Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 272348
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
548 PM MDT SAT SEP 27 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 430 PM MDT SAT SEP 27 2014

SCATTERED SHOWERS AND ISOLATED TSTMS HAVE DEVELOPED THIS AFTN OVER
PORTIONS OF CARBON COUNTY. THE FAR WESTERN PORTION OF THE CWA IS
CLOSEST TO THE MOISTURE PLUME THAT IS STREAMING NORTHWARD FROM THE
SOUTHWEST. WATER VAPOR IMAGERY SHOWS THE UPPER LOW SPINNING ACROSS
CENTRAL CALIFORNIA WITH ABUNDANT MOISTURE TO THE EAST OF IT. KEPT
POPS LARGELY CONFINED TO CARBON COUNTY THROUGH THE NIGHT AS THE
MODELS DO NOT INDICATE MUCH EASTWARD PROGRESS IN THE UPPER LEVEL
SYSTEM AND ITS ASSOCIATED MOISTURE PLUME. THAT BEGINS TO CHANGE BY
SUN AS A SHORTWAVE PIVOTS NORTHWARD ACROSS SOUTHEAST WY BY MIDDAY
THROUGH THE AFTN. WIDESPREAD RAIN WILL DEVELOP MAINLY TO THE WEST
OF THE LARAMIE RANGE DURING THE MORNING AND THEN WILL SPREAD OVER
PORTIONS OF THE PLAINS OF SOUTHEAST WYOMING THROUGH THE EARLY
EVENING. PW VALUES ARE QUITE HIGH FOR LATE SEP (GENERALLY 0.75-0.9
INCHES) DUE TO THE DEEP MOIST SOUTHERLY FLOW...SO CAN NOT RULE
OUT SOME HEAVY RAIN PRODUCERS. TEMPS WILL BE COOLER ON SUN BY
AROUND 10 DEGREES WITH MORE CLOUD COVER AND PRECIPITATION.

BY MON THE UPPER LOW RAPIDLY LIFTS TO THE NORTHEAST WITH
INCREASING UPPER LEVEL DIFFLUENCE DURING THE AFTN...ESPECIALLY
OVER THE PLAINS. THE GFS SHOWS WIDESPREAD QPF OF OVER 0.5 INCHES
TO THE EAST OF THE LARAMIE RANGE FROM 18Z SUN THRU 06Z MON. THESE
LARGE AMOUNTS MAKE SENSE WITH THE UPPER JET JUST TO THE SOUTH OF
THE AREA AND GREAT VERTICAL ASCENT. CANNOT RULE OUT A FEW STRONGER
STORMS OVER THE PANHANDLE ON MON AFTN...ALTHOUGH THE POTENTIAL
WILL BE LIMITED BY THE ABUNDANT CLOUD COVER AND MARGINAL
INSTABILITY. FRONTAL PASSAGE OCCURS LATE IN THE DAY ON MON WITH
700MB TEMPS FALLING TO ABOUT 2C. LIGHT SNOW WILL BE POSSIBLE IN
THE HIGHER ELEVATIONS OF THE SIERRA MADRE AND SNOWY RANGES FROM
THE AFTN THROUGH THE EVENING...ALTHOUGH NOT EXPECTING MUCH MORE
THAN AN INCH DUE TO THE INCREASING SUBSIDENCE BY THAT TIME. THE
FOCUS FROM MON NIGHT THRU TUES MORNING WILL SHIFT TO THE
INCREASING WINDS. THE MODELS INDICATE CYCLOGENESIS OCCURRING BY
LATE MON NIGHT OVER WESTERN SOUTH DAKOTA. 700MB WINDS OFF THE GFS
ARE 50-60 KTS OVER THE PLAINS BY SUNRISE ON TUES SO COULD BE
LOOKING AT LEAST WIND ADVISORY POTENTIAL IN THE PANHANDLE. THE
WIND PRONE AREAS OF SOUTHEAST WY COULD ALSO SEE THE FIRST HIGH
WIND EVENT OF THE SEASON.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 430 PM MDT SAT SEP 27 2014

A COOL PERIOD SHAPING UP FOR TUE-FIR AS A LONGWAVE TROUGH CONSISTING
OF SEVERAL SHORTWAVES SLOWLY SWINGS THRU. ALTHOUGH SMALL CHANCES FOR
PRECIP WILL EXIST PERIODICALLY TUE-THU...THE BEST CHANCES WILL BE NR
THE PINE RIDGE WITH THE FIRST DEPARTING SHORTWAVE ON TUESDAY AND
AGAIN WITH THE 2ND SHORTWAVE THAT PUSHES THRU CWA-WIDE ON WEDNESDAY.
WILL NEED TO KEEP ON EYE ON STRONG WIND POTENTIAL TUESDAY MORNING AS
WELL AS H7 PROGS CLIMB TO NR 50 KNOTS. ITS NOT EXACTLY A
CLIMATOLOGICALLY FAVORABLE FOR STRONG WINDS...BUT NOT OUT OF THE
REALM OF POSSIBILITY EITHER. EACH SHORTWAVE WILL PROVIDE A
REINFORCING SHOT OF COOL AIR...COOLING HIGH TEMPERATURES FROM THE
LOW 60S TUESDAY INTO THE MID/UPPER 50S BY FRIDAY. SNOW-LEVELS WILL
HOVER 9-10 KFT TUESDAY AND WEDNESDAY...DIPPING TO AROUND 8 KFT
THURSDAY MORNING...WHICH SHOULD BE THE LOWEST OF THE PERIOD.
ALTHOUGH SIGNIFICANT SNOW ACCUMULATIONS ARE NOT EXPECTED...
ELEVATIONS ABOVE 8 KFT COULD SEE A SKIFF UP TO SEVERAL INCHES AT THE
HIGHER PEAKS...ESPECIALLY ON WEDNESDAY. ONE FINAL SHORTWAVE DROPS
SOUTHEAST WITHIN THE NW FLOW ON THURSDAY...MAINLY IMPACTING AREAS
FROM THE NRN LARAMIE RANGE EAST ALONG THE PINE RIDGE. FRIDAY LOOKS
DRY AT THIS POINT AND LIKELY STILL COOL AS THE PATTERN TRANSITIONS
FROM CYCLONIC TOWARDS ANTICYCLONIC AHEAD OF WARMING ANTICIPATED NEXT
WEEKEND.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY AFTERNOON)
ISSUED AT 548 PM MDT SAT SEP 27 2014

MAIN CONCERN IN THE NEAR TERM WILL BE CONTINUED DEVELOPMENT OF
CONVECTION OVER THE MOUNTAINS PUSHING NNW AND POSSIBLE IMPACTING
KRWL. MARGINAL MVFR CONDITIONS WILL OCCUR WITH ANY SHRA/TSRA
ACTIVITY THAT MOVES OVERHEAD THRU ABOUT 06Z...WITH MOSTLY DRY
CONDITIONS EXPECTED THRU THE MORNING HERE. ELSEWHERE...WILL SEE
CONTINUED DRY AND BREEZY CONDITIONS THIS EVENING WITH WINDS
DIMINISHING OVERNIGHT. FORECAST SOUNDINGS HINT AT THE POSSIBILITY
OF FOG AT THE NEBRASKA TERMINALS EARLY SUNDAY MORNING IN SOUTHEAST
UPSLOPE FLOW...BUT CONFIDENCE RIGHT NOW IS LOW IN FOG DEVELOPING
AS THE FLOW WILL BE RELATIVELY WEAK. LEFT MENTION OF FOG OUT OF
THE FORECAST NOW...BUT WILL RE-EVALUATE FOR 06Z TAFS. A BETTER
CHANCE FOR SHOWERS AND THUNDERSTORMS WILL DEVELOP SUNDAY MORNING
IN THE FAR WEST...AND STEADILY PUSH EAST THROUGH THE AFTERNOON AND
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 430 PM MDT SAT SEP 27 2014

MINIMAL FIRE WEATHER CONCERNS THROUGH EARLY NEXT WEEK. COOLER
TEMPERATURES ALONG WITH INCREASING MOISTURE WILL CAUSE AFTERNOON
HUMIDITY VALUES TO RISE OVER THE NEXT FEW DAYS. THE ABUNDANT
MOISTURE WILL COMBINE WITH LIFT FROM AN APPROACHING SYSTEM TO
PRODUCE A GOOD CHANCE OF WIDESPREAD WETTING RAINS ON SUNDAY ACROSS
SOUTHEAST WYOMING AND THEN OVER THE PLAINS OF SOUTHEAST WYOMING
AND THE WESTERN NEBRASKA PANHANDLE ON MONDAY. WINDY CONDITIONS
WILL DEVELOP ON TUESDAY...HOWEVER MINIMUM RELATIVE HUMIDITY VALUES
WILL REMAIN ABOVE 35 PERCENT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&

$$

SHORT TERM...FINCH
LONG TERM...HAHN
AVIATION...RJM
FIRE WEATHER...FINCH






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