Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 300445
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1045 PM MDT FRI APR 29 2016

.SHORT TERM...TONIGHT THROUGH SATURDAY (ISSUED AT 211 PM MDT)

VERY SLOW PROGRESSING 2/3 UPR WAVE PATTERN ACROSS THE NRN HEMISPHERE
IN PLACE WITH KLUDGEY LW TROF ACROSS THE CONUS WITH EMBEDDED DEEP
TROF AND ASSOCIATED CLOSED LOW(S) OVER THE WEST WITH THE CENTER OF
CIRC STILL NEAR THE FOUR CORNERS AREA. TWO EMBEDDED SEVERAL EMBEDDED
DISTURBANCES...KEEP ROTATING UP FROM ERN CO...PROVIDING MUCH OF THE
IMPETUS FOR LIGHT -SHRASN TODAY...MAINLY FROM THE CNTRL BASINS SOUTH
AND SOUTHEAST INTO NRN COLORADO. SFC HAS MAIN SFC LOW WELL TO THE
SOUTH ACROSS CNTRL CO...WITH ONLY A WEAK INVERTED TROF UP INTO ERN
WY. LOW PRESSURE RESIDES OVR THE GB...WITH GENERAL HIGH P TO THE
E/NE INTO THE PLAINS....KEEPING MUCH OF THE LOW LVL FLOW ACROSS THE
FA FROM THE NORTH AND EAST.

SEASONALLY COOL/COLD CONDITIONS CONTINUE AND WILL CONTINUE THROUGH
THE FCST PERIOD...WITH RELATIVELY HIGH PWS READY TO HEAD BACK INTO
EASTERN AND CENTRAL WYOMING ON SATURDAY. OTHERWISE...A RATHER
PERSISTENT STRAT CU CLOUD DECK REMAINS OVR MUCH OF WY WITH ONLY A
FEW BREAKS IN THE CLOUDS. AS NIGHTTIME ROLLS AROUND...THE BROKEN
STRATUS DECK WILL TIGHTEN UP ONCE AGAIN AS TEMPS FALL AND MOISTURE
INCREASES FROM THE EAST TO NORTHEAST OVERNIGHT AND SATURDAY MORNING
AROUND THE DEVELOPING CYCLONE OVR THE CNTRL PLAINS. LIGHT SNOW OR
RAIN MIXED WITH SNOW WILL SLOWLY INCREASE INTO THE ERN AND CNTRL
ZONES OVERNIGHT SO THAT BY SATURDAY MORNING...RAIN/MIX/SNOWFALL
RATES WILL INCREASE TO MODERATE FROM SRN JOHNSON AND ALL OF NATRONA
COUNTIES...WWD INTO FREMONT COUNTY...PUSHING INTO THE ERN WIND RIVER
MOUNTAINS AND SRN ABSAROKAS UNDER GOOD UPSLOPE CONDITIONS.

A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR PORTIONS OF CENTRAL
WYOMING AND THE ABSAROKA MOUNTAINS...INCLUDING ZONES 2 11 16 17 18
19 20 AND 22...BEGINNING AT 12Z SAT...LASTING THRU 06Z SUN. ACROSS
THE ADVISORY AREA...THRU THOSE 18 HRS OF THE FCST PERIOD...SNOW
ACCUMULATION SHOULD GENERALLY RANGE FROM 2 TO 5 INCHES ACROSS THE
LOWER ELEVATIONS...AND FROM 3 TO 10 INCHES IN THE MOUNTAINS.
PRECIPITATION SHOULD TAPER OFF BY MIDNIGHT SATURDAY.
LIGHTER AMOUNTS OF A HALF TO A COUPLE OF INCHES IS EXPECTED
ELSEWHERE...WITH PERHAPS UP TO 4 INCHES IN THE TETONS OR
WYOMING/SALT MOUNTAIN RANGES THROUGH THE SAME PERIOD. BRISK NORTH TO
EAST WINDS WILL ALSO ACCOMPANY THIS SYSTEM...HELPING IN REDUCING
VISIBILITIES TO ONE MILE OR LESS FOR EXTENDED PERIODS.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

A COLD LOW PRESSURE TROUGH WILL BE OVER THE AREA SATURDAY NIGHT WITH
MOIST LOW LEVEL EASTERLY FLOW PRODUCING AREAS OF SNOW OR A RAIN AND
SNOW MIX.  THIS WILL TAPER OFF ON SUNDAY AS THE UPPER LOW PRESSURE
AREA SPLITS WITH THE NORTHEASTERN PART OF THE LOW EXITING TO THE
EAST WHILE A LARGE CLOSED LOW CIRCULATION REFORMS OVER THE SOUTHERN
GREAT BASIN AND DESERT SOUTHWEST WEST OF THE FOUR CORNERS AREA.
DRYING OCCURS FROM NORTH TO SOUTH AS A DRY SURFACE HIGH PRESSURE
AREA MOVES SOUTH FROM ALBERTA ON MONDAY AND MONDAY NIGHT. THE
WEAKENING OF THE SOUTHWEST LOW MAY BE TOO FAST AND THE MODELS START
TO DIFFER WITH THE DEMISE OF THE LOW AS AN UPPER LEVEL HIGH PRESSURE
RIDGE BUILDS INTO THE WEST.  THIS LEADS TO SIGNIFICANT DRYING AND
WARMING TUESDAY THROUGH WEDNESDAY.  WHEN THE RIDGE AXIS MOVES INTO
EASTERN WYOMING...SOUTH SOUTHWEST FLOW MOVES INTO WESTERN WYOMING
WITH SOME SHOWERS DEVELOPING WEDNESDAY NIGHT AND THURSDAY OVER THE
WESTERN MOUNTAINS. THE SPREAD BETWEEN THE MODEL SOLUTIONS BECOMES
QUITE LARGE...BUT WITH A GENERAL LONG WAVE HIGH PRESSURE RIDGE...THE
MAIN DIFFERENCES ARE TO THE WEST AND EAST OF THE AREA WHERE LONG
WAVE TROUGHS BRACKET THE RIDGE. WEDNESDAY AND THURSDAY HIGHS WARM
NICELY INTO THE UPPER 60S AND 70S WITH THE WARMEST TEMPERATURES IN
THE BIGHORN BASIN.  AS THE PACIFIC TROUGH DIGS INTO THE GREAT BASIN
ON FRIDAY AND FORMS YET ANOTHER CUT OFF LOW...UPLSOPE EAST TO
NORTHEAST FLOW WILL RETURN TO THE AREA WITH COOLING TEMPERATURES AND
INCREASED MOISTURE AND LIFT SUPPORTING A RETURN TO AREAS OF SNOW AND
RAIN MOVING INTO NEXT WEEKEND.

&&

.AVIATION.../06Z ISSUANCE/

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

ISOLATED RAIN OR SNOW SHOWERS OVER NORTHWEST WY OVERNIGHT WITH SOME
MVFR CIGS EXPECTED. OTHERWISE VFR CONDITIONS OVER WESTERN WY THROUGH
SATURDAY MORNING. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL
DEVELOP OVER THE WEST SATURDAY AFTERNOON INTO THE EVENING. AREAS OF
MVFR CONDITIONS WILL OCCUR ALONG WITH PARTIAL MOUNTAIN OBSCURATION.
SHOWERS WILL DECREASE TO ISOLATED ACTIVITY BY 06Z SUNDAY.

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

PERIODS OF RAIN AND SNOW THROUGH EARLY EVENING SATURDAY OVER MOST OF
THE REGION. FAR NORTHERN WY WILL SEE LESS RAIN COVERAGE. EXPECT MVFR
TO IFR CONDITIONS OVER MOST OF THE REGION. MOUNTAINS WILL BE
FREQUENTLY OBSCURED. THE RAIN AND SNOW WILL DECREASE AFTER 00Z
SUNDAY. AREAS OF MVFR/IFR CIGS WILL REMAIN OVER MUCH OF THE REGION
THROUGH 06Z SUNDAY.

&&

.FIRE WEATHER...

TODAY...LOW FIRE DANGER ALL LOCATIONS WITH RELATIVELY LIGHT WIND
HIGH RH VALUES...ONLY BOTTOMING OUT IN THE MID 40S TO MID 70S
(PERCENT). SMALL CHANCES FOR ISOLATED TO SCATTERED SHOWERS OR AN
ISOLATED THUNDERSTORM ACROSS SOUTH AND SOUTHWEST WY THIS AFTERNOON.
SHOWERS...BOTH RAIN AND SNOW...WILL BE ON THE INCREASE EAST OF THE
DIVIDE AND ACROSS THE WESTERN MOUNTAINS SATURDAY...KEEPING FIRE
DANGER LOW ACROSS ALL OF WYOMING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

WINTER WEATHER ADVISORY FROM 6 AM SATURDAY TO MIDNIGHT MDT
SATURDAY NIGHT FOR WYZ002-011-015>020-022.

&&

$$

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



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