Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 240635
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1131 PM MST SUN NOV 23 2014

UPDATE...UPDATED TO ADD 06Z AVIATION DISCUSSION.

.SHORT TERM...TONIGHT THROUGH MONDAY (ISSUED AT 308 PM MST)

NORTHWEST FLOW ALOFT WILL REMAIN OVER WESTERN AND CENTRAL WYOMING.
A FAST MOVING PACIFIC LOW PRESSURE TROUGH IN THE FLOW WILL SWEEP
THROUGH THE AREA TONIGHT AND MONDAY MORNING. THE NORTHERN AND
WESTERN MOUNTAINS WILL SEE SOME LIGHT SNOWFALL. SOME OF THE SNOW
WILL MAKE IT TO THE VALLEYS OF THE WEST. EAST OF THE DIVIDE LITTLE
IF ANY SNOWFALL IS EXPECTED BUT BRISK NORTHWEST WINDS WILL CONTINUE.
THE LOWER AIR MASS WILL BE WELL MIXED KEEPING OVERNIGHT LOWS UP
WITH SLIGHT COOLING ON MONDAY BEHIND THE TROUGH. THE SNOWFALL IN
THE WEST AND NORTH SHOULD TAPER OFF FROM LATE MORNING THROUGH
EARLY AFTERNOON.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

THE LOW SPINNING OVER SOUTHWEST ALASKA WILL EJECT ANOTHER SHORTWAVE
TROUGH THAT WILL EVENTUALLY TRACK SOUTHEAST IN THE FORM OF AN
ALBERTA CLIPPER ACROSS THE NORTHERN PLAINS BY TUE.. AS A
RESULT...THE ON GOING LIGHT SNOWFALL OVER THE FAR WEST BEING FED BY
A MOIST PACIFIC NORTHWEST FLOW WILL BECOME ENHANCED AS THIS WEATHER
FEATURE DRAWS CLOSER. SNOWFALL WILL CONTINUE TO INCREASE IN THE WEST
TUESDAY AND CONTINUE TUESDAY NIGHT. SNOWFALL WILL SPREAD INTO
NORTHERN WY EAST OF THE DIVIDE TUESDAY AS ISENTROPIC LIFT...Q VECTOR
FORCING AND THE NORTHEAST PROGRESSION OF THE JET ACROSS THE CWA
ENHANCES THE PULL OF PACIFIC MOISTURE FROM THE NORTHWEST. THE
SNOWFALL WILL CONTINUE IN NORTHERN WY THROUGH TUESDAY NIGHT.
SNOWFALL WILL END WEDNESDAY AS THE SYSTEM PULLS TO THE SOUTHEAST.
SNOWFALL AMOUNTS WITH THIS SYSTEM WILL LIKELY AMOUNT TO 3 TO 6
INCHES IN THE WESTERN MTNS...1 TO 3 INCHES IN THE WESTERN VALLEYS
AND 3 TO 9 INCHES IN THE BIG HORN MTNS. MOST OF THE LOWER ELEVATIONS
EAST OF THE DIVIDE WILL HAVE LITTLE IF ANY ACCUMULATION.

THE OTHER CONCERN WITH THIS PARTICULAR WEATHER FEATURE IS WIND. H7
WIND WIND SPEEDS ARE PROJECTED TO INCREASE TO AT LEAST 55 KNOTS LATE
TUESDAY NIGHT AND INTO WEDNESDAY MORNING OVER NORTHERN...CENTRAL AND
EASTERN WY. IN ADDITION...MTN WAVE POTENTIAL CANNOT BE RULED OUT
WITH A FROUDE NUMBER OF 1 NEAR CLARK ALONG WITH A BACKING WIND WITH
TIME. HOWEVER...FAVORABLE MTN TOP INVERSIONS APPEAR TO BE LACKING.
ANOTHER FAVORABLE MARKER ARE 6 DECAMETER HEIGHT LINES SPACED APART
EVERY 3 DECAMETERS OVER WY TUESDAY NIGHT. HAVE INDICATED BORDERLINE
HIGH WIND CRITERIA IN THE GRIDS FOR NOW FROM 03Z WED THROUGH 21Z WED
WITH THE STRONG WIND POTENTIAL FOR THE CODY FOOTHILLS TUE NT/WED AND
FRO THE SOUTHERN WIND CORRIDOR MAINLY ON WED. THE EAST SLOPE OF THE
WIND RIVER...ABSAROKA AND BIG HORN MTNS WILL EXPERIENCE CONSIDERABLE
BLOWING SNOW DURING THIS EVENT.

FOR THANKSGIVING DAY...THE EURO AND THE GFS APPEAR...AT LEAST FOR
NOW...TO BE MORE IN AGREEMENT THEN PAST RUNS WITH THE IDEA OF A
FLATTENING RIDGE FOR THURSDAY WITH THE NEXT SHORTWAVE WAVE THAT HAS
BEEN IN QUESTION FINALLY COMING INTO PLAY FRIDAY. HAVE KEPT HIGHER CHANCES
OF SNOW IN THE NORTHERN MTNS FOR THU TO TAKE INTO ACCOUNT THE
UNCERTAINTY OF WHAT THE NORTHERN STREAM ENERGY MAY HAVE IN STORE FOR
US. THEN INCREASED POPS IN NW WY FOR SNOW FRIDAY WITH THAT DELAYED
SHORTWAVE WAVE. HAVE SNOW INCREASING IN THE WEST SATURDAY GIVEN THE
TROUPHPA AND WEAK ISENTROPIC LIFT. THEN WITH THE WARM AIR
ADVECTION/ISENTROPIC LIFT...KEPT IDEA OF SPREADING SOME OF THE SNOW
TO AREAS EAST OF THE DIVIDE SUNDAY. IF ITS ANY CONSOLATION...BOTH
THE GFS AND THE EURO AGREE ON THE FACT THAT A COL REGION WILL SHOW
UP OFF THE PAC NW COAST WHICH WOULD AT LEAST...IF NOTHING ELSE...ADD
CREDIBILITY TO THE LONG TERM SOLNS OF BOTH MODELS.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES A FAST-MOVING
UPPER LEVEL DISTURBANCE WILL PUSH SE ACROSS WYOMING EARLY MONDAY
MORNING SPREADING AREAS OF LIGHT SNOW AND FRQT MTN OBSCURATIONS
ACROSS THE BIGHORN RANGE WITH LOCAL AREAS OF MVFR -SN MAINLY VCNTY
AND EAST OF A KCOD-KWRL-KCPR LINE THROUGH 15Z.  DRIER AIR WILL PUSH
NW-SE BEHIND THIS SYSTEM 15Z-18Z MONDAY.  GUSTY NW SFC WINDS WILL
CONTINUE THROUGH MID-AFTN...ESPECIALLY VCNTY KDUB-KRIW AND EAST OF
THE BIGHORN RANGE.  THERE WILL BE SOME DECREASE IN THE WIND 21Z
MON-03Z TUE AND THEN RIDGE TOP WEST WINDS WILL INCREASE TO 40-50KTS
ALONG THE EAST SLOPES OF THE DIVIDE WITH MOUNTAIN WAVE ACTIVITY
LIKELY ALONG WITH AREAS OF LLWS VCNTY KCOD-KDUB 3Z-12Z TUESDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
A FAST-MOVING UPPER LEVEL DISTURBANCE WILL DIVE SE ALONG THE DIVIDE
EARLY MONDAY MORNING WITH WIDESPREAD MVFR...AREAS OF IFR -SN BLSN
EXPECTED TO CONTINUE THROUGH 10Z...PUSHING INTO SW WY...VCNTY
KPNA-KBPI-KRKS 9Z-15Z.  DRIER AIR WILL PUSH INTO NW WYOMING AFTER
10Z BEHIND THIS SYSTEM...WITH MOST OF THE MVFR/IFR -SN EXITING SW WY
BY 15Z.  GUSTY NW SFC WINDS WILL FOLLOW THE SYSTEM THROUGH MONDAY
AFTN...ESPECIALLY ACROSS THE UPPER GREEN RIVER BASIN AND INTERSTATE
80 CORRIDOR.  A MOIST WESTERLY FLOW WILL BRING INCREASING SNOWFALL
VCNTY AND NORTH OF A KPNA-KEMM LINE 08Z-12Z TUESDAY WITH WIDESPREAD
MVFR -SN...AREAS OF IFR -SN EXPECTED BY 12Z ALONG WITH MTNS MOSTLY
OBSCD.

&&

.FIRE WEATHER...

NORTHWEST FLOW ALOFT WILL REMAIN OVER WESTERN AND CENTRAL WYOMING.
A FAST MOVING PACIFIC LOW PRESSURE TROUGH IN THE FLOW WILL SWEEP
THROUGH THE AREA TONIGHT AND MONDAY MORNING. THE NORTHERN AND
WESTERN MOUNTAINS WILL SEE SOME LIGHT SNOWFALL. SOME OF THE SNOW
WILL MAKE IT TO THE VALLEYS OF THE WEST. EAST OF THE DIVIDE LITTLE
IF ANY SNOWFALL IS EXPECTED BUT BRISK NORTHWEST WINDS WILL CONTINUE.
THE LOWER AIR MASS WILL BE WELL MIXED KEEPING OVERNIGHT LOWS UP
WITH SLIGHT COOLING ON MONDAY BEHIND THE TROUGH. THE SNOWFALL IN
THE WEST AND NORTH SHOULD TAPER OFF FROM LATE MORNING THROUGH
EARLY AFTERNOON.  RELATIVE HUMIDITY WILL BE ELEVATED WITH GENERALLY
LOW MIXING HEIGHTS. WINDIER AREAS MAY SEE FAIR SMOKE DISPERSAL IN THE
AFTERNOON EAST OF THE CONTINENTAL DIVIDE.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...HIGH WIND WATCH FROM MONDAY
EVENING THROUGH TUESDAY MORNING WYZ002-003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...LIPSON
AVIATION...AEM
FIRE WEATHER...C.BAKER











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