Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 250856
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
256 AM MDT MON APR 25 2016

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

A FEW SHOWERS LINGER OVER THE CENTRAL WYOMING THIS MORNING...AS THE
SYSTEM WHICH BROUGHT SIGNIFICANT RAIN AND SNOWFALL WORKS TO LOSE ITS
INFLUENCE OVER THE FORECAST AREA. BEHIND THIS SYSTEM WILL BE A VERY
BRIEF TRANSITORY RIDGE. THIS RIDGE WILL PERMIT ENOUGH CLEARING TO
RESULT IN PATCHY FOG FOR LOW LYING AREAS HAVING RECEIVED RECENT
PRECIPITATION. THIS FOG SHOULD GENERALLY LIFT BY THE MID MORNING
HOURS.

AS THE DAY PROGRESSES...THE NEXT AREA OF LOW PRESSURE WILL MOVE INTO
THE DESERT SOUTHWEST AS IT PROGRESSES EASTWARD. RAIN AND SNOW WILL
DEVELOP OVER AREAS WEST OF THE DIVIDE THIS AFTERNOON. INSTABILITY
HAS BEEN NOTED WITH ACTIVITY THIS AFTERNOON WITH ISOLATED
THUNDERSTORMS POSSIBLE...ESPECIALLY WEST OF THE DIVIDE. SMALL
HAIL...GUSTY WIND...AND PERIODS OF HEAVY RAIN WILL BE POSSIBLE WITH
ACTIVITY TODAY. AS THE AREA OF LOW PRESSURE PROGRESSES EASTWARD THIS
AFTERNOON AND EVENING...SHOWER ACTIVITY WILL MOVE EAST OF THE
DIVIDE. MODELS STILL SHOWING DECENT INSTABILITY THROUGH THE EARLY
EVENING HOURS...WITH A FEW THUNDERSTORMS POSSIBLE FOR AREAS EAST OF
THE DIVIDE THROUGH THE EVENING HOURS.

DURING THE EVENING HOURS TONIGHT...THE COLD POOL ASSOCIATED WITH
THIS SYSTEM WILL RESULT IN SNOWFALL OVER THE WIND RIVER MOUNTAINS
AND THE SOUTHERN HALF OF THE BIG HORN MOUNTAINS. HERE BEGINS THE
TIMEFRAME FOR THE NEXT POTENTIAL SIGNIFICANT WINTRY SYSTEM. PERIODS
OF MODERATE TO HEAVY SNOW WILL BE POSSIBLE...ESPECIALLY WITH THE
ONGOING CONVECTIVE COMPONENT. SNOWFALL WILL CONTINUE THROUGH THE
OVERNIGHT HOURS FOR THE MOUNTAIN LOCATIONS...WITH SIGNIFICANT
ACCUMULATIONS POSSIBLE. A WINTER STORM WATCH HAS BEEN ISSUED AS MOST
NATIONAL GUIDANCE CONTINUES TO SUPPORT THE NOTION OF THIS HEAVIER
SNOWFALL. MOST LOWER ELEVATIONS WILL CONTINUE WITH RAIN
TONIGHT...THOUGH SOME MIXING OF SNOW WILL OCCUR ESPECIALLY ACROSS
NATRONA COUNTY AND INTO SWEETWATER AND AREAS OF SOUTHWESTERN WYOMING.

BY TUESDAY MORNING...COLDER TEMPERATURES WILL MOVE OVER NATRONA
COUNTY WITH ACTIVITY TURNING TO MOSTLY SNOWFALL BY THE LATE MORNING
HOURS. THIS AREA REMAINS THE QUESTION MARK REGARDING THE POTENTIAL
FOR THE SIGNIFICANT WINTER SYSTEM. THOUGH SNOWFALL WILL BE
PRESENT...IMPACTS REMAIN IN QUESTION AS SURFACES WILL STILL BE
WARM...AND SNOWFALL DEPTH MAY BE DIMINISHED WITH THE INABILITY FOR
SNOWFALL TO ACCUMULATE EFFICIENTLY. FOR NOW...THIS AREA HAS BEEN
LEFT OUT OF THE WINTER STORM WATCH...THOUGH IT DOES NEED MONITORING.
ADDITIONAL AREAS NOT MEETING WINTER STORM CRITERIA MAY NEED
ALTERNATE WINTER WEATHER RELATED STATEMENTS. SINCE THESE AREAS ARE
NOT EXPECTED TO SEE SNOWFALL UNTIL TUESDAY...THEY WILL CONTINUE TO
BE EVALUATED BY FUTURE SHIFTS.

SNOWFALL FROM THIS SYSTEM WILL TAPER OFF TUESDAY NIGHT...THOUGH SOME
ACTIVITY WILL LINGER THROUGH WEDNESDAY. PERIODS OF SHOWERS WILL
REMAIN ACROSS THE AREA THROUGH WEDNESDAY NIGHT AS THE INFLUENCING
AREA OF LOW PRESSURE WOBBLES AROUND WYOMING/SOUTH DAKOTA/MONTANA.

.LONG TERM...THURSDAY THROUGH MONDAY

INCLEMENT WEATHER WITH BELOW AVERAGE TEMPERATURES CONTINUES THROUGH
THE EXTENDED...BUT NOT AS IMPACTFUL AS WHAT WILL OCCUR DURING THE
SHORT TERM. BY THURSDAY MORNING...GLOBAL MODELS SHOW YET ANOTHER
UPPER LEVEL LOW OVER THE SOUTHERN GREAT BASIN REGION. THIS FEATURE
IS EXPECTED TO PUSH INTO THE DESERT SOUTHWEST/ARIZONA ON THURSDAY.
AT THE SAME TIME...SOME SHEARED ENERGY FROM THE UPPER LOW THAT
IMPACTS THE AREA TUESDAY/EARLY WEDNESDAY...IS PROGGED TO RETROGRADE
WEST ACROSS MONTANA. FORCING LOOKS TO BE WEAK THURSDAY...BUT ENOUGH
MOISTURE AROUND FOR CONTINUATION OF SLIGHT VALLEY/CHANCE MTN POPS
FOR NOW. PRECIPITATION TYPE WILL BE MOUNTAIN SNOW AND MIX OF
RAIN/SNOW IN THE VALLEYS. ON FRIDAY...MODELS SHOW THE UPPER LOW
EJECTING NORTHEAST INTO EASTERN COLORADO...BUT THIS UPPER LOW IS
PROGGED TO BE WEAKER AND A BIT FARTHER SOUTH THAN THE UPPER LOWS
THAT IMPACTED THE AREA YESTERDAY...AND THE ONE ON TUESDAY.  THE BEST
SHOT AT PRECIPITATION WILL PROBABLY BE ACROSS THE FAR EAST/SOUTHEAST
WHERE THE INFLUENCE OF THE UPPER LOW WOULD BE THE GREATEST...AS WELL
AS A MOIST LOW LEVEL EASTERLY UPSLOPE FLOW. THE 00Z ECMWF KEEPS THE
UPPER LOW FARTHER SOUTH WITH A DRIER SOLUTION FRIDAY. MODELS THEN
SHOW ANOTHER UPPER LOW DIVING FROM THE PACIFIC NORTHWEST...SOUTHEAST
INTO NEVADA SATURDAY. AT THE SAME TIME...THE 00Z GFS TRIES TO
RETROGRADE SOME ENERGY FROM THE UPPER LOW ON FRIDAY BACK INTO THE
FORECAST AREA...WHILE THE ECMWF PUSHES ALL THE ENERGY ASSOCIATED
WITH THE UPPER LOW INTO THE MISSOURI VALLEY. THE AFOREMENTIONED
UPPER LOW IN NEVADA SATURDAY THEN PUSHES INTO ARIZONA SUNDAY AND
REMAINS ACROSS ARIZONA/FOUR CORNERS REGION THROUGH MONDAY. WILL KEEP
LOW END PRECIPITATION CHANCES SATURDAY THROUGH MONDAY WITH THIS
ACTIVE PATTERN.

&&

.AVIATION.../12Z 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 THE MORNING.

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

AREAS OF LOWER MVFR/IFR CIGS ARE EXPECTED TO REMAIN BANKED UP
AGAINST THE EAST SLOPES OF THE DIVIDE VCNTY KCOD-KLND....AND PATCHY
FOG MAY PARTIALLY OBSCURE TERRAIN ACROSS THE CENTRAL BASINS
ESPECIALLY VCNTY KRIW-KWRL...UNTIL 16Z.

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.

&&

.FIRE WEATHER...

THE SYSTEM WHICH RESULTED IN WIDESPREAD RAIN AND SNOW WILL CONTINUE
TO MOVE EASTWARD TODAY...WITH A BRIEF ROUND OF HIGH PRESSURE
ANTICIPATED THIS MORNING. CLEARING WILL RESULT IN AREAS OF PATCHY
FOG FOR THE LOW LYING AREAS. THE NEXT SYSTEM WILL THEN BEGIN TO MOVE
INTO WESTERN WYOMING THIS AFTERNOON...SPREADING SHOWERS AND
THUNDERSTORMS ACROSS THE AREA. SOME STORMS MAY CONTAIN GUSTY WIND
WITH SMALL HAIL AND PERIODS OF HEAVY RAIN. THIS ACTIVITY WILL MOVE
EAST OF THE DIVIDE LATER THIS AFTERNOON...WITH THUNDERSTORMS
POSSIBLE THROUGH THE EVENING HOURS. THEN THE NEXT WINTRY SYSTEM WILL
BEGIN TO IMPACT MUCH OF CENTRAL AND EASTERN WYOMING WITH ONGOING
SNOWFALL FOR THE MOUNTAINS AND RAIN AND RAIN MIXED WITH SNOW ACROSS
THE LOWER ELEVATIONS. MORE DETAILS CAN BE FOUND IN THE WINTER
WEATHER PRODUCTS...ESPECIALLY THE WINTER STORM WATCH WHICH HAS
BEEN ISSUED FOR THE WIND RIVER MOUNTAINS...BIG HORN
MOUNTAINS...CASPER MOUNTAIN...AND THE GREEN MOUNTAINS AND
RATTLESNAKE RANGE.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM THIS EVENING THROUGH LATE TUESDAY NIGHT
FOR WYZ022.

WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY EVENING FOR
WYZ008-009-015-019.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...BRANHAM



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