Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 170518
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1018 PM MST TUE DEC 16 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY (ISSUED AT 247 PM MST)

WV IMAGERY SHOWING PROGRESSIVE WAVE PATTERN WITH WEAK RIDGING OVR
WY...WITH A WEAK SW TRANSLATING THRU THE WRN SIDE OF THE RIDE AND
OVR THE SWRN TO CNTRL PORTIONS OF THE FA. STRONG JET TO THE SOUTH
ACROSS ERN AZ AND THRU CO THEN INTO THE CNTRL PLAINS. SFC HAS WEAK
LOW P AND A TROF/WEAK STATIONARY FRONT FROM THE FRONT RANGE OF CO UP
THRU AND IN THE LEE OF THE BIGHORNS...THEN UP INTO CNTRL MT.

TEMPS AND FOG STILL PRESENTING SOME TRICKY PROBLEMS IN A FEW AREAS
LATE THIS MORNING...WIND RIVER AND NORTHERN BIGHORN BASINS IN
ADDITION TO JOHNSON COUNTY...WHILE FOG HAS DISSIPATED MOST
EVERYWHERE ELSE. CLOUD TOP EROSION HAS LIFTED CIGS AND VIS
SIGNIFICANTLY ACROSS THE WIND RIVER BASIN AROUND NOON...WITH
SUNSHINE TRYING TO PEAK THRU. HOWEVER...THE EXTREME NORTH PORTION OF
THE BIGHORN BASIN AND THE AREA FROM BUFFALO SOUTH TO THE NATRONA
COUNTY LINE...EASTWARD ARE HAVING PROBLEMS GETTING THE FOG OUT.
HOPEFULLY WEAK SW CURRENTLY MOVING ACROSS THE FA FROM SW TO NE  WILL
BE ENOUGH TO LIFT THOSE SKIES TOO...AT LEAST FOR A FEW HRS. WITH
WEAKENING FLOW ALOFT THRU THE FCST PERIOD...A QUICK RETURN TO PATCHY
FOG IS PROBABLY IN STORE ONCE AGAIN EARLY THIS EVENING EVEN IF MID
LVL CLOUDS DO NOT CLEAR OUT AS MANY OF THESE LOCATIONS WILL NOT HAVE
TOO FAR TO GO TO DROP TEMPS ENOUGH TO SATURATE OUT...IN ADDITION TO
SOME DRYING NEAR SFC TO 600MB THRU THE EVE EAST OF THE DIVIDE AND
ALSO ACROSS THE UPPER GREEN BASIN.

OTHERWISE...RIDGE MOVES E AND OUT OF WY BY 09-12Z WITH WEAKENING FLOW
ALOFT. WEAK VORT MAX/SW MOVES INTO AND THRU THE WRN/NWRN FA AT THAT
TIME AND ACTING ON A...WHAT ELSE...WEAK GLOB OF MOISTURE THAT WV
IMAGERY JUST NOW SHOWS TO BE OVR NRN/NERN NV. THIS WILL INCREASE
PRECIP CHCS FROM THE WCNTRL MOUNTAINS N AND THRU THE NW CORNER
INCLUDING YELLOWSTONE THRU AT LEAST WED MORNING...CLEARING OUT IN
THE AFTERNOON ON WED. EXPECTING LESS THAN AN INCH OVR MOST VALLEYS...A
COUPLE OF INCHES IN THE MOUNTAINS...WITH 3 TO 4 INCHES OVR THE
FAVORED REACHES FROM THE TETONS NORTH INTO SWRN
YELLOWSTONE.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY
THE TROUGH OFF THE PACIFIC COAST AT 150W WILL BE THE NEXT SHORTWAVE
TO IMPACT THE CWA MAINLY THU NT IN THE FORM OF MORE LIGHT SNOW IN
WESTERN WY. THIS TROUGH WILL ARRIVE FROM THE WEST NORTHWEST AS IT
RIDES UP AND OVER A FLAT RIDGE TO OUR WEST. THIS FEATURE WILL LACK
MUCH IN THE WAY OF DYNAMICS SO NOT MUCH IN THE WAY OF ACCUMULATION
IS EXPECTED. DECIDED TO TAKE OUT POPS IN THE LANDER FOOTHILLS AS
THIS TROUGHPA NOW SEEMS TO BE A REACH AS FAR AS IT RESEMBLING A
FAVORABLE TRACK FOR EVEN A BRIEF LANDER SNOW EVENT. THE NEXT IN A
SERIES OF QUICK HITTING TROUGHS WILL ARRIVE SATURDAY. THIS SYSTEM
WILL PRODUCE A BIT MORE SNOW IN WESTERN WY WITH THE MORE DIRECT
NORTHWEST UPSLOPE FLOW FOR WESTERN WY ALONG WITH THE NORTHWESTERLY
DIFLUENT FLOW BEHIND THIS TROUGH. THEN THE WEATHER GETS A BIT MORE
INTERESTING BY SUNDAY AS COLD NORTHERN PACIFIC AIR BUILDS SOUTHEAST
AND FLATTENS THE LARGE HIGH OFF THE CALIFORNIA COAST THUS INCREASING
THE PRESSURE GRADIENT AND THE RESULTING NORTHWEST FLOW. THIS MEANS
MORE UPSLOPE SNOWFALL FOR WESTERN WY AND THE BIG HORN MTNS FOR
SUNDAY. A VIGOROUS SHORTWAVE WITHIN THE NORTHWEST FLOW MONDAY WILL
JUST ENHANCE THE GRADIENT RESULTING IN QUITE A WINDY DAY WITH THE
RIGHT FRONT QUAD OF THE ASCT 150 KNOT JET MAX PULLING ADDITIONAL
STRONG WINDS ALOFT TO THE SURFACE. SNOWFALL WILL LIKELY BE ENHANCED
ACROSS THE NORTH AND WEST WITH THIS FEATURE. THEN ON TUESDAY...A
CLOSED LOW OVER MANITOBA WILL BECOME ESTABLISHED WHICH WILL PINWHEEL
ANOTHER VIGOROUS SHORTWAVE SOUTHEAST INTO WY WITHIN THE CONTINUED FAST
NORTHWEST FLOW FOR ANOTHER SHOT OF SNOWFALL...MAINLY FOR THE NORTH
AND WEST ALONG WITH CONTINUED WINDY CONDITIONS. IN ADDITION...AN
ASSOCIATED COLD FRONT WILL SIDE SWIPE OUR EASTERN CWA SO PULLED DOWN
THE HIGHER POPS SOUTH INTO NATRONA COUNTY. NO GREAT TEMPERATURE
FLUCTUATIONS ARE ANTICIPATED FOR THE NEXT WEEK WITH CLOSE TO NORMAL
TEMPS.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL OCCUR AT MOST TERMINAL SITES OVERNIGHT INTO
WEDNESDAY. IFR TO LIFR CONDITIONS WILL OCCUR AT KRIW AIRPORT
OVERNIGHT AND THROUGH MUCH OF WEDNESDAY AS FOG AND VERY LOW CLOUDS
OCCUR. CONDITIONS MAY IMPROVE SLIGHTLY AT KRIW AROUND 21Z BUT
CEILINGS ARE LIKELY TO LOWER BY 03Z THURS ALONG WITH MORE FOG.
KLND AIRPORT MAY ALSO SEE FOG AND LOW CLOUDS AND IFR CONDITIONS
OVERNIGHT THROUGH 16Z.

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

LIGHT SNOW WILL OCCUR IN THE NORTHWEST WY MOUNTAINS THROUGH 15Z
BEFORE GRADUALLY ENDING BY 20Z. EXPECT MOUNTAINS TO BE FREQUENTLY
OBSCURED THROUGH 20Z. AT KJAC AIRPORT SOME LIGHT SNOW AND MVFR
CONDITIONS ARE FORECAST THROUGH 12Z WITH MVFR CEILINGS CONTINUING
UNTIL 18Z...THEN VFR CONDITIONS WILL PREVAIL THERE. THE SOUTHWEST
AND SOUTH WILL SEE VFR CONDITIONS PREVAILING THROUGH THE FORECAST
PERIOD.

&&

.FIRE WEATHER...

WINTER LIKE CONDITIONS CONTINUE ACROSS THE FORECAST
AREA...KEEPING TEMPS ON THE LOWER SIDE...AND RH VALUES ON THE
HIGHER SIDE...WITH FIRE DANGER OBVIOUSLY REMAINING LOW FROM NOW
THROUGH AT LEAST SATURDAY. AGAIN...DUE TO THE COLDER NEAR SURFACE
TEMPERATURES AND WEAK FLOW ALOFT....POOR SMOKE DISPERSION CAN ALSO
BE EXPECTED TO CONTINUE THROUGH MOST OF THE SAME PERIOD.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...LIPSON
AVIATION...AR
FIRE WEATHER...BRAUN










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