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000
FXUS65 KRIW 050955
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
255 AM MST THU DEC 5 2013

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

SAT IMAGERY STILL SHOWING LW TROF ENVELOPING MOST OF THE CONUS
EXCEPT FOR THE ERN COASTAL STATES. EMBEDDED SW PULLING THROUGH N
CNTRL CONUS WITH ANOTHER WEAKER SW PLUNGING DOWN THE W SIDE OF THE
LW TROF TOWARDS SRN CALIFORNIA. AT THE SFC...A COUPLE OF DAYS BEHIND
THE ORIGINAL FRONT LEAVING MOST OF THE WEST UNDER INCREASING HIGH
PRESS...WITH INVERTED TROF UP THRU CALIFORNIA AND A SFC LOW CENTER
DOWN IN NM...NEITHER OF WHICH IS OF ANY CONSEQUENCE FOR OUR WX.

VERY COLD TEMPS CONTINUE THRU THE FCST PERIOD WITH NIGHTTIME LOWS RANGING
FROM -10 TO -25 DEPENDING ON LOCATION AND ELEVATION.
ADDITIONALLY...THE MID/UPR LVLS WILL BEGIN TO TRANSITION TO MORE
WRLY FLOW AT H7 THROUGH THE DAY ON THU...THEN TO SWRLY ON FRI AHEAD
OF THE NEXT SW TROF. THIS PATTERN CHANGE...WITH THE ADDITION OF A
LITTLE MOISTURE FROM THE EPAC...WILL ALLOW FOR TERRAIN INDUCED LIGHT
SNOW OVR THE WRN/NWRN MOUNTAINS BEGINNING FRI DAYTIME AND CONTINUING
THROUGH SAT NIGHT. BY FRI NIGHT...A SMALL FAST MOVING SW IS EXPECTED
TO BUMP INTO THE THE WRN PORTION OF THE CWA IN A TRANSITIONAL ZONAL
FLOW SCENARIO AHEAD OF A MORE SUBSTANTIAL SW THAT WILL PULL THROUGH
THE REGION SATURDAY AND WHICH NOW IS LOCATED UP IN THE YUKON.
ATTM...MOISTURE STILL LOOKS TO BE THE LIMITING FACTOR WITH THIS
SYSTEM...WITH WRN MOUNTAIN SNOWFALL TOTALS FROM FRI THRU SUN MORNING
RANGING FROM 3 TO 6 INCHES...WITH LOWER AMOUNTS IN THE LOWER
ELEVATIONS. BEST LIFT FROM THE UPR PORTIONS OF THE WAVE ACROSS THE
REST OF THE CWA WILL OCCUR BY SAT AFTERNOON...EXITING THE ERN FA BY
SUNDAY MORNING. SFC CYCLOGENESIS LOOK LIKE IT WILL BEGIN TO DEVELOP
IN THE NRN GREAT BASIN AND TRACK JUST AHEAD OF THE STRONG PORTION OF
THE UPR WAVE AXIS...MOSTLY S OF THE STATE THROUGH CO. THE POSITION
OF BOTH THE SFC AND UPR PARTS OF THIS SYSTEM LEAVE MOST OF THE CWA
WITHOUT THE BENEFIT OF GOOD UPWARD VV AS THE WAVE PASSES...SO ONLY
LIGHT SNOW IS EXPECTED...EVEN WITH SOME EXPECTED LL UPSLOPE
DEVELOPING BY SAT NIGHT. THE NRN PORTION OF THE CWA IS MOST LIKELY
TO GET SHUT OUT OF SNOWFALL WITH THIS SYSTEM.

.LONG TERM...SUNDAY THROUGH THURSDAY

A SHORTWAVE TROUGH AROUND THE FOUR CORNERS EARLY SUNDAY MORNING WILL
QUICKLY PUSH INTO THE PLAINS SUNDAY. THERE COULD BE SOME LINGERING
LIGHT SNOWFALL ACROSS THE SOUTH AND EASTERN SECTIONS OF THE FORECAST
AREA SUNDAY MORNING. HOWEVER THE MAIN ATTENTION WILL BE A SHORTWAVE
DIVING SOUTH OUT OF CANADA ACROSS THE REGION LATE SUNDAY INTO SUNDAY
NIGHT. THIS WILL GIVE THE AREA A CHANCE FOR ADDITIONAL LIGHT
SNOWFALL...MAINLY ACROSS THE NORTH SUNDAY NIGHT. HOWEVER THE MAIN
IMPACT WILL BE A REINFORCING SHOT OF ARCTIC AIR. 700 MB TEMPS BY 12Z
MONDAY ARE EXPECTED TO BE IN THE -23 TO -28 CELSIUS RANGE.

NORTHWEST FLOW IS THEN EXPECTED MONDAY NIGHT THROUGH TUESDAY
NIGHT WITH MODELS SHOWING THE POSSIBILITY OF A CLIPPER SYSTEM
AFFECTING THE FORECAST AREA IN THE MONDAY NIGHT/TUESDAY TIME FRAME.
FLAT RIDGING IS THEN EXPECTED WEDNESDAY AHEAD OF A PACIFIC TROUGH
THAT COULD BEGIN TO IMPACT AREA THURSDAY.

ARCTIC AIR WILL REMAIN IN PLACE THROUGH MONDAY...WITH FINALLY SOME
WARMING TUESDAY THROUGH THURSDAY...WITH TRAPPED BASINS/VALLEYS
SLOWER TO WARM THAN MIXED AREAS. WENT WELL BELOW MEX MOS GUIDANCE
TUESDAY THRU THURSDAY IN TRAPPED BASINS...AND ONLY SLIGHTLY BELOW IN
MIXED AREAS.

&&

.AVIATION.../12Z ISSUANCE/

AREAS OF MVFR CIGS AND -SN...WITH LOCAL IFR CONDITIONS WILL BE
ENCOUNTERED PRIMARILY WEST OF THE DIVIDE AND FROM VCNTY KWRL-KCOD
THROUGH 12Z WITH THESE CONDITIONS BECOMING MORE LOCALIZED AFTER
15Z.  VFR CONDITIONS WILL PREVAIL ELSEWHERE WITH LOCAL IFR/MVFR IC
AND FG PARTIALLY OBSCURING THE TERRAIN.

A WEAK SHORTWAVE WILL PUSH SE ACROSS THE WEST FROM 22Z THUR-06Z
FRIDAY...SPREADING AREAS OF MVFR -SN INTO VCNTY KJAC AROUND 22Z AND
SE ACROSS VCNTY KBPI-KRKS 23Z THUR-03Z FRI. THESE CONDITIONS WILL
PERSIST THROUGH THURSDAY NIGHT. VFR CONDITIONS WILL PREVAIL EAST OF THE
DIVIDE WITH LOCAL MVFR/IFR IC AND FG FORMING ONCE AGAIN AFTER
SUNSET.

&&

.FIRE WEATHER...

NO FIRE WEATHER CONCERNS THROUGH THE REST OF THIS WORK WEEK AND
WEEKEND AS BITTER COLD TEMPERATURES ARE FOLLOWED BY A ROUND OF
LIGHT SNOWFALL OVER THE WESTERN DISPATCH ZONES FRIDAY AND
SATURDAY...SPREADING EASTWARD QUICKLY SATURDAY NIGHT THROUGH
SUNDAY.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...BRAUN