Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 280125
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
725 PM MDT MON APR 27 2015

.UPDATE...
ISSUED AT 717 PM MDT MON APR 27 2015

THE MAIN CONCERN TONIGHT IS THE POTENTIAL FOR DENSE FOG ALONG THE
LARAMIE RANGE AND THE FOOTHILLS TOWARDS CHEYENNE. LATEST WEB CAMS
WERE SHOWING THE DENSE FOG ALREADY BEGINNING TO OBSCURE THE
SUMMIT. THIS DENSE FOG SHOULD CONTINUE TO SPREAD EAST TOWARDS THE
FOOTHILLS DURING THE NEXT COUPLE OF HOURS...DUE TO THE POTENTIAL
FOR FOG TOP COOLING. WE ARE ALSO A LITTLE WORRIED THAT THIS DENSE
FOG MAY SPREAD INTO CHEYENNE AFTER MIDNIGHT ESPECIALLY IF OUR
BOUNDARY LAYER FLOW TURNS TO THE SOUTH. WE WILL KEEP AN EYE ON
THIS FOR THE NEXT COUPLE OF HOURS BEFORE WE MAKE THAT DECISION.
OTHERWISE...WE WENT AHEAD AND ISSUED A DENSE FOG ADVISORY FOR THE
I-80 SUMMIT EASTWARD TO THE I-25/I-80 INTERCHANGE THROUGH MID
MORNING TUESDAY. IN ADDITION...TO THE DENSE FOG THERE COULD BE
SOME SLICK ROADS FROM BLACK ICE NEAR THE SUMMIT THIS EVENING.



&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 300 PM MDT MON APR 27 2015

STRATUS CONTINUES TO PLAGUE SOUTHEAST WYOMING LOCATIONS ALONG AND
EAST OF THE LARAMIE RANGE TODAY...WITH SOME SUNSHINE PEAKING
THROUGH THE CLOUDS ACROSS THE PANHANDLE AND FURTHER WEST IN THE
HIGH COUNTRY AS DRIER AIR FILTERS INTO THESE LOCATIONS. A FEW
SHOWERS ARE DEVELOPING OFF THE HIGHER PEAKS THIS AFTERNOON AND
EXPECT LIGHT SHOWERS TO BECOME MORE WIDELY SCATTERED IN COVERAGE
THROUGH THE AFTERNOON AS THE DEFORMATION BAND REMAINS OVERHEAD IN
ADVANCE OF AN UPPER LEVEL TROUGH APPROACHING FROM THE NORTHWEST.
NORTHEASTERLY SFC FLOW WILL ADD IN AN UPSLOPE ELEMENT TO THE
EQUATION...SO FIGURE MUCH OF THE ACTIVITY WILL ORIGINATE OFF
NORTH-NORTHEAST FACING SLOPES OF TERRAIN FEATURES AND MOVE TO THE
NORTHEAST. WITH COLDER AIR ALOFT...EXPECT PRECIP TYPE TO BE SNOW
IN THE MOUNTAINS AND WOULD NOT BE SURPRISED TO SEE SOME SNOW MIX
DOWN INTO THE HIGH VALLEYS AND PERHAPS THE WYOMING PLAINS AT TIMES
AS WELL. THE UPPER TROUGH WILL MOVE OVER THE FORECAST AREA TONIGHT
AND SOUTHEAST OF THE AREA ON TUESDAY. SHOULD SEE SHOWERS LINGER
OVERNIGHT ESPECIALLY FROM SOUTHWEST TO NORTHEAST ACROSS THE AREA
UNDERNEATH MID AND UPPER LEVEL FORCING AND CONTINUED UPSLOPE FLOW.
CANT RULE OUT PATCHY AREAS OF FOG OVERNIGHT AS WELL...FIRST
DEVELOPING IN THE HIGH VALLEYS OUT WEST AS WINDS LIGHTEN AND TEMPS
COOL AND THEN OUT EAST WITHIN THE CONTINUED VERY MOIST BOUNDARY
LAYER.

TUESDAY AND WEDNESDAY WILL SEE INCREASING TEMPS BACK INTO THE
50S/60S AND THEN 60S/70S RESPECTIVELY AS A POSITIVELY TILTED
RIDGE MOVES OVERHEAD THROUGH THIS TIME. DRY CONDITIONS WILL
PREVAIL UNDER PARTLY CLOUDY SKIES. A SHORTWAVE TROUGH MOVING INTO
THE PAC NW TUESDAY NIGHT AND WEDNESDAY WILL DEEPEN THE LEESIDE SFC
TROUGH...WITH WINDS ALONG AND WEST OF THE LARAMIE RANGE INCREASING
IN RESPONSE. NOT EXPECTING ANY SIGNIFICANT WIND SPEEDS...BUT
GUSTS OF 30 TO 35 MPH ARE CERTAINLY A HIGH LIKELIHOOD IN THE WIND
PRONE AREAS THROUGH WEDNESDAY NIGHT.

.LONG TERM...(THURSDAY THROUGH SUNDAY)
ISSUED AT 300 PM MDT MON APR 27 2015

THE WEATHER IN THE EXTENDED PERIOD WILL BE QUITE NICE WITH ABOVE
NORMAL TEMPS AND ONLY SLIGHT CHANCES OF SHOWERS/TSTMS DURING THE
AFTERNOONS AND EVENINGS. A SHORTWAVE IS PROGGED TO MOVE ACROSS THE
CANADIAN BORDER ON THURS WITH A WEAK FRONT PUSHING OVER AREAS TO
THE EAST OF THE LARAMIE RANGE DURING THE DAY. THE GFS SHOWS SOME
WEAK SBCAPE (100-300 J/KG) DURING THE AFTN...SO COULD SEE ISOLATED
HIGH BASED STORMS. ZONAL FLOW ALOFT WILL REMAIN IN PLACE THROUGH
THE WEEKEND WITH 700MB TEMPS OF 6-8C. THIS WILL TRANSLATE INTO
HIGHS IN THE UPPER 60S AND 70S ACROSS THE PLAINS. THE ECMWF
DIFFERS FROM THE GFS IN SHOWING A MORE SCATTERED COVERAGE OF AFTN
SHOWERS ON FRI AND ESPECIALLY SAT. HAVE SLIGHT CHANCE POPS ON SAT
AFTN OVER MUCH OF THE CWA. A COLD FRONT WILL APPROACH THE REGION
BY SUN NIGHT AND MON MORNING WITH A SHORTWAVE MOVING OVER THE
NORTHERN PLAINS. THE MODELS ARE HINTING AT COOLER TEMPS BY EARLY
NEXT WEEK WITH UPSLOPE DEVELOPING ALONG WITH MORE WIDESPREAD
PRECIP.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 630 PM MDT MON APR 27 2015

MVFR CIGS WILL LINGER OVER THE SOUTHEAST WYOMING TERMINALS THRU
TONIGHT. LIGHT WINDS WILL ALLOW FOG TO DEVELOP AFTER MIDNIGHT...
ESPECIALLY ALONG AND EAST OF THE LARAMIE RANGE. IFR CEILINGS AND
VISIBILITIES ARE EXPECTED AT KCYS AND POSSIBLY KLAR/KRWL BY EARLY
TUE MORNING. CONDITIONS WILL SLOWLY IMPROVE AFTER SUNRISE TUE.


&&

.FIRE WEATHER...
ISSUED AT 243 PM MDT MON APR 27 2015

NO FIRE WEATHER CONCERNS THIS WEEK DUE TO RECENT WETTING RAINFALL.
ISOLATED RAIN SHOWERS ARE EXPECTED TO CONTINUE THROUGH TONIGHT AS
ANOTHER WEAK SYSTEM APPROACHES FROM THE NORTHWEST. DRIER
CONDITIONS AND WARMER TEMPERATURES WILL RETURN BY MIDWEEK WITH
DAYTIME RELATIVE HUMIDITIES TRENDING LOWER BUT REMAINING ABOVE 15
PERCENT THROUGH THIS TIME. SHOWERS AND TSTORMS WILL RETURN TO THE
AREA BY LATE THIS WEEK AS ANOTHER SERIES OF PACIFIC DISTURBANCES
MOVE ACROSS THE FORECAST AREA.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...DENSE FOG ADVISORY UNTIL 10 AM MDT TUESDAY FOR WYZ116-117.

NE...NONE.
&&

$$

UPDATE...REC
SHORT TERM...RJM
LONG TERM...ZF
AVIATION...CLH
FIRE WEATHER...RJM


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