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000
FXUS65 KRIW 041757
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST WED DEC 4 2013

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

SAT IMAGERY CURRENTLY SHOWING LW TROF IN CONTROL OF MOST OF THE
CONUS TONIGHT WITH AN ENHANCED DEEP TROF...WITH CENTER OVR NWRN
WY...CONTINUING TO PIVOT THRU THE GREAT BASIN AND INTERMOUNTAIN
WEST.

CURRENTLY WE ARE CAUGHT UNDER CLOSED PORTION OF THE
LOW...EFFECTIVELY SPLITTING LOCATIONS OF SNOWFALL...WITH SLIGHTLY
HEAVIER SNOW OCCURRING ACROSS THE ERN PORTION OF SWEETWATER COUNTY
AND ERN NATRONA...WHICH ARE CLOSEST TO THE EFFECTS OF UPR JET
VELOCITIES UPWARDS OF 120 KTS...WITH A NICE TRANSVERSE WAVE PATTERN
EMBEDDED THROUGH THE COLD CLOUD TOPS. OTHERWISE...MUCH LIGHTER SNOW
TO THE NORTH INTO ERN FREMONT COUNTY...WITH VERY LIGHT
SNOWFALL/FLURRIES  UP NORTH NEAR THE WY/MT BORDER UNDER THE QUICKLY
EXITING INFLUENCE OF THE JET EXIT REGION. OVERALL...HOWEVER...THERE
IS LITTLE IN THE WAY OF MOISTURE LEFT TO WORK WITH AS A VERY COLD
AIR MASS CONTINUES TO PUSH INTO THE FA FROM THE N. H7 TEMPS EARLIER
THIS EVENING WERE FOUND TO RANGE FROM -15C IN THE SOUTH TO -25C IN
THE NORTH.

THIS MORNING...MOST OF THE INFLUENCE FROM THE UPR LVLS WILL BE MOVING OUT
OF THE AREA...WITH MAINLY LL WIND/TERRAIN AND INCREASINGLY COLD
TEMPERATURES DOING THE WORK TO SQUEEZE ANY REMAINING MOISTURE AND
PUTTING IT ON THE GROUND. AS MOST ADV/WARN CRITERIA ARE NOT BEING
MET ATTM...I WILL CANCEL THE ADVISORIES AND WARNINGS FOR ALL ZONES
EXCEPT FOR ERN SWEETWATER AND NORTHERN JOHNSON COUNTIES...AND ALSO
DIAL BACK THE EXPIRATION TIME FROM 5PM (12Z) LOCAL TO NOON LOCAL
(19Z).

OTHERWISE...COLD...COLD AND MORE COLD IS THE NAME OF THE GAME FROM
WED NIGHT THRU FRIDAY NIGHT WITH NIGHTTIME LOWS RANGING FROM -10 TO
-25 DEPENDING ON LOCATION AND ELEVATION. ADDITIONALLY...THE UPR LVLS
WILL BEGIN TO TRANSITION TO MORE WRLY FLOW AT H7 THROUGH THE DAY ON
THU...THEN TO SWRLY ON FRI. THIS PATTERN CHANGE WITH THE ADDITION OF
A LITTLE MOISTURE FOR THE EPAC...WILL ALLOW FOR TERRAIN INDUCED
LIGHT SNOW OVR THE WRN/NWRN MOUNTAINS FRI AND FRI NIGHT. BY FRI
NIGHT...ANOTHER UPSTREAM SW WILL DIVE DOWN THE WRN PORTION OF THE
LW...AND PUNCH INTO THE WRN FA...PERHAPS ENHANCING SNOW CHANCES
OVERNIGHT IF THE TIMING OF THE UPR SW IS CORRECT. ATTM...MOISTURE
LOOKS TO BE THE LIMITING FACTOR...SO SNOWFALL THROUGH SAT MORNING
WILL BE ON THE LOWER SIDE AT GENERALLY LESS THAN 3 INCHES...EVEN AT
ELEVATION.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

A POSITIVELY TILTED TROUGH ACROSS THE WEST WILL SWING INTO THE GREAT
BASIN SATURDAY...AND THEN EASTWARD ACROSS THE SOUTHERN AND CENTRAL
ROCKIES SATURDAY NIGHT AND SUNDAY. THE BULK OF THE ENERGY...AND MAIN
AREA OF SNOWFALL WILL REMAIN SOUTH OF THE AREA. HOWEVER WILL
PROBABLY SEE SOME VERY LIGHT SNOW/FLURRIES WITH THE BEST CHANCE
ACROSS THE WEST AND SOUTH SATURDAY AND SATURDAY EVENING.  AT THE
SURFACE SATURDAY...THE FORECAST AREA WILL BETWEEN A STRONG SURFACE HIGH
1045+ MB OVER THE NORTHERN HIGH PLAINS...AND A SURFACE LOW ACROSS
THE GREAT BASIN. THIS WILL KEEP THE ARCTIC AIR MASS IN PLACE.  A
NORTHERN STREAM SHORTWAVE TROUGH IS PROJECTED TO QUICKLY DIVE SOUTH
OUT OF ALBERTA ACROSS THE AREA LATE SUNDAY/SUNDAY NIGHT...RESULTING
IN A REINFORCING SHOT OF ARCTIC AIR. GLOBAL MODELS SHOW 700MB TEMPS
DROPPING BACK DOWN AGAIN TO -20 TO -28 CELSIUS BY 12Z MONDAY. ALSO
THE ATMOSPHERE COULD SQUEEZE OUT SOME VERY LIGHT SNOW...MAINLY
ACROSS THE NORTHERN MOUNTAINS AS THIS SYSTEM PULLS ACROSS THE AREA SUNDAY
NIGHT...AND IN THE NORTHERLY FLOW IN WAKE OF THIS SYSTEM MONDAY.

NORTHWEST FLOW IS THEN EXPECTED TUESDAY AND WEDNESDAY WITH THE
POTENTIAL OF A SHORTWAVE TROUGH IMPACTING THE FORECAST AREA. MODELS
ARE SHOWING THIS POTENTIAL SHORTWAVE HAS LITTLE MOISTURE TO WORK
WITH AT THE MOMENT. THUS WILL KEEP A MAINLY DRY FORECAST WITH A
SLIGHT CHANCE OF SNOW...MAINLY ACROSS THE NORTHWEST MOUNTAINS.
GLOBAL MODELS ARE ALSO SHOWING THE ARCTIC AIR MASS MODIFYING...WITH
A WARMING TREND MOST NOTED IN MIXED AREAS...WHILE TRAPPED
BASINS/VALLEYS WILL CONTINUE TO STRUGGLE.

&&

.AVIATION.../18Z ISSUANCE/

IMPROVING CONDITIONS EXPECTED THROUGH THE FORECAST PERIOD. SOME
LINGERING -SN OR HZ NOTED AT SOME TERMINALS THIS MORNING...WHICH
WILL CONTINUE TO TAPER OFF AS THE MOST RECENT WINTER SYSTEM MOVES
FURTHER SOUTHEAST. EXPECT GENERALLY VFR CONDITIONS ACROSS THE
AREA...THOUGH SOME LOW CLOUDS MAY ATTEMPT TO DEVELOP DURING THE
LATER PORTIONS OF THE FORECAST PERIOD. SOME TERMINAL FORECASTS
INCLUDE THE MENTION OF -SN WITH LOWERED CLOUD DECKS DURING THE
TIME OF CONCERN. SHOULD THIS SCENARIO DEVELOP...PERIODS OF MVFR
CONDITIONS WILL BE POSSIBLE AS LOW CLOUDS PRODUCE ENOUGH FALLING
CRYSTALS TO REGISTER AS -SN. OTHERWISE...VFR CONDITIONS WILL
CONTINUE THROUGH THURSDAY.

&&

.FIRE WEATHER...

OVERALL...NORTH WINDS GUSTING 25 TO 30 MPH CAN BE EXPECTED AT TIMES
ACROSS AREAS MAINLY EAST OF THE DIVIDE TODAY. HOWEVER...FIRE WEATHER
CONCERNS WILL CONTINUE ON THE LOW SIDE  THROUGH THE REST OF THIS
WORK WEEK AND WEEKEND AS BITTER COLD TEMPERATURES AND OCCASIONAL
FLURRIES OR LIGHT SNOWFALL OCCUR ACROSS THE DISPATCH ZONES OVER THE
NEXT SEVERAL DAYS.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL NOON MST TODAY WYZ030.

WINTER WEATHER ADVISORY UNTIL NOON MST TODAY WYZ010.

&&

$$

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