Area Forecast Discussion
Issued by NWS Cheyenne, WY

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000
FXUS65 KCYS 211748
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1148 AM MDT SUN SEP 21 2014

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 400 AM MDT SUN SEP 21 2014

TODAY...INFRARED SATELLITE LOOPS EARLY THIS MORNING SHOWING A
PROMISING TREND FOR SHOWERS AND THUNDERSTORMS TO FALL ACROSS OUR
COUNTIES IN THE NEXT FEW DAYS...WITH THUNDERSTORMS ERUPTING AROUND
3 AM MDT IN SOUTHERN NEVADA NORTH OF LAS VEGAS...AS WELL OVER
SOUTHWEST COLORADO EAST OF DURANGO.

FROM THE PARENT UPPER TROUGH OVER NORTHERN NEVADA...INITIAL
SHORTWAVE TROUGH ALOFT EJECTS NORTHWARD ACROSS SOUTHWEST WYOMING
THIS AFTERNOON WITH THE INITIAL SLUG OF LOW AND MID LEVEL MOISTURE
ROTATING ACROSS OUR SOUTHWEST COUNTIES OF CARBON...ALBANY AND
WESTERN LARAMIE. RATHER IMPRESSIVE 850/700 MB THETA-E RIDGE AXIS
WILL DEVELOP THIS AFTERNOON OVER CARBON COUNTY WITH DECENT POSITIVE
THETA-E ADVECTION...AND COMBINED WITH DIFFERENTIAL HEATING OVER THE
HIGHER TERRAIN AND UPWARD VERTICAL MOTION FROM THE SHORTWAVE TROUGH
ALOFT...WILL SEE ISOLATED TO SCATTERED SHOWERS THIS AFTERNOON FROM
CARBON COUNTY TO ALBANY COUNTY TO WESTERN LARAMIE COUNTY...WITH
NUMEROUS SHOWERS OVER THE SNOWY AND SIERRA MADRE RANGES...AS WELL AS
ISOLATED THUNDERSTORMS MOSTLY OVER SOUTHERN CARBON COUNTY.

TONIGHT...NICELY DIFFLUENT FLOW ALOFT MOVES ACROSS OUR COUNTIES...
WITH DECENT 850 MB AND 700 MB POSITIVE THETA-E ADVECTION...SPREADING
ELEVATED INSTABILITY ALONG AND EAST OF INTERSTATE 25. WITH A
PLETHORA OF LOW AND MID LEVEL MOISTURE...AND DECENT UPWARD MOTION
ALONG WITH THETA-E ADVECTION...EXPECT SCATTERED TO NUMEROUS
SHOWERS WEST OF A DOUGLAS TO CHEYENNE LINE...MOST NUMEROUS
OROGRAPHICALLY OVER THE SNOWY AND SIERRA MADRE RANGES. ENOUGH
INSTABILITY FOR ISOLATED THUNDERSTORMS.

MONDAY...AS PROMISED...THIS DAY WILL BE CLOUDY WITH SCATTERED TO
NUMEROUS SHOWERS...AND ISOLATED THUNDERSTORMS...WITH BEAUCOUP LOW
AND MID LEVEL MOISTURE...DECENT SYNOPTIC AND MESOSCALE LIFT FROM
THE PASSING SHORTWAVE TROUGH ALOFT...AND SHOWERS FOCUSED ALONG THE
SURFACE TROUGH ALONG THE SPINE OF THE LARAMIE RANGE AND INTERSTATE
25 CORRIDOR. WE MAY SEE A FEW STRONG TO SEVERE THUNDERSTORMS FROM
LUSK TO CHEYENNE IF CAPE AND SHEAR ARE ADEQUATE...AND HAVE BOOSTED
POPS OROGRAPHICALLY TO NEAR 100 PERCENT OVER THE SNOWY AND SIERRA
MADRE RANGES...AND 50 TO 70 PERCENT IN THE AFTERNOON FROM LARAMIE
TO CHEYENNE WHERE LOCAL TERRAIN FAVORS GREATER AREAL COVERAGE OF
SHOWERS AND THUNDERSTORMS.

MONDAY NIGHT...SHORTWAVE TROUGH ALOFT MOVES INTO WESTERN SOUTH
DAKOTA AND WESTERN NEBRASKA WITH THE CORRESPONDING SURFACE TROUGH IN
THE SAME POSITION...THUS EXPECT A DRYING TREND FROM WEST TO EAST
WITH ONLY ISOLATED SHOWERS AND THUNDERSTORMS AFTER MIDNIGHT ACROSS
WESTERN NEBRASKA.

TUESDAY...SHORTWAVE TROUGH ALOFT MOVES ACROSS CENTRAL SOUTH DAKOTA
AND CENTRAL NEBRASKA WITH LOW AND MID LEVEL NORTHWEST FLOW ALOFT
ACROSS OUR COUNTIES. STILL THOUGH...WILL BE ENOUGH LOW AND MID LEVEL
MOISTURE FOR ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS IN THE
AFTERNOON ALONG AND EAST OF INTERSTATE 25...MOST NUMEROUS EAST OF A
LUSK TO WHEATLAND LINE WHERE MOISTURE WILL BE MOST PLENTIFUL AND LOW
LEVEL DOWNSLOPING IS OF A LESSER EFFECT.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 400 AM MDT SUN SEP 21 2014

THE CWA WILL BE DOMINATED BY A HIGH AMPLITUDE LARGE SCALE RIDGE FOR
THE LATTER PART OF THE WEEK...WHICH WILL MAINTAIN A WARM AND DRY
PATTERN. DEEP UPPER TROUGH OVER THE EASTERN PACIFIC WILL SLOWLY MOVE
INTO THE GREAT BASIN BY THE WEEKEND. MODELS HANDLE THIS TROUGH
DIFFERENTLY WITH THE GFS MORE PROGRESSIVE THAN THE DEEPER SLOWER
ECMWF. SUBTROPICAL MOISTURE WILL RETURN TO THE REGION WITH ISOLATED
AFTERNOON AND EVENING SHOWERS AND TSTORMS ALONG AND WEST OF THE
LARAMIE RANGE SATURDAY. A PACIFIC FRONT IS PROGGED TO MOVE ACROSS
THE COWBOY STATE SATURDAY BRINGING COOLER TEMPERATURES. LIGHT
SOUTHERLY WINDS WILL INCREASE LATE IN THE WEEK WITH A TIGHTENING
PRESSURE GRADIENT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY MORNING)
ISSUED AT 1143 AM MDT SUN SEP 21 2014

VFR CONDITIONS THROUGH THE TAF PERIOD. MID LEVEL CLOUD COVER WILL
BE ON THE INCREASE THIS AFTERNOON AND OVERNIGHT AS MOISTURE
STREAMS INTO THE REGION FROM THE SOUTHWEST. THE BEST CHANCE OF
SCATTERED SHOWERS AFTER AROUND 00Z WILL BE TO THE WEST OF THE
LARAMIE RANGE...ESPECIALLY AT RWL. SOUTHEAST WINDS WILL PREVAIL
WITH SPEEDS GENERALLY LESS THAN 15 KTS EXCEPT AT LAR WHERE A FEW
GUSTS TO 25 KTS WILL BE POSSIBLE THIS AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 400 AM MDT SUN SEP 21 2014

MINIMAL CONCERNS DUE TO PROJECTED WINDS AND HUMIDITIES THE NEXT
SEVERAL DAYS. DRYING AND WARMING TREND AS THE WEEK PROGRESSES.

&&

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

$$

SHORT TERM...RUBIN
LONG TERM...JAMSKI
AVIATION...FINCH
FIRE WEATHER...RUBIN





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