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000
FXUS65 KRIW 180954
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
354 AM MDT SAT MAY 18 2013

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

A VERY UNSETTLED FEW DAYS EXPECTED ACROSS CENTRAL AND WYOMING. A FEW
SHOWERS LINGER OVER WESTERN WYOMING THIS MORNING...WITH A WEAK
BOUNDARY MOVING WEST THROUGH FREMONT COUNTY. WEBCAMS HAVE BEEN
INDICATING THE PRESENCE OF FOG ACROSS THE BIG HORN BASIN AND JOHNSON
COUNTY. PATCHY FOG WILL REMAIN IN THE FORECAST THROUGH THE MID
MORNING HOURS...WITH SHOWER ACTIVITY REMAINING FOR MUCH OF WESTERN
AND CENTRAL WYOMING.

A CIRCULATION EMBEDDED IN THE TROUGH OVER NORTHEASTERN UTAH
CONTINUES TO LIFT TOWARDS SOUTHWESTERN WYOMING WITH THE PROGRESSION
OF THE TROUGH. THIS CIRCULATION IS ANTICIPATED TO MOVE THROUGH MUCH
OF THE STATE TODAY. SHOWERS ARE EXPECTED THROUGH THE DAY...WITH
THUNDERSTORMS DEVELOPING IN THE LATE MORNING AND EARLY AFTERNOON
HOURS. INSTABILITY TO MOVE NORTHEAST THROUGH THE DAY...WITH THE BIG
HORN BASIN AND JOHNSON COUNTY AGAIN EXPECTED TO SEE THE GREATEST
AMOUNT OF INSTABILITY TODAY. ANY THUNDERSTORMS MAY CONTAIN GUSTY
WIND TODAY. IN ADDITION...STORMS ACROSS NORTHEASTERN WYOMING MAY
CONTAIN SMALL HAIL. STORMS MAY CONTAIN PERIOD OF HEAVY RAIN...WHICH
MAY RESULT IN LOCALIZED FLOODING.

NATIONAL GUIDANCE INDICATES A SLIGHT CHANCE FOR STRONG WIND AND
LARGE HAIL TO OCCUR...PRIMARILY ACROSS EASTERN JOHNSON COUNTY. AS
MENTIONED BEFORE....FLOODING WILL BE POSSIBLE...WITH MODELS
INDICATING THE HIGHEST PRECIPITABLE WATER VALUES ACROSS THIS AREA.
SPECIAL ATTENTION WILL CONTINUE TO BE PAID TO THE BURN SCAR
REGIONS...ESPECIALLY THE GILEAD BURN SCAR SHOULD SIGNIFICANT RAIN
FALL NEAR THE AREA. THE BIG HORN BASIN AND JOHNSON COUNTY ARE AGAIN
NOTED TO HAVE THE GREATEST CAPE AND LOWEST LIFTED INDEX VALUES
THROUGH THE AFTERNOON AND EARLY EVENING HOURS. CONSEQUENTLY...IT IS
CERTAINLY NOT OUT OF THE QUESTION FOR A STORM OR TWO TO TURN SEVERE
ACROSS NORTHEASTERN WYOMING TODAY. NOTABLE CAPE AND LIFTED INDEX
VALUES SNEAK INTO NATRONA COUNTY DURING THE LATE AFTERNOON AND EARLY
EVENING HOURS. DAYLIGHT WILL BE FADING WITH THIS ARRIVAL...BUT SOME
STRONGER STORMS MAY OCCUR.

THUNDERSTORM ACTIVITY IS EXPECTED TO WANE WITH THE LOSS OF DAYLIGHT
THIS EVENING...WITH SHOWER ACTIVITY CONTINUING THROUGH THE OVERNIGHT
HOURS. PATCHY FOG DEVELOPMENT WILL AGAIN BE POSSIBLE ACROSS NORTHERN
WYOMING IN RESPONSE TO ANTICIPATED SHOWER ACTIVITY.

UNDER THE CONTINUED INFLUENCE OF THE TROUGH OF LOW
PRESSURE...THUNDERSTORMS WILL AGAIN BE POSSIBLE ON SUNDAY. A
NORTHWEST FLOW WILL BEGIN TO BUILD OVER THE AREA EARLY MONDAY
MORNING...THOUGH SOME INSTABILITY MAY KEEP ISOLATED THUNDERSTORM
ACTIVITY ACROSS THE SOUTHERN TWO THIRDS OF THE STATE ON MONDAY
AFTERNOON.

.LONG TERM...TUESDAY THROUGH SATURDAY

A REX BLOCK ACROSS SOUTHERN CANADA AND CENTRAL U.S. WILL GRADUALLY
WEAKEN BY LATE IN THE WEEK...WITH THE GENERAL FLOW ACROSS THE MUCH
OF THE CONUS REMAINING RATHER STAGNATE THROUGH THE EXTENDED. THERE
COULD BE SOME LINGERING LIGHT PRECIPITATION ACROSS THE EAST TUESDAY
ASSOCIATED WITH AN UPPER LOW NEAR SIOUX FALLS SOUTH DAKOTA.
HOWEVER...MODELS ARE SHOWING SOME WEAK RIDGING MOVING ACROSS THE
FORECAST AREA TUESDAY/TUESDAY NIGHT WHICH WOULD SUGGEST A DRYING
TREND AND THE BEGINNING OF A WARMING TREND.

FOR THE REST OF THE EXTENDED...ATTENTION TURNS TO A STRONG UPPER LOW
THAT MOVES INTO THE PACIFIC NORTHWEST TUESDAY/TUESDAY NIGHT. GLOBAL
MODELS KEEP THIS STRONG UPPER LOW AROUND THE PACIFIC NORTHWEST AREA
THROUGH SATURDAY. THIS WILL RESULT IN INCREASING SOUTH TO SOUTHWESTERLY
FLOW OVER THE REGION AND ABOVE AVERAGE TEMPERATURES...AND POSSIBLY
SOME STRONG CONVECTION AT TIMES.

ON WEDNESDAY...MEDIUM RANGE MODELS ARE SHOWING A DECENT DIFLUENT
FLOW OVER THE FORECAST AREA AHEAD OF A SIGNIFICANT SHORTWAVE
ROTATING AROUND THE UPPER LOW. IN ADDITION...AT THE
SURFACE...MODELS ARE PROGGING A MOIST EAST/SOUTHEAST FLOW
DEVELOPING EAST OF THE DIVIDE. MODELS ARE SHOWING THE BULK OF
INSTABILITY/STEEP LAPSE RATES ON WEDNESDAY ACROSS THE
WEST/NORTHWEST. THUS COULD SEE SOME STRONG CONVECTION ACROSS THE
WEST/NORTHWEST WEDNESDAY...AND POSSIBLY FARTHER EAST IF MORE
INSTABILITY OCCURS THAN CURRENTLY FORECAST. THIS SYSTEM COULD ALSO
SURGE A COLD FRONT EASTWARD INTO WESTERN WYOMING LATE
WEDNESDAY/WEDNESDAY NIGHT...BUT QUICKLY RETREAT DURING THE DAY
BACK WEST/NORTHWEST THURSDAY. MODELS THEN SHOW A DRY SLOT MOVING
INTO SOUTHWEST WYOMING THURSDAY...BUT A CONTINUED MOIST
EAST/SOUTHEAST SURFACE FLOW ACROSS THE EXTREME EAST...WITH A
QUICKLY VEERING WIND PROFILE JUST ABOVE THE SURFACE. GLOBAL
MODELS ARE SHOWING THE BULK OF THE INSTABILITY THURSDAY ACROSS THE
EAST...WITH THE WEST FAIRLY STABLE. THUS THE BULK OF THE CONVECTION
SHOULD BE CONCENTRATED ACROSS THE NORTH AND EAST THURSDAY...WITH
SOME STRONG CONVECTION POSSIBLE ESPECIALLY ALONG AND NORTH AND
EAST OF THE PSEUDO DRY LINE/FRONT...WHICH SHOULD BE ACROSS JOHNSON
AND NATRONA COUNTY AS WELL AS THE BIG HORN BASIN. THE BASIC SET UP
WILL REMAIN THE SAME FRIDAY AND SATURDAY...WITH MODELS SHOWING THE
DRIER SOUTHWEST FLOW PUSHING EVER SO SLIGHTLY FARTHER EAST.

&&

.AVIATION.../12Z ISSUANCE/

SHOWERS CONTINUE ACROSS THE WEST TERMINAL AREA AS ANOTHER WAVE MOVES
OVERHEAD IN SOUTHWEST FLOW...KJAC KBPI AND KPNA WILL CONTINUE TO
BE IN AND OUT OF MVFR TO IFR CONDITIONS THROUGH THE MORNING WITH
WIDESPREAD MOUNTAIN OBSCURATIONS ONGOING. MVFR TO IFR CONDITIONS
ARE ALSO POSSIBLE ACROSS THE BIGHORN BASIN AND AT KBYG THROUGH THE
EARLY MORNING HOURS AS FOG FORMS IN LOCATIONS WHERE HEAVY
RAIN FELL WITH THE STORMS ON FRIDAY AFTERNOON.

SHOWERS AND SOME STORMS WILL INCREASE IN COVERAGE ACROSS THE
ENTIRE FORECAST AREA AFTER 18Z...SO WILL KEEP VCTS AND VCSH IN
FORECAST FOR ALL TERMINALS. THE HIGHEST BASED STORMS WILL BE VCNTY
KCPR BETWEEN 20Z SAT AND 02Z SUN...THE THREAT FOR DOWNBURST WINDS
WILL BE GREATEST AT THIS TIME. SHOWERS AND THUNDERSTORMS WILL CLEAR
FROM SOUTHWEST TO NORTHEAST AFTER 03Z SUN...WITH SOME SHOWERS
CONTINUING ACROSS THE NORTHEAST AND IN THE KCPR AREA THROUGH THE END
OF THE TAF PERIOD.

&&

.FIRE WEATHER...

PATCHY MORNING FOG WILL BE POSSIBLE ACROSS THE BIG HORN BASIN AND
JOHNSON COUNTY TODAY IN RESPONSE TO PREVIOUS RAIN SHOWERS. ANOTHER
ROUND OF THUNDERSTORMS WILL OCCUR THIS AFTERNOON...WITH THE PRIME
SPOT AGAIN BEING FOUND OVER THE BIG HORN BASIN AND JOHNSON COUNTY.
STORMS IN THESE AREAS MAY PRODUCE GUSTY WIND AND SMALL HAIL...WITH A
FEW STORMS BECOMING STRONG. ISOLATED THUNDERSTORMS EXPECTED
ELSEWHERE...WITH GUSTY WIND POSSIBLE. THIS UNSETTLED PATTERN
CONTINUES THROUGH THE WEEKEND. NORTHWEST FLOW WILL BEGIN TO MOVE
OVER WESTERN WYOMING MONDAY MORNING...THOUGH THUNDERSTORMS MAY AGAIN
BE FOUND ACROSS CENTRAL AND SOUTHERN WYOMING.

&&

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

&&

$$

SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...ALLEN
FIRE WEATHER...BRANHAM