Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 010812
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
212 AM MDT SAT AUG 1 2015

.SHORT TERM...(TODAY THROUGH MONDAY NIGHT)

ISSUED AT 152 AM MDT SAT AUG 1 2015

TODAY...FLOW ALOFT REMAINS NORTHWEST. IN THE AFTERNOON...NAM PROGS A
LOW LEVEL CONVERGENCE AXIS TO SETUP FROM NEAR CHEYENNE TO NEAR
CHADRON WITH A LOW AND MID LEVEL THETA-E RIDGE AXIS ALSO SETTING UP
SOUTH OF THE CHEYENNE TO CHADRON LINE. LOOKS LIKE ENOUGH LOW LEVEL
CONVERGENCE DESPITE THE WARM TEMPERATURES ALOFT TO SPARK ISOLATED
AFTERNOON THUNDERSTORMS ALONG THE CONVERGENCE AXIS AND WILL CONTINUE
TO PAINT 10 TO 25 PERCENT POPS...DRY ELSEWHERE.

TONIGHT...ISOLATED THUNDERSTORMS SHOULD QUICKLY END IN THE EVENING
WITH LOSS OF DAYTIME HEATING...WITH DECREASING CLOUD COVER.

SUNDAY/SUNDAY NIGHT...AGAIN...WARM TEMPERATURES AT MID LEVELS WILL
LIMIT CONVECTIVE POTENTIAL AND CONVECTIVE DEVELOPMENT.
HOWEVER...WITH A LOW LEVEL INSTABILITY AXIS FROM NEAR GRAND JUNCTION
COLORADO TO DOUGLAS WYOMING...BELIEVE THAT ISOLATED THUNDERSTORMS
WILL BE SPARKED IN THE AFTERNOON OVER MUCH OF ALBANY COUNTY NEAR
LARAMIE AND OVER SOUTHERN LARAMIE COUNTY NEAR CHEYENNE. STORMS
EXPECTED TO END SUNDAY EVENING WITH LOSS OF DAYTIME HEATING.

MONDAY/MONDAY NIGHT...MODELS FORECAST THE LOW AND MID LEVEL
MONSOONAL MOISTURE TO SLIDE ACROSS OUR COUNTIES AND COMBINED WITH A
NEGATIVELY TILTED SHORTWAVE TROUGH ALOFT...WE EXPECT SCATTERED TO
NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS TO ERUPT IN THE
AFTERNOON AND EVENING...MAINLY ALONG AND WEST OF INTERSTATE 25 NEAR
THE LOW AND MID LEVEL THETA-E RIDGE AXIS.

.LONG TERM...(TUESDAY THROUGH FRIDAY)
ISSUED AT 300 AM MDT SAT AUG 1 2015

STILL A LOT OF FLIP FLOPPING WITH MEDIUM RANGE GUIDANCE ON WHAT IS
GOING TO HAPPEN IN THE LONG TERM. NOW THE GFS IS THE MORE BULLISH ON
POPS AND QPF FOR TUESDAY. ECMWF WAS THE MORE BULLISH 24 HOURS AGO.
LEADS TO LESS CONFIDENCE WITH THESE RUN TO RUN INCONSISTENCIES.

BOTH BRING A SHORTWAVE THROUGH THE CWFA MONDAY NIGHT INTO TUESDAY.
GFS BRINGS THE SHORTWAVE FURTHER NORTH WHILE THE ECMWF HAS THE
SHORTWAVE TRACKING ALONG THE COLORADO/WYOMING BORDER. DECIDED TO
MAINTAIN LOW CHANCE TO SLIGHT CHANCE POPS IN THE FORECAST FOR
TUESDAY WITH THE HOPES THAT RUN TO RUN CONSISTENCY INCREASES IN
ORDER TO RAISE POPS AS THE EVENT DRAWS CLOSER. SHOULD THE GFS
SOLUTION CURRENTLY BEING PROPOSED HOLDS TRUE...PANHANDLE AND
EXTREME SOUTHEAST WYOMING ZONES WOULD BE IN FOR HEAVY RAINFALL.
GFS FORECAST OVER 2 INCHES OF RAIN IN THE PANHANDLE FOR TUESDAY AS
THE FRONT STALLS ALONG THE LARAMIE RANGE.

BOTH MODELS SHOWING A FAIRLY DRY DAY WEDNESDAY AS SHORTWAVE MOVES
EAST AND IS REPLACED WITH UPPER LEVEL RIDGING. SURFACE BOUNDARY
GETS FORCED OUT INTO THE PANHANDLE WEDNESDAY AFTERNOON. MOST OF
SOUTHEAST WYOMING WOULD BE DRY AS WESTERLY WINDS CREATE DRY
DOWNSLOPING CONDITIONS OFF THE LARAMIE RANGE. COULD BE QUITE
BREEZY OUT WEST WEDNESDAY AS GFS 700MB WINDS INCREASE TO 30-35KTS.
IN FACT...THE GFS SHOWS THESE STRONG WESTERLY WINDS CONTINUING FOR
THE REST OF THE WEEK. WE WOULD BE DEALING WITH ELEVATED TO
CRITICAL FIRE WEATHER ISSUES UNDER THIS SCENARIO FOR MUCH OF NEXT
WEEK AS AFTERNOON HUMIDITIES LIKELY TO BECOME CRITICAL.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1107 PM MDT FRI JUL 31 2015

WENT AHEAD AND DROPPED TS WORDING FROM THE KCDR TAF OVERNIGHT AS
MOSAIC RADAR SHOWING THE CONVECTION DEVELOPING FURTHER NORTHEAST
IN SOUTH DAKOTA. WILL CONTINUE TO MONITOR THOUGH AS THE OVERNIGHT
HOURS PROGRESS. VFR CONDITIONS OTHERWISE.

&&

.FIRE WEATHER...
ISSUED AT 152 AM MDT SAT AUG 1 2015

LOW AFTERNOON RELATIVE HUMIDITIES WEST OF INTERSTATE
25 TODAY AND SUNDAY...THOUGH FORTUNATELY...WINDS AND WIND GUSTS WILL
REMAIN BELOW CRITERIA FOR A MAJORITY OF LOCATIONS. RAIN CHANCES
INCREASE MONDAY AND TUESDAY AS MONSOONAL MOISTURE CREEPS BACK INTO
OUR COUNTIES.

&&

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

$$

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


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