Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 180539
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1039 PM MST WED DEC 17 2014

.UPDATE...
ISSUED AT 907 PM MST WED DEC 17 2014

DECIDED TO ISSUE A DENSE FOG ADVISORY FOR THE PLATTE RIVER VALLEY
BETWEEN TORRINGTON AND BRIDGEPORT. SFC OBSERVATIONS AND AREA WEB
CAMS CONFIRM VISIBILITIES OF ONE QUARTER OF A MILE OR LESS AT TOR
AND BFF AS OF 03Z THIS EVE. BIGGEST QUESTION IS JUST HOW LONG THIS
WILL LAST AS DRIER AIR IS TRYING TO WORK IN. RECENT HIGHRES MODEL
RUNS ARE TOO QUICK TO SHIFT WINDS AROUND TO THE WEST IN THIS LOW
GRADIENT PATTERN...SO AM CONFIDENT THE PLATTE RIVER VALLEY WILL
HANG ON TO A MOIST UPVALLEY FLOW OVERNIGHT. WITH SIGNIFICANT SNOW
COVER IN SCOTTS BLUFF COUNTY...THESE AREAS SHOULD HAVE NO PROBLEM
STAYING IN THE SOUP FOR SEVERAL HOURS. THE 01Z HRRR RUN SHOWS VSBY
LESS THAN ONE HALF MILE PERSISTING THROUGH AT LEAST 12Z AND FCST
SOUNDINGS SHOW EXCELLENT LLVL MOISTURE DURING THIS TIME. FREEZING
FOG HAS ALSO HAD A TENDENCY TO CREATE LIGHT ICING THE PAST FEW
NIGHTS...SO FELT AN ADVISORY WAS WARRANTED WITH THE ADDED RISK TO
TRAVEL. ALL OTHER ASPECTS OF THE FORECAST LOOK GOOD. UPDATES AND
NPW HAVE BEEN SENT.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY NIGHT)
ISSUED AT 351 PM MST WED DEC 17 2014

FOG AND LOW STRATUS LOOKS TO RETURN TONIGHT ACROSS THE PANHANDLE
AND ALSO CENTRAL AND WESTERN PORTIONS OF CARBON COUNTY AS
FORECAST SOUNDINGS SHOW NEARLY SATURATED LLVLS WITH LIGHT SSW
SURFACE WINDS IN PLACE FOR THESE AREAS. UPPER LEVEL WINDS WILL
REMAIN LIGHT AS WELL WITH LITTLE IN THE MEANS OF ANY DISTURBANCES
ALOFT DISRUPTING THE LOWER LEVELS...SO PERSISTENCE FORECAST SEEMS
REASONABLE. LIGHT SNOW WILL CONTINUE OVER THE MOUNTAINS IN THIS
PATTERN AS WELL...WITH GENERALLY LESS THAN AN INCH OF ACCUMULATION
EXPECTED. THINKING THAT THE FOG AND LOW STRATUS WILL NOT STICK
AROUND AS LONG TOMORROW AS TODAY/YESTERDAY AS A SHORTWAVE TROUGH
APPROACHES FROM THE PAC NW AND DEEPENS THE LEESIDE SFC PRESSURE
TROUGH...THUS INCREASING WEST WINDS ACROSS THE CWA AND NUDGING THE
LLVL MOISTURE EASTWARD. THE EXCEPTION COULD BE OUT WEST IN THE
LOWER ELEVATIONS OF CARBON COUNTY WHERE THE WESTERLY WINDS COULD
MAINTAIN INFLUX OF LLVL MOISTURE TO THIS AREA. LIKELY TO SEE WIND
GUSTS OF 30 TO 35 MPH IN THE WIND PRONE AREAS ALONG AND WEST OF
THE LARAMIE RANGE THROUGH THE DAY AS THE PRESSURE GRADIENT
STRENGTHENS IN ADVANCE OF THE UPPER TROUGH...WITH WARMING TEMPS
ACROSS THE EASTERN PLAINS WITH THESE DOWNSLOPE WINDS IN PLACE.

WINDS WILL INCREASE SLIGHTLY FOR THE WIND PRONE AREAS FOR TOMORROW
NIGHT AND FRIDAY AS THE UPPER LEVEL TROUGH MOVES OVERHEAD WITH
GUSTS OF 40 TO 50 MPH POSSIBLE THROUGH EARLY FRIDAY AFTERNOON.
EXPECTING LIGHT SNOW SHOWERS TO CONTINUE THROUGH THIS TIME ALONG
WITH SLIGHTLY WARMER TEMPS ACROSS THE PLAINS.
OTHERWISE...CONDITIONS WILL REMAIN DRY AND BREEZY THROUGH FRIDAY
NIGHT.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 351 PM MST WED DEC 17 2014

RATHER ZONAL FLOW SATURDAY WILL BECOME NWLY SATURDAY NIGHT AND
SUNDAY AS RIDGING AMPLIFIES ALONG THE WEST COAST. MAINLY DRY
OUTSIDE OF THE MTNS WHERE OROGRAPHICS SHOULD ALLOW FOR SOME SNOW
SHOWERS BOTH DAYS. LOOKING RATHER WINDY SAT NIGHT AND SUNDAY AS AN
UPPER JET MOVES INTO THE PACIFIC NW INTO THE NRN ROCKYS AND SFC
PRESSURE FALLS OCCUR OVER THE HIGH PLAINS AHEAD OF SHORTWAVE
ENERGY OVER THE PACIFIC NW. A COOL FRONT SHOULD THEN PASS ACROSS
LATE SUNDAY WITH A DECENT SURGE OF MOISTURE INCREASING SNOW SHOWER
ACTIVITY ESPECIALLY OVER THE SW PART OF THE CWA SUNDAY NIGHT AND
MONDAY. COOL AND SOMEWHAT BREEZY CONDITIONS EXPECTED FOR TUESDAY
AND WEDS AS THE CWA REMAINS UNDER NWLY FLOW ALOFT WITH SNOW
SHOWERS CONTINUING OVER THE HIGHER MTNS AS MOISTURE RIDES UP
FACING SLOPES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1031 PM MST WED DEC 17 2014

IFR/LIFR CONDITIONS WILL CONTINUE THROUGH ABOUT 15Z FOR THE NEB
PANHANDLE TERMINALS. VSBYS IN THE PLATTE RIVER VALLEY MAY BE LESS
THAN ONE QUARTER OF A MILE...ESPECIALLY AT KBFF/KTOR. CIGS WILL BE
AT OR NEAR AIRPORT MINIMUMS AROUND 200-300 FT AGL. CONDITIONS WILL
QUICKLY IMPROVE BY LATE THU MORNING OR EARLY AFTERNOON. WEST WINDS
WILL KEEP WIDESPREAD FOG AT BAY OVER SOUTHEAST WYO. HOWEVER PATCHY
DENSE FOG CANNOT BE RULED OUT OVER WESTERN CARBON COUNTY/KRWL OVER
THE NEXT FEW HOURS.

&&

.FIRE WEATHER...
ISSUED AT 351 PM MST WED DEC 17 2014

NO FIRE WEATHER CONCERNS THROUGH FRIDAY.  COLD TEMPERATURES
WILL KEEP SNOW COVER ON THE GROUND ACROSS MUCH OF THE REGION.
AFTERNOON HUMIDITY VALUES WILL GENERALLY BE ABOVE 45 PERCENT AND
WINDS WILL BE WEAK THROUGH THURSDAY. BY THURSDAY NIGHT AND
FRIDAY...WEST WINDS WILL BECOME BREEZY FOR AREAS ALONG AND WEST
OF THE LARAMIE RANGE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...DENSE FOG ADVISORY UNTIL 8 AM MST THURSDAY FOR WYZ108.

NE...DENSE FOG ADVISORY UNTIL 8 AM MST THURSDAY FOR NEZ003-019-021-
     096.

&&

$$

UPDATE...CLH
SHORT TERM...RJM
LONG TERM...RE
AVIATION...CLH
FIRE WEATHER...RJM


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