Area Forecast Discussion
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KCYS 220458
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
958 PM MST FRI NOV 21 2014

.UPDATE...
ISSUED AT 906 PM MST FRI NOV 21 2014

H25-H50 WIND/HEIGHT SHOWED THE LEADING EDGE OF 90KT JET MAXIMA
MOVING ACROSS ID/WESTERN MT...AND WILL PROGRESS EASTWARD INTO WY
OVERNIGHT. COUPLED WITH H70-H85 GEOPOTENTIAL HEIGHT GRADIENTS FROM
CRAIG-CASPER EXCEEDING 60M...EXPECT HIGH WIND CRITERIA TO BE MET
IN THE ARLINGTON/BORDEAUX AREAS BETWEEN 09Z AND 12Z SAT. MOIST
ENERGETIC FLOW STILL FORECAST TO AFFECT AREAS WEST OF THE LARAMIE
RANGE BEGINNING SAT AFTERNOON. NO CHANGES PLANNED TO THE HIGH
WIND/WINTER STORM HEADLINES THIS EVENING.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 345 PM MST FRI NOV 21 2014

QUIET WEATHER IS QUICKLY COMING TO AN END AS WE TRANSITION INTO A
VERY ACTIVE PATTERN FOR THE SHORT TERM PERIOD. HIGHLIGHTS REVOLVE
AROUND POTENTIAL FOR VERY STRONG WINDS OVER SOUTHEAST WYOMING AND
POSSIBLY WESTERN NEBRASKA...AND MOUNTAIN SNOWS. LATEST WATER VAPOR
SATELLITE LOOP SHOWS A VIGOROUS UPPER-LEVEL SHORTWAVE JUST ABOUT TO
CRASH INTO THE PACIFIC NORTHWEST THIS EVE. OBJECTIVE UPPER ANALYSIS
SHOWS A STRONG 110+ KT JET CORE OFFSHORE AT 21Z. THIS WILL BE OUR
MAJOR WEATHER MAKER OVER THE NEXT COUPLE OF DAYS AS THE SYSTEM MOVES
RAPIDLY SOUTHEAST AND STRENGTHENS. NOT EXPECTING ANYTHING MAJOR IN
THE NEAR TERM THOUGH. SHOULD BE A QUIET EVENING WITH WINDS STARTING
TO RELAX AS MIXING DWINDLES WITH THE LOSS OF AFTN HEATING. A BROAD
AREA OF SURFACE HIGH PRESSURE WILL KEEP THINGS ON THE DRY SIDE.

THINGS CHANGE QUICKLY INTO TONIGHT. THE NAM H85 CAG-CPR GRADIENT IS
PROGGED TO CLIMB ABOVE 60 METERS BY ABOUT 09Z SAT. MODELED LOW
LEVEL FLOW IS IMPRESSIVE TO SAY THE LEAST WITH AN EXTENSIVE CORE
OF 60 TO 70 KT WINDS BETWEEN 700 AND 800 MILLIBARS OVER A GOOD
CHUNK OF OUR WYOMING ZONES BY SUNRISE. WITH EXCELLENT SUBSIDENCE
OVER THE TRADITIONAL GAP AREAS AND GOOD 6-HR PRESSURE FALLS ON THE
ORDER OF 5-10 MB PER THE GFS...CONFIDENCE IS HIGH IN A WIDESPREAD
AND POTENTIALLY SIGNIFICANT WIND EVENT. WENT AHEAD AND UPGRADED TO
A HIGH WIND WARNING WITH ALL ZONES STARTING AT 09Z. ARL AND BRX
SHOULD HIT FIRST...WITH THE WIND CORE ALOFT SPREADING INTO THE
SOUTHERN LARAMIE RANGE/FOOTHILLS AT OR AROUND SUNRISE. ADDED THE
NORTHERN LARAMIE RANGE TO THE WARNING AS WELL AS BOTH THE GFS AND
NAM SHOW 65 KT WINDS AT H75 TO THE SOUTH OF DEER CREEK IN WESTERN
CONVERSE COUNTY. THIS MAY BE QUITE THE EVENT WITH MULTIPLE GUSTS
OVER 70 MPH. ANOTHER EVENTUAL CONCERN IS THE POTENTIAL FOR LIGHT
SNOW WEST OF THE LARAMIE RANGE LATER IN THE AFTERNOON AND EVENING.
WITH STRONG WINDS WILL COME THE POTENTIAL FOR SIGNIFICANTLY
REDUCED VISIBILITIES IN BLOWING SNOW EVEN THOUGH LOWER ELEVATIONS
SHOULD NOT SEE MUCH FOR ACCUMULATIONS. MADE IT A POINT TO MENTION
THIS IN THE NPW PRODUCT.

SOMEWHAT CONCERNED THAT SOME OF THE ADJACENT VALLEYS AND HIGH PLAINS
MAY GET IN ON SOME OF THE WINDY FUN TOMORROW AS WELL. THERE ARE SOME
KEY DIFFERENCES IN THE GFS AND NAM WHICH WILL HAVE A ROLE IN WHETHER
OR NOT WE SEE WARNING CRITERIA WINDS AT AREAS SUCH AS CHEYENNE AND
THE LARAMIE VALLEY. FORECAST SOUNDINGS FROM BOTH MODELS SHOW A BELT
OF VERY STRONG FLOW NOT FAR OFF THE SURFACE. THE DIFFERENCES ARE IN
THE MIXING. MAIN LIMITING FACTOR WILL BE CLOUD COVER...BUT BOTH THE
LOW AND MID LEVEL RH FIELDS DO NOT SUGGEST ANYTHING THICK ENOUGH.
COULD EVENTUALLY SEE AN ABUNDANCE OF LENTICULARS EAST OF THE
MOUNTAINS AS MOUNTAIN WAVE ACTIVITY BECOMES INTENSE IN THE AFTN.
IF THIS DOES NOT IMPACT SURFACE HEATING...GFS SOUNDINGS SUGGEST
50-60 KT AT THE TOP OF THE MIXED LAYER AT LARAMIE AND CHEYENNE.
THE NAM IS CONSIDERABLY LESS...HOWEVER IT DOES SHOW SUBSIDENCE IN
ITS OMEGA FIELDS SPREADING SLOWLY ONTO THE PLAINS BETWEEN 18-00Z.
DECIDED TO ISSUE A HIGH WIND WATCH FOR LOWER ELEVATIONS
IMMEDIATELY ADJACENT TO THE LARAMIE RANGE AND FOOTHILLS. EVEN IF
AFTERNOON MIXING IS NOT THE CULPRIT...MODELS ARE IN GOOD AGREEMENT
WITH A TRANSITION TO A BORA WIND EVENT ON SAT NIGHT THROUGH EARLY
SUN AS A COLD FRONT SWEEPS ACROSS THE CWA. COULD SEE WIND GUSTS
RAMP UP AGAIN FOR A FEW HOURS AROUND MIDNIGHT...WITH A FEW GUSTS
TO 60 MPH POSSIBLE OVERNIGHT.

SUNDAY WILL BE VERY WINDY OVER THE PLAINS OF SOUTHEAST WYOMING AND
THE WESTERN PANHANDLE. THE CWA WILL BE IN THE POST FRONTAL AIR MASS
AND THE MODELS SHOW A RIBBON OF 60 TO 70 KT FROM NEAR LUSK
SOUTHEAST TOWARD SIDNEY AT 00Z MON. WILL LIKELY NEED MORE WIND
HEADLINES FOR THIS TIME FRAME...BUT WILL GET THROUGH THE SATURDAY
EVENT FIRST. NOW THAT THE WIND DISCUSSION IS OUT THE WAY...ONTO
THE SNOW POTENTIAL. DIDN`T MAKE ANY CHANGES TO THE WINTER STORM
WATCH FOR THE MOUNTAINS...BUT IT STILL LOOKS GOOD. CONVEYOR BELT OF
AN UPPER JET WITH 150+ KT H25 CORE IS PROGGED TO REMAIN ANCHORED
OVER THE WESTERN US FOR SEVERAL DAYS WITH OUR MOUNTAINS REMAINING
IN THE FAVORED LEFT EXIT REGION. THIS COMBINED WITH FAVORABLE
OROGRAPHICS IN WEST-NORTHWEST FLOW AND AND SEVERAL REINFORCING
SHOTS OF 700-300 MILLIBAR MOISTURE EMBEDDED IN THE ACTIVE FLOW
ALOFT WILL SUPPORT PERIODS OF HEAVY SNOW. SHOULD SEE ONE OR TWO
FEET THROUGH MON WITH ADDITIONAL SNOW POSSIBLE IN THE DAYS
FOLLOWING. SHOULD BE PRIMARILY A MOUNTAIN EVENT WITH AREAS EAST OF
THE LARAMIE RANGE STAYING DRY IN DOWNSLOPING LOW LEVEL FLOW. MAY
SEE A FEW RAIN OR SNOW SHOWERS OVER THE NORTHERN PANHANDLE ON SUN
AFTN AS PVA OVERSPREADS THE AREA.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 345 PM MST FRI NOV 21 2014

BASED ON GFS/ECMWF MODEL SOLUTIONS...SHOULD SEE A BREAK IN SNOW
ACCUMULATIONS OVER SOUTHEAST WYOMING MOUNTAINS SUNDAY EVENING WITH
A SHORTWAVE RIDGE IN PLACE. THEN THE NEXT SHOT OF SNOW LIKELY TO
DEVELOP AFTER MIDNIGHT SUNDAY NIGHT. COULD SEE SOME LIGHT SNOW
INTO LOWER ELEVATIONS BUT MOST SNOW ACCUMULATIONS WILL GENERALLY
BE IN THE MOUNTAINS. VERY LITTLE CHANCE FOR ANY ACCUMULATIONS
EAST OF THE LARAMIE RANGE SUNDAY NIGHT THROUGH MONDAY. WINDS WILL
SUBSIDE ACROSS MOST OF THE AREA SUNDAY NIGHT BUT ANOTHER PUSH OF
STRONGER WINDS POSSIBLE MONDAY NIGHT AS ANOTHER STRONG UPPER LEVEL
JET MOVES OVER THE AREA. MAIN CONCERN FOR HIGH WINDS WILL BE OVER
THE FAVORED WIND PRONE LOCATIONS IN SOUTHEAST WYOMING SUCH AS
ARLINGTON...BORDEAUX AND THE SOUTHERN LARAMIE RANGE.

THE NEXT QUICK MOVING CLIPPER SYSTEM ALONG WITH THE UPPER JET
WILL BRING A CHANCE FOR LIGHT SNOW SHOWERS THROUGH TUESDAY
AFTERNOON...INCLUDING INTO THE NEBRASKA PANHANDLE. AT THIS TIME
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATIONS...IF ANY. MAINLY
LOOKING FOR LIGHT SNOW SHOWERS AND FLURRIES.

UNCERTAINTY REMAINS FOR LATER PORTIONS OF THE WEEK AND HOLIDAY
WEEKEND GIVEN THE GFS AND ECMWF WERE COMPLETELY DIFFERENT IN
THEIR SOLUTIONS YESTERDAY. HOWEVER...BOTH MODELS TRENDED TOWARD
EACH OTHER TODAY AND HAVE RATHER SIMILAR SOLUTIONS. WOULD LIKE TO
SEE RUN OR TWO OF CONSISTENCY BUT BASED ON LATEST SOLUTIONS IT
WOULD WARM BOTH THURSDAY AND FRIDAY WITH A FLATTENING RIDGE OVER
THE NORTHERN ROCKIES PRODUCING DOWNSLOPE WARMING. INTO THE WEEKEND
THE MODELS SUGGEST A FAST MOVING BUT RELATIVELY WEAK WAVE MOVING
ACROSS THE AREA...SO NO BIG HAZARDOUS WEATHER THREAT EXPECTED AT
THIS TIME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1000 PM MST FRI NOV 21 2014

PRIMARY AVIATION CONCERNS WILL FOCUS ON STRONG WINDS OVERNIGHT
TONIGHT THROUGH SATURDAY NIGHT...WITH ACCUMULATING SNOW DEVELOPING
OVER THE MOUNTAINS SATURDAY AFTERNOON. FREQUENT GUSTS TO 50 KT AND
HIGHER WILL DEVELOP IN THE ARLINGTON AND BORDEAUX AREAS BETWEEN
09Z AND 12Z TONIGHT. THESE STRONG WEST TO SOUTHWEST WINDS WILL
THEN SPREAD INTO THE SOUTHERN AND NORTHERN LARAMIE RANGES SATURDAY
MORNING. GUSTY WINDS WILL ALSO SPREAD INTO LOWER ELEVATIONS AND
INTO THE PLAINS OF SOUTHEAST WYOMING SATURDAY AFTERNOON WITH GUSTS
OF 30 TO 40 KT COMMON. WINDS WILL NOT BE AS STRONG ACROSS THE
WESTERN NEBRASKA PANHANDLE BUT STILL BREEZY. THE MOUNTAINS WILL BE
OBSCURED DUE TO FALLING AND BLOWING SNOW SATURDAY AFTERNOON AND
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 559 AM MST FRI NOV 21 2014

ONE LAST MILD...BREEZY AND DRY DAY IS EXPECTED FOR THE DISTRICT
TODAY. STRONG WINDS AND PERIODS OF SNOW WILL OCCUR IN AND NEAR THE
MOUNTAINS OF SOUTHEAST WYOMING THROUGH MIDDLE OF NEXT WEEK. WINDY
CONDITIONS WILL EXPAND TO THE PLAINS ON SUNDAY AND WILL CONTINUE
THROUGH MIDWEEK AS WELL

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY
     AFTERNOON FOR WYZ112-114.

     HIGH WIND WARNING FROM 2 AM SATURDAY TO 5 AM MST SUNDAY FOR
     WYZ103>106-110-116-117.

     HIGH WIND WATCH FROM SATURDAY MORNING THROUGH LATE SATURDAY
     NIGHT FOR WYZ101-107-115-118.

NE...NONE.
&&

$$

UPDATE...MJ
SHORT TERM...CLH
LONG TERM...SML
AVIATION...MJ
FIRE WEATHER...RJM



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.