Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290111 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
305 PM MST FRI NOV 28 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY

WV IMAGERY DEPICTING FLAT RIDGING OVER WY WITH INCREASING MOISTURE
FLOW STREAMING IN FROM THE WEST AND MAJOR MOUNTAIN WAVE CLOUDS AND
GAPS SHOWING THROUGH. JET(S) PLOWING INTO WRN WY AND THRU MT...WITH
SW TROF JUST COMING INTO NWRN CONUS. ACROSS MT TO NRN ID...AND UNDER
ALL THE WV IMAGERY...SFC HAS MAJOR FRONTO/CYCLO-GENESIS GOING ON.
ALL SFC FRONT WELL NORTH OR EAST OF THE FA ATTM...BUT GOOD STRONG
LEE TROF FORMING DOWN ERN WY AND INTO NERN CO.

FRI...NW FLOW CONTINUES BUT BEGINS TO FLATTEN AND SAG SWD IN
RESPONSE TO THE ENCROACHMENT OF THE JET(S) AND SW TROF OVR NW COAST.
THE CURRENT MAIN EVENT STILL THE WINDS...PARTICULARLY OVR THE
ABSAROKAS AND ADJACENT CODY FOOTHILLS WHERE HIGH WIND WARNINGS HAVE
BEEN POSTED FOR AN EXTENDED PERIOD LASTING THRU THE DAY ON SAT. THIS
IS IN RESPONSE TO GREATLY INCREASING MID/UPR WRLY FLOW NEARLY
PERPENDICULAR TO THE MOUNTAIN RANGES...WITH EXCELLENT THERMAL AND
PRESSURE GRADS (30 PLUS DEG...UP TO 5 MB/25NM) DEVELOPING ACROSS THE
MOUNTAINS AND INTO THE LEE SIDE FOOTHILLS. KCRK HAS ALREADY GIVEN
50+G100+ WINDS. ADDITIONALLY...MOUNTAIN WAVE PRODUCTION IS
CONTINUING WITH HORIZONTAL JUMP AREAS BECOMING VERY LARGE AND
VERTICAL DISPLACEMENTS OF 1-2K FT COMMON. THIS WILL CONTINUE TO HELP
PIN WINDS CLOSE TO THE SFC. HIGH WIND CRITERIA ALSO LOOKS MORE
PROMISING...BUT NOT QUITE AS STRONG AS THE NORTH...NOW ACROSS THE
USUAL WIND CORRIDOR FROM SERN FREMONT...ERN SWEETWATER AND E THRU
NATRONA COUNTIES. HIGH WIND WATCH/WARNING NOW POSTED FOR LANDER
FOOTHILLS FROM THIS EVENING ONWARD...AND THE REST OF THE REGION TO
THE EAST BEGINNING  AFTER MIDNIGHT. FOR AVIATION PURPOSES...LLWS
WILL REIGN SUPREME ACROSS MOST OF THE REGION.

LATE TONIGHT THROUGH SATURDAY...THE SECOND PORTION OF THIS WINTER
SYSTEM MAKES ITS WAY INTO THE FA...ARRIVING WITH MUCH INCREASED
MOISTURE CURRENTLY LOCATED TO THE NW OVR NRN ID...ALONG WITH A
ANOTHER VERY STRONG JET STREAK. ALL WILL PHASE...INCLUDING THE TWO
JETS...BY SATURDAY MORNING WHEN ALL DYNAMICS WILL COME TOGETHER
ALONG WITH CONTINUING HELP FROM THE TERRAIN TO GIVE HEAVY SNOW RATES
ACROSS THE WRN MOUNTAINS...PARTICULARLY OVR TETON AND WRN PARK
COUNTIES. EXPECTING 5 TO 9 INCHES IN THE VALLEYS...AND 10 TO 18+ IN
THE MOUNTAINS BY SUN MORNING.

ALL WATCHES...REMAINING WIND AND WINTER STORM...WILL BE CONVERTED TO
WARNINGS THIS AFTERNOON. ADDITIONALLY...ZONES 23 24 25 IN THE SWRN
FA...AND 14 15 AND 16 IN THE CNTRL WINDS AND UPR WIND RIVER BASIN
WILL HAVE AN WINTER WX ADVISORY HOISTED BEGINNING AT 12Z ON THE 29TH.
THESE ARE FOR BOTH MODERATE SNOW AND BLOWING SNOW. WILL ALSO ASK
EVENING GROUP TO CHANGE THE HIGH WIND WARNING OVR ZONE 2 TO AN
ADVISORY FOR BOTH WIND AND SNOW LATER TONIGHT AS THESE TWO PHENOM
COME TOGETHER.

OTHERWISE...WARM...NEAR RECORD HIGHS AND HIGH LOWS AROUND THE AREA
TODAY/TONIGHT.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE UPPER LEVEL TROUGH AND COLD FRONT WILL MOVE EVER CLOSER TO THE
FORECAST AREA SATURDAY NIGHT...EVENTUALLY MOVING THROUGH BY
SUNDAY MORNING AND KICKING DOWN A COLD FRONT AND AN ASSOCIATED
BAND OF MODERATE TO HEAVY SNOW ALONG WITH A NORTHERLY WIND SHIFT.
PRESSURE RISES BEHIND THE FRONT WILL BE PRETTY STEEP...SO EXPECT A
PERIOD OF STRONG NORTH WIND BEHIND THE FRONT. PREVIOUS MODEL RUNS
HAD THE ARCTIC AIR BEHIND THE FRONT PENETRATING A LITTLE FURTHER
SOUTH THAN CURRENT RUNS...WHICH GIVE THE STATE MORE OF A GLANCING
BLOW WITH THE BRUNT OF THE COLD AIR REMAINING WELL TO OUR
NORTHEAST. HOWEVER...IT WILL DROP TEMPERATURES QUITE A BIT AFTER
THE RELATIVELY MILD SATURDAY DAYTIME TEMPERATURES. MUCH OF THE
SNOW CLEARS OUT BY SUNDAY AFTERNOON EXCEPT FOR A PERSISTENT BAND
OF SNOW SETTING UP ALONG THE WYOMING COLORADO BORDER.
OTHERWISE...A MODERATING AIRMASS AND A WEAKER GRADIENT WILL LEAVE
BEHIND A RATHER CALM SUNDAY AFTERNOON AND EVENING.

DISTURBED WESTERLY FLOW STICKS AROUND FOR MUCH OF THE REST OF THE
LONG TERM WITH ANOTHER ROUND OF SNOW ALREADY MOVING INTO THE WEST
BY MONDAY EVENING. AT THE SURFACE...A LEE SIDE TROUGH WILL ALSO
BEGIN TO FORM MONDAY EVENING AS THE GRADIENT INCREASES ALOFT AT
THE SAME TIME. THIS WILL TURN THE SNOW EATING WIND MACHINE BACK ON
WITH DOWNSLOPE WARMING AND DRYING EXPECTED ALONG THE FOOTHILLS AND
INCREASED WINDS EXPECTED ALONG THE SOUTHERN WIND CORRIDOR FROM
ROCK SPRINGS TO CASPER.

SIGNIFICANT MODEL DIFFERENCES ARISE AFTER MONDAY SO A LOT OF
WEIGHT WAS GIVEN TO CONTINUITY FOR THE REMAINDER OF THE FORECAST
PERIOD. HOWEVER THEY HAVE BEEN COMING TOGETHER A LITTLE MORE THAN
PREVIOUS RUNS WITH THE POTENTIAL ROUND OF PACIFIC MOISTURE
ARRIVING SOMETIME MID WEEK. POPS WERE KEPT MOSTLY IN THE SLIGHT
CHANCE CATEGORY HOWEVER DUE TO THE UNCERTAINTY.

&&

.AVIATION.../00Z ISSUANCE/

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

THE MAIN HAZARD THROUGH THE PERIOD WILL BE LLWS ACROSS THE AREA WITH
VFR CONDITIONS PREVAILING THROUGH 18Z SATURDAY.

STRONG WEST TO SOUTHWEST WIND AT 50-60KT AT FL080-100 WILL CONTINUE
TO CAUSE AREAS OF LLWS AND MDT-SVR TURBULENCE ACROSS THE AREA
THROUGH  TONIGHT.  MOUNTAIN WAVE ACTIVITY WITH SOME OF THESE
STRONGER WINDS MIXING DOWN THE EAST SLOPES OF THE DIVIDE WILL
PRODUCE VERY STRONG ERRATIC WIND GUSTS OVER 50KTS VCNTY KCOD...WITH
THESE STRONGER WINDS SURFACING BELOW 6KFT BECOMING MORE LIKELY VCNTY
KDUB-KLND AFTER 00Z.

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

THE MAIN HAZARD THROUGH THE PERIOD WILL BE LLWS ACROSS THE AREA.
VFR CONDITIONS WILL PREVAIL THROUGH 06Z WITH AREAS OF MVFR/IFR
CONDITIONS SPREADING SOUTH 07Z-12Z SATURDAY AND STAYING MVFR/IFR
THROUGH THE END OF THE FORECAST PERIOD.

STRONG WEST WIND AT 50-60KT AT FL080-100 WILL CONTINUE TO CAUSE
AREAS OF LLWS AND MDT-SVR TURBULENCE ACROSS THE AREA THROUGH
TONIGHT.  OCNL HIGHER MTN OBSCURATION IN -SN WILL CONTINUE VCNTY
AND NORTH OF A KJAC-KCOD LINE THROUGH 00Z SATURDAY...AND THEN IN
THE MNTS ABOVE 6K FT WILL BECOME MOSTLY OBSCURED IN -SN BY 12Z
WITH AREAS OF IFR/MVFR -SN DEVELOPING OVER THE VALLEYS VCNTY KJAC-
KAFO-KPNA. HEAVY SNOW AND BRISK WINDS CAN BE EXPECTED NORTH OF
KJAC AFTER 12Z SAT...LASTING THROUGH THE END OF THE FORECAST
PERIOD...WITH MAJOR OBSTRUCTION TO VIS IN MOUNTAINOUS AREAS.

&&

.FIRE WEATHER...

OVERALL FIRE DANGER WILL BE LOW FOR MOST OF THE AREA...REMAINING LOW
THROUGH THE WEEKEND. HOWEVER THERE WILL BE BRIEF PERIODS IN THE
LANDER FOOTHILLS THIS AFTERNOON AND EARLY EVENING WHEN RH VALUES
WILL DROP BELOW 15 PERCENT. THIS COMBINED WITH VERY GUSTY WEST TO
SOUTHWEST WINDS WILL ELEVATE THE FIRE DANGER FOR A FEW HOURS TODAY.

OTHERWISE...LIGHT SNOW OR FLURRIES WILL CONTINUE OVER THE HIGHER
PEAKS OF THE WESTERN REGION TODAY...PARTICULARLY THE NORTHWEST
MOUNTAINS...WHILE TEMPERATURES WARM DRAMATICALLY ONCE AGAIN EAST
OF THE DIVIDE AS STRONG WEST WINDS AND DOWNSLOPING INCREASE ACROSS
THE AREA. HIGH WINDS WILL REMAIN A THREAT EAST OF THE CONTINENTAL
DIVIDE...ESPECIALLY IN THE ABSAROKA MOUNTAINS AND CODY
FOOTHILLS...FROM TODAY THROUGH THE DAY ON SATURDAY. THE REGION
BETWEEN SOUTH PASS AND CASPER IN ADDITION TO THE LANDER FOOTHILLS
WILL REACH HIGH WIND CRITERIA LATER TONIGHT. HOWEVER...RELATIVELY
WIDESPREAD SNOW COVER AND SEASONALLY WARM TEMPERATURES WILL STILL
KEEP MINIMUM RH VALUES AT MOST LOCATIONS ABOVE CRITICAL LEVELS EVEN
WITH THE WIND. A RETURN TO WINTER EXPECTED THIS WEEKEND AS ANOTHER
STORM BRINGS MORE SNOW TO THE WEST ON SATURDAY...TO THE EAST
OVERNIGHT SATURDAY AND THROUGH SUNDAY MORNING.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO NOON MST SATURDAY
WYZ019-020-022.

HIGH WIND WARNING UNTIL NOON MST SATURDAY WYZ018.

WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 11 AM MST SUNDAY
WYZ001-012-013.

WINTER WEATHER ADVISORY FROM 5 AM SATURDAY TO NOON MST SUNDAY
WYZ014>016-023>025-027.

HIGH WIND WARNING UNTIL 5 PM MST SATURDAY WYZ002-003.

&&

$$

SHORT TERM...BRAUN
LONG TERM...ALLEN
AVIATION...BRAUN
FIRE WEATHER...BRAUN









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