Severe Thunderstorm Warning 242, NWS Cheyenne, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
504 PM MDT WED SEP 4 2013

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 400 PM MDT WED SEP 4 2013

ANOTHER ROUND OF SCATTERED SHOWERS AND THUNDERSTORMS HAVE
DEVELOPED THIS AFTERNOON IN UNSEASONABLY WARM AND MOIST AIRMASS.
WATER VAPOR IMAGERY SHOWS THE UPPER LEVEL RIDGE CENTERED ACROSS
SOUTHEASTERN COLORADO WITH WESTERLY MIDLEVEL FLOW TRANSPORTING
GOOD MIDLEVEL MOISTURE INTO THE REGION. PW VALUES CONTINUE TO BE
QUITE HIGH FOR EARLY SEPTEMBER...WITH AREAS TO THE LARAMIE RANGE
ABOVE 1 INCH. WITH WEAK STEERING FLOW OF 10-15 KTS...SOME OF THE
STORMS COULD PRODUCE HEAVY RAIN. A FEW STRONGER CELLS HAVE
DEVELOPED OVER THE NORTHERN NEBRASKA PANHANDLE IN THE PAST HOUR.
LAPS ANALYSIS SHOWS HIGHER CAPE VALUES (AROUND 2000 J/KG) ALONG
WITH BETTER MIDLEVEL WINDSPEEDS AND DEEP LAYER SHEAR (35 KTS)
OVER THE NORTHERN PANHANDLE. PRIMARY THREAT WITH THESE STRONGER
STORMS WOULD BE SMALL HAIL. TSTMS WILL LIKELY CONTINUE THROUGH
THE LATE EVENING AS WARMTH AND INSTABILITY MORE RESEMBLE THE
CONDITIONS IN JULY THAN SEPTEMBER.

SYNOPTIC PATTERN DOES NOT CHANGE MUCH THROUGH THE REMAINDER OF THE
SHORT TERM. WITH THE MIDLEVEL RIDGE CENTERED TO THE SOUTHEAST OF
THE AREA...700-500MB MOISTURE WILL STREAM ACROSS THE CWA IN
SOUTHWEST-TO-WEST FLOW. INSTABILITY ACROSS THE PLAINS LOOKS VERY
SIMILAR TO THIS AFTERNOON. FLOW ALOFT AND DEEP LAYER SHEAR IS WEAK
...SO STORMS WILL BE SLOW MOVING. ANOTHER VERY WARM DAY IS IN
STORE WITH 700MB TEMPS AROUND 16C...RESULTING IN HIGHS AROUND 15
DEGREES ABOVE NORMAL. RIDGE BEGINS TO SHIFT EASTWARD INTO THE
CENTRAL PLAINS BY LATE FRIDAY IN RESPONSE TO AN UPPER LOW MOVING
OVER THE PACIFIC NORTHWEST. PW VALUES DROP SLIGHTLY ON FRIDAY (TO
0.75-1 INCH)...BUT ARE STILL HIGH ENOUGH COMBINED WITH GOOD SFC
HEATING TO SUPPORT ISOLATED TO SCATTERED STORMS.

.LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 400 PM MDT WED SEP 4 2013

BY SHOWING SHORTWAVES BECOMING STRONG ENOUGH TO BEGIN TO PENETRATE
THE PERSISTENT CENTRAL CONUS RIDGE...LATEST MEDIUM RANGE GUIDANCE
ARE FINALLY SHOWING THE VERY EARLY STAGES OF THE SEASONAL SHIFT.
THIS TRANSITION WILL NOT HAPPEN OVERNIGHT...BUT WILL SLOWLY OCCUR
OVER THE NEXT FEW WEEKS.

CENTRAL CONUS RIDGING WILL STILL BE VERY MUCH IN CONTROL OVER THE
UPCOMING WEEKEND. SO EXPECT MUCH OF THE SAME FOR SATURDAY AND SUNDAY
AS DIRTY MOIST SOUTHWEST FLOW PRODUCES MAINLY AFTERNOON/EVENING
CONVECTION ACROSS THE REGION. PROGD H7 TEMPERATURES AGAIN IN EXCESS
OF 16C WILL RESULT IN AFTERNOON HIGHS THAT WILL CLIMB WELL INTO THE
80S OVR SE WY AND INTO THE 90S ACROSS WRN NEBRASKA BOTH DAYS.

BY SUNDAY NIGHT...AN UPPER LOW WILL EMERGE FROM THE NRN ROCKIES ONTO
THE NRN PLAINS DRAGGING A SFC COOL FRONT ACROSS THE CWA.  WEAK COLD
AIR ADVECTION BEHIND THE FRONT SHOULD COOL THE CWA BY ABOUT 5F FOR
MONDAY. MONDAYS PRECIPITATION CHANCES WILL BE TIED TO HOW QUICKLY
SUNDAY NIGHTS COLD FROPA MOVES THRU. FOR NOW...HAVE LINGERED
PRECIPITATION CHANCES IN MONDAY...BUT THESE MAY NEED TO BE REMOVED
IN TIME.

ALTHOUGH TIMING DIFFERENCES EXIST...BOTH THE GFS/ECMWF SHOW A
TRAILING SHORTWAVE CLIPPING THE NRN ZONES ON TUESDAY. THIS SHOULD
REINFORCE THE COOLER AIR MASS LIKELY MAKING TUESDAY THE COOLEST DAY
OF THE PERIOD. ALSO WILL NOT BE ABLE TO RULE OUT CONVECTIVE CHANCES
ESPECIALLY ACROSS THE SOUTHERN TIER OF ZONES TUESDAY.

RIDGE WILL BEGIN TO RE-FORM ACROSS THE WEST COAST BY THE MIDDLE OF
NEXT WEEK. THIS WILL EFFECTIVELY SHUNT THE FLOW OF MID-LEVEL
MOISTURE SOUTH OF THE AREA. IT SHOULD ALSO BEGIN TO AMPLIFY THE LLVL
THERMAL RIDGE AS WELL...THOUGH THE GREATEST IMPACT MAY NOT BE FELT
UNTIL THURSDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY AFTERNOON)
ISSUED AT 501 PM MDT WED SEP 4 2013

VFR CONDITIONS THROUGH THE TAF PERIOD. SCATTERED SHOWERS AND
THUNDERSTORMS WILL CONTINUE OVER THE PLAINS THROUGH AROUND 04Z.
THE STRONGER STORMS COULD PRODUCE BRIEF HEAVY RAIN AND MVFR VIS.
OTHERWISE...STORM COVERAGE SHOULD DECREASE BY EARLY TONIGHT WITH
THE LOSS OF DAYTIME HEATING. MIDLEVEL CLOUDS WILL REMAIN OVER THE
REGION OVERNIGHT. WINDS THROUGH THE PERIOD WILL GENERALLY REMAIN
LIGHT AWAY FROM STORMS.

&&

.FIRE WEATHER...
ISSUED AT 400 PM MDT WED SEP 4 2013

THE VERY WARM CONDITIONS WILL CONTINUE THROUGH THE WEEKEND.
TEMPERATURES WILL BE AROUND 15 DEGREES ABOVE NORMAL WITH
WIDESPREAD 80S AND 90S ACROSS LOWER ELEVATIONS. AFTERNOON
HUMIDITIES WILL GENERALLY BE IN THE 15-25 PERCENT RANGE. MIDLEVEL
MOISTURE WILL CONTINUE TO MOVE ACROSS THE REGION THROUGH FRIDAY
WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPING
EACH AFTERNOON AND EVENING. WEAK PRESSURE GRADIENTS WILL RESULT IN
WINDS GENERALLY STAYING BELOW 15 MPH.

&&

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

SHORT TERM...FINCH
LONG TERM...HAHN
AVIATION...FINCH
FIRE WEATHER...FINCH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHEYENNE WY
439 PM MDT WED SEP 4 2013

WYZ101>119-052245-
CONVERSE COUNTY LOWER ELEVATIONS-NIOBRARA COUNTY-
NORTH LARAMIE RANGE-FERRIS/SEMINOE/SHIRLEY MOUNTAINS-
SHIRLEY BASIN-CENTRAL LARAMIE RANGE AND SOUTHWEST PLATTE COUNTY-
EAST PLATTE COUNTY-GOSHEN COUNTY-CENTRAL CARBON COUNTY-
NORTH SNOWY RANGE FOOTHILLS-SOUTHWEST CARBON COUNTY-
SIERRA MADRE RANGE-UPPER NORTH PLATTE RIVER BASIN-SNOWY RANGE-
LARAMIE VALLEY-SOUTH LARAMIE RANGE-SOUTH LARAMIE RANGE FOOTHILLS-
CENTRAL LARAMIE COUNTY-EAST LARAMIE COUNTY-
439 PM MDT WED SEP 4 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL WYOMING...
SOUTH CENTRAL WYOMING AND SOUTHEAST WYOMING.

.DAY ONE...TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS PORTIONS
OF SOUTHEAST WYOMING THROUGH THE EVENING. HEAVY RAINFALL WILL BE
THE PRIMARY HAZARD AS THESE STORMS WILL NOT BE MOVING FAST.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

ISOLATED TO SCATTERED AFTERNOON AND EVENING THUNDERSTORMS WILL
DEVELOP MOST DAYS. THE THUNDERSTORMS ARE NOT EXPECTED TO PRODUCE
SEVERE WEATHER.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE REQUIRED THROUGH TONIGHT.

&&

THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND
CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT...
HTTP://WEATHER.GOV/CHEYENNE

NEZ002-003-019>021-054-055-095-096-052245-
DAWES-BOX BUTTE-SCOTTS BLUFF-BANNER-MORRILL-KIMBALL-CHEYENNE-
NORTH SIOUX-SOUTH SIOUX-
439 PM MDT WED SEP 4 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN NEBRASKA
PANHANDLE.

.DAY ONE...TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH THE
EVENING OVER THE NEBRASKA PANHANDLE. WHILE WIDESPREAD SEVERE
STORMS ARE NOT EXPECTED...THE STRONGEST STORMS COULD PRODUCE
QUARTER SIZED HAIL AND GUSTY WINDS TO 50 MPH.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

ISOLATED AFTERNOON AND EVENING THUNDERSTORMS WILL DEVELOP MOST
DAYS. THE THUNDERSTORMS ARE NOT EXPECTED TO PRODUCE SEVERE
WEATHER.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE REQUIRED THROUGH TONIGHT.

&&

THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC...AND
CLIMATE INFORMATION IS AVAILABLE ON THE WEB AT...
HTTP://WEATHER.GOV/CHEYENNE

FINCH

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