Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 251007
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
307 AM MST THU DEC 25 2014

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

WELL...PEOPLES WISHES OF A WHITE CHRISTMAS LOOK TO BE COME TRUE
ACROSS THE VAST MAJORITY OF THE STATE. POCATELLO RADAR IS LIT UP
LIKE A CHRISTMAS TREE WITH PLENTY OF MOISTURE MOVING INTO WESTERN
WYOMING. THE HIGHEST CLOUD TOPS AND BEST MOISTURE...AS EXPECTED ARE
IN NORTHWESTERN WYOMING WITH SOME UPPER LEVEL DYNAMICS FROM THE
RIGHT REAR QUAD OF THE JET AND THE COLD FRONT DROPPING SOUTHWARD.
SNOW HAS ALSO SPREAD INTO THE NORTHERN PORTION OF THE COUNTY WARNING
AREA WITH COLD FRONT DROPPING SOUTHWARD. AS OF AROUND 1 AM...THE
SOUTHWEST IS FAIRLY QUIET AS A DRY SLOT HAS WRAPPED INTO THE AREA.
HOWEVER...WE STILL EXPECT SNOW TO SPREAD ACROSS ALL AREAS BY EARLY
THIS MORNING. WE STILL EXPECT THE HEAVIEST SNOW TO BE AREAS THAT ARE
FAVORED BY NORTHEASTERLY UPSLOPE FLOW...MAINLY FROM THE EASTERN WIND
RIVER RANGE AND LANDER FOOTHILLS WHERE SOME AREAS WILL SEE MORE THAN
A FOOT. FOR THE MOST PART...THE WARNINGS AND ADVISORIES LOOK
REASONABLE AND WE WILL MAKE FEW CHANGES AT THIS TIME. THE UPPER
LEVEL LOW DRIVING THE STORM WILL MOVE FROM WESTERN UTAH SLOWLY
TOWARD THE SOUTHEAST TO A POSITION NEAR THE FOUR CORNERS BY FRIDAY
MORNING. THE STEADIEST AND HEAVIEST SNOW SHOULD END THIS EVENING AS
THE BEST DYNAMICS MOVE AWAY TO THE SOUTH. HOWEVER...LIGHT UPSLOPE
WILL CONTINUE INTO THURSDAY NIGHT AND POSSIBLY FRIDAY MORNING ACROSS
SOME AREAS. FRIDAY SHOULD FEATURE IMPROVING CONDITIONS AS THE STORM
MOVES AWAY. A WEAK SHORTWAVE WILL THEN DROP SOUTHWARD BUT IT DOES
NOT HAVE A LOT OF ENERGY OR MOISTURE TO WORK WITH SOME ONLY LIGHT
MOUNTAIN SNOW SHOWERS ARE EXPECTED. WITH THE FRESH SNOW COVER IT
WILL BE A MUCH COLDER DAY TOMORROW AND AS A RESULT WE LOWERED
TEMPERATURES A BIT.

AS WE HEAD TOWARD FRIDAY NIGHT...THE QUESTION WILL BE HOW MUCH
CLEARING WE WILL SEE. MOST THE INGREDIENTS ARE IN PLACE FOR A RATHER
COLD NIGHT FRIDAY NIGHT...A COLD AIR MASS...LIGHT WIND AND SOME OF
THE LONGEST NIGHTS OF THE YEAR. THE X FACTOR IS HOW MUCH CLEARING
WILL THERE BE. FOR NOW...WE LOWERED TEMPERATURES A BIT BUT WITH THE
UNCERTAINTY CHANGES WERE MINIMAL.

THE MODELS DO DIVERGE JUST A BIT WITH THE ARRIVAL OF THE NEXT SYSTEM
FOR THE WEEKEND. AT THIS POINT...THE GFS IS AROUND 6 TO 12 HOURS
FASTER THAN THE NAM. A THIS POINT...WE BLENDED THE NEW MODELS WITH
CONTINUITY. HOWEVER...BOTH MODELS AGREE THAT THE HEAVIEST
PRECIPITATION WOULD BE LATER SATURDAY NIGHT. IT COULD BE HIGHLIGHT
WORTHY AS WELL. WILL HAVE A CHANCE TO TAKE A BETTER LOOK AT IT
TOMORROW EVENING AFTER THE CHRISTMAS SNOWSTORM PASSES.

.LONG TERM...SUNDAY THROUGH THURSDAY

THE NEXT WEATHER SYSTEM WILL DIVE TOWARD THE GREAT BASIN SUNDAY AND
THEN SLIDE SLOWLY SOUTH INTO NEVADA AND UTAH ON MONDAY. THIS
SYSTEM DRAGS THE COLDEST AIR OF THE SEASON SOUTHWARD SUNDAY NIGHT
INTO WY AND THEN THIS BITTER COLD AIRMASS HANGS AROUND MONDAY AND
TUESDAY. THE SNOW THAT OCCURS SUNDAY INTO MONDAY WILL BE MORE
FLUFFY AND HAVE LESS WATER EQUIVALENT THAN THE CURRENT STORM IS
PRODUCING. THAT DOES NOT MEAN THAT DECENT SNOWFALL ACCUMULATIONS
WOULD NOT OCCUR. WILL HAVE TO WATCH THE TRACK IN THE COMING DAYS
AND ADJUST AS NEEDED. THE SNOW ON MONDAY WILL DECREASE TO FLURRIES
IN THE AFTERNOON AND END IN THE EVENING. HIGHS SUNDAY WILL BE
SEASONAL. MONDAY AND TUESDAY HIGH TEMPS WILL BE MUCH BELOW NORMAL.
LOWS TEMPS TUESDAY AND WEDNESDAY MORNING WILL BE BITTER COLD. MOST
LOWS WILL RANGE FROM 5 TO 20 DEGREES BELOW ZERO BUT SOME PLACES
WILL LIKELY DROP TO THE 20 TO 30 BELOW ZERO RANGE. WEDNESDAY AND
THURSDAY LOOK TO BE MOSTLY DRY WITH SOME MODERATION FOR THE
MOUNTAINS AND THOSE PLACES THAT CAN MIX OUT. THERE WILL BE
BASIN/VALLEY INVERSIONS FORMING WED THAT WILL CONTINUE INTO THURS.
THUS HIGH TEMPS WED WILL STRUGGLE TO REACH 10 ABOVE...THEN HIGHS
THURSDAY IN THE TEENS. AGAIN THE AMOUNT OF SNOW COVER WILL ALSO
PLAY A ROLE IN HOW COLD THE DAYS AND NIGHTS WILL BE IN THE
VALLEYS/BASINS. BOTTOM LINE...A BLAST OF WINTER WEATHER TO END THE
YEAR 2014...BUT THE WEATHER TO RING IN THE NEW YEAR LOOKS DOES
LOOK DRY SO FAR.

&&

.AVIATION.../12Z ISSUANCE/

AN UPPER LEVEL LOW PRESSURE SYSTEM WILL DIG SE ACROSS THE GREAT
BASIN INTO THE FOUR CORNERS AREA CHRISTMAS AND THURSDAY NIGHT.

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

A COLD FRONT AND IFR -SN AREAS OF LIFR SN WILL CONTINUE TO PUSH SOUTH
INTO VCNTY KLND-KRIW-KCPR EARLY THIS MORNING.  THE FRONT WILL
ALSO BE ACCOMPANIED BY GUSTY NORTH WINDS 15-20KTS WITH GUSTS TO
30KTS AND AREAS OF BLSN.  THESE CONDITIONS WILL PERSIST ACROSS MOST
AREAS THROUGH 00Z FRI...FOLLOWED BY GRADUALLY IMPROVING CONDITIONS
AND DIMINISHING WIND FROM NW-SE THURSDAY NIGHT.  THE LAST AREAS TO
SHOW IMPROVEMENT WILL BE UPSLOPE FAVORED AREAS VCNTY KLND-KCPR WHERE
AREAS OF IFR CIGS AND VSBY IN -SN MAY PERSIST THROUGH 12Z FRIDAY.

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

CONDITIONS WILL CONTINUE TO DETERIORATE OVERNIGHT WITH WIDESPREAD
IFR -SN...MTNS OBSCD...PREVAILING VCNTY AND NORTH OF A
KEVW-KBPI-KPNA LINE BY 12Z.  A NORTHEAST FLOW WILL BRING DOWNSLOPE
WINDS AND IMPROVING CONDITIONS ACROSS THE NORTHWEST TO VCNTY KJAC
AND KPNA AROUND 18Z...BUT IFR CONDITIONS WILL LIKELY PERSIST TO THE
SOUTH AND WEST.

ALONG THE INTERSTATE 80 CORRIDOR AND VCNTY KRKS...A COLD FRONT AND
INCREASING NE WINDS WILL BRING WIDESPREAD IFR -SN/BLSN 15-18Z
TODAY.   THESE CONDITIONS WILL LIKELY PERSIST WELL INTO THURSDAY
NIGHT WITH SOME IMPROVEMENT POSSIBLE EARLY FRIDAY MORNING.

&&

.FIRE WEATHER...

WIDESPREAD SNOW AND GUSTY WIND THROUGH TONIGHT. BASINS AND VALLEYS
WILL DEVELOP INVERSIONS FOR FRIDAY NIGHT THAT WILL LEAD TO POOR
MIXING AND SMOKE DISPERSAL. ON SATURDAY...MILDER AIR MOVES IN ALONG
WITH SOME STRONGER WINDS THAT WILL ENCOURAGE SOME MIXING. ANOTHER
SNOW STORM IS POSSIBLE ON SATURDAY NIGHT IN THE WEST AND SPREADING
EAST OF THE DIVIDE SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

WINTER STORM WARNING UNTIL 11 PM MST THIS EVENING
WYZ015-017>020-022-027>030.

WINTER WEATHER ADVISORY UNTIL 8 PM MST THIS EVENING
WYZ001>004-006-008>014-016-023>026.

WINTER STORM WARNING UNTIL 8 PM MST THIS EVENING WYZ005-007.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...HATTINGS




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