Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 240600
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1200 AM MDT SUN APR 24 2016

.UPDATE...ADDED 06Z AVIATION DISCUSSION

&&

.AVIATION.../06Z ISSUANCE/

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

AN UPPER LOW PRESSURE SYSTEM WILL CONTINUE TO SLOWLY DRIFT EAST
ACROSS WYOMING INTO THE CENTRAL PLAINS TONIGHT AND SUNDAY. A MOIST
NW FLOW BEHIND THIS SYSTEM WILL CONTINUE TO BRING NMRS IFR/MVFR
SHRA/SHSN ACROSS THE AREA WITH SNOW LEVELS NEAR 7KFT THROUGH 14Z.
DRIER AIR AND IMPROVING CONDITIONS WILL PUSH INTO SW WYOMING WITH
IMPROVING CONDITIONS BUT CONTINUED GUSTY WEST WIND 20-30KT ACROSS
THE INTERSTATE 80 CORRIDOR. NMRS MTN SHSN WILL REMAIN VCNTY AND
NORTH OF A KAFO-KPNA LINE WITH MTNS MOSTLY OBSCURED ABOVE 8KFT.
THIS ACTIVITY SHOULD GRADUALLY LIFT NWD SUNDAY NIGHT. SOME
CLEARING MAY RESULT IN PATCHY FOG PARTIALLY OBSCURING TERRAIN IN
THE WESTERN VALLEYS SUNDAY NIGHT.

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

AN UPPER LOW PRESSURE SYSTEM WILL CONTINUE TO DRIFT SLOWLY EAST
ACROSS SOUTHERN WYOMING TONIGHT AND OUT INTO THE PLAINS ON SUNDAY.
NMRS VALLEY RAIN AND MTN SNOW SHOWERS WILL OCCUR VCNTY AND NORTH OF
A KCPR-KLND LINE TONIGHT WITH THIS ACTIVITY TAKING A MORE N-S
ORIENTATION ALONG AND EAST OF A KPOY-KRIW LINE SUNDAY MORNING WITH
THE MOST WIDESPREAD IFR CONDITIONS IN MODERATE RA FROM VCNTY KBYG-
KCPR THROUGH THE DAY.  SNOW LEVELS WILL BE NEAR 8KFT WITH MTNS
MOSTLY OBSCURED...ESPECIALLY THE BIGHORN RANGE AND CASPER MOUNTAIN
DURING THE DAY SUNDAY.  GRADUAL IMPROVEMENT IS EXPECTED SUNDAY
EVENING WITH SOME LINGERING IFR/MVFR SHRA MAINLY VCNTY AND
NORTH OF A VCNTY KDUB-MIDWEST LINE.

&&

.PREV DISCUSSION... /ISSUED 237 PM MDT SAT APR 23 2016/

SHORT TERM...TONIGHT THROUGH SUNDAY

AN UPPER LEVEL LOW PRESSURE CENTER OVER LOGAN UTAH WILL EJECT
EAST NORTHEAST ACROSS SOUTHERN WYOMING THROUGH SUNDAY.  THE
LOW WILL CONTINUE TO BRING MOISTURE AND INSTABILITY WITH RATHER
STRONG UPPER LEVEL DIVERGENCE SUPPORTING DEEP CONVECTION.
WIDESPREAD SHOWERS RAIN IN THE LOWER ELEVATIONS WITH SNOW STARTING
OUT AT 9000 FEET LOWERING TO AROUND 7200 FEET BY MIDNIGHT.
THIS EVENING EMBEDDED THUNDERSTORMS WILL PRODUCE SMALL HAIL TO
HEAVY SNOW IN THE MOUNTAINS. THE HEAVIEST SNOW WILL BE OVER THE
WESTERN MOUNTAINS THIS EVENING SPREADING INTO THE NORTHERN
MOUNTAINS BY MIDNIGHT...THEN DECREASING IN THE WEST AND CONTINUING
CENTRAL AND NORTH THROUGH SUNDAY. MOST AREAS WILL RECEIVE WETTING
PRECIPITATION WITH THE SOUTH THE LEAST LIKELY AREA DEPENDING ON
THE ACTUAL TRACK OF THE UPPER LOW. TEMPERATURES WILL BE MUCH
COLDER. MOST MOUNTAIN AREAS WILL SEE 4 TO 8 INCHES OF SNOW WITH
AREAS OVER A FOOT IN THE TETONS AND BIGHORN MOUNTAINS. MOST
MOUNTAIN AREAS UNDER WINTER WEATHER ADVISORIES. PLEASE REFER TO
THE WINTER WEATHER ADVISORY FOR DETAILS AND TIMING. IMPROVING
CONDITIONS WILL OCCUR IN THE FAR WEST IN THE AFTERNOON WHILE
CONDITIONS DETERIORATE IN THE NORTH AND EAST.

LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

BY SUNDAY NIGHT...THE WELL DEFINED CLOSED LOW WILL BE OVER SOUTH
DAKOTA AND THE BIG HORN MTNS WILL STILL BE ON THE RECEIVING END OF
THE WRAP AROUND MSTR. WILL KEEP THE WINTER WEATHER ADVISORY GOING
FOR THE BIG HORN MTNS THROUGH 06Z MONDAY. LIGHT SNOW WILL BE ENDING
OVER THE REST OF THE MTNS. THEN ON MONDAY WE WILL EXPERIENCE A VERY
SHORT RESPITE IN THE ACTIVE WEATHER AS A SHORT LIVED RIDGE AXIS
POKES INTO THE CWA BRIEFLY EARLY MONDAY MORNING BEFORE THE NEXT
CLOSED LOW...NOW SPINNING OUT AT 55N/148W...RAPIDLY APPROACHES THE
AREA AS A PIECE OF THIS LOW CLOSES OFF AHEAD AND TO THE SOUTHEAST OF
THE PARENT LOW AND APPROACHES WYOMING IN FRAGMENTS UNDERNEATH A
BAGGY TROUGH. MONDAY AFTERNOON LOOKS RATHER UNSTABLE WITH WIDESPREAD
LIFTED INDICES OF -3 COMBINED WITH A STRONG SOUTHERLY DIFLUENT FLOW
ONCE AGAIN AHEAD OF THIS NEXT SYSTEM. HIGHS MONDAY WILL LIKELY BE IN
THE 50S EAST OF THE DVD AT THE LOWER ELEVATIONS AND IN THE 40S WEST.
THIS WILL RESULT IN A LIKELIHOOD OF SHOWERS AND THUNDERSTORMS...SOME
WITH GUSTY WINDS AND SMALL HAIL. THEN AS THE COLDER AIR FILTERS INTO
TO THE AREA UNDERNEATH OF THE LOW AND AROUND THE BACKSIDE OF
IT...RAIN WILL TURN TO SNOW ONCE AGAIN MONDAY NIGHT IN THE MTNS. THE
HEAVIEST SNOW ACCUMULATIONS SHOULD OCCUR OVER THE EAST SLOPE OF THE
WIND RIVER MTNS AND BIG HORN MTNS UNDERNEATH THE PATH OF THE UPPER
LOW AND MID LEVEL CIRCULATION AND FAVORABLE FLOW WHERE WARNING AMNTS
OF SNOWFALL HAVE THE POTENTIAL TO FALL MONDAY NIGHT THROUGH TUESDAY
NIGHT. ADVISORY AMNTS COULD OCCUR OVER THE REST OF THE MTNS DURING
THIS TIME FRAME. SOME WET SNOW COULD ALSO FALL AT THE LOWER
ELEVATIONS EAST AND WEST OF THE DVD WITH ONLY BRIEF LIGHT
ACCUMULATIONS ON GRASSY AREAS LATE TUESDAY NIGHT OR EARLY WEDNESDAY
MORNING.THIS WEATHER EVENT WILL HAVE TO BE WATCHED OVER THE NEXT
COUPLE OF DAYS. THE MODELS HAVE BEEN FAIRLY CONSISTENT WITH THIS
SCENARIO FOR THE PAST 3 DAYS. ON WEDNESDAY...THE MID AND UPPER
CIRCULATION WILL HAVE MOVED EAST TO NEBRASKA WITH OUR FLOW OVHD FROM
THE NORTHWEST. THIS COMBINED WITH A SLIGHTLY UNSTABLE AIRMASS COULD
LEAD TO BANDS OF RAIN SHOWERS COMING OFF THE OWL CREEK MTNS ACROSS
EASTERN FREMONT AND NATRONA COUNTIES AS WELL AS OVER THE REST OF THE
MTNS. THEN A FEW SHOWERS ALONG WITH SEASONABLY COOL WX CAN BE
EXPECTED THU AS WE SIT UNDERNEATH A COL REGION BETWEEN STORM
SYSTEMS. THEN THE NEXT CLOSED LOW APPROACHED FROM THE SOUTHWEST
CONTINUING THE PATTERN OF WINDY DIFLUENT WARMING SOUTHERLY FLOW
AHEAD OF THE NEXT SYSTEM FRIDAY WITH THE LOW TRACKING RIGHT ON TOP
OF US SATURDAY FOR HIGHER POPS ONCE AGAIN FRIDAY AND SATURDAY.

AVIATION.../00Z ISSUANCE/

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

AIRPORTS WILL SEE INCREASED MVFR...LOCALLY IFR...CEILINGS AND
VISIBILITY REDUCED IN RAIN RAIN AND SNOW MIXED AND FOG THROUGH 15Z
SUNDAY AS UPPER LEVEL LOW PRESSURE TROUGH OVER LOGAN UTAH EJECTS
EAST NORTHEAST ACROSS SOUTHERN WYOMING THROUGH SUNDAY. THIS
EVENING WIDESPREAD RAIN AND SNOW SHOWERS...SNOW LEVEL AROUND 9000
FEET LOWERING TO 7200 FEET BY 03Z...WITH EMBEDDED THUNDERSTORMS
WITH SMALL HAIL AND HEAVY SNOW IN THE MOUNTAINS. MOST MOUNTAINS
WILL BE OBSCURED ABOVE 8000 FEET LOWERING TO 7500 FEET BY 06Z.
CEILINGS WILL LIFT THROUGH THE DAY SUNDAY BUT STILL MOST AREAS
WILL HAVE MVFR CONDITIONS WITH AREAS BELOW 8000 FEET BECOMING
VFR FROM 21Z TO 00Z AS THE UPPER LOW MOVES TO THE EAST AND HIGH
PRESSURE BEGINS TO MOVE INTO THE WEST.

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

AIRPORTS WILL SEE INCREASED MVFR...LOCALLY IFR...CEILINGS AND
VISIBILITY REDUCED IN RAIN RAIN AND SNOW MIXED AND FOG THROUGH 15Z
SUNDAY AS UPPER LEVEL LOW PRESSURE TROUGH OVER LOGAN UTAH EJECTS
EAST NORTHEAST ACROSS SOUTHERN WYOMING THROUGH SUNDAY. THIS
EVENING WIDESPREAD RAIN AND SNOW SHOWERS...SNOW LEVEL AROUND 9000
FEET LOWERING TO 7200 FEET BY 06Z...WITH EMBEDDED THUNDERSTORMS
WITH SMALL HAIL AND HEAVY SNOW IN THE MOUNTAINS. MOST MOUNTAINS
WILL BE OBSCURED ABOVE 8000 FEET LOWERING TO 7500 FEET BY 09Z.
CEILINGS WILL LIFT THROUGH THE DAY SUNDAY BUT STILL MOST AREAS
WILL HAVE PERIODS OF MVFR CONDITIONS WITH AREAS BELOW 8000 FEET
BECOMING VFR FROM 18Z TO 00Z AS THE UPPER LOW MOVES TO THE EAST
AND HIGH PRESSURE BEGINS TO MOVE INTO THE WEST.

FIRE WEATHER...

AN UPPER LEVEL LOW PRESSURE CENTER OVER LOGAN UTAH WILL EJECT
EAST NORTHEAST ACROSS SOUTHERN WYOMING THROUGH SUNDAY.  THE
LOW WILL CONTINUE TO BRING MOISTURE AND INSTABILITY WITH RATHER
STRONG UPPER LEVEL DIVERGENCE SUPPORTING DEEP CONVECTION.
WIDESPREAD SHOWERS RAIN IN THE LOWER ELEVATIONS WITH SNOW STARTING
OUT AT 9000 FEET LOWERING TO AROUND 7200 FEET BY MIDNIGHT.
THIS EVENING EMBEDDED THUNDERSTORMS WILL PRODUCE SMALL HAIL TO
HEAVY SNOW IN THE MOUNTAINS. THE HEAVIEST SNOW WILL BE OVER THE
WESTERN MOUNTAINS THIS EVENING SPREADING INTO THE NORTHERN
MOUNTAINS BY MIDNIGHT...THEN DECREASING IN THE WEST AND CONTINUING
CENTRAL AND NORTH THROUGH SUNDAY. MOST AREAS WILL RECEIVE WETTING
PRECIPITATION WITH THE SOUTH THE LEAST LIKELY AREA DEPENDING ON
THE ACTUAL TRACK OF THE UPPER LOW. TEMPERATURES WILL BE MUCH
COLDER AND RELATIVE HUMIDITY WILL INCREASE SIGNIFICANTLY.  MOST
MOUNTAIN AREAS WILL SEE 4 TO 8 INCHES OF SNOW WITH AREAS OVER A
FOOT IN THE TETONS AND BIGHORN MOUNTAINS. MOST MOUNTAIN AREAS
UNDER WINTER WEATHER ADVISORIES. PLEASE REFER TO THE WINTER
WEATHER ADVISORY FOR DETAILS AND TIMING. WITH THE WIDESPREAD CLOUD
COVER AND PRECIPITATION...MIXING HEIGHTS WILL BE LOW WITH POOR
SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT SUNDAY NIGHT FOR
WYZ002-008-009.

WINTER WEATHER ADVISORY UNTIL NOON MDT SUNDAY FOR WYZ001-012-024.

&&

$$

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



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