Area Forecast Discussion
Issued by NWS Cheyenne, WY

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FXUS65 KCYS 031151
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
551 AM MDT WED JUN 3 2015

.SHORT TERM...(TODAY THROUGH THURSDAY NIGHT)
ISSUED AT 550 AM MDT WED JUN 3 2015

LOW CLOUDS AND FOG ARE STEADILY DEVELOPING ACROSS THE FORECAST
AREA AS EXPECTED...WITH MODELS KEEPING SOME CLOUD COVER ACROSS THE
EASTERN PLAINS THROUGH THE DAY. SEEMS REASONABLE IN THE COOLER AND
MOIST POST FRONTAL AIRMASS...WITH PERHAPS MORE PERSISTENT CLOUDS
ALSO A RESULT OF OVERNIGHT CONVECTION OVER IN CENTRAL NEBRASKA
THAT PUSHED A NUMBER OF BOUNDARIES WESTWARD. HOWEVER...SINCE THE
OVERALL COVERAGE OF LOW CLOUDS/FOG SEEMS TO BE SOMEWHAT LESS THAN
MODELS ARE PROJECTING...THINK THAT ENOUGH INSOLATION WILL OCCUR TO
MODIFY THIS AIRMASS FOR AT LEAST MODERATELY UNSTABLE CONDITIONS
LATER THIS AFTERNOON OVER THE PLAINS. FORECAST SOUNDINGS FROM THE
NAM SHOW THE CAP ERODING AT MOST SITES ACROSS THIS AREA BY EARLY
AFTERNOON WHILE THE GFS KEEPS CONDITIONS CAPPED. WILL TREND CLOSER
TO THE NAM BUT WILL NOT COMPLETELY DISCOUNT WHAT THE GFS HAS TO
OFFER.

THE UPPER LEVEL SHORTWAVE APPROACHING FROM THE SOUTHWEST TODAY WILL
VEER LLVL WINDS TO THE EAST-SOUTHEAST THROUGH THE DAY WITH SPEEDS
INCREASING AS WELL. THIS WILL ALLOW DEW POINTS TO RETURN BACK TO THE
MID/UPPER 50S WHICH ARE LURKING JUST EAST OF THE CWA THIS
MORNING. HIGHER MOISTURE SHOULD ALSO PUSH EAST INTO THE HIGH
VALLEYS OUT WEST WHERE LESS CLOUD COVER WILL BE OVERHEAD...LEADING
TO A MORE UNSTABLE ENVIRONMENT EARLIER THIS AFTERNOON OVER THIS
AREA. BOTH NAM AND GFS SHOW A RIBBON OF HIGHER CAPE ALONG AND JUST
WEST OF THE LARAMIE RANGE INTO THE LARAMIE VALLEY ON THE ORDER OF
1000-2500 J/KG. THIS...COMBINED WITH OROGRAPHICS AND UPPER LEVEL
FORCING SHOULD ALLOW FOR A FEW SEVERE STORMS TO DEVELOP EARLY IN
THE AFTERNOON. FURTHER EAST...STILL LOOKING AT AN AVERAGE
1500-2500 J/KG OF SBCAPES WITH THE HIGHEST VALUES VCTY THE LARAMIE
RANGE AND CHEYENNE RIDGE. BULK SHEAR VALUES WILL AVERAGE 40 TO 50
KTS ACROSS THE CWA...WHICH IS SUFFICIENT FOR STORM ORGANIZATION
INTO SUPERCELLS. STRENGTHENING EAST-SOUTHEAST SFC-700MB FLOW
THROUGH THE DAY WILL INCREASE LLVL HELICITY PARTICULARLY FROM THE
LARAMIE VALLEY EASTWARD TOWARD THE LARAMIE RANGE AND EASTERN
FOOTHILLS ENOUGH SO THAT IF A STORM WERE TO MOVE OVER THESE
AREAS...AN ISOLATED TORNADO IS CERTAINLY NOT OUT OF THE QUESTION.
PERHAPS COULD SEE THE THREAT EXPAND EASTWARD ACROSS THE PLAINS IN
THE LATE AFTERNOON/EVENING ALONG TERRAIN INDUCED POOLS OF HIGHER
HELICITY BUT THE LIKELIHOOD FOR TORNADOES IS LESS BASED ON LOWER
INSTABILITY PROGS. STORMS SHOULD EVENTUALLY MERGE INTO A LINE AS
THEY PROGRESS EASTWARD. IN GENERAL...LOOKING AT A FAIRLY WIDESPREAD
THREAT FOR LARGE HAIL AND DAMAGING WINDS FROM THUNDERSTORMS TODAY
AND ALSO LOCALLY HEAVY RAIN.

THE UPPER WAVE WILL MOVE OVERHEAD THROUGH THE EVENING AND
OVERNIGHT WITH CONVECTION LIKELY CONTINUING FROM WEST TO EAST AT
TIMES THROUGH THIS TIME. PERSISTENT SOUTHEAST UPSLOPE SHOULD
PROMOTE THE REDEVELOPMENT OF STRATUS/FOG OVERNIGHT.

THURSDAY WILL SEE LESS FORCING ALOFT AS THE STRONGEST JET WINDS
WILL REMAIN IN COLORADO...ALTHOUGH SOME MIDLEVEL ENERGY WILL MOVE
OVERHEAD IN THE LATE AFTERNOON. SFC FLOW WILL REMAIN OUT OF THE
EAST SOUTHEAST WITH CAPES PERHAPS APPROACHING 3000 J/KG RANGE
ACROSS THE PLAINS WITH BULK SHEAR VALUES IN EXCESS OF 40 KTS.
SO...LOOKING AT ANOTHER ROUND OF SEVERE STORMS ALONG AND EAST OF
THE LARAMIE RANGE IN THE AFTERNOON. MAIN THREATS WILL AGAIN BE
LARGE HAIL AND DAMAGING WINDS WITH THE TORNADO THREAT LOOKING
OVERALL LESS...BUT NON-ZERO...AND SHIFTED EAST OUT ONTO THE
WYOMING PLAINS.

.LONG TERM...(FRIDAY THROUGH TUESDAY)
ISSUED AT 550 AM MDT WED JUN 3 2015

SEE LITTLE CHANGE OVERALL IN THE WEATHER ACROSS THE CWA FRIDAY
THROUGH SUNDAY AS SEVERAL UPPER DISTURBANCES PASS ACROSS THE AREA
AHEAD OF AN UPPER LOW THAT WILL BE SLOWLY FILLING OVER THE DESERT
SW. THESE DISTURBANCES WILL INTERACT WITH DECENT AFTERNOON AND
EVENING INSTABILITY ALONG WITH A PERSISTENT SFC BOUNDARY ALONG THE
MTNS TO PRODUCE SCTD MAINLY LATE DAY SHOWERS AND TSTRMS PRETTY
MUCH THROUGH THE PERIOD. TEMPS WILL BE CLOSE TO SEASONAL AVERAGES
WITH FRIDAY LIKELY THE COOLEST DAY AS COOLER AIR BACKS UP AGAINST
THE MTNS. SOME DRIER CONDITIONS SHOULD ARRIVE EARLY NEXT WEEK AS
THE FILLING UPPER LOW OPENS AND MOVES OUT INTO THE CENTRAL PLAINS
AND A DRIER WESTERLY UPPER FLOW SETS UP OVER THE AREA.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 550 AM MDT WED JUN 3 2015

EXPECT TO SEE AN INCRG AREA OF MAINLY MVFR CIGS OVER THE PLAINS
THIS MORNING IN INCREASINGLY MOIST UPSLOPE FLOW. SOME BREAKS THIS
AFTERNOON TO VFR BUT LIKELY RETURNING TO MVFR/IFR CIGS TONIGHT.
SCTD SHOWERS AND TSTRMS DVLPG THIS AFTERNOON AROUND THE MTNS THEN
SPREADING EAST THROUGH THIS EVENING.

&&

.FIRE WEATHER...
ISSUED AT 550 AM MDT WED JUN 3 2015

NO FIRE WEATHER CONCERNS ARE ANTICIPATED THROUGH THE WEEKEND WITH
GREEN FUELS AND A DAILY CHANCE OF SHOWERS AND THUNDERSTORMS.

&&

.HYDROLOGY...
ISSUED AT 550 AM MDT WED JUN 3 2015

THE NORTH PLATTE RIVER WILL CONTINUE TO FALL THIS WEEK AS UPSTREAM
RESERVOIRS LIMIT THEIR RELEASES. HOWEVER...MITCHELL WILL REMAIN
ABOVE FLOOD STAGE THROUGH TODAY  BEFORE FALLING BELOW FLOOD STAGE
BY THURSDAY EVENING. OTHERWISE...THE NORTH PLATTE RIVER FROM
HENRY TO MINATARE WILL REMAIN IN ACTION STAGE OF THE NEXT FEW
DAYS.

RIVER LEVELS WILL INCREASE THIS WEEK ALONG THE LARAMIE RIVER AT
LARAMIE AND ALSO AT FILMORE. THE STAGE AT FORT LARAMIE WILL
REMAIN ELEVATED THROUGH THE WEEK.

&&

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

$$

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


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