000
FXUS65 KRIW 150851
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
251 AM MDT WED MAY 15 2013

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

AN AREA OF LOW PRESSURE MOVING THROUGH THE DESERT SOUTHWEST WILL
DISORGANIZE TO FORM A WAVE OF LOW PRESSURE BY THE EARLY AFTERNOON
HOURS. THIS DISTURBANCE WILL IMPACT THE STATE...WITH INSTABILITY
EXPECTED ALONG WITH SOME AFTERNOON MOISTURE. SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE WITH THIS SYSTEM. SCATTERED SHOWERS
WITH ISOLATED THUNDERSTORMS ANTICIPATED THIS AFTERNOON...ESPECIALLY
ACROSS SOUTHERN AND WESTERN WYOMING. AS THE SYSTEM MOVES THROUGH THE
STATE...THE SHOWER ACTIVITY WILL MOVE NORTHEAST...IMPACTING JOHNSON
COUNTY BY THE EARLY EVENING HOURS.

THIS IS THE FIRST IN A SERIES OF DISTURBANCES EXPECTED TO IMPACT THE
STATE THROUGH THE NEXT COUPLE OF DAYS. THE RIDGE OF HIGH PRESSURE
WILL HAVE MOVED EAST OF THE CWA BY THURSDAY AFTERNOON...WITH
SOUTHWEST FLOW PREVAILING ACROSS THE STATE. MEANWHILE...A WAVE OF
LOW PRESSURE WILL CONTINUE TO DIG SOUTH THROUGH FRIDAY...WITH
ANOTHER ROUND OF AFTERNOON SHOWERS AND THUNDERSTORMS EXPECTED. THE
APPROACHING WAVE OF LOW PRESSURE IS TAKING A NEGATIVE TILT AS IT
DIVES SOUTH...WITH MODELS INDICATING SLIGHTLY MORE INSTABILITY FOR
FRIDAY AFTERNOON AND EVENING.

TEMPERATURES WILL COOL SLIGHTLY OVER THE NEXT COUPLE OF DAYS IN
RESPONSE TO THE APPROACHING DISTURBANCES. A SLIGHT REBOUND WILL
OCCUR ON FRIDAY...AHEAD OF THE ARRIVAL OF THE STRONGER WAVE OF LOW
PRESSURE.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ACTIVE MEDIUM RANGE PERIOD AS THE FLOW AMPLIFIES AGAIN AND A LARGE
SCALE TROUGH DEVELOPS OVER THE WEST OVER THE WEEKEND AND INTO EARLY
NEXT WEEK BEFORE SOME IMPROVEMENT. MODELS STILL DIVERGE OVER THE
DETAILS AND HOW THE SECONDARY SHORTWAVE BEHIND THE SATURDAY SYSTEM
ACTS ON THE TROUGH BUT THERE IS STRONG AGREEMENT NOW THAT A MAJOR
CHANGE TO COOLER AND UNSETTLED WEATHER WILL DEVELOP OVER THE WEST
AND NORTH SATURDAY AND SPREAD AT LEAST INTO THE CENTRAL ZONES SUNDAY
THROUGH MONDAY. THE ECMWF IS STILL ADVERTISING A CLOSED CIRCULATION
DEVELOPING NEAR THE ID...UT...WY TRIPLE POINT ON SUNDAY AND THEN
TRACKING ACROSS SRN WYOMING BEFORE WEAKENING AND BEING ABSORBED INTO
THE MAIN LOW OVER THE PLAINS. WIDESPREAD SHOWERS AND SOME
THUNDERSTORMS WILL LIKELY COVER THE WEST AND PROBABLY NORTH ON
SATURDAY AS THE COLD FRONT AND DYNAMICS IMPACT THIS AREA. A DRIER SW
FLOW MAY KEEP MUCH OF THE CENTRAL AND SOUTH FAIRLY DRY EXCEPT FOR
SOME STORMS COMING OFF THE UINTAS. WILL KEEP SOME 20-30 PERCENT POPS
IN DUE TO THE ALL BLEND CONSENSUS BUT WOULDN`T BE SURPRISED IF IT`S
DRIER THAN THIS. MUCH COOLER AND WETTER SUNDAY THROUGH MONDAY AS
COLD TROUGH WITH ORIGINS NEAR THE NORTH POLE DIG INTO THE NRN GREAT
BASIN AND THEN TRACK ACROSS SRN WYOMING. LOOKING MORE AND MORE LIKE
A WIDESPREAD RAIN EVENT FOR THE FAVORED UPSLOPE AREAS OF CENTRAL
WYOMING WITH SNOW ABOVE 9000 FEET OR SO SUNDAY....LOWERING TO 8000
FEET OR POSSIBLY LOWER SUNDAY NIGHT INTO MONDAY. GRADUAL IMPROVEMENT
MONDAY NIGHT AND TUESDAY WITH SHORTWAVE RIDGING MOVING IN AHEAD OF
ANOTHER LARGE SCALE TROUGH WHICH LOOKS TO DEVELOP ALONG THE PACNW
COAST FOR THE SECOND HALF OF NEXT WEEK. LOWERED HIGHS FOR SUNDAY
AND MONDAY BUT THESE COULD BE QUITE A BIT COOLER IN THE UPSLOPE
AREAS IF TRENDS CONTINUE. CONVECTION COULD RETURN TO THE WESTERN
MOUNTAINS BY WEDNESDAY WITH THE FIRST PIECE OF ENERGY AND DIFFLUENT
FLOW AHEAD OF OUR LARGE COLD PACNW TROUGH.

&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH 21Z. SHOWERS AND THUNDERSTORMS
WILL FORM ACROSS THE REGION AFTER 20Z AND CONTINUE THROUGH 04Z.
LOCAL MVFR CONDITIONS MAY OCCUR VCNTY STORMS AND OUTFLOW WIND GUSTS
TO 30 KNOTS ARE LIKELY NEAR SHOWERS AND STORMS. MOST TERMINAL SITES
WILL HAVE VCTS IN THEM BETWEEN 20Z AND 02Z. LINGERING SHOWERS ARE
EXPECTED THROUGH 06Z.

&&

.FIRE WEATHER...

SLIGHTLY COOLER TEMPERATURES EXPECTED TODAY AS A DISTURBANCE LOOKS
TO IMPACT THE STATE. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE THIS
AFTERNOON...ESPECIALLY ACROSS SOUTHERN AND WESTERN WYOMING. MUCH OF
THE AREA WILL SEE AT LEAST A SMALL POTENTIAL FOR THUNDERSTORM
ACTIVITY TODAY. A SERIES OF DISTURBANCES WILL CONTINUE TO IMPACT THE
STATE FOR THE NEXT COUPLE DAYS...BRINGING AFTERNOON SHOWERS AND
THUNDERSTORMS. TEMPERATURES WILL CONTINUE TO COOL THROUGH THURSDAY
WITH A SLIGHT REBOUND ANTICIPATED FRIDAY AFTERNOON AHEAD OF A
STRONGER WAVE OF LOW PRESSURE.

&&

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

&&

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...AR
FIRE WEATHER...BRANHAM