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000
FXUS65 KRIW 252103
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
303 PM MDT SAT MAY 25 2013

.SHORT TERM...TONIGHT THROUGH SUNDAY

WEAK SHOWERS MOVING QUICKLY TO THE NORTHEAST ACROSS THE NORTHWEST
QUARTER OF THE FORECAST AREA THIS AFTERNOON. GREATEST INSTABILITY
LIES JUST TO OUR EAST AND NORTH...AND CORRESPONDINGLY HAVE NOT SEEN
ANY THUNDER IN OUR FORECAST AREA THROUGH 21Z. WE STILL WILL NOT RULE
OUT THE POSSIBILITY IN AND NEAR THE ABSAROKAS...BUT OVERALL TREND IS
FOR ANY STORMS TO BE MARGINAL AT BEST. DRY SOUTHWEST FLOW IS
CONTINUING TO LIMIT CLOUD DEVELOPMENT ACROSS THE CENTRAL AND SOUTH
WHERE SURFACE RH IS BETWEEN 8 AND 15 PERCENT. SOUTH TO SOUTHWEST
WIND OF 15 TO 30 MPH WILL DECREASE IN THIS REGION BETWEEN
01Z-02Z/SUNDAY. OVERALL...CONDITIONS LOOK TO REMAIN VERY SIMILAR ON
SUNDAY WITH AFTERNOON WINDS AND ABOVE NORMAL TEMPERATURES AGAIN IN
THE MIX. THE ONE BIG DIFFERENCE WILL BE ACROSS THE NORTHERN BIG HORN
BASIN AND JOHNSON COUNTY WHERE INSTABILITY LOOKS TO BE GREATER FOR
SUNDAY AFTERNOON. LOW-LEVEL WIND FIELDS FROM THE NORTH OR NORTHEAST
WILL INCREASE BOUNDARY LAYER RH IN THIS REGION. THIS WILL BE COUPLED
WITH CONTINUING SOUTHWEST FLOW ALOFT...SO WIND SHEAR WILL BE
SUFFICIENT TO SUPPORT STRONG CONVECTION. THE NOSE OF A 250MB 80KT
JET STREAK WILL ALSO AID IN DYNAMIC SUPPORT OF STORMS IN THIS REGION.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

THE THETA E RIDGE WILL ARCH ACROSS FAR NORTHERN WYOMING SUNDAY NIGHT
WITH STRONG THUNDERSTORMS LINGERING IN THOSE AREAS THROUGH THE LATE
EVENING HOURS FOLLOWED BY SHOWERS AFTER MIDNIGHT. THEN ON MONDAY WE
SHOULD SEE A REPEAT OF THUNDERSTORMS IN FAR NORTHERN WYOMING BUT NOT
AS STRONG SINCE THE CAPE WILL BE LOWER AS WILL THE DEW POINTS.
JOHNSON COUNTY WILL HAVE THE BEST CAPES. THESE STORMS SHOULD BE
EVEN MORE NUMEROUS THAN THE ONES SUNDAY EVENING GIVEN THE FACT THAT
THE LOW PRESENTLY DUMBELLING AROUND THE WEST SIDE OF THE PARENT LOW
OVER THE PACIFIC NORTHWEST WILL BE TRACKING EAST-NORTHEAST ACROSS
MONTANA AND SWINGING A TRAILING SHORTWAVE TROUGH ACROSS WY BY THEN
INCREASING THE LIFT POTENTIAL. GARDEN VARIETY HIGHER BASED
THUNDERSTORMS WITH STRONG GUSTY WINDS AND SMALL HAIL WILL LIKELY
OCCUR OVER CENTRAL WYOMING WITH A POSSIBILITY OF SEVERE OVER THE
NORTH. THESE STORMS WILL LIKELY PERSIST WELL INTO THE NIGHT MONDAY
NIGHT AS WE GET UNDERNEATH THE RIGHT ENTRANCE REGION OF THE
EXITING JET.

THEN THE NEXT UPSTREAM NEGATIVELY TILTED TROUGH WILL FOLLOW RIGHT
BEHIND THE OTHER EXITING TROUGH AS IT PINCHES OFF A DISAPPEARING
RIDGE BETWEEN THE TWO TROUGHS. THE STEERING FLOW WILL QUICKLY BACK
TO A SOUTHERLY DIFLUENT FLOW AHEAD OF THIS APPROACHING TROUGH
RESULTING IN NUMEROUS SHOWERS AND THUNDERSTORMS TO FORM OVER
NORTHWEST WYOMING THAT WILL QUICKLY SPREAD SOUTHEAST ACROSS THE
ENTIRE CWA. AS THIS TROUGH NOSES INTO WYOMING FROM THE NORTHWEST IT
WILL EVENTUALLY CUT OFF RIGHT OVER WYOMING BY 12Z THURSDAY. THE
LATEST MODEL RUNS SHOW A MORE BULLISH WELL DEFINED LOW OVER WYOMING
THAN PREVIOUS RUNS. H7 TEMPS WILL FALL TO BETWEEN -3C AND -4C UNDER
THIS ASSOCIATED COLD POCKET OF AIR OVER WESTERN WYOMING BY 12Z
THURSDAY. AS SHOWERS AND LATE THUNDERSTORMS AND GENERALLY UNSETTLED
WEATHER CONTINUES OVER WYOMING WEDNESDAY AND THURSDAY...THE SNOW
LEVEL SHOULD DIP DOWN TO 8000 FEET BY WEDNESDAY MORNING AND THEN TO
BETWEEN 6500 AND 7000 FEET BY THURSDAY MORNING. SHOULD SEE
ACCUMULATING SNOWS IN ALL OF THE WESTERN MOUNTAINS AND ESPECIALLY
OVER THE ABSAROKA MTNS UNDERNEATH OF THE TRACK OF THE H7 LOW.
THEN AS THE LOW EXITS TO THE EAST OVER THE PLAINS...CENTRAL AND
NORTHERN WYOMING WILL CONTINUE TO SEE PRECIP THROUGH FRIDAY AND
SATURDAY WITH THE WRAP AROUND MOISTURE AS THE PRECIP ENDS
GRADUALLY FROM SOUTH TO NORTH. THE EURO SEEMS TO BE AT LEAST 6
HOURS SLOWER THEN THE GFS BUT INDICATE THE SAME GENERAL PLACEMENT
OF THE LOW. SHOULD NOT SEE AN APPRECIABLE REBOUND IN TEMPS UNTIL
NEXT SATURDAY WHEN H7 TEMPS CLIMB BACK UP TO AROUND 9C. WILL LOWER
HIGH TEMPS FOR THE MIDDLE OF THE WEEK TO TAKE INTO ACCOUNT THE
COOLING AFFECT FROM CLOUDS AND PRECIP.


&&

.AVIATION.../00Z ISSUANCE/

AFTERNOON CONVECTION ONGOING OVER NORTHWEST WYOMING...MAINLY OVER
THE ABSAROKA RANGE AND NEARBY PORTIONS OF YELLOWSTONE NATIONAL
PARK. ENOUGH SURFACE MOISTURE TO GENERATE WEAK CONVECTION ACROSS
NORTHERN JOHNSON COUNTY AS WELL. GUSTY SOUTHWEST WIND OF 15-30KTS
PREVALENT ACROSS THE SOUTHERN AND CENTRAL THIRDS OF THE STATE
ALONG WITH DEW POINTS IN THE TEENS AND 20S. TERMINALS WILL SEE
VFR CONDITIONS THROUGH THE ENTIRE FORECAST PERIOD. THERE
IS...HOWEVER...A BETTER CHANCE OF VCTS AT KCOD AND POSSIBLY KJAC
SUNDAY AFTERNOON. SUNDAY LOOKS TO BE ALMOST AN EXACT CARBON COPY
OF TODAY WITH CONVECTION FIRING IN GENERALLY THE SAME LOCATIONS.
BEST INSTABILITY FOR DEEP CONVECTION REMAINS ACROSS THE FAR
NORTHERN TIER OF THE STATE FROM JUST NORTH OF KJAC TO KBYG. THIS
REGION WILL BE THE MAIN FOCUS FOR CONTINUED SHOWER AND
THUNDERSTORM DEVELOPMENT INTO SUNDAY EVENING. GUSTY OUTFLOW WIND TO
AROUND 40KTS AND SMALL HAIL WILL BE THE MAIN HAZARDS IN
ASSOCIATION WITH THE STRONGER STORMS. LOSS OF DIURNAL HEATING AND
SOUTHWEST-NORTHEAST MOVEMENT OF THE CONVECTION WILL LEAD TO
DIMINISHED ECHOES BETWEEN 03Z-06Z/MON.

&&

.FIRE WEATHER...

SLIGHTLY ABOVE NORMAL TEMPERATURES ARE ANTICIPATED THROUGH MEMORIAL
DAY AS A LARGE UPPER LEVEL LOW REMAINS ACROSS THE PACIFIC NORTHWEST.
THIS WILL KEEP THE CENTRAL AND SOUTHERN THIRDS OF THE STATE IN DRY
SOUTHWEST FLOW. GUSTY AFTERNOON WINDS OF 15 TO 30 MPH ARE EXPECTED
ACROSS ZONES 277...278...279...280...283...288...AND 289. THE LOWEST
RH VALUES OF 8-15 PERCENT WILL OCCUR IN THESE SAME AREAS. MANY OTHER
LOWER ELEVATION LOCATIONS CAN EXPECT RH READINGS IN THE MID TEENS
TO LOWER 20S. AFTERNOON AND EVENING ISOLATED SHOWERS AND
THUNDERSTORMS WILL MAINLY BE CONFINED TO THE NORTH HALF OF THE
CODY DISPATCH AREA...ZONE 140...AND THE FAR NORTH PORTION OF ZONE
281. THE BEST CHANCE OF SHOWERS AND STRONG STORMS IS LIKELY TO BE
LATE SUNDAY AFTERNOON AND EVENING IN THESE AREAS. ADDITIONAL MOISTURE
PUSHES INTO THE STATE FROM THE SOUTHWEST ON MEMORIAL DAY. MOST
AREAS CAN EXPECT AT LEAST ISOLATED THUNDERSTORMS THAT AFTERNOON
BUT THE STORMS LOOK TO BE LESS INTENSE. BIGGER CHANGES IN THE
OFFING BY MIDWEEK AS A TROUGH APPROACHES THE CENTRAL ROCKIES. THIS
WILL LEAD TO COOLER TEMPERATURES AND A BETTER CHANCE OF
PRECIPITATION FROM TUESDAY THROUGH THURSDAY.

&&

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

$$

SHORT TERM...CNJ
LONG TERM...LIPSON
AVIATION...CNJ
FIRE WEATHER...CNJ