Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 250603 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1203 AM MDT MON APR 25 2016

.UPDATE...ADDED 06Z AVIATION DISCUSSION

&&

.AVIATION.../06Z ISSUANCE/

WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI AIRPORTS

PATCHY FOG OR LOWER IFR/LIFR CIGS WILL LIKELY PARTIALLY OBSCURE
TERRAIN IN THE WESTERN VALLEYS...MAINLY VCNTY KBPI-KJAC...THROUGH
16Z.  SCT-NMRS SHSN WILL CONTINUE TO FQTLY OBSCURE MTNS NORTH OF A
KJAC-KDUB LINE THROUGH 12Z.

AN UPPER LEVEL LOW PRESSURE SYSTEM WILL PUSH INTO THE GREAT BASIN
TODAY WITH RAIN AND SNOW SHOWERS BECOMING MORE NUMEROUS OVER THE
WESTERN MTNS THROUGH THE MORNING WITH SNOW LEVELS 8KFT-9KFT BY
AFTERNOON.  INCREASING INSTABILITY ACROSS SW WYOMING...VCNTY AND
SOUTH OF A KAFO-KPNA LINE...WILL RESULT IN ISOLD AFTN TS...WITH
GUSTY ERRATIC WIND AND SMALL HAIL THE MAIN HAZARDS.  INCREASING NE
FLOW MONDAY NIGHT WILL BRING DOWNSLOPE FLOW AND SOME IMPROVEMENT
ACROSS NW WYOMING WHILE MVFR/IFR SHRASN BECOME MORE NUMEROUS ACROSS
THE SW QUARTER OF WYOMING.


EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KWRL/KLND AIRPORTS

SCT MVFR SHRA ACROSS CENTRAL WYOMING...MAINLY IN THE VCNTY OF KLND-
KRIW-KWRL...WILL DECREASE AFTER 09Z.  AREAS OF LOWER MVFR/IFR CIGS
ARE EXPECTED TO REMAIN BANKED UP AGAINST THE EAST SLOPES OF THE
DIVIDE...VCNTY KCOD-KLND...THROUGH 12Z.  OTHERWISE...PATCHY FOG MAY
PARTIALLY OBSCURE TERRAIN 9Z-16Z ACROSS THE CENTRAL BASINS
ESPECIALLY VCNTY KRIW-KWRL.

AN UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE INTO THE GREAT BASIN
TODAY WITH INCREASING INSTABILITY ACROSS THE SOUTH HALF OF WYOMING.
ISOLD TS WILL LIKELY FORM VCNTY AND SOUTH OF A KCPR-KRIW-KPNA LINE
IN THE AFTN WITH THE MAIN HAZARDS OF STRONG ERRATIC WIND GUSTS AND
SMALL HAIL.  MVFR/IFR SHRA WILL BECOME MORE WIDESPREAD MONDAY
EVENING WITH THE HEAVIEST BAND OF PRECIPITATION AND MORE WIDESPREAD
IFR CONDITIONS EXPECTED VCNTY KLND-KRIW-KCPR LINE.  SNOW LEVELS WILL
BE AROUND 8KFT WITH MOUNTAINS BECOMING MOSTLY OBSCURED MONDAY
EVENING AND OVERNIGHT.

&&

.PREV DISCUSSION... /ISSUED 920 PM MDT SUN APR 24 2016/

UPDATE...CANCELLED REMAINING WINTER WEATHER ADVISORIES FOR THE
BIGHORN MOUNTAINS AND CASPER MOUNTAIN...WHERE SNOW SHOWERS HAVE
DECREASED OVER THE LAST FEW HOURS.

PREV DISCUSSION... /ISSUED 316 PM MDT SUN APR 24 2016/

SHORT TERM...TONIGHT THROUGH MONDAY

COLD NORTHWEST FLOW WITH RESIDUAL MOISTURE...ESPECIALLY EAST OF
THE CONTINENTAL DIVIDE...WILL BE OVER THE AREA TONIGHT...AS THE
UPPER LEVEL LOW DRIFTS EAST ACROSS SOUTHERN SOUTH DAKOTA AND
NORTHERN NEBRASKA. WIDESPREAD MOUNTAIN SNOW SHOWERS WILL LINGER
OVER THE BIGHORN MOUNTAINS AND CASPER MOUNTAIN WITH MORE SCATTERED
SHOWERS OVER THE WESTERN MOUNTAINS.  AS BRIEF HIGH PRESSURE MOVES
IN WITH PARTIAL CLEARING LATE TONIGHT...LOW STRATUS AND AREAS OF
FOG IS EXPECTED TO DEVELOP IN THE VALLEYS AND BASINS ESPECIALLY
ALONG THE RIVERS AND LAKES. BY MID DAY...AS ANOTHER LOW PRESSURE
CENTER DEEPENS IN THE GREAT BASIN...THE FLOW ALOFT WILL SWITCH TO
THE SOUTHWEST WITH INCREASING MID LEVEL MOISTURE AND INSTABILITY
MOVING IN OVER THE WEST. SHOWERS WILL INCREASE THROUGH THE
AFTERNOON ACROSS THE WESTERN MOUNTAINS AND ALONG AND EAST OF THE
CONTINENTAL DIVIDE. EAST OF THE MOUNTAINS SHOWERS WILL BE MORE
WIDELY SCATTERED. EMBEDDED THUNDERSTORMS WITH SMALL HAIL AND
STRONG WIND GUSTS WILL ALSO INCREASE WITH SOME MAKING IT OVER THE
WIND RIVER AND BIGHORN BASINS. TEMPERATURES WILL BE GENERALLY
WARMER

LONG TERM...MONDAY NIGHT THROUGH SUNDAY

THE NEXT UPSTREAM CIRCULATION OVER THE GULF OF ALASKA HAS EJECTED A
DOWNSTREAM TROUGH NOW OUT AT 130W WHICH WILL CLOSE OFF OVER THE
GREAT BASIN AND SHOULD BE OVER UTAH BY 00Z TUE. BY 00Z TUESDAY WE
WILL HAVE COME FULL CIRCLE FROM LAST SATURDAY AS THIS NEXT
CIRCULATION ONCE AGAIN DRAWS UP A SOUTHERLY DIFLUENT FLOW AHEAD OF
IT AS IT BISECTS A FIELD OF INSTABILITY FOR A CONTINUATION OF THE
THREAT OF NUMEROUS SHOWERS AND THUNDERSTORMS MONDAY EVENING.
THEN THE LOW WILL TRACK EAST ACROSS THE COLORADO/UTAH BORDER MONDAY
NIGHT WITH THE MID LEVEL CIRCULATION TRACKING EAST ACROSS SOUTHERN
WY. LEFT FRONT QUAD DYNAMICS AND Q VECTOR FORCING WILL KEEP PRECIP
GOING ALL NIGHT STATEWIDE MONDAY NIGHT WITH THE PRECIP STRATIFORMING
OUT AFTER MIDNIGHT. A WEAK SFC LOW WILL BE OVHD AS WELL. THE PRECIP
WILL BE ALL SNOW IN THE MOUNTAINS AFTER MIDNIGHT MONDAY NIGHT. THEN
ON TUE SNOW LEVELS WILL DROP TO AROUND 5500 FEET AS COLDER AIR WRAPS
AROUND THE BACKSIDE OF THE LOW. BY TUESDAY THE CONTINUED DIFLUENT
FLOW WILL BACK TO THE EAST ACROSS THE CWA WITH EVER DEEPENING
UPSLOPE FLOW EAST OF THE DIVIDE. ALSO...WE WILL SEE WRAP AROUND
ISENTROPIC LIFT IN THE EASTERN ZONES. BY 00Z WEDNESDAY THE H5 LOW
WILL BE OVER SOUTHEAST WY WITH CONTINUED DEEP UPSLOPE AS WELL AS
CONTINUED WRAP AROUND ISENTROPIC LIFT IN THE EAST. SNOW LEVELS
WILL DROP TO THE VALLEY AND BASIN BOTTOMS TUE NT. FOR NOW HAVE
SNOW AMOUNTS JUST OVER WARNING AMNTS ON THE BIG HORN AND EAST
SLOPE OF THE WND RVR MTNS AS WELL AS OVER CPR MTN FOR THE PERIOD
MONDAY NIGHT THROUGH TUE NT. RATHER THAN ISSUE A WINTER STORM
WATCH FOR THESE ZONES NOW ...WILL JUST ISSUE AN SPS FOR THE EAST
SLOPE OF THE WIND RVRS FOR NOW. WE ALREADY HAVE ONGOING HILITES
FOR THE BIG HORN MTNS AND CASPER MTN...SO LATER SHIFTS CAN EITHER
ISSUE HILITES OR AN SPS FOR THE BIG HORNS AND CASPER MTN FOR THE
NEXT SNOW EVENT. SNOW ADVISORY AMNTS ARE IN PLACE FOR THE
SALT/WYOMING RANGE AS WELL AS FOR THE ABSAROKA MTNS FOR MON NT
THROUGH TUE NT. FOR THE REST OF THE MTNS INCLUDING THE GREEN
MTNS...2 TO 5 INCHES WILL BE COMMON MON NT THROUGH TUE NT. LATER
SHIFTS CAN DECIDE WHETHER OF NOT OTHER HILITES ARE JUSTIFIED FOR
THESE OR OTHER AREAS. 1 TO 2 INCHES OF SNOW WILL BE COMMON ACROSS
THE WIND RIVER BASIN AS WELL AS THE WESTERN VALLEYS AND BASINS...1
TO 3 INCHES IN THE POWDER RIVER BASIN AND CASPER ALONG WITH LESS
THAN AN INCH IN THE BIG HORN BASIN. BY 12Z WEDNESDAY THE MID LEVEL
CIRCULATION WILL BE IN THE CENTRAL PLAINS UNDER A WEAKLY UNSTABLE
NW FLOW WHICH IS A GOOD FLOW FOR CONVECTIVE RAIN/SNOW BANDS SO
INCREASED POPS SOMEWHAT OVER EASTERN FREMONT AND NATRONA COUNTIES
WITH A CONTINUED GOOD CHANCE OF RAIN AND SNOW SHOWERS OVER THE
HIGH COUNTRY. PRECIP WILL SLOWLY DECREASE DURING WED AFTERNOON
UNDER A COL REGION. ON WED NT WE WILL HAVE AN ALMOST TRANSPARENT
BREAK IN THE ACTION BEFORE THE TENTACLES OF THE TROUGH EXTENDING
NORTHEAST FROM THE NEXT EJECTED LOW OVER VEGAS REACHES WY ON 12Z
THU. RAIN AND SNOW SHOWERS WILL CONTINUE OVER THE NORTH HALF WED
NT BEFORE RAIN AND MTN SNOW SHOWERS INCREASE AGAIN THU WITH
SOUTHERLY DIFLUENT FLOW AHEAD OF THIS NEXT LOW ONCE AGAIN
ENHANCING LIFT. THIS LOW WILL ARRIVE AS A BAGGY TROUGH AXIS BY
FRIDAY. THEN ANOTHER WEAK LOW WILL DUMBBELL AROUND THE EXITING
TROUGH PROLONGING THE THREAT OF SHOWERS THROUGH NEXT WEEKEND. WITH
THIS PARTICULAR WX FEATURE BEING LESS ORGANIZED ALONG WITH
INCREASING INSTABILITY DURING THE AFTERNOON HOURS WILL JUST WORD
THE REST OF THE FCST FOR NEXT FRIDAY THROUGH SUNDAY AS SHOWERY BUT
MAINLY OCCURRING IN THE AFTERNOONS. TEMPERATURES WILL WARM DURING
THE WEEK BUT WILL REMAIN SEASONABLY COOL.

AVIATION.../00Z ISSUANCE/

WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI AIRPORTS

COLD NORTHWEST FLOW WITH LIMITED MOISTURE WILL BE OVER THE WEST
TONIGHT.  SOME MOUNTAIN SNOW SHOWERS WILL LINGER OVER THE HIGHER
TERRAIN. AS BRIEF HIGH PRESSURE MOVES IN WITH PARTIAL CLEARING...
LOW STRATUS AND AREAS OF FOG IS EXPECTED TO DEVELOP IN THE VALLEYS
ESPECIALLY ALONG THE RIVERS AND LAKES WITH AREAS OF IFR CEILINGS
AND VISIBILITY REDUCED IN FOG.  THE AIRPORTS MOST LIKELY TO
EXPERIENCE MVFR TO IFR CONDITIONS FROM 09Z - 15Z WILL BE KJAC...
KAFO...KEMM...KBPI AND KPNA. BY MID DAY...AS ANOTHER LOW PRESSURE
CENTER DEEPENS IN THE GREAT BASIN...THE FLOW ALOFT WILL SWITCH TO
THE SOUTHWEST WITH INCREASING MID LEVEL MOISTURE AND INSTABILITY
MOVING IN OVER THE WEST. SHOWERS WILL INCREASE TROUGH 18Z - 00Z
TIMEFRAME WITH MOUNTAIN OBSCURATIONS BECOMING FREQUENT. EMBEDDED
THUNDERSTORMS WITH SMALL HAIL AND STRONG WIND GUSTS WILL ALSO
INCREASE WITH A THREAT OF MVFR CONDITIONS AT ALL AIRPORTS.

EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KWRL/KLND AIRPORTS

COLD NORTHWEST FLOW WITH RESIDUAL MOISTURE WILL BE OVER THE AREA
EAST OF THE CONTINENTAL DIVIDE TONIGHT...AS THE UPPER LEVEL LOW
DRIFTS EAST ACROSS SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA.
WIDESPREAD MOUNTAIN SNOW SHOWERS WILL LINGER OVER THE BIGHORN
MOUNTAINS AND CASPER MOUNTAIN OBSCURING THE HIGHER TERRAIN. AS
BRIEF HIGH PRESSURE MOVES IN WITH PARTIAL CLEARING LATE TONIGHT...
LOW STRATUS AND AREAS OF FOG IS EXPECTED TO DEVELOP IN THE VALLEYS
AND BASINS ESPECIALLY ALONG THE RIVERS AND LAKES WITH AREAS OF
IFR CEILINGS AND VISIBILITY REDUCED IN FOG. THE AIRPORTS MOST
LIKELY TO EXPERIENCE MVFR TO IFR CONDITIONS FROM 09Z - 15Z WILL BE
KLND...KRIW...KWRL AND KGEY. BY MID DAY...AS ANOTHER LOW PRESSURE
CENTER DEEPENS IN THE GREAT BASIN...THE FLOW ALOFT WILL SWITCH TO
THE SOUTHWEST WITH INCREASING MID LEVEL MOISTURE AND INSTABILITY
MOVING IN OVER THE WEST. SHOWERS WILL INCREASE TROUGH 18Z - 00Z
TIMEFRAME ALONG AND EAST OF THE CONTINENTAL DIVIDE WITH SOME
MOUNTAIN OBSCURATIONS BECOMING MORE FREQUENT. EAST OF THE
MOUNTAINS SHOWERS WILL BE MORE WIDELY SCATTERED. EMBEDDED
THUNDERSTORMS WITH SMALL HAIL AND STRONG WIND GUSTS WILL ALSO
INCREASE WITH A THREAT OF MVFR CONDITIONS ACROSS THE WIND RIVER
AND BIGHORN BASINS FROM 12Z - 00Z.

FIRE WEATHER...

COLD NORTHWEST FLOW WITH RESIDUAL MOISTURE...ESPECIALLY EAST OF
THE CONTINENTAL DIVIDE...WILL BE OVER THE AREA TONIGHT...AS THE
UPPER LEVEL LOW DRIFTS EAST ACROSS SOUTHERN SOUTH DAKOTA AND
NORTHERN NEBRASKA. WIDESPREAD MOUNTAIN SNOW SHOWERS WILL LINGER
OVER THE BIGHORN MOUNTAINS AND CASPER MOUNTAIN WITH MORE SCATTERED
SHOWERS OVER THE WESTERN MOUNTAINS.  AS BRIEF HIGH PRESSURE MOVES
IN WITH PARTIAL CLEARING LATE TONIGHT...LOW STRATUS AND AREAS OF
FOG IS EXPECTED TO DEVELOP IN THE VALLEYS AND BASINS ESPECIALLY
ALONG THE RIVERS AND LAKES. BY MID DAY...AS ANOTHER LOW PRESSURE
CENTER DEEPENS IN THE GREAT BASIN...THE FLOW ALOFT WILL SWITCH TO
THE SOUTHWEST WITH INCREASING MID LEVEL MOISTURE AND INSTABILITY
MOVING IN OVER THE WEST. SHOWERS WILL INCREASE TROUGH THE
AFTERNOON ACROSS THE WESTERN MOUNTAINS AND ALONG AND EAST OF THE
CONTINENTAL DIVIDE. EAST OF THE MOUNTAINS SHOWERS WILL BE MORE
WIDELY SCATTERED. EMBEDDED THUNDERSTORMS WITH SMALL HAIL AND
STRONG WIND GUSTS WILL ALSO INCREASE WITH SOME MAKING IT OVER THE
WIND RIVER AND BIGHORN BASINS. TEMPERATURES WILL BE GENERALLY
WARMER WITH ELEVATED RELATIVE HUMIDITY. MIXING HEIGHTS WILL BE
RATHER LOW WITH FAIR TO LOW END GOOD SMOKE DISPERSAL IN THE
AFTERNOON.

&&

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

&&

$$

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



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