Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 210353
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
953 PM MDT MON APR 20 2015

.UPDATE...
ISSUED AT 953 PM MDT MON APR 20 2015

MAIN CONCERN OVERNIGHT IS CERTAINLY THE POTENTIAL FOR FOG
DEVELOPMENT FOR AREAS WEST OF THE LARAMIE RANGE...INCLUDING I-80
BETWEEN RAWLINS AND LARAMIE. 00Z NAM IS KEEPING FOG AT BAY WITH
LOW BL HUMIDITIES AND A DRIER NEAR SURFACE LAYER BASED OFF THE
KLAR FORECAST SOUNDINGS. HRRR IS ALSO CONSISTENTLY SHOWING NO
DEVELOPMENT OF FOG OVERNIGHT. BASED ON THIS ENSEMBLE OF
GUIDANCE...AND SOME MID CLOUDS DEVELOPING AND MOVING IN FROM THE
NORTHWEST WITH A FORECAST WIND DIRECTION FROM THE SOUTHWEST...AM
NOT SO CONFIDENT WIDESPREAD DENSE FOG WILL DEVELOP OVERNIGHT.
LINGERING SNOWPACK AND LIGHT WINDS WILL CERTAINLY AID IN
DEVELOPMENT OF MORE PATCHY AREAS OF FOG ESPECIALLY LATE IN THE
NIGHT IN THE LARAMIE VALLEY...WITH VISIBILITIES DROPPING TO
PERHAPS ONE HALF MILE OR SO...BUT A WIDESPREAD EVENT SEEMS
UNLIKELY AT THIS TIME. THE HIGHEST PROBABILITY OF FOG WILL BE FOR
EASTERN AND SOUTHERN PORTIONS OF THE LARAMIE VALLEY...AND PERHAPS
NORTHERN CARBON COUNTY AS WELL. WILL HOLD OF ON ISSUING A DENSE
FOG ADVISORY FOR NOW DUE TO LOW CONFIDENCE...BUT WILL CLOSELY
MONITOR THE SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 250 PM MDT MON APR 20 2015

TONIGHT...LOOKS LIKE ENOUGH INSTABILITY IN THE THETA E RIDGE ACROSS
OUR FAR SOUTHWEST COUNTIES FOR ISOLATED TO WIDELY SCATTERED EARLY
EVENING SHOWERS OVER SOUTHERN CARBON AND ALBANY COUNTIES. DRY
ELSEWHERE. BASED ON PERSISTENCE...WILL AGAIN FORECAST AREAS OF FOG
OVERNIGHT AND ESPECIALLY AFTER MIDNIGHT FOR MUCH OF CARBON COUNTY
AND ESPECIALLY OVER THE LARAMIE VALLEY AND THE SNOWPACK WHERE
TEMPERATURE AND DEWPOINT SPREADS ARE STILL ONLY 2 DEGREES AT MID
AFTERNOON.

TUESDAY...NON DESCRIPT NORTHWEST FLOW ALOFT CONTINUES. LOOKS LIKE
ENOUGH LOW AND MID LEVEL MOISTURE ALONG WITH DIFFERENTIAL HEATING
AND UPSLOPE TO GENERATE ISOLATED TO WIDELY SCATTERED AFTERNOON
SHOWERS...WITH ISOLATED THUNDERSTORMS WEST OF INTERSTATE 25.

TUESDAY NIGHT...SHOWERS AND THUNDERSTORMS SHOULD END IN THE EVENING
WITH THE LOSS OF DAYTIME HEATING AND LACK OF SIGNIFICANT
LIFTING...THOUGH STILL ENOUGH LOW AND MID LEVEL MOISTURE FOR
SCATTERED TO BROKEN CLOUD COVER...AND AREAS OF FOG ONCE AGAIN OVER
THE LARAMIE VALLEY.

WEDNESDAY...TRANSITORY RIDGING ALOFT MOVES OVERHEAD. STILL
THOUGH...ENOUGH LOW AND MID LEVEL MOISTURE AND INSTABILITY FOR
ISOLATED TO SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS WITH AN
INCREASE IN THUNDERSTORM COVERAGE DUE TO INCREASED INSTABILITY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 250 PM MDT MON APR 20 2015

SHORTWAVE RIDGE MOVES OVER THE AREA WEDNESDAY NIGHT. MOST AREAS
EAST OF THE LARAMIE RANGE WILL BE DRY...THOUGH GFS DOES SHOW SOME
LIGHT SHOWERS OUT OVER CARBON COUNTY INTO THURSDAY MORNING.

RIDGE AXIS MOVES EAST OF THE CWFA THURSDAY WITH AN UPPER SHORTWAVE
PUSHING INTO NORTHWESTERN COLORADO AND WESTERN WYOMING. BOTH THE
GFS AND ECMWF PAINTING MODERATE QPF OVER THE CWFA THURSDAY
AFTERNOON. LIFTED INDICES -2 TO -4C ACROSS THE CWFA WITH -5 TO -6C
ACROSS THE PANHANDLE. ADDED THUNDERSTORM MENTION IN THE FORECAST
FOR THURSDAY AFTERNOON/EVENING.

FRIDAY COULD BE AN INTERESTING DAY THUNDERSTORM WISE AS A SURFACE
LOW DEVELOPS OVER NORTHEASTERN COLORADO. UPPER LEVEL LOW ALMOST
VERTICALLY STACKED OVER THE SURFACE LOW ON BOTH THE GFS AND
ECMWF. GFS MOST BULLISH ON QPF...WITH AN AREA OVER HEAVY RAIN OVER
THE SOUTHERN PANHANDLE. LOW SLOW TO MOVE OUT OF THE AREA WITH
SHOWER ACTIVITY CONTINUING INTO SATURDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 420 PM MDT MON APR 20 2015

GUSTY WEST AND NORTHWEST WINDS DECREASING BY EARLY THIS EVENING
WITH RELATIVELY LIGHT WINDS OVERNIGHT. SCATTERED TO BROKEN
CLOUDS TONIGHT FROM 4000 TO 8000 FEET AGL. AREAS OF FOG...WITH
VISIBILITIES AT OR BELOW ONE MILE AT LARAMIE FROM 06Z TO 15Z WITH
CEILINGS BELOW 1000 FEET AGL.

NORTH AND NORTHWEST WINDS 20 TO 30 KNOTS DEVELOPING AGAIN TUESDAY
BY LATE MORNING AND CONTINUING IN THE AFTERNOON WITH ISOLATED
TO SCATTERED SHOWERS DEVELOPING.


&&

.FIRE WEATHER...
ISSUED AT 250 PM MDT MON APR 20 2015

RECENT RAIN AND CONTINUED SNOW PACK FROM LAST WEEKS STORM WILL
KEEP FIRE WEATHER CONCERNS MINIMAL THROUGH THE WEEK. GOING TO SEE
INCREASED CHANCES FOR WETTING RAINS AND MOUNTAIN SNOWS LATE IN THE
WEEK AS ANOTHER PACIFIC LOW PRESSURE SYSTEM TRACKS ACROSS NORTHERN
COLORADO.

&&

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

$$

UPDATE...RJM
SHORT TERM...RUBIN
LONG TERM...GCC
AVIATION...RUBIN
FIRE WEATHER...GCC


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