Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 250955
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
355 AM MDT WED MAR 25 2015

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 258 AM MDT WED MAR 25 2015

WATER VAPOR IMAGERY LOOP DEPICTED A MEAN RIDGE-TROUGH-RIDGE PATTERN
WITH SEVERAL SHORTWAVES EMBEDDED WITHIN THE MEAN TROUGH. ONE WAS
MOVING FROM EASTERN ND INTO NORTHWEST MN...ANOTHER WAS MOVING FROM
IL INTO IN/LOWER MI...AND A THIRD WAS DROPPING SOUTHEAST ACROSS WY.
REGIONAL RADARS DETECTED LIGHT RETURNS OVER FAR SOUTHEAST WY AND
SOUTHERN NE PANHANDLE ASSOCIATED WITH LEFT FRONT QUAD OF UPPER JET.
ADDITIONAL LIGHT SHOWER ACTIVITY OVER NORTH AND CENTRAL WY WAS
ASSOCIATED WITH THE SHORTWAVE. WINDS WERE WEST TO NORTHWEST 15 TO 25
MPH AND GUSTY FOR THE WIND PRONE AREAS OF SOUTHEAST WY. TEMPERATURES
RANGED FROM THE UPPER 20S TO MID 40S.

THE 00Z/06Z NUMERICAL MODELS AND THEIR ENSEMBLES ARE IN GOOD AGREEMENT
SHOWING A PROGRESSIVE AND MORE AMPLIFIED LARGE SCALE PATTERN THROUGH
THE END OF THE WEEK. THE WEST COAST UPPER RIDGE EXPANDS EAST INTO THE
INTERMOUNTAIN WEST BY THE END OF THE SHORT TERM. MEANWHILE...THE
UPPER TROUGH DEEPENS AS IT TRANSLATES EAST FROM THE GREAT PLAINS
TO THE MS VALLEY. CONSEQUENTLY...THE FLOW ALOFT WILL BE
NORTHWESTERLY.

FOR TODAY...LIGHT RAIN/SNOW SHOWERS WILL BE FOCUSED MAINLY WEST OF
A LINE FROM LUSK WY TO SIDNEY NE...IN CLOSER PROXIMITY TO THE UPPER
TROUGH AND LARGE SCALE LIFT. THE SHOWERS WILL END FROM NORTH TO
SOUTH THIS EVENING AS LARGE SCALE SUBSIDENCE DRIES OUT THE ATMOSPHERE.
A TIGHT PRESSURE GRADIENT ACROSS THE PLAINS WILL GENERATE GUSTY
NORTHWEST SURFACE WINDS ALONG AND EAST OF I-25. IT WILL BE MUCH COOLER
THAN RECENT DAYS WITH HIGHS IN THE 30S AND 40S. SNOWFALL ACCUMULATIONS
WILL BE CONCENTRATED OVER THE HIGHER TERRAIN TODAY...WITH 2 TO 4 INCHES
FORECAST FOR THE SNOWY AND SIERRA MADRE RANGES. HIGHER VALLEYS OUT WEST
COULD MEASURE UP TO AN INCH OF WET SNOW.

WINDS WILL DECREASE THIS EVENING ACROSS THE PLAINS...BUT INCREASE IN
SOUTHEAST WY AS A LEE SIDE TROUGH DEEPENS. LOW TEMPERATURES TONIGHT
WILL BOTTOM OUT IN THE TEENS AND 20S. A FAST MOVING WEAK SHORTWAVE AND
SURFACE FRONT WILL MOVE SOUTHEAST ACROSS THE CWA THURSDAY MORNING. IT
WILL BE WINDY THURSDAY WITH NORTHWEST WINDS GUSTING 30 TO 40 MPH. THE
DOWNSLOPE FLOW WILL MODERATE TEMPERATURES INTO THE 50S LOWER
ELEVATIONS... WITH 30S AND 40S FOR THE MOUNTAINS. THE MODELS HAVE
BEEN CONSISTENT GENERATING AT LEAST ISOLATED SHOWERS NORTHEAST OF
A DOUGLAS WY TO SIDNEY NE LINE THURSDAY. THE SHOWERS WILL LINGER
THURSDAY EVENING BEFORE ENDING. IT WILL BE MILDER THURSDAY NIGHT
WITH LOW TEMPERATURES IN THE 20S AND 30S.

FRIDAY WILL NOT BE AS WINDY AS THURSDAY WITH WEST TO NORTHWEST WINDS
GUSTING TO 30 MPH. H7 TEMPERATURES NEAR 2 DEG C AND DOWNSLOPE FLOW
WILL PROMOTE A NICE WARM-UP WITH AFTERNOON HIGHS IN THE 60S LOWER
ELEVATIONS...40S AND 50S MOUNTAINS AND HIGH VALLEYS.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 258 AM MDT WED MAR 25 2015

A SEASONABLY WARM AND DRY START TO THE EXTENDED PERIOD AS LOW-LEVEL
DOWNSLOPE FLOW STRENGTHENS BENEATH PRONOUNCED RIDGING. GFS/ECMWF/NAM
ALL SHOW H7 TEMPS ON THE ORDER OF 4-5 DEG C ON SAT AFTN. WITH A DRY
COLUMN AND LARGE SCALE SUBSIDENCE PROMOTING SUNSHINE...FULLY EXPECT
THAT HIGHS WILL BE ON THE WARMER SIDE OF GUIDANCE. ANOTHER WINDY DAY
LIKELY FOR SAT AFTN WITH A 50 METER GFS H85 CAG-CPR GRADIENT. MODELS
PROG 40 TO 50 KT H8-H7 FLOW OVER THE WIND CORRIDORS WHICH SHOULD BE
EASY TO MIX DOWN WITH STEEP NEAR-SURFACE LAPSE RATES. POTENTIAL WILL
DEFINITELY BE THERE FOR RED FLAG CONDITIONS IN THIS PATTERN. A WEAK
MID LEVEL SHORTWAVE AND COLD FROPA WILL OCCUR SAT NIGHT. MODELS ARE
SHOWING LITTLE IF ANY QPF WITH MODEST MOISTURE. CANNOT RULE OUT SOME
SHOWER ACTIVITY WITH THE FROPA...BUT IT WILL BE ISOLATED. COOLER FOR
SUN AS H7 TEMPS FALL BELOW 0 DEG C EARLY. A WARMER AIR MASS IS QUICK
TO REBUILD LATE IN THE WEEKEND INTO EARLY NEXT WEEK WITH SPLIT FLOW
TAKING OVER ON THE LARGER SCALE. GENERALLY WEAK FLOW ALOFT WILL HELP
TO MITIGATE ANY CONCERNS FOR GRADIENT WINDS. HOWEVER...IT APPEARS A
FEW WEAK DISTURBANCES WILL TRAVERSE THE FLOW LATE IN THE PERIOD. WE
COULD SEE SOME WEAK CONVECTION WITH 100-300 J/KG OF MU CAPE PER THE
GFS. WITH A DEEP/WELL MIXED BOUNDARY LAYER...GUSTY WINDS COULD OCCUR
WITH ANY SHOWERS OR THUNDERSTORMS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 532 PM MDT TUE MAR 24 2015

THE MAIN CONCERN WITH THIS TAF ISSUANCE IS THE POTENTIAL FOR MVFR/IFR
CONDITIONS DEVELOPING AFTER 12Z.

LATEST AIRCRAFT DATA WAS SHOWING ANOTHER JET STREAK MOVING THROUGH
THE PACIFIC NORTHWEST. THIS FEATURE WILL CONTINUE TO NOSE INTO THE
NORTHERN ROCKIES THIS EVENING AND CAUSE A WEAK MID LEVEL TROUGH TO
DEVELOP OVER NORTHWEST WYOMING TONIGHT WITH THIS TROF SHIFTING
SOUTHEAST THROUGH THE REMAINDER OF WYOMING WEDNESDAY MORNING. THIS
WILL ALSO CAUSE A FRONTAL BOUNDARY TO SHIFT THROUGH THE FORECAST
AREA. AS A RESULT...WE COULD SEE QUITE A BIT OF COVERAGE OF SNOW
SHOWERS LATE TONIGHT INTO TOMORROW MORNING. THE GREATEST COVERAGE
APPEARS TO BE AT RWL WHERE THEY MAY SEE MVFR CONDITIONS AFTER 13Z
WITH THE VISIBILITY POSSIBLY DROPPING BELOW 1 MILE AT TIMES.
MEANWHILE...THE REST OF THE WYOMING TAF SITES MAY SEE SCATTERED
SNOW SHOWERS WITH VISIBILITIES POSSIBLY DROPPING TO NEAR 1 MILE AT
TIMES. MEANWHILE...THE NEBRASKA TAF SITES MAY ESCAPE THE BULK OF
THE SHOWERS WITH MAINLY VFR CONDITIONS.

&&

.FIRE WEATHER...
ISSUED AT 258 AM MDT WED MAR 25 2015

A COOLER AND MORE MOIST PATTERN THE NEXT FEW DAYS WILL PRECLUDE
FIRE WEATHER CONCERNS. MINIMUM HUMIDITIES WILL RANGE FROM 25 TO 35
PERCENT. WARMER...DRIER AND BREEZY CONDITIONS WILL RETURN FRIDAY
AND SATURDAY...WITH A ELEVATED FIRE WEATHER THREAT FOR THE PLAINS.

&&

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

$$

SHORT TERM...MAJ
LONG TERM...CLH
AVIATION...REC
FIRE WEATHER...MAJ


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