Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 291147
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
547 AM MDT FRI MAY 29 2015

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 332 AM MDT FRI MAY 29 2015

CURRENT IR SATELLITE LOOP SHOWS A MIDLEVEL CIRCULATION OVER
CENTRAL WYOMING EARLY THIS MORNING AS THE UPPER LEVEL TROUGH
AXIS SLOWLY MOVES ACROSS THIS STATE. THUNDERSTORMS HAVE
DIMINISHED LAST NIGHT WITH ONLY ISOLATED TO SCATTERED SHOWERS
SLOWLY MOVING EASTWARD ACROSS THE AREA. THIS WILL CONTINUE THROUGH
SUNRISE...WITH THE COVERAGE INCREASING FROM NORTH TO SOUTH AS THE
MAIN TROUGH AXIS MOVES SOUTHWARD TOWARDS COLORADO.

EXPECT ACTIVITY TO PICK UP LATE THIS MORNING AS SOME SUNSHINE IS
EXPECTED. THE TROUGH WILL CONTINUE TO DIG SOUTHWARD...WITH SOME
COOLER AIR ALOFT MOVING INTO THE REGION. THIS WILL CREATE
MORE INSTABILITY ACROSS SOUTHEAST WYOMING AND WESTERN NEBRASKA
INITIALLY...WITH SCATTERED THUNDERSTORMS POSSIBLE. ONCE THE TROUGH
AXIS MOVES ACROSS THE AREA...EXPECT THUNDERSTORMS TO BECOME MORE
ISOLATED WITH LIGHTER RAINFALL AMOUNTS INTO THIS EVENING. IT WILL
BE CONSIDERABLY  COOLER TODAY...WITH HIGHS IN THE 50S TO AROUND
60. SURFACE WINDS WILL SHIFT INTO THE NORTHEAST LATER ON
TODAY...SO THE DAYTIME HIGHS MAY OCCUR AROUND NOON WITH
TEMPERATURES LOWERING SLIGHTLY THROUGH THE AFTERNOON. WILL
CONTINUE TO MONITOR RIVER LEVELS AFTER TODAYS RUNOFF...BUT DO NOT
EXPECT ANY MAJOR IMPACTS AT THIS TIME. SEE THE HYDROLOGY
DISCUSSION BELOW FOR MORE DETAILS.

MODEL SOUNDINGS THEN SHOW THE MIDLEVELS BECOMING DRIER INTO
SATURDAY MORNING AS SOME SUBSIDENCE DEVELOPS BEHIND THE UPPER
LEVEL TROUGH. HOWEVER...CAN NOT RULE OUT A FEW ISOLATED TSTORMS
NEAR AND JUST EAST OF THE LARAMIE RANGE SATURDAY AFTERNOON DUE TO
DECENT LLVL CONVERGENCE...AVAILABLE MOISTURE...AND DAYTIME
INSTABILITY. INCREASED POP BETWEEN 15 TO 20 PERCENT FROM CHEYENNE
TO LARAMIE AND NEAR DOUGLAS WYOMING FOR A FEW TSTORMS.
REGARDLESS...IT WILL BE A PLEASANT START TO THE WEEKEND WITH
PARTLY TO MOSTLY SUNNY SKIES. HIGH TEMPERATURES WILL REBOUND INTO
THE 60S TO LOW 70S...WARMEST OVER THE NORTH PLATTE RIVER VALLEY.
SUNDAY WILL BE 10 DEGREES WARMER WITH HIGHS IN THE MID 70S TO MID
80S ACROSS SOUTHEAST WYOMING...AND LOW TO ID 80S ACROSS WESTERN
NEBRASKA. LOOKS TO BE A PLEASANT DAY ON SUNDAY...BUT CAN NOT RULE
OUT A 20 TO 30 PERCENT CHANCE OF THUNDERSTORMS IN THE AFTERNOON.
MOST MODELS DO SHOW A WEAKNESS IN THE UPPER LEVEL RIDGE AXIS AS IT
MOVES INTO THE ROCKY MOUNTAINS...AND COMBINED WITH LLVL
CONVERGENCE NEAR THE LARAMIE RANGE AND INSTABILITY...SOME
CONVECTION IS POSSIBLE IN THE AFTERNOON.


.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 332 AM MDT FRI MAY 29 2015

THE UPPER RIDGE WILL MOVE OVER THE FORECAST AREA SUNDAY NIGHT AND
MONDAY WITH H7 TEMPS WARMING TO BETWEEN 10 AND 14C BY MONDAY
AFTERNOON. SOME ENERGY MOVING UP ON THE WESTERN EDGE OF THE RIDGE
WILL LIKELY INITIATE CONVECTIVE ACTIVITY ESPECIALLY OVER THE
MOUNTAINS AND NEARBY PLAINS...BUT MARGINAL LLVL MOISTURE AND WARM
TEMPS ALOFT SHOULD KEEP COVERAGE ISOLATED AND ON THE WEAKER SIDE.
TUESDAY LOOKS TO BE SOMEWHAT SIMILAR...ALTHOUGH THE ECMWF DEVELOPS
A SFC LOW FURTHER WEST OVER WY/CO THAN THE GFS WHICH ALLOWS MORE
CONVERGENCE OVER THE FORECAST AREA AND THUS A BETTER CHANCE FOR
SHOWERS AND THUNDERSTORMS OVERALL. WILL KEEP MAINLY A SLIGHT
CHANCE FOR AREAS ALONG AND EAST OF THE LARAMIE RANGE TO ACCOUNT
FOR THESE MODEL DIFFERENCES. MORE ENERGETIC FLOW WILL MOVE
OVERHEAD FOR WEDNESDAY...ALONG WITH COOLER TEMPS ALOFT SO SHOULD
SEE A BETTER CHANCE AND COVERAGE OF AFTERNOON/EVENING SHOWERS AND
THUNDERSTORMS. MODELS DIFFER FOR THURSDAY WITH HANDLING AN UPPER
TROUGH OVER THE WESTERN CONUS. THE ECMWF DEVELOPS A SIGNIFICANTLY
DEEPER TROUGH WITH STRONG VORT MAX OVER THE FAR SOUTHWEST DESERT
LOCATIONS. THE GFS IS SOMEWHAT MORE DIFFUSE WITH MAIN ENERGY
PACKET OVER THE GREAT BASIN. FOR NOW WILL MAINTAIN CHANCE POPS
OVER THE REGION. TEMPS WILL START OFF ABOVE NORMAL THE BEGINNING
PART OF THE WEEK BUT LOOK TO DIP BACK TO NEAR NORMAL OR SLIGHTLY
BELOW NORMAL BY THE WEEKS END. &&

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 547 AM MDT FRI MAY 29 2015

SHOWERS WILL EXPAND IN COVERAGE THROUGH THE MORNING AS A COLD
FRONT DROPS SOUTH ACROSS THE FORECAST AREA. SOME SUNSHINE PEAKING
THROUGH THE CLOUDS WILL DESTABILIZE CONDITIONS ENOUGH FOR WIDELY
SCATTERED THUNDERSTORMS TO DEVELOP EARLY THIS AFTERNOON. EXPECTING
MAINLY MVFR CONDITIONS WITH THIS ACTIVITY...BUT CANT RULE OUT
POCKETS OF IFR AS WELL WITHIN NORTHEASTERLY UPSLOPE FLOW ALONG THE
PINE RIDGE IN NORTHERN NEBRASKA. SHOWERS AND T-STORMS WILL
CONTINUE THROUGH EARLY THIS EVENING BEFORE SHIFTING SOUTH OF THE
AREA TONIGHT. GUSTY NORTHERLY WINDS WILL ACCOMPANY THE COLD FRONT
TODAY...WITH WINDS EASING AND SHIFTING TO THE SOUTHEAST THIS
EVENING. THIS SHOULD MAINTAIN IFR/MVFR CONDITIONS ACROSS THE
WYO/NEB PLAINS TERMINALS OVERNIGHT.

&&

.FIRE WEATHER...
ISSUED AT 332 AM MDT FRI MAY 29 2015

NO FIRE WEATHER CONCERNS THIS WEEKEND AND INTO NEXT WEEK. A
SLIGHTLY DRIER AND MORE STABLE AIRMASS WILL MOVE OVER THE
AREA THIS WEEKEND...AS DAYTIME MINIMUM RH LOWERS BETWEEN 25 TO 40
PERCENT. HOWEVER...SHOWERS AND TSTORMS WILL QUICKLY RETURN TO THE
AREA BY NEXT WEEK WITH INCREASING HUMIDITIES.

&&

.HYDROLOGY...
ISSUED AT 332 AM MDT FRI MAY 29 2015

MODERATE FLOODING CONTINUES AT FORT LARAMIE THIS MORNING. RIVER
LEVELS HAVE LEVELED OFF AND WILL BE STEADY INTO THE
WEEKEND...WITH THE RIVER LOWERING SLIGHTLY INTO MINOR FLOOD STAGE
CATEGORY BY LATE THIS WEEKEND DUE TO REDUCED WATER RELEASES FROM
NEARBY RESERVOIRS. FURTHER UPSTREAM NEAR THE CITY OF
LARAMIE...BANKFULL CONDITIONS WILL CONTINUE INTO EARLY NEXT WEEK
WITH LITTLE TO NO CHANGE IN THE RIVER LEVEL ACROSS THE LARAMIE
VALLEY.

FOR THE NORTH PLATTE RIVER...THE CREST IS BETWEEN HENRY AND
MITCHELL THIS MORNING. THIS CREST WILL CONTINUE DOWNSTREAM THIS
WEEKEND...LIKELY NEAR BRIDGEPORT BY LATE SATURDAY. THE RIVER AT
MINATARE IS EXPECTED TO REMAIN JUST BELOW FLOOD STAGE AT THIS
TIME...WITH THE RIVER LEVEL SLOWLY FALLING FURTHER UPSTREAM THIS
WEEKEND. THANKFULLY...RAINFALL AMOUNTS YESTERDAY WERE RATHER
LIGHT. EXPECT AN ADDITIONAL 0.25 TO 0.50 INCHES OF RAIN TODAY
ACROSS THE HIGH PLAINS WITH MOST LOCATIONS CLOSER TO 0.25. IMPACTS
FROM ADDITIONAL RUNOFF APPEAR TO BE MINOR INTO THIS WEEKEND FOR
THE NORTH PLATTE RIVER.

ATTENTION THEN SHIFTS TO THE SNOW MELT IN THE MOUNTAINS WHICH WILL
LIKELY COMMENCE LATE THIS WEEKEND AND EARLY NEXT WEEK AS
TEMPERATURES RISE INTO THE 60S TO LOW 70S OVER THE HIGHER
ELEVATIONS.

&&

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

$$

SHORT TERM...TJT
LONG TERM...RJM
AVIATION...RJM
FIRE WEATHER...TJT
HYDROLOGY...TJT


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