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000
FXUS65 KRIW 211055
AFDRIW

AREA FORECAST DISCUSSION...RESENT
NATIONAL WEATHER SERVICE RIVERTON WY
328 AM MDT TUE MAY 21 2013

.SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT

RADAR IS STILL SHOWING A COUPLE OF AREAS OF SHOWERS ACROSS EASTERN
AND SOUTHERN PORTIONS OF THE COUNTY WARNING AREA ON THE OUTER EDGE
OF THE UPPER LEVEL LOW NOW SPINNING OVER SOUTH DAKOTA. A FEW SHOWERS
WILL LINGER ACROSS EASTERN AREAS EARLY THIS MORNING BUT A VAST
MAJORITY OF THE DAY LOOKS TO BE RAIN FREE WITH WARMER TEMPERATURES
THAN RECENT DAYS. THE DRIER WEATHER IS DUE TO A SHORTWAVE RIDGE THAT
WILL BE MOVING OVER THE AREA. THE AREA WILL NOT BE COMPLETELY DRY AS
THERE IS JUST ENOUGH INSTABILITY IN THE AIR FOR A COUPLE OF
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS TO FIRE OVER THE
HIGHER ELEVATIONS OF THE MOUNTAINS WITH THE HIGH ELEVATION HEAT
SOURCE. ALMOST ALL AREAS SHOULD BE DRY FROM LATER TONIGHT INTO
WEDNESDAY MORNING.

THE WEATHER MAY GET A BIT MORE INTERESTING ON WEDNESDAY AFTERNOON
AND EVENING...ESPECIALLY EAST OF THE DIVIDE. FLOW LOOKS TO TURN MORE
SOUTHERLY BRINGING IN WARMER TEMPERATURES. AT THE SAME TIME...AN
APPROACHING SHORTWAVE WILL HELP TO DECREASE HEIGHTS AND DECREASE
INSTABILITY A BIT. EAST OF THE DIVIDE...LOW LEVEL FLOW LOOKS TO TURN
MORE SOUTHEASTERLY WHICH WILL DRIVE PRECIPITABLE WATER VALUES UP
FROM AROUND 0.35 TO AROUND 0.5 TO 0.6 INCHES ON WEDNESDAY AFTERNOON.
MODELS ALSO SHOW LIFTED INDICES TO AROUND MINUS 3 ACROSS MUCH OF
THE AREA WITH CAPE VALUES OVER 300 J/KG WITH THE HIGHEST VALUES IN
THE ABSAROKAS WITH THE UPSLOPE SOUTHEASTERLY FLOW. WITH SOME DECENT
DIRECTIONAL SHEAR AS WELL WITH SOUTHWEST WINDS AT 500
MILLIBARS...ANY THUNDERSTORMS THAT FIRE COULD BECOME STRONG WITH
GUSTY WINDS OR HAIL. THESE STORMS LOOK TO END WEDNESDAY EVENING WITH
LEFTOVER SHOWERS IN NORTHWESTERN WYOMING FOR LATER WEDNESDAY NIGHT.
COVERAGE OF SHOWERS AND THUNDERSTORMS WILL LIKELY BE LESS ON
THURSDAY AS MUCH OF THE COUNTY WARNING AREA WILL BE IN A DRY SLOT
WITH LOW PRESSURE OVER NORTHWESTERN WYOMING. ANY CONVECTION THAT DAY
WILL LIKELY BE CONFINED TO AREAS NORTH OF THE OWL CREEK RANGE AND
EAST OF THE BIG HORN RANGE. SOUTH TO SOUTHWEST FLOW WILL KEEP ABOVE
NORMAL TEMPERATURES ACROSS MOST OF THE STATE.

.LONG TERM...FRIDAY THROUGH TUESDAY

A SOUTHWEST FLOW WILL PREVAIL THROUGH THIS PERIOD THAT WILL BRING
CHANCES OF AFTERNOON AND EVENING THUNDERSTORMS TO PRIMARILY THE FAR
WEST AND NORTH WHILE A DRIER AIRMASS PREVAILS ACROSS SOUTHERN AND
CENTRAL WYOMING.

A SHORTWAVE WILL ROTATE NORTH ACROSS THE AREA EARLY FRIDAY
DOWNSTREAM OF UPPER LOW OVER THE NW U.S.  THE GFS IS FASTER AND
FURTHER WEST WITH THIS SHORTWAVE...PUTTING IT OVER SW MONTANA 12Z
FRIDAY AND LIFTING IT INTO SOUTHERN CANADA BY 00Z SATURDAY.  THE
ECMWF AND CANADIAN ARE SLOWER AND HAVE TRENDED FURTHER EAST WITH
THIS FEATURE...LIFTING IT ACROSS THE NW HALF OF WYOMING 12Z-18Z
FRIDAY.  FORECAST WEIGHTED TOWARD THIS LATTER...SLOWER SCENARIO AND
MAINTAINS CHANCES OF THUNDERSTORMS ACROSS THE NORTH AND FAR WEST.
THE ASSOCIATED COLD FRONT WILL RESULT IN TEMPERATURES 5 TO 10
DEGREES COOLER THAN ON THURSDAY...ALONG WITH BREEZY TO WINDY
CONDITIONS BEHIND THE FRONT.

UPPER RIDGE STRENGTHENS OVER THE SOUTHERN AND CENTRAL PLAINS THROUGH
THE WEEKEND WITH REMNANTS OF UPPER LOW OVER THE NW U.S. LIFTING INTO
SW CANADA.  SW FLOW WITH EMBEDDED WEAK SHORTWAVES WILL INTERACT WITH
MEAN SURFACE TROUGH ACROSS NORTHERN AND EASTERN WYOMING WITH HIGHER
DEWPOINTS TO THE NORTH AND EAST OF THIS BOUNDARY...PRIMARILY ALONG
AND NORTH OF A JACKSON-MEETEETSE-BUFFALO LINE.  ISOLATED TO
SCATTERED AFTERNOON AND EVENING THUNDERSTORMS WILL FIRE OFF NEAR
THIS SURFACE BOUNDARY AND MOVE OFF TO THE NE WITH SHORTWAVES MOVING
THROUGH DURING MAX HEATING RESULTING IN BETTER ORGANIZATION...THOUGH
WE DO NOT HAVE MUCH CONFIDENCE IN ANY ONE MODEL`S TIMING WITH THESE
IMPULSES.

A WARMING TREND WILL OCCUR OVER THE WEEKEND WITH CENTRAL
BASINS SEEING MOSTLY 80S. A SLIGHT COOLING TREND WILL FOLLOW EARLY
NEXT WEEK THOUGH WE WILL REMAIN IN ABOVE NORMAL TERRITORY FOR THE
MOST PART.

&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL OVER THE AREA TODAY AND TONIGHT.
ISOLATED SHOWERS ARE POSSIBLE UNTIL 16Z FROM THE BIGHORN MOUNTAINS
SOUTH TO CASPER MOUNTAIN. ISOLATED SHOWERS AND THUNDERSTORMS WILL
OCCUR OVER AND NEAR THE WESTERN MOUNTAINS FROM 18Z UNTIL 03Z. LOCAL
MVFR CONDITIONS ARE POSSIBLE IN STORMS ALONG WITH GUSTY WIND TO 25
KNOTS.
&&

.FIRE WEATHER...

A RIDGE BUILDING ACROSS THE AREA WILL BRING A WARMER AND DRIER DAY
TO THE AREA TODAY. THERE COULD STILL BE ISOLATED SHOWERS AND
THUNDERSTORMS BUT THESE SHOULD BE CONFINED TO THE HIGHER ELEVATIONS
OF THE MOUNTAINS.  ANOTHER STORM SYSTEM WILL BRING A CHANCE OF
THUNDERSTORMS TO THE NORTHWEST FIRE ZONES ON WEDNESDAY WITH GUSTY
SOUTH TO SOUTHEAST WINDS ACROSS THE AREA.
&&

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

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...HATTINGS