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000
FXUS65 KRIW 221008
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
408 AM MDT TUE APR 22 2014

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

RAIN CHANCES INCREASE ACROSS THE FAR WEST EARLY THIS MORNING AS A
LEADING SHORT WAVE EJECTS FROM THE MAIN TROUGH ALONG THE WEST COAST.
ANOTHER WARM DAY IN STORE TODAY AS WARM SOUTHWEST FLOW INCREASES
AHEAD OF THE MAIN TROUGH. ALONG WITH TEMPERATURES...SURFACE WINDS
WILL BE ON THE INCREASE TOO WITH SOME DOWNSLOPE WARMING AND DRYING
EXPECTED EAST OF THE DIVIDE...SOME AREAS COULD SEE 80 DEGREE TEMPS
THIS AFTERNOON WITH CONSIDERABLE SNOW MELT EXPECTED TODAY. BROAD
ASCENT AHEAD OF THE MAIN TROUGH THIS AFTERNOON WILL ENHANCING PRECIP
CHANCES ACROSS THE WEST AS THE COLD FRONT NEARS...THIS BROAD FORCING
FOR ASCENT WILL ALSO SUPPORT GROWING INSTABILITY AS STEEP LAPSE
RATES DEVELOP IN THE MID AFTERNOON WARM UP. IT LOOKS LIKE THE BEST
INSTABILITY WILL BE ACROSS THE NORTHWEST WHERE THE LOW LEVELS WERE
PRIMED WITH MOISTURE BY THE EARLY MORNING DISTURBANCE...IN
ADDITION...THE LOW TO MID LEVEL SHEAR COULD BE SUFFICIENT ENOUGH FOR
SOME MORE ORGANIZED CELLS TO DEVELOP... POTENTIALLY LEADING TO SOME
SMALL HAIL AND STRONG GUSTY WIND WITH THE STRONGER CELLS. RICHER
MOISTURE TRANSPORT EAST OF THE FORECAST AREA MAY ALSO LEAD TO SOME
STRONGER CELLS IN JOHNSON COUNTY BUT STORM MOTION WOULD LIKELY TAKE
THOSE CELLS OUT OF THE AREA BEFORE THEY WOULD DEVELOP INTO ANYTHING
SEVERE. OTHERWISE...STRONG SLY WINDS AND LOW RH`S WILL INCREASE FIRE
DANGER WHERE FUELS ARE RECEPTIVE TO FIRE...ESPECIALLY IN EASTERN
SWEETWATER COUNTY AND INTO NATRONA COUNTY TODAY.

A STRONGLY FORCED COLD FRONT SWEEPS WEST TO EAST TONIGHT INTO
WEDNESDAY. THE SURFACE LOW IS PRETTY FAR NORTH AND FLOW REMAINS WEST
TO NORTHWESTERLY...WHICH IS MOST FAVORABLE FOR THE HIGHER ELEVATIONS
AND NORTHERN BIGHORN BASIN BUT POPS WERE KEPT BROAD AT THIS TIME AS
STRONG QG AND FRONTOGENETIC FORCING RAKING WEST TO EAST ALONG WITH
THE TROUGH COULD ENCOURAGE SOME PRECIP JUST ABOUT ANYWHERE THIS
EVENING. WEDNESDAY WILL BE CONSIDERABLY COOLER WITH MOUNTAIN SNOW
SHOWERS...DECREASING TO SCATTERED RAIN OR SNOW SHOWERS IN AND NEAR
THE FOOTHILLS AND MORE ISOLATED OUT IN THE BASINS AND SOUTH. THE
COOLER TEMPERATURES ON WEDNESDAY WILL HELP TO SLOW SNOW MELT AFTER
TODAY`S BIG MELT OFF. SNOW LEVELS WILL BE QUITE HIGH TODAY AND
MAINLY ABOVE 10K FEET LOWERING TO THE VALLEY FLOOR TONIGHT AND
REMAINING THERE ON WEDNESDAY. SOME MEASURABLE SNOW IS STILL
POSSIBLE THROUGH WEDNESDAY IN THE WRN MOUNTAINS AND BIGHORNS...BUT
THE STEADIEST AND HEAVIEST PRECIPITATION WILL BE TONIGHT AROUND
FRONTAL PASSAGE.

WIND WILL BE QUITE STRONG AGAIN ON WEDNESDAY IN THE SINKING MOTION
ASSOCIATED WITH THE BACK SIDE OF THE TROUGH...ESPECIALLY MOUNTAINS
AND EAST OF THE DIVIDE. ANOTHER WAVE ASSOCIATED WITH A SEPARATE LOW
PRESSURE SYSTEM JOGGING ALONG THE CANADIAN BORDER WILL GRAZE THE
NORTHERN ZONES ON THURSDAY...BRINGING ANOTHER CHANCE FOR
PRECIPITATION TO THE NORTHWESTERN MOUNTAINS...BIGHORNS AND NORTHERN
BIGHORN BASIN. FLAT RIDGING BUILDS IN QUICKLY BEHIND THIS WAVE BY
THURSDAY AFTERNOON WITH WARM AND DRY CONDITIONS EXPECTED TO HOLD FOR
MOST OF THE FORECAST AREA...WITH SOME MOISTURE ALREADY ARRIVING IN
THE FAR WEST AHEAD OF THE NEXT PACIFIC SYSTEM.

.LONG TERM...FRIDAY THROUGH TUESDAY

GLOBAL MODELS SHOW A TROUGH PUSHING INTO CALIFORNIA FRIDAY...THEN
INTO THE FOUR CORNERS REGION SATURDAY. THE TROUGH IS THEN EXPECTED
TO LIFT NORTHEAST...AND EVENTUALLY BECOME A STACKED LOW OVER THE
CENTRAL HIGH PLAINS SUNDAY/SUNDAY NIGHT. THIS UPPER LOW/TROUGH IS
THEN EXPECTED TO GRADUALLY SHIFT EAST MONDAY/MONDAY NIGHT ACROSS
THE PLAINS AND REACH THE MIDWEST/MISSISSIPPI VALLEY AREA TUESDAY.

THIS STORM SYSTEM HAS THE POTENTIAL TO IMPACT THE FORECAST AREA
FRIDAY THROUGH MONDAY...WITH THE BIGGEST IMPACTS SATURDAY AND SUNDAY.

FRIDAY WILL BE THE WARMEST DAY IN THE EXTENDED WITH SEASONAL TO
SLIGHTLY ABOVE AVERAGE READINGS...WITH A WARM SOUTH/SOUTHWEST FLOW
ALOFT. HOWEVER A SHALLOW BACKDOOR COLD FRONT FRIDAY SHOULD LIMIT
THE WARMING ACROSS THE NORTHEAST/EAST...THAN WOULD NORMALLY BE
EXPECTED. CONVECTION SHOULD BE MAINLY CONFINED TO THE WEST FRIDAY
WITH A MAINLY DRY DAY EAST.

00Z MODELS ARE SUGGESTING AS THE BACKDOOR COLD FRONT RETREATS
NORTHWARD FRIDAY NIGHT...SOME ISENTROPIC LIFT OVER THIS FRONT WILL
CAUSE PRECIPITATION TO BREAK OUT NORTH OF THIS FRONT. THIS
PRECIPITATION SHOULD LIFT NORTHWARD WITH THE FRONT...WITH MORE
PRECIPITATION BREAKING OUT ACROSS THE WEST WITH THE APPROACH OF
THE MAIN TROUGH AND COLD FRONT.

THE MAIN COLD FRONT THEN PUSHES INTO THE FORECAST AREA SATURDAY AND
EVOLVES INTO AN INVERTED SURFACE TROUGH/OCCLUDED FRONT LATE SATURDAY
INTO SATURDAY NIGHT...WITH COLDER AIR GRADUALLY WORKING INTO THE
AREA. THIS CONTINUES SUNDAY AS THE SYSTEM IS PROJECTED TO BECOME
STACKED OVER WESTERN NEBRASKA/SOUTH DAKOTA. THE PRECIPITATION FOCUS
SHOULD SHIFT FROM THE WEST SATURDAY...TO AREAS ALONG AND EAST OF THE
DIVIDE SATURDAY NIGHT INTO SUNDAY. MUCH OF THE PRECIPITATION SHOULD
END SUNDAY NIGHT OR MONDAY DEPENDING ON HOW FAST THIS SYSTEM EXITS.

SIGNIFICANT MOUNTAIN SNOWFALL WILL BE POSSIBLE SATURDAY AND
SUNDAY...WITH EVEN WET SNOW POSSIBLE EVEN IN THE LOWEST ELEVATIONS
EAST OF THE DIVIDE LATE SATURDAY NIGHT INTO SUNDAY. HOWEVER...EVEN
IF SNOW OCCURS IN THE LOWER ELEVATIONS ONLY MINOR IMPACTS WOULD BE
EXPECTED. OF COURSE THIS ALL DEPENDS ON HOW THIS SYSTEM
EVOLVES...AND THERE IS PLENTY OF TIME TO WATCH IT.

HAVE INCREASED POPS FOR THIS SYSTEM...ESPECIALLY SATURDAY AND
SUNDAY...WITH A GRADUAL DECREASE SUNDAY NIGHT AND MONDAY. ALSO
TRENDED TEMPERATURES COOLER FOR SUNDAY AND MONDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS WILL OCCUR TODAY AND TONIGHT. EXPECT A GUSTY WIND AT
MOST TERMINAL SITES TODAY INTO THIS EVENING. ISOLATED SHOWERS AND
THUNDERSTORMS WILL OCCUR AFTER 19Z UNTIL 03Z. A STRONG COLD FRONT
WILL PUSH EAST OF THE DIVIDE BETWEEN 05Z AND 10Z WEDNESDAY. ISOLATED
SHOWERS WILL OCCUR WITH THE FRONTAL PASSAGE ALONG WITH A WIND SHIFT
TO THE WEST. SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR CONDITIONS WILL PREVAIL THROUGH 00Z ACROSS THE REGION. EXPECT A
GUSTY WIND AT MOST TERMINAL SITES. SCATTERED SHOWERS WILL DEVELOP
OVER THE AREA AFTER 18Z WITH ISOLATED THUNDERSTORMS. WIND GUSTS TO
50 MPH MAY OCCUR WITH STORMS. LOCAL MVFR CONDITIONS MAY OCCUR OVER
AND NEAR THE MOUNTAINS DURING THE AFTERNOON AND EARLY EVENING. A
STRONG COLD FRONT WILL MOVE THROUGH THE WEST BETWEEN 00Z AND 05Z
WEDNESDAY. THIS WILL USHER IN COLDER AIR WITH RAIN SHOWERS TURNING
TO SNOW SHOWERS. THE WESTERN MOUNTAINS WILL SEE SNOW SHOWERS TONIGHT
WITH WIDESPREAD MVFR TO IFR CONDITIONS. AS THE FRONT MOVES ACROSS
THE WEST THE WIND WILL SHIFT TO THE WEST OR SOUTHWEST AND WILL BE
GUSTY. SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

&&

.FIRE WEATHER...

...HAZARDOUS BURNING CONDITIONS TODAY AND WEDNESDAY...

A WEAK WEATHER DISTURBANCE AHEAD OF A MAJOR WEATHER SYSTEM WILL MOVE
INTO THE NORTHWEST EARLY WITH A CHANCE OF SHOWERS WITH HIGH SNOW
LEVELS. SOUTHERLY WINDS WILL BE ON THE INCREASE TODAY AND WEDNESDAY.
THE COMBINATION OF STRONG TO VERY STRONG SOUTHERLY WINDS THIS
AFTERNOON COMBINED WITH VERY WARM TEMPERATURES AND LOW RH`S WILL
INCREASE THE FIRE DANGER. OUT WEST...RAIN SHOWERS WITH BE LIKELY
TODAY WITH AN EMBEDDED THUNDERSTORM OR TWO...THE SNOW LEVEL WILL BE
NEAR 10K FEET. A STRONG COLD FRONT WILL SWEEP EAST ACROSS THE AREA
TONIGHT WITH A BAND OF SHOWERS AND ISOLATED THUNDERSTORMS. IT
WILL CONTINUE VERY WINDY THROUGH WEDNESDAY. WEDNESDAY WILL ALSO BE
CONSIDERABLY COOLER THAN TUESDAY BUT STILL RATHER DRY EAST OF THE
DIVIDE WITH MIN RH`S IN THE TEENS AND 20S.

&&

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

&&

$$

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