Area Forecast Discussion
Issued by NWS North Platte, NE

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000
FXUS63 KLBF 170903
AFDLBF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTH PLATTE NE
403 AM CDT WED SEP 17 2014

.SYNOPSIS...
ISSUED AT 400 AM CDT WED SEP 17 2014

WEAK SURFACE LOW PRESSURE CURRENTLY RESIDES ACROSS THE DAKOTAS
AND WESTERN NEBRASKA. PORTIONS OF CENTRAL AND SOUTHWEST NEBRASKA
REPORTING LIGHT FOG 3-5SM WITH LOCALLY DENSE FOG AT THE KLBF
ASOS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM CDT WED SEP 17 2014

NEAR TERM CONCERN IS CONTINUED FOG DEVELOPMENT ACROSS PORTIONS OF
CENTRAL AND SOUTHWEST NEBRASKA. LOW VISIBILITY 1/4-1/2SM AT KLBF
AND KBBW IS LIKELY TO CONTINUE THROUGH 14Z. CURRENTLY THE DENSE
FOG IS VERY LOCALIZED AND AREA WEBCAMS DO NOT INDICATE A CONCERN
YET. HOWEVER...IF FOG BECOMES DENSE AND WIDESPREAD ENOUGH A DENSE
FOG ADVISORY MAY BE NEEDED.

A FALL LIKE WEATHER PATTERN ACROSS NORTH AMERICA WITH A DEEP
UPPER LOW OVER THE HUDSON BAY REGION CONTRASTED BY AN AMPLIFIED
RIDGE ACROSS THE GREAT BASIN AND DESERT SOUTHWEST INTO ALBERTA
CANADA. ACROSS THE CENTRAL PLAINS...NORTHWEST FLOW
CONTINUES...WITH THE UPPER RIDGE TO THE WEST INFLUENCING WARM AIR
ADVECTION INTO THE REGION TODAY AND BEYOND.

SURFACE LOW PRESSURE WILL EXTEND FROM IDAHO AND OREGON INTO
COLORADO TODAY. THIS WILL KEEP A LIGHT EAST OR SOUTHEAST WIND
ACROSS WESTERN NEBRASKA. THIS WILL KEEP HIGHER DEWPOINTS OF 55 TO
60 GOING TODAY AND TONIGHT. WARMER AIR WILL ALSO BE TRANSPORTED
INTO WRN NEBR...WITH THE WARMEST H85 TEMPS OF 27C IN FAR SWRN
NEBR. HIGHS SHOULD REACH NEAR 90 FAR SWRN ZONES WITH MID AND
UPPER 80S MUCH OF THE WESTERN SANDHILLS AND SOUTHWEST. FURTHER
EAST...AT ONL AND BUB...HIGH SHOULD TOP OUT NEAR 80.

A WARM FRONT WILL ROUGHLY EXTEND THROUGH A MCCOOK THROUGH EMPORIA
KS LINE TONIGHT. 0-3KM CAPES AS HIGH AS 1200 J/KG WILL BE
AVAILABLE AND EXTEND NORTHWEST INTO LBF AND BBW. CONTINUED A
SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS AFTER 03Z FOR MUCH OF
THE SERN ZONES. IN ADDITION...A SATURATED LOW LEVEL (1000-850MB)
WILL DEVELOP OVERNIGHT WITH A DRY LAYER H8-H6. SOUNDINGS LOOK
FAVORABLE FOR PATCHY DRIZZLE AND FOG TO DEVELOP ACROSS WRN NEBR
OVERNIGHT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 400 AM CDT WED SEP 17 2014

TRICKY FORECAST FOR THURSDAY AS CLOUDS...FOG AND SHOWERS/DRIZZLE
TO START THE DAY. VERY MOISTURE ENVIRONMENT WITH UPSLOPE
SOUTHEASTERLY FLOW THROUGH MOST OF THE DAY. A WARM FRONTAL
BOUNDARY WILL LIFT NE ACROSS THE AREA BRINGING DRIER AIR IN FROM
THE WEST. QUESTION IS HOW FAST THE FRONT LIFTS ACROSS THE AREA.
MORNING SHOULD BE CLOUDY THEN CLEARING FROM THE WEST FOR THE
AFTERNOON. EASTERN ZONES LIKELY WILL BE LATE AFTERNOON...OR LATER
SO TEMPS TO HOLD IN THE 70S. HIGHER CONFIDENCE PANHANDLE AND FAR
SW NEB TO CLEAR AND WARM WELL INTO THE 80S...MAYBE 90. MODELS
VARY FOR THE 83 CORRIDOR CLEARING. THE NAM KEEPS CLOUDS IN
THROUGH MUCH OF THE DAY WITH 2M TEMPS CLOSER TO 70...MEANWHILE
MOS GUIDANCE IS IN THE 80S. FORECAST TRENDS TEMPS DOWN AS MOS
DOES KEEP SKIES OVERCAST THROUGH THE DAY...ALTHOUGH NOT NEARLY
DOWN AS LOW OF WHAT IS POSSIBLE.

ALL MODELS IN AGREEMENT WITH FRONT LIFTING ACROSS THE AREA
OVERNIGHT WITH DECREASING CLOUDS...BL MOISTURE DECENT AND WILL
HELP HOLD TEMPS AT OR ABOVE SEASONAL NORMS. AFTER A WARM
FRIDAY...A COLD FRONT WILL SLIDE ACROSS THE HIGH PLAINS.
THUNDERSTORMS WILL BE POSSIBLE ALONG THE FRONT.

OVER THE WEEKEND REMNANTS OF ODILE WILL TRACK ACROSS
KS...POSSIBLE SEEING SOME MOISTURE INTO SRN NEB. CURRENT
EXPECTATION IS THE FRONT WILL HELP TO KEEP MOISTURE GENERALLY
SOUTH OF THE CWA. TEMPS COOL CLOSER TO SEASONAL.

TO START OFF NEXT WEEK...THE AREA WILL BE UNDER NW FLOW...WITH A
TROUGH ACROSS THE GREAT LAKES AND A WESTERN RIDGE INTO SW CANADA.
A CLOSED LOW LIFTS FROM CENTRAL CA ACROSS THE CENTRAL ROCKIES AND
WILL BRING A SLGHT CHANCE FOR RAIN TO THE WESTERN ZONES. THE LOW
IS NOT IN THE MEAN FLOW AND MODELS MAY BE TOO QUICK TO BRING IT
ACROSS THE ROCKIES SO PRECIP MAY BE DELAYED. FOR NOW CONTINUED
WITH A MODEL BLEND ON TIMING...ALTHOUGH CONFIDENCE IS LOW.

&

.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.

&&

$$

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





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