Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 020513
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1113 PM MDT WED OCT 1 2014

.SHORT TERM...TONIGHT AND THURSDAY (ISSUED AT 215 PM MDT)

UPPER CIRCULATION APPEARS TO BE MOVING RIGHT THROUGH CENTRAL WYO
ATTM WITH SEVERAL WEAK CIRCULATIONS BETWEEN THE SRN ABSAROKAS AND
SERN FREMONT COUNTY. CONSIDERABLE SHOWER ACTIVITY AROUND AND AHEAD
OF THE TROUGH WITH SNOW DOWN AS LOW AS 6500-7K. TEMPS HOVERING IN
THE UPPER 30S TO MID 40S WHERE THE THICK CLOUDS AND SHOWERS CONTINUE
IN THE LOWER ELEVATIONS WITH 30S IN THE NEARBY MOUNTAINS. VORT ON
THE SOUTH END OF THE TROUGH IS IGNITING A FEW TSTMS BUT SOUTH OF OUR
AREA ATTM. SHOWERS WILL CONTINUE AROUND THE CIRCULATION AND AHEAD OF
THE TROUGH FOR A FEW MORE HOURS INTO THE EARLY EVENING BEFORE ALL
BUT EXITING THE AREA. SOME LOW CLOUDS AND PATCHY FOG WILL BE
POSSIBLE OVERNIGHT AHEAD OF OUR NEXT SYSTEM. THIS SYSTEM OVER FAR
NRN B.C. AND ALBERTA HAS -30C AIR AT H5 AND UP TO -18C AIR AT H7 SO
IT WILL BE COLDER. MODELS ARE SHOWING QUITE THE FRONTAL PASSAGE UP
NORTH WITH NAM12 SHOWING ALMOST 8MB 3HR PRESSURE RISES LATE THURSDAY
AFTERNOON. BUMPED UP THE WINDS ACROSS THE NORTH...ESPECIALLY NRN
JOHNSON COUNTY WHERE 50 MPH+ GUSTS QUITE POSSIBLE. IN
ADDITION...SHOWERS WILL BECOME LIKELY IN THE FAR NRN
MOUNTAINS...ESPECIALLY THE BIGHORNS BY LATE AFTERNOON WITH A GOOD
CHANCE OF SHOWERS ACROSS THE LOWER ELEVATIONS OF OUR FAR NRN ZONES.
TEMPERATURES DROP QUICKLY AND IF THE PRECIP LINGERS LONG ENOUGH
COULD SEE IT BEGIN TO CHANGE TO SNOW IN THE LOWER ELEVATIONS BY THE
END OF THIS PERIOD (6 PM THURSDAY). AHEAD OF THIS SYSTEM...WE GET
SOME MOUNTAIN WAVE ACTION IN THE LEE OF THE ABSAROKAS AND BIGHORNS.
SIGNATURE IS NOT IMPRESSIVE BUT ENOUGH TO INCREASE THE WIND ALONG
THE EAST SLOPE...ESPECIALLY THE FAVORED CODY FOOTHILL/EAST SLOPE OF
THE ABSAROKAS. GENERALLY WENT 25G40MPH IN THE FAVORED AREAS. FROUDE
CALCULATION IS RATHER LOW AS MOUNTAIN TOP FLOW IS NOT STRONG ENOUGH
TO CAUSE WAVE BREAKING OVER THE BIGGER MOUNTAINS. SOME MARGINALLY
STABLE AIR IS POSSIBLE BUT DOESN`T LOOK OPTIMAL. SO WINDY BUT NOT
EXPECTING HIGH WINDS.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

THURSDAY NIGHT CANADIAN COLD FRONT WILL CONTINUE PASSING SOUTH
IN THE EVENING WITH AREAS OF RAIN...AND MOUNTAIN SNOW SHOWERS IN THE
NORTH AND EAST...ESPECIALLY IN THE NORTHERN MOUNTAINS.  SOME SHOWERS
WILL LINGER ALONG THE FRONT OVER NATRONA COUNTY WHILE CLEARING
OCCURS TO THE NORTH AND WEST.  TEMPERATURES CONTINUE TO COOL AND
HAVE GONE COLDER THAN PREVIOUS FORECAST WITH MOST AREAS BELOW
FREEZING AND SOME TEEN POSSIBLE IN THE NORTHWEST MOUNTAINS.

FRIDAY AND FRIDAY NIGHT  FLOW ALOFT REMAINS NORTH NORTHWEST WITH COLD
AIR ADVECTION AND HAVE CONTINUED COOLER TREND WITH HIGHS ON FRIDAY
AND LOWS LATE FRIDAY NIGHT.  UPPER LEVEL HIGH PRESSURE RIDGE BUILDS
TO THE WEST STARTING A LONG DRY SPELL.

SATURDAY AND SATURDAY NIGHT  TEMPERATURES WILL BEGIN TO WARM AS THE
WESTERN HIGH PRESSURE RIDGE ALOFT BUILDS INTO THE WEST WITH MOSTLY
CLEAR CONDITIONS.

SUNDAY AND SUNDAY NIGHT  DRY AND WARMER CONDITIONS CONTINUE AS HIGH
PRESSURE RIDGE CONTINUES TO DOMINATE THE WEATHER ACROSS THE REGION.

MONDAY AND MONDAY NIGHT LITTLE ADDITIONAL WARMING IS EXPECTED WITH
DRY CONDITIONS CONTINUING.  SOME SHORT WAVE LOW PRESSURE TROUGHS
MOVING ACROSS SOUTHWEST CANADA WILL KEEP THE WESTERN HIGH PRESSURE
RIDGE FROM BUILDING.

TUESDAY AND TUESDAY NIGHT  FLOW ALOFT BECOMES MORE WESTERLY RETAINING
SOME NORTHERLY COMPONENT AS  SHORT WAVE LOW PRESSURE TROUGHS CONTINUE
MOVING ACROSS SOUTHWEST CANADA AND NORTHERN MONTANA SUPPRESSING THE
RIDGE.  NORTH MAY SEE SOME INCREASED CLOUD COVER BUT EXPECT THE COLD
FRONT ASSOCIATED WITH THE SERIES OF SHORT WAVE LOW PRESSURE TROUGHS
TO REMAIN NORTH AND EAST OF THE FORECAST AREA.

WEDNESDAY  FLOW BECOMES ZONAL AS RIDGE CONTINUES TO FLATTEN.
EXTENDED MODELS SHOW THE CANADIAN/MONTANA COLD FRONT REMAINS JUST TO
THE NORTH KEEPING WYOMING DRY.  WILL SEE INCREASING WEST SURFACE
WINDS AND CONTINUED DRYING.  WILL HAVE TO KEEP AN EYE ON THE COLD
FRONT TO THE NORTH OVER TIME AS A MOVEMENT FARTHER TO THE SOUTH WILL
BRING CLOUDS...SHOWERS COLDER TEMPERATURES TO THE NORTH AND POSSIBLY
THE EAST.

.AVIATION.../06Z ISSUANCE/

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

PATCHY LOW LYING FOG IS POSSIBLE IN THE CENTRAL BASINS. A NEW COLD
FRONT WILL ARRIVE ACROSS THE NORTH THURSDAY AFTERNOON WITH AN
INCREASING CHANCE OF SHOWERS AND LOWERING CIGS. VFR CONDITIONS WILL
PREVAIL THROUGH IN MOST AREAS THROUGH THE AFTERNOON EXCEPT FROM NEAR
A KCOD TO KBYG LINE WHERE MVFR/IFR CIGS WILL DEVELOP BEFORE 00Z
FRIDAY AND THEN MOVE SOUTH TO A KLND TO KCPR LINE BY 03Z. EXPECT
RAIN TO CHANGE TO SNOW BEHIND THE COLD FRONT WITH MOUNTAIN
OBSCURATION. MVFR TO IFR VISIBILITY WILL OCCUR DUE TO SNOW.

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

PATCHY LOW FOG AND LOW CLOUDS MAY REDEVELOP LATER TONIGHT WITH MTN
OBSCURATION AND BRIEF VSBYS UNDER 3 MILES. OTHERWISE...MOST AREAS
WILL BE VFR OVERNIGHT BUT WITH SOME MTN OBSCURATION IN LOW CLOUDS.
ONCE ANY LOW CLOUDS OR FOG BURNS OFF...ALL AREAS SHOULD SEE VFR
CONDITIONS ON THURSDAY WITH THE POSSIBLE EXCEPTION OF YELLOWSTONE
NATIONAL PARK WHERE SOME LATE DAY SHOWERS DEVELOP AND CONTINUE
THROUGH ABOUT 04Z.

.FIRE WEATHER...

CONSIDERABLE SHOWERS AND PERHAPS AN ISOLATED THUNDERSTORM OR TWO IN
CENTRAL WYOMING INTO THE EARLY EVENING BEFORE MOVING SOUTHEAST AND
DECREASING. MORE WIDELY SCATTERED TO SCATTERED SHOWERS ELSEWHERE
UNTIL AROUND SUNSET. GUSTY WEST TO NORTHWEST WINDS ACROSS THE WEST
AND SOUTH WILL DECREASE THIS EVENING BUT PICK BACK UP AGAIN
THURSDAY. A NEW WEATHER SYSTEM WILL PUSH A STRONG COLD FRONT INTO
THE FAR NORTHERN ZONES DURING THE AFTERNOON WITH STRONG NORTH WIND
GUSTS OF 40 TO 50 MPH AND AN INCREASING CHANCE OF SHOWERS. SOUTH OF
THE FRONT IN CENTRAL AND SOUTHERN WYOMING...IT WILL BE DRY BUT WITH
SOME GUSTY WEST TO NORTHWEST WIND. THE COLD FRONT WILL PUSH SOUTH
INTO CENTRAL WYOMING BY EARLY EVENING.

&&

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

&&

$$

SHORT TERM...SKRBAC
LONG TERM...C.BAKER
AVIATION...AR
FIRE WEATHER...SKRBAC









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