Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 300408
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
908 PM MST THU JAN 29 2015

.UPDATE...
ISSUED AT 908 PM MST THU JAN 29 2015

NO BIG CHANGES TO THE OVERNIGHT FORECAST. CIRRUS CLOUDS ARE
SPILLING IN A BIT FASTER THAN EXPECTED BUT THE INITIAL SURGE IS
VERY THIN HIGH CLOUDS. CLOUD COVER WILL THICKEN UP THROUGH THE
OVERNIGHT. TEMPERATURES UNDER THE CLOUD COVER WILL NOT DROP QUITE
AS MUCH AS FORECAST SO BUMPED LOWS UP A FEW DEGREES IN SOUTHEAST
WYOMING.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 324 PM MST THU JAN 29 2015

SUNNY TO MOSTLY SUNNY SKIES PREVAIL THIS AFTERNOON WITH A BROAD AREA
OF HIGH PRESSURE ANCHORED OVER THE CWA. VISIBLE SATELLITE IMAGERY IS
STARTING TO SHOW MORE WIDESPREAD CLOUD COVER THOUGH...WITH PLENTIFUL
CIRRUS EXPANDING NORTHWARD ACROSS CENTRAL UT AND WESTERN CO. THIS IS
IN RESPONSE TO INCREASING MOISTURE AHEAD OF A BROAD UPPER-LEVEL LOW
NEAR THE BAJA COASTLINE. THIS WILL EVENTUALLY CONTRIBUTE TO MOUNTAIN
SNOW SHOWERS BY LATE TONIGHT...BUT EXPECT ACCUMULATIONS TO BE MODEST
AT BEST. THE MODELS ARE IN GOOD AGREEMENT WITH SPLIT FLOW ALOFT OVER
THE CWA THROUGH SAT. WE WILL BE SANDWICHED IN BETWEEN THE UPPER LOW
TO THE SOUTH AND A FAIRLY ACTIVE NORTHERN STREAM...SO KEPT OUR POPS
ON THE LOW END EVEN IN THE MOUNTAINS. GFS/ECMWF ARE STARTING TO COME
INTO BETTER AGREEMENT THOUGH WITH LIGHT QPF ALONG AND SOUTH OF THE
I80 CORRIDOR ON SAT WITH WEAK MIDLVL ENERGY INTERACTING WITH DEEPER
MOISTURE ALOFT...SO CONFIDENCE IS DEFINITELY HIGHER WITH LIGHT SNOW
SPREADING INTO THE LOWER ELEVATIONS. WEAK LLVL UPSLOPE WILL DEVELOP
ALONG THE LARAMIE RANGE ON SAT AS WINDS BECOME NORTHEASTERLY BEHIND
A PRE-FRONTAL SURFACE TROUGH...ALSO AIDING IN PCPN DEVELOPMENT. THE
MAIN SURGE OF COLD AIR ARRIVES LATE SAT NIGHT / PERHAPS AFTER 06Z
PER THE LATEST NAM / WITH H7 TEMPS PLUNGING BETWEEN -10 AND -15 DEG
C OVER THE EASTERN ZONES. DEPENDING ON THE EXACT TIMING OF THE BEST
COLD ADVECTION...WE COULD SEE STEADY OR FALLING TEMPS ON SAT AND/OR
SUN. INSTABILITY SNOW SHOWERS ARE EXPECTED TO BECOME MORE WIDESPREAD
ON SUN AFTN WITHIN COOL CYCLONIC FLOW ALOFT.

.LONG TERM...(MONDAY THROUGH WEDNESDAY)
ISSUED AT 324 PM MST THU JAN 29 2015

BY EARLY NEXT WEEK THE WEATHER PATTERN WILL BECOME MORE FAVORABLE
FOR WINDY CONDITIONS AND MOUNTAIN SNOWS. A STRONG UPPER LEVEL JET
WILL EXTEND FROM THE PACIFIC NORTHWEST INTO WYOMING. THE LLVL
GRADIENT WILL INCREASE OVER SOUTHEAST WYOMING...WITH THE GFS
SHOWING THE 850MB CAG-CPR GRADIENT RISING TO 60 METERS BY 12Z MON
AND REMAINING IN THE 60-70 RANGE THROUGH 12Z WED. IT APPEARS THAT
THE STRONGEST WINDS COULD BE ON MON NIGHT INTO TUES WHEN HIGH
WINDS COULD EVEN SPREAD TO ZONES OUTSIDE THE WIND PRONE AREAS.
HOWEVER THE TIMING OF SHORTWAVES IN FAST ZONAL FLOW ALOFT AND
ASSOCIATED PRESSURE FALLS IS DIFFICULT TO PINPOINT AT THIS TIME.
SNOW WILL BE POSSIBLE AT TIMES FROM MONDAY THROUGH TUESDAY NIGHT
ACROSS THE SIERRA MADRE AND SNOWY RANGES AS MOIST NORTHWESTERLY
FLOW WILL RESULT IN FAVORABLE OROGRAPHICS. LLVL WESTERLY WINDS
WILL KEEP PRECIP CHANCES MINIMAL OVER LOWER ELEVATIONS THROUGH
TUESDAY. BOTH THE GFS AND ECMWF INDICATE A COLD FRONT PUSHING OVER
THE AREA BY LATE TUESDAY INTO WEDNESDAY. TEMPS WILL BE SLIGHTLY
ABOVE NORMAL ON MONDAY AND TUESDAY BEFORE FALLING BY MIDWEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 449 PM MST THU JAN 29 2015

VFR CONDITIONS THROUGH MUCH OF THE TAF PERIOD. MID TO HIGH LEVEL
CLOUDS WILL INCREASE OVERNIGHT ESPECIALLY ACROSS SOUTHEAST WY.
MVFR/VFR CIGS WILL BE POSSIBLE AT THE WY SITES BY FRI AFTERNOON.
WINDS THROUGH THE TAF PERIOD WILL BE WEAK.


&&

.FIRE WEATHER...
ISSUED AT 324 PM MST THU JAN 29 2015

NO FIRE WEATHER CONCERNS. SEASONABLY MILD CONDITIONS WILL COME TO AN
END BY THE WEEKEND AS A STRONG ARCTIC FRONT TRANSLATES SOUTH ACROSS
THE AREA ON SATURDAY AND SATURDAY NIGHT. COOLER TEMPERATURES SHOULD
KEEP RH VALUES WELL ABOVE CRITICAL THRESHOLDS. WINDS WILL GENERALLY
BE LIGHT.

&&

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

&&

$$

UPDATE...SML
SHORT TERM...CLH
LONG TERM...ZF
AVIATION...ZF
FIRE WEATHER...CLH



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