Severe Thunderstorm Warning 18, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1111 AM MDT SAT MAY 31 2014

...UPDATE FOR AVIATION...

.SHORT TERM...SATURDAY THROUGH MONDAY NIGHT

STILL SOME SHOWERS OCCURRING EARLY THIS MORNING WITH A WEAK RIPPLE
MOVING THROUGH THE AREA. HOWEVER...TODAY STILL LOOKS TO BE AN ACTIVE
DAY ACROSS THE AREA. THE LATEST SPC SLIGHT RISK HAS SHIFTED A BIT
FURTHER TO THE WEST NOW RUNNING EAST OF A POWELL TO WORLAND TO
CASPER LINE. LATEST NAM NOW SHOWS CAPE VALUES OF GREATER THAN
1400 J/KG FROM THE BIG HORN BASIN EASTWARD THROUGH NATRONA AND
JOHNSON COUNTY AROUND NOON TODAY. HOWEVER...THE GFS IS NOT AS
BULLISH AND KEEPS THE DEEPER CAPE MAINLY ACROSS EASTERN JOHNSON
COUNTY. LIFTED INDICES ARE THE SAME WITH THE NAM SHOWING VALUES AS
LOW AS -7 WHILE THE GFS KEEPS THEM AROUND -3. MODEL SOUNDINGS ALSO
SHOW DECENT DIRECTIONAL SHEAR THAT COULD GET SOME OF THE STORMS
ROTATING. ONE CAVEAT IS THAT THE BEST INSTABILITY LOOKS TO BE
NORTH AND EAST OF THE COUNTY WARNING AREA. NEVERTHELESS...IT LOOKS
LIKE A DECENT POTENTIAL FOR STRONG TO POSSIBLY SEVERE
THUNDERSTORMS ACROSS NORTHERN AND EASTERN PORTIONS OF THE AREA.
THE CHANCE OF THUNDERSTORMS WILL DECREASE FURTHER SOUTH AND WEST
AS MODELS SHOW DRIER AIR MIXING OUT THE ATMOSPHERE WITH THE
SMALLEST CHANCE OF STORMS ACROSS FAR SOUTHWESTERN WYOMING. WITH
MID LEVEL FLOW BECOMING SOUTHWESTERLY...TEMPERATURES WILL BE
WARMER THAN YESTERDAY WITH MOST LOWER ELEVATIONS RISING INTO THE
80S. THE THREAT FOR SEVERE WEATHER SHOULD END THIS EVENING...BUT
WITH THE TROUGH AXIS AND ASSOCIATED COLD FRONT STILL TO THE WEST
AND SOME INSTABILITY STILL AROUND WE KEPT CHANCES FOR GENERAL
THUNDERSTORMS GOING INTO THE NIGHTTIME.

THINGS SHOULD BE COOLER AND A BIT QUIETER FOR SUNDAY AFTER THE
PASSAGE OF THE FRONT. THERE WILL STILL BE SOME CYCLONIC CURVATURE
OVER THE AREA ALONG WITH SOME LEFTOVER INSTABILITY SO WE HAVE
MAINTAINED A CHANCE ACROSS ROUGHLY THE NORTHERN HALF OF THE COUNTY
WARNING AREA WHERE THE BEST FORCING WILL BE. HIGH TEMPERATURES
SHOULD AVERAGE AROUND 10 DEGREES COOLER THAN ON SATURDAY WITH A
COOLER NORTHWEST FLOW OVER THE AREA.

THINGS QUIET DOWN SIGNIFICANTLY ON MONDAY AS SOME TRANSITORY RIDGING
MOVES ACROSS THE COWBOY STATE. MOST MODELS KEEP ANY FORCING NORTH OF
THE AREA SO WE REMOVED POPS FROM A LOT OF AREAS WITH THE EXCEPTION
OF THE FAR NORTH AND SOME OF THE NORTHERN MOUNTAINS.

.LONG TERM...TUESDAY THROUGH SATURDAY

NORTH AND CENTRAL WYOMING WILL SEE A CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS THROUGH THIS PERIOD WHILE THE SOUTHWEST WILL BE
DRIER...THUNDERSTORM ACTIVITY MUCH MORE ISOLATED.

MEDIUM RANGE GLOBAL MODELS IN GENERAL AGREEMENT ON DROPPING UPPER
LOW CURRENTLY ALONG THE SW COAST OF ALASKA DOWN ALONG THE CANADIAN
ROCKIES MID-WEEK WITH RIDGE AMPLIFYING ACROSS THE EASTERN PACIFIC.
THIS OVERALL PATTERN CONTINUES TO AMPLIFY LATE IN THE WEEK WITH
UPPER TROUGH DIGGING INTO THE INTERMOUNTAIN WEST.  SPREAD INCREASES
BETWEEN GFS AND ECMWF FRIDAY AND SATURDAY WITH ECMWF SHOWING MORE
AMPLIFICATION...LOWER HEIGHTS ACROSS THE NORTHERN ROCKIES BY
SATURDAY.

ON TUESDAY...A DISTURBANCE FROM THE SUB-TROPICAL EASTERN PACIFIC
GETS KICKED INLAND ACROSS THE GREAT BASIN AND CENTRAL ROCKIES.  THIS
SYSTEM WILL INTERACT WITH FRONTAL BOUNDARY ALONG THE EAST SLOPES OF
THE DIVIDE.  STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE OVER THE
EASTERN ZONES WHERE BETTER CAPE AND DIRECTIONAL SHEAR IS SHOWN.

WEDNESDAY THROUGH SATURDAY...RIPPLES ROTATING AROUND THE BASE OF
INTERMOUNTAIN/ROCKIES MEAN TROUGH WILL CONTINUE TO INTERACT WITH
QUASI-STATIONARY FRONT ALONG THE EAST SLOPES OF THE DIVIDE WITH
SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS ALONG AND EAST OF THE
FRONT.  THE BEST MOISTURE AND INSTABILITY WILL REMAIN ACROSS EAST
CENTRAL ZONES AND THE BIG HORN BASIN WHERE THE BEST POTENTIAL FOR
STRONG TO SEVERE STORMS WILL REMAIN...ALONG WITH HEAVY RAIN AND THE
THREAT OF FLASH FLOODING.  HIGHS WILL MOSTLY BE IN THE 70S ACROSS
THE VALLEYS AND BASINS THROUGH THE PERIOD.

&&

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER AND NEAR THE MOUNTAINS
AROUND 19Z AND MOVE NORTHEAST ACROSS THE LOWER ELEVATIONS. SOME
STORMS WILL PRODUCE LARGE HAIL AND WIND GUSTS TO 55 KNOTS. STORMS
WILL BE THE STRONGEST AND MOST NUMEROUS LATE IN THE AFTERNOON AND
EVENING HOURS...ESPECIALLY FROM EAST OF KLND...TO KCPR AND NORTH TO
KBYG... AND ALSO IN THE BIG HORN BASIN INCLUDING KCOD. HOWEVER...VFR
CONDITIONS WILL PREVAIL WITH LOCAL MVFR CONDITIONS IN/NEAR
THUNDERSTORMS. MORE IN THE WAY OF ISOLATED SHOWERS AND STORMS WILL
OCCUR AFTER 03Z SUNDAY LASTING THROUGH 15Z SUNDAY...AND UNTIL 18Z
NEAR KCOD.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

SHOWERS AND THUNDERSTORMS WILL DEVELOP OVER AND NEAR THE MOUNTAINS
AROUND 19Z AND MOVE NORTHEAST ACROSS THE LOWER ELEVATIONS. SOME
STORMS WILL PRODUCE SMALL HAIL AND WIND GUSTS TO 45 KNOTS. STORMS
WILL BE MORE NUMEROUS OVER NORTHWEST WY. VFR CONDITIONS WILL PREVAIL
WITH LOCAL MVFR CONDITIONS IN STORMS. MORE IN THE WAY OF ISOLATED
SHOWERS AND STORMS WILL OCCUR AFTER 03Z SUNDAY LASTING THROUGH 12Z
SUNDAY...AND UNTIL 18Z IN NORTHWEST WY.

&&

.HYDROLOGY...

FRIDAY EVENING THUNDERSTORMS DUMPED AN ESTIMATED 0.75 TO 1 INCH OF
RAIN IN THE HYATTVILLE AREA RESULTING IN MEDICINE LODGE CREEK
PUSHING BACK ABOVE FLOOD STAGE. A FLOOD WARNING HAS BEEN ISSUED
UNTIL 1130 AM. THE CREEK APPEARS TO BE CRESTING AT AROUND 3.9
FEET AT 2 AM...FLOOD STAGE IS 3.5 FEET.

TEMPERATURES WILL WARM AGAIN TODAY ALTHOUGH NOT BE AS WARM AS THE
MIDDLE OF THE WEEK. WEST OF THE DIVIDE...TEMPERATURES WILL REMAIN
MILD OR SLIGHTLY WARMER TODAY BEFORE COOLING OFF AGAIN ON SUNDAY.
EXPECT COOLER TEMPERATURES ON SUNDAY WITH NEAR TO SLIGHTLY BELOW
NORMAL TEMPERATURES FOR MUCH OF NEXT WEEK.

SHOWERS AND THUNDERSTORMS WILL BECOME MORE NUMEROUS EAST OF THE
DIVIDE TODAY WITH BEST CHANCES FOR PRECIPITATION
OCCURRING ACROSS NORTHERN AND EASTERN PORTIONS OF THE COUNTY
WARNING AREA. THERE WILL BE A CHANCE FOR STRONG THUNDERSTORM EAST
OF THE DIVIDE MAINLY EAST OF A LINE FROM POWELL TO WORLAND TO
CASPER. FEWER BUT MORE INTENSE THUNDERSTORMS WITH LOCALLY HEAVY
RAINFALL AND SOME SEVERE WEATHER EXPECTED. LESS CHANCE FOR
PRECIPITATION WILL BE POSSIBLE SOUTH AND WEST OF THIS LINE. EXPECT
MORE SHOWERS FOR SUNDAY ALTHOUGH THE THREAT FOR STRONG
THUNDERSTORMS WILL BE GREATLY DIMINISHED.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH IN EFFECT THROUGH SUNDAY AFTERNOON
WYZ004-006-008>010-011545.
FLOOD WATCH NOW IN EFFECT THROUGH SUNDAY AFTERNOON WYZ003-011545

&&

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...JB
HYDROLOGY...HATTINGS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
951 AM MDT SAT MAY 31 2014

WYZ001>020-022>030-011100-
ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST-
BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS-
EAST SWEETWATER COUNTY-FLAMING GORGE-
GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS-
NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN-
NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS-
ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES-
SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN-
SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY-
TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN-
UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN-
WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST-
YELLOWSTONE NATIONAL PARK-
951 AM MDT SAT MAY 31 2014

...FLOOD WARNING CONTINUES FOR THE WIND RIVER NEAR DUBOIS AND
RIVERTON...
...FLOOD WARNING FOR MEDICINE LODGE CREEK NEAR HYATTVILLE UNTIL
1130 AM...
...FLOOD WATCH THROUGH THIS MORNING ACROSS PORTIONS OF NORTHWEST
AND NORTH CENTRAL WYOMING...

.DAY ONE...TODAY AND TONIGHT

ISOLATED SEVERE THUNDERSTORMS WITH LARGE HAIL AND DAMAGING WIND
POSSIBLE THIS AFTERNOON AND EVENING ALONG AND EAST OF A POWELL TO
GREYBULL TO CASPER LINE.  OTHERWISE SCATTERED AFTERNOON AND EVENING
THUNDERSTORMS MOST AREAS WITH FREQUENT LIGHTNING...SMALL HAIL...AND
WIND GUSTS OVER 40 MPH POSSIBLE.

HIGH RIVER AND CREEK LEVELS FROM MOUNTAIN SNOWMELT...WITH MAINLY
MINOR FLOODING EXPECTED IN SOME LOCATIONS.  PLEASE SEE RIVER FLOOD
PRODUCTS FOR ADDITIONAL DETAILS ON ONGOING OR EXPECTED FLOODING IN
YOUR AREA.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THROUGH THE PERIOD...HIGH RUNNING RIVERS AND CREEKS WITH SOME
FLOODING IN A FEW LOCATIONS.

SUNDAY...THUNDERSTORMS POSSIBLE ACROSS NORTH AND CENTRAL WYOMING.

TUESDAY THOUGH FRIDAY...A CHANCE OF AFTERNOON AND EVENING
THUNDERSTORMS EACH DAY...MAINLY ACROSS NORTH AND CENTRAL WYOMING.

.SPOTTER INFORMATION STATEMENT...

PLEASE REPORT ANY HAIL...THUNDERSTORM WIND GUSTS OF 50 MPH OR
HIGHER...ANY RAINFALL AMOUNTS...AS WELL AS ANY OBSERVED FLOODING OR
STREAMS RUNNING NEAR BANKFULL. THANK YOU.

TEAM RIVERTON

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