Severe Thunderstorm Warning 3, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
153 PM MDT TUE MAY 18 2004

.TODAY THROUGH THURSDAY NIGHT...
NUMEROUS THUNDERSTORMS AND LIGHTNING STRIKES THIS AFTERNOON IN WEST
AND NORTHWEST WYOMING AHEAD OF AN UPPER LEVEL TROUGH CURRENTLY
LOCATED IN SE ID/SW OR.  LOW CLOUDS THIS MORNING IN CENTRAL WYOMING
HAVE KEPT TEMPERATURES DOWN SLIGHTLY AND LIMITED CONVECTIVE
DEVELOPMENT UNTIL LATER THIS AFTERNOON AND EARLY EVENING...BUT HAS
ALSO ALLOWED DEW POINTS TO REMAIN FAIRLY HIGH IN THE MID 40S AND LOW
50S. NW AND N WY ARE PRESENTLY IN SPC SLIGHT RISK AREA FOR SEVERE
THUNDERSTORMS...WITH EXPECTATIONS OF THREAT OF HAIL AND
DAMAGING WINDS. LATEST SPC MESOSCALE DISCUSSION INDICATES CONDITIONS
LOOKING BETTER FOR CONVECTION IN CENTRAL TO SE WY OVER NEXT FEW HOURS
WITH DAYTIME HEATING ERODING INHIBITION. MODERATE SW WINDS IN SW
WY...MOVING INTO CENTRAL WYOMING...WILL ALLOW FOR BETTER SHEAR NEAR
BOUNDARY OF EASTERLY FLOW...BUT ALSO BRING IN DRY INTRUSION WHICH MAY
LIMIT CONVECTIVE DEVELOPMENT IN SW WY.  OVERALL...EXPECTING GENERAL
THUNDERSTORMS OVER MUCH OF THE AREA THIS AFTERNOON AND EARLY
EVENING...WITH CHANCE OF SEVERE STORMS ALONG NORTHERN AND EASTERN
BOUNDARIES AS STORMS DEVELOP IN OUR AREA AND BECOME SEVERE AS THEY
MOVE INTO OTHER CWAS. MAIN IMPETUS FOR SEVERE STATUS OUTSIDE OF THE
AREA IS SURFACE LOW MOVING INTO SE MT AND LOWER LIFTED INDICES ALONG
FRONT RANGE OF ROCKIES FROM CO TO WY INTO MT. SHORT TERM MODELS
APPEAR TO BE IN FAIRLY GOOD AGREEMENT WITH REGARDS TO SHORTWAVE
ACTIVITY OVER THE NEXT FEW DAYS.

NEXT ROUND OF ACTION COMES OUR WAY OVERNIGHT FROM WEDNESDAY NIGHT
INTO THURSDAY MORNING AS NEXT SHORTWAVE OUT OF WEST COAST TROUGH
MOVES UP THROUGH UTAH INTO WYOMING.  MOSTLY EXPECTING SCATTERED AREAS
OF RAIN SHOWERS DURING THE COOL HOURS WITH VERY LOW CHANCE OF
THUNDERSTORMS.  THEN ANOTHER SHORTWAVE MOVES THROUGH WYOMING FROM
IDAHO ON FRIDAY...BRINGING A BETTER CHANCE OF SHOWERS AND
THUNDERSTORMS TO MUCH OF THE AREA. TEMPERATURES IN THE SHORT TERM
WILL REMAIN NEAR NORMAL...WITH COOLING IN NW WY CLOSER TO LARGE
SCALE TROUGH.

.FRIDAY THROUGH TUESDAY...UNSETTLED AND COMPLEX PATTERN CONTINUES
THROUGH EXTENDED.  REMAINING ENERGY OVER CENTRAL CALIFORNIA GETS
EJECTED ACROSS CENTRAL ROCKIES SATURDAY AS COLD TROUGH DIGS INTO NW
U.S.  BEST INSTABILITY CONTINUES TO BE PROGGED ALONG
QUASISTATIONARY FRONTAL BOUNDARY FRIDAY ACROSS NORTH AND EAST WHERE
HIGHEST POPS WARRANTED...WHILE DRIER AIRMASS MOVES ACROSS
SOUTHERN WYOMING.  TROFPA ACROSS CENTRAL ROCKIES SATURDAY WILL BRING
A BIT COOLER TEMPS OVER WEEKEND WITH CONTINUED CHANCES FOR
PRECIPITATION...AGAIN MAINLY ACROSS NORTHERN WYOMING NEAR SURFACE
TROUGH. DIFFERENCES ARISE BETWEEN ECMWF AND GFS EARLY NEXT WEEK AS
GFS MORE PROGRESSIVE SWINGING NW TROUGH THROUGH AREA MONDAY WHILE
ECMWF HOLDS IT BACK OVER NW U.S.  WILL COVER RIGHT NOW WITH CONTINUED
CHANCES FOR PRECIPITATION AND TREND TOWARD COOLER TEMPS THOUGH NOT
GOING QUITE AS COLD AS MEX GUIDANCE.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

MCDONALD/AEM

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
500 AM MDT TUE MAY 18 2004

WYZ001>020-022>030-191100-
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-
500 AM MDT TUE MAY 18 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT...

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS JOHNSON AND
NATRONA COUNTIES THIS AFTERNOON AND EVENING.  THESE
ISOLATED SEVERE STORMS COULD PRODUCE LARGE HAIL AND DAMAGING WIND
GUSTS OVER 60 MPH.  THUNDERSTORMS COULD ALSO BECOME QUITE STRONG
OVER NORTHWEST AND CENTRAL WYOMING THIS AFTERNOON...ACCOMPANIED BY
SMALL HAIL...FREQUENT LIGHTNING AND WIND GUSTS OVER 40 MPH.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY...

STRONG THUNDERSTORMS WILL BE POSSIBLE ON FRIDAY ACROSS NORTH AND
CENTRAL WYOMING.  ISOLATED SEVERE THUNDERSTORMS MAY PRODUCE LARGE
HAIL AND DAMAGING WIND...ESPECIALLY ACROSS JOHNSON AND NATRONA
COUNTIES.

.SPOTTER INFORMATION STATEMENT.

SPOTTERS MAY BE NEEDED ACROSS JOHNSON AND NATRONA COUNTIES THIS
AFTERNOON AND EVENING.  SPOTTERS ELSEWHERE ARE ALSO ENCOURAGED TO
REPORT HAIL AND STRONG WIND GUSTS WITH ANY THUNDERSTORMS AS WELL AS
RAINFALL AMOUNTS TO THE NATIONAL WEATHER SERVICE.

CF/AEM