SOUTHEAST WIND AND ONLY HIGH CLOUDS...
PATCHY FOG IS EXPECTED IN SOUTH CENTRAL AND SOUTHWEST NEBRASKA. THE
EVENING LBF SOUNDING SHOWS A UNIFORMLY MOIST LAYER JUST ABOVE THE
BOUNDARY LAYER. USING THE EQUIVALENT DEWPOINT...THIS WOULD SIGNAL
FOG FOR THE LBF AREA WITH TEMPERATURE GOING BELOW 52F. ALSO...THE
HOURLY REFRESH CYCLE SHOWS LOW VISIBILITY IN A RELATIVELY NARROW
SWATH FROM BUB...THROUGH LBF AND OGA...TO IML. BECAUSE OF THE RIVER
AND WETLANDS IN THE PLATTE RIVER VALLEY...THOSE AREAS WOULD BE MORE
LIKELY TO HAVE VISIBILITY AT OR BELOW 1SM. THERE IS SOME
POSSIBILITY...ABOUT 40 PERCENT PROBABILITY...THAT THE VISIBILITY AT
LBF COULD DECREASE TO 1/2SM OR LESS. STATISTICAL OUTPUT FROM THE
EVENING MODEL RUN SUPPORTS THIS SCENARIO. FOR LBF THEN...WE WILL USE
1SM BCFG WITH A FIELD THRESHOLD TEMPO 1/2SM FG VV002. BOTH
CONDITIONAL CLIMATOLOGY AND THE HOURLY REFRESH MODELS INDICATE THE
FOG LIFTING RAPIDLY AFTER SUNRISE OR BY 14Z. ONE FACTOR LIMITING OUR
CONFIDENCE IS THE WIND. IF IT DOES NOT DROP TO LESS THAN 5KT...THE
PROBABILITY OF FOG IS LOWER.

&&

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

$$

UPDATE...SPRINGER
SYNOPSIS...CLB
SHORT TERM...TAYLOR
LONG TERM...CLB
AVIATION...SPRINGER





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