Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 282308
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
408 PM MST FRI NOV 28 2014

.SHORT TERM...(TONIGHT THROUGH SUNDAY)
ISSUED AT 402 PM MST FRI NOV 28 2014

HIGH WIND WARNINGS CONTINUE THIS AFTERNOON FOR THE WIND PRONE AREAS
AS WELL AS THE PLAINS OF EASTERN PLATTE COUNTY. HIGHEST GUSTS SO FAR
HAVE BEEN IN THE SOUTHERN LARAMIE RANGE FOOTHILLS AND EASTERN PLATTE
COUNTY WITH GUSTS AROUND 65 MPH OBSERVED IN THE PAST COUPLE OF HOURS
AT COLEMAN ALONG I25 AND OTTO ROAD SOUTHWEST OF CYS. AM SURPRISED WE
HAVE NOT BEEN ABLE TO ACHIEVE GUSTS OVER THE I80 SUMMIT...OR ARL/BRX
YET AS MIXING SHOULD NOT BE INHIBITED. A FEW WAVE CLOUDS ARE HANGING
AROUND BUT RECENT VISIBLE SATELLITE SHOWS GENERALLY THIN CIRRUS AND
SFC OBS SHOW DECENT SFC HEATING. PERHAPS THE CAG-CPR GRADIENT IS NOT
STRONG ENOUGH YET FOR THE GAP AREAS...BUT THOSE VALUES SHOULD CLIMB
ABOVE 65 METERS AT BOTH 700 AND 850 HPA AFTER 03Z TONIGHT. GAP AREAS
SHOULD GET WINDIER OVER THE NEXT FEW HOURS...AND KEEP GUSTING AROUND
60 MPH THROUGH THE NIGHT. WARNING ISSUED EARLIER LOOKS GOOD AND WILL
MAKE NO CHANGES WITH THE AFTN PACKAGE. NOT A GOOD PATTERN WITH LLVL
INVERSIONS TO KEEP BIG WINDS GOING OVER THE LOW ELEVATIONS OUTSIDE
OF THE GAPS OVERNIGHT...SO EXPECT A LULL OVER EASTERN PLATTE COUNTY
AFTER DARK.

STILL SOME QUESTIONS AS TO HOW THIS WIND EVENT WILL EVOLVE OVER THE
NEXT 12 TO 24 HOURS. WARNING CRITERIA GUSTS WILL REMAIN A CONCERN AS
LONG AS LLVL GRADIENTS REMAIN HIGH. THE NAM SHOWS AT LEAST 60 METERS
FOR A CAG-CPR GRADIENT AT H85 AND 70 METERS AT H7 THRU 06Z SUN. IT
WOULD NOT BE SURPRISING IF LATER SHIFTS NEED TO EXTEND THE HIGH WIND
WARNING BEYOND THE CURRENT 00Z SUN EXPIRATION AS WINDS ALOFT LOOK TO
REMAIN VERY STRONG. GFS AND NAM CONTINUE TO SHOW A CORRIDOR OF H75-
H8 WINDS ABOVE 50 KTS ALONG AND EAST OF THE LARAMIE RANGE...AS WELL
AS THE FERRIS AND SEMINOE MOUNTAINS IN NORTHERN CARBON. MIGHT SEE A
FEW GUSTS CLOSE TO 75 MPH AT BORDEAUX IF THE NAM IS RIGHT. 60 TO 65
KTS AT H75 IS MORE THAN A LITTLE CONCERNING AT 18Z WHEN AFTN MIXING
SHOULD PEAK. NOT NEARLY AS MANY CLOUDS TOMORROW WITH FAIRLY DRY RH
PROGS OVER THE PLAINS. JUST DEPENDS ON WHERE THE LENTICULARS DECIDE
TO SET UP. MIGHT NEED TO CONSIDER ADDING THE NORTHERN LARAMIE RANGE
TO THE WARNING AS ALL MODELS SHOW H7 WINDS IN EXCESS OF 60 KTS...75
KTS PER THE MORE AGGRESSIVE NAM. NOT AN EASY ZONE TO HIT FOR THE 60
MPH SUSTAINED WITH GUSTS TO 75 MPH CRITERIA THOUGH. FCST SOUNDINGS
SHOW GOOD LLVL MIXING TOMORROW SO EXPECT WINDS WILL REALLY CRANK UP
OVER THE PLAINS AS WELL WITH SUCH STRONG FLOW ALOFT. OPTED TO KEEP
EASTERN PLATTE IN THE WARNING. LATER SHIFTS WILL NEED TO LOOK INTO
CONVERSE COUNTY AND CENTRAL LARAMIE COUNTY. CONCERN HERE IN CHEYENNE
IS WEAK COLD ADVECTION AT H7 LATER IN THE AFTN WHICH COULD STEEPEN
LAPSE RATES. SUBSIDENCE WILL BE IMPRESSIVE TOO IN ASSOCIATION WITH A
120 KT H25 JET. DID NOT GO WITH A WATCH FOR THIS ZONE AS THE MAV MOS
GUIDANCE DOES NOT SHOW ANYTHING MORE THAN 25 KTS SUSTAINED. MIGHT
SEE A BIT OF A BORA ALONG AND JUST EAST OF THE LARAMIE RANGE LATE SAT
NIGHT AS COLD ADVECTION KICKS IN. BULLSEYE OF STRONGEST FLOW ALOFT
IN THE MODELS IS OVER THOSE ZONES AT 06Z SUN. LOOKS A LITTLE MORE
FAVORABLE FOR OUR NEIGHBORS TO THE SOUTH IN THE BOU CWA AS THE
COLD INTRUSION ALOFT IS SLIGHTLY MORE EVIDENT.

ASIDE FROM THE WIND...ANOTHER WARM DAY IS EXPECTED FOR SAT WITH H7
TEMPS AROUND 2 DEG C OVER THE EASTERN PLAINS AND GOOD DOWNSLOPING
WINDS ALLOWING FOR COMPRESSIONAL WARMING. BELIEVE IT OR NOT...WINDS
SHOULD FINALLY START TO COME DOWN ON SUN. WE HAVE A COLD FRONT TO
THANK FOR THAT WITH FROPA OCCURRING LATE SAT NIGHT. STRONG PRESSURE
RISES IN EXCESS OF 12 MB / 6 HR SPREADING INTO OUR NORTHERN ZONES
SHOULD EFFECTIVELY KILL THE LLVL GRADIENTS AND WEAKEN THE ATTENDANT
FLOW IN THE LOW TO MIDLVLS. PROBABLY STILL STAYING A LITTLE BREEZY
WEST OF THE LARAMIE RANGE THOUGH AS MODELS TEND TO STALL THE FRONT
ALONG THE TERRAIN. SFC CONVERGENCE AND INCREASING MIDLVL MOISTURE
SHOULD SUPPORT LIGHT SNOW PRODUCTION ACROSS THE AREA FROM SOUTHWEST
TO NORTHEAST. SHOULD ALSO SEE SOME DECENT LIFT IN THE RIGHT REAR
QUAD OF THE UPPER JET. INCREASED POPS TO NEAR LIKELIES ACROSS THE
NORTH ON SUNDAY AFTERNOON PER COORDINATION WITH UNR AND RIW. DO NOT
EXPECT ANYTHING CRAZY WITH THE STRONGEST PVA BEING WELL TO THE NORTH
OF THE CWA...BUT SHOULD SEE AN INCH OR TWO OF ACCUMULATION. IT WILL
BE A GOOD 15 TO 20 DEGREES COOLER ON SUN WITH H7 TEMPS FALLING TO
AROUND -10 DEG C ACROSS THE NORTH PER THE GFS.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 402 PM MST FRI NOV 28 2014

THE PROGRESSIVE PATTERN CONTINUES DURING THIS PERIOD AS A SERIES OF
SHORTWAVE TROUGHS RIDE ACROSS THE NRN CONUS VIA SWIFT ZONAL FLOW.
THE PERIOD WILL BEGIN WITH A STATIONARY SFC FRONT THAT WILL BE
LOCATED ACROSS CARBON AND ALBANY COUNTIES EXTENDING SOUTH ALONG THE
FRONT RANGE. FORCING ALONG THE SFC FRONT ALONG WITH MOISTURE AND RRQ
SUPPORT SHOULD BE ENOUGH TO PRODUCE A PERIOD OF LIGHT SNOW ACROSS
CARBON...ALBANY AND LARAMIE COUNTIES. THE BRIEF RESIDENCE TIME OF
THE FORCING WILL LIMIT SNOWFALL TOTALS...WHICH WILL BE GENERALLY 1-3
INCHES ACROSS THIS AREA. HIGHEST AMOUNTS WILL BE OVER THE
SNOWY/SIERRA MADRE RANGES. THE FRONT RETREATS QUICKLY FROM WEST TO
EAST ON MONDAY...BUT NOT BEFORE PRODUCING WHAT LOOKS TO BE THE
COLDEST DAY OF NEXT WEEK WITH HIGHS ONLY REACHING INTO THE 30S MOST
PLACES.

ANOTHER BRIEF HIGH WIND EVENT WILL TAKE SHAPE FOR MONDAY NT/EARLY
TUESDAY AS GRADIENT BEHIND THE DEPARTING FRONT COMBINES WITH A FAST
MOVING SHORTWAVE TROUGH TRACKING ALONG THE US/CANADIAN BORDER. H7
WIND PROGS OF AROUND 60 KNOTS SUGGESTS AT LEAST THE POTENTIAL FOR
HIGH WINDS AT WIND PRONE LOCALES. OTHERWISE MILD TEMPS RETURN FOR
TUESDAY WITH 40S TO LOW 50S EXPECTED.

FLOW WILL BACK ON WEDNESDAY AHEAD OF AN APPROACHING SHORTWAVE
TROUGH. TIMING AND STRENGTH DIFFERENCES EXIST ON THIS FTR WITH THE
GFS STRONGEST AND EARLIER WITH PRECIP ONSET. MEANWHILE THE ECMWF IS
SIGNIFICANTLY SLOWER AND DRIER BY COMPARISON. FOR NOW WILL GENERALLY
SIDE WITH THE DRIER OUTCOME...BUT DID KEEP SOME SMALL PRECIP CHANCES
OVR NRN AND WRN ZONES ON WEDNESDAY. FLOW WILL TURN MORE ZONAL AGAIN
FOR THU AND FRIDAY AS A WEAK RIDGE DEVELOPS OVR THE WRN CONUS. FOR
NOW THE LATTER HALF OF NEXT WEEK LOOKS TO REMAIN DRY AND MILD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 402 PM MST FRI NOV 28 2014

VFR CONDITIONS WILL PREVAIL THRU THE PERIOD. STRONG WINDS WILL CARRY
THE GREATEST IMPACT TO AVIATION INTERESTS OVER THE UPCOMING TAF
CYCLE. WEST/SOUTHWEST WINDS WILL GUST TO 25-35 KNOTS AT SE WY
AIRFIELDS THROUGH THE ENTIRE UPCOMING PERIOD. THE LIGHTEST AMOUNTS
WILL LIKELY BE DURING THE OVERNIGHT HOURS...WHILE THE STRONGEST WILL
BE DURING THE AFTERNOONS. WINDS WILL BE LESS AT NEBRASKA PANHANDLE
SITES WITH WEST WINDS AT 10 TO 15 KNOTS WITH OCCASIONAL GUSTS OF UP
TO 25 KNOTS. WINDS OVER THE PANHANDLE WILL BECOME LESS GUSTY AS WELL
DURING THE OVERNIGHT HOURS. OTHERWISE...JUST EXPECT DECREASING HIGH-
LEVEL CLOUDS THRU THE PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 300 AM MST FRI NOV 28 2014

MINIMAL FIRE WEATHER ISSUES ANTICIPATED THIS HOLIDAY WEEKEND.
UNSEASONABLY MILD TEMPERATURES WILL CONTINUE THROUGH SATURDAY.
LOWEST RELATIVE HUMIDITIES WILL RANGE FROM 15 TO 20 PERCENT
IMMEDIATELY EAST OF THE LARAMIE RANGE. STRONG AND GUSTY WEST TO
SOUTHWEST WINDS WILL PREVAIL ACROSS MUCH OF SOUTHEAST WYOMING...
MAINLY DURING THE DAYLIGHT HOURS. A ARCTIC COLD FRONT WILL PUSH
SOUTH ACROSS THE PLAINS AND STALL NEAR THE FRONT RANGE
SUNDAY...BRINGING MUCH COLDER TEMPERATURES AND CHANCES FOR LIGHT
RAIN AND SNOW.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL 6 PM MST SATURDAY FOR WYZ104-106-107-110-
     116-117.

NE...NONE.
&&

$$

SHORT TERM...CLH
LONG TERM...CAH
AVIATION...CAH
FIRE WEATHER...MJ/CLH



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