Severe Thunderstorm Warning 29, NWS Riverton, WY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
237 PM MDT FRI JUN 25 2004

.TONIGHT THROUGH MONDAY...SCATTERED THUNDERSTORMS FIRING OFF THIS
AFTERNOON IN UNSTABLE AIRMASS ALONG AND WEST OF STATIONARY FRONT
PARKED ALONG EAST SLOPES OF DIVIDE.   A COUPLE OF UPPER LEVEL
FEATURES TO CONTINUE TO ENHANCE ACTIVITY THIS EVENING...WITH
A FEW SHOWERS LIKELY LINGERING INTO EARLY SATURDAY MORNING.  THE
FIRST SLOW-MOVING VORT LOBE MOVING INTO THE SOUTHWEST CORNER IS
MOVING INTO THE MOST UNSTABLE AIRMASS WTIH -4 LIS AND CAPES NEAR
600 J/KG...NOT MUCH CAPPING.  SECOND SHORTWAVE MOVING DOWN EAST
SIDE OF DIVIDE (NEAR MISSOULA) TO BE NEAR NORTHERN BORDER 06Z AND SE
TOWARD CPR BY 12Z. THIS FEATURE LIKELY TO KEEP SOME SHOWERS GOING
PAST MIDNIGHT...ALTHOUGH AIRMASS REMAINS ONLY MARGINALLY UNSTABLE
AHEAD OF THIS FEATURE.  THUS BEST CHANCE FOR STRONGER STORMS THIS
EVENING FROM EAST SLOPES OF WIND RIVERS AND SOUTH OF LND-CPR LINE.
A DRIER NW FLOW INTERCEDES AS THIS SHORTWAVE EXITS EASTERN WYOMING
SATURDAY MORNING WHICH SHOULD HOLD OFF ORGANIZED CONVECTION UNTIL
LATE IN THE DAY.  NEXT SHORTWAVE DIVING DOWN ALBERTA/SASKATCHEWAN
BORDER TO DRIVE FRONT THROUGH SATURDAY EVENING WITH BEST
INSTABILITY ONCE AGAIN ACROSS WEST AND SOUTHERN WYOMING.  BETTER
INSTABILITY AND THETA-E CREEPING UP LARAMIE RANGE WILL BRING MORE
INSTABILITY TO EASTERN ZONES AHEAD OF THE FRONT...SO THUNDERSTORM
COVERAGE SHOULD BE A BIT BETTER ALONG INTERSTATE 25 CORRIDOR
TOWARD SATURDAY EVENING.  STRONG FRONTAL PASSAGE SATURDAY
NIGHT WILL BRING SOME UPSLOPE CLOUDS AND SHOWERS OVERNIGHT WITH SOME
COUPLETING INDICATED OVER YELLOWSTONE NATIONAL PARK...WHERE EVEN A
FEW THUNDERSTORMS MAY FIRE OFF AFTER 06Z SUNDAY.  FRONT STALLS OUT
AGAINST DIVIDE AGAIN SUNDAY WITH BEST INSTABILITY ONCE AGAIN ACROSS
SOUTH AND WEST. SOME RIGHT ENTRANCE REGION JET DYNAMICS WILL AID LIFT
SUNDAY FOR BETTER CHANCE AT STRONGER STORMS...ESPECIALLY FROM SOUTH
PASS THROUGH SOUTH CENTRAL AREAS.  HIGHS TO BE TRICKY SUNDAY AS
STRATIFORM CLOUDS MAY LINGER WELL INTO THE DAY ACROSS NORTH AND
EAST WHERE NORTHEAST ZONES MAY NOT BREAK 60F.  HAVE BACKED OFF HIGHS
ABOUT 5 TO 10F SO FAR...AFTER COORDINATING WITH SURROUNDING
OFFICES.  NOT MUCH CHANGE TO STORMY PATTERN MONDAY WITH FRONT PARKED
AGAINST DIVIDE AND UNSTABLE AIRMASS ALONG AND WEST OF FRONT.

.TUESDAY THROUGH FRIDAY...
LARGE UPPER LEVEL LOW PRESSURE CENTER SETS UP OVER PACIFIC NORTHWEST
COASTAL AREA WITH WEAK RIDGE OVER WYOMING.  SERIES OF WEAK SHORT
WAVE TROUGHS ALOFT WILL EJECT NORTHEAST FROM GREAT BASIN IN
SOUTHWEST FLOW BETWEEN PACIFIC NORTHWEST LOW AND RIDGE OVER WYOMING.
CANADIAN SURFACE COLD FRONT REMAINS HUNG UP IN WESTERN MOUNTAINS
PROVIDING WEAK UPSLOPE FLOW EAST OF CONTINENTAL DIVIDE KEEPING
HIGHER LOW LEVEL MOISTURE IN PLACE.  COMBINATION OF WEAK SHORT WAVE
TROUGHS WITH COLD FRONT AND AVAILABLE LOW LEVEL MOISTURE WILL KEEP
SCATTERED SHOWERS AND THUNDERSTORMS OVER THE AREA.  EXPECT
CONVECTION TO BE MAINLY THERMALLY DRIVEN WITH LATE AFTERNOON AND
EARLY EVENING MAXIMUM.  NOT MUCH CHANGE IN PATTERN EXPECTED
TUESDAY AND WEDNESDAY...AND HAVE ADDED SLIGHT CHANCE OF
THUNDERSTORMS AFTERNOON AND EVENING ON WEDNESDAY WITH DECREASING
MAINLY MOUNTAIN COVERAGE ON WEDNESDAY EVENING.  ADDED ISOLATED TO
WIDELY SCATTERED RAIN SHOWERS MAINLY WEST AND MOUNTAINS LATE NIGHT
AND MORNINGS. COLD FRONT EXPECTED TO LIFT NORTHEAST ON WEDNESDAY
NIGHT AS SOUTHWEST FLOW INCREASES AND BRINGS SOME DRIER AIR INTO THE
AREA. LEFT THURSDAY AND THURSDAY NIGHT DRY. GRADUAL WARMING TREND
THROUGH THE PERIOD. NOT MUCH CHANGE IN TEMPERATURES FROM PREVIOUS
FORECAST. OVERALL EXTENDED MODELS IN GOOD AGREEMENT WITH UPPER LEVEL
MASS FIELDS THROUGH THE PERIOD.

&&

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

&&

AEM/C.BAKER

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RIVERTON WY
537 AM MDT FRI JUN 25 2004

WYZ001>020-022>030-261105-
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-
537 AM MDT FRI JUN 25 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL MOVE OVER WESTERN AND NORTHERN
WYOMING THIS MORNING...AND THEN SPREAD ACROSS THE REST OF WESTERN AND
CENTRAL WYOMING THIS AFTERNOON AND THIS EVENING. SOME OF THESE STORMS
HAVE THE POTENTIAL TO PRODUCE DIME SIZED OR LARGER HAIL...DANGEROUS
LIGHTNING...WIND GUSTS TO 50 MPH...AND LOCAL VERY HEAVY RAIN. THE
STRONGER THUNDERSTORMS OVER CENTRAL WYOMING ARE NOT EXPECTED TO
DIMINISH UNTIL AFTER MIDNIGHT.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS WILL OCCUR
SATURDAY THROUGH WEDNESDAY ACROSS WESTERN AND CENTRAL WYOMING.
ISOLATED STORMS WILL LIKELY BECOME SEVERE AND PRODUCE LOCAL VERY
HEAVY RAINFALL.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ASKED TO REPORT LARGE HAIL...STRONG WINDS AND VERY
HEAVY RAINFALL THIS AFTERNOON AND TONIGHT.

CF/C.BAKER