Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 010502
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1102 PM MDT SAT APR 30 2016

.SHORT TERM...TONIGHT THROUGH SUNDAY (ISSUED AT 151 PM MDT)

BROAD LOW WITH A COUPLE OF EMBEDDED CLOSED LOWS ACROSS THE WRN
2/3RDS OF THE CONUS. DEEPER CLOSED SYSTEM NOW CENTERED ACROSS THE
CNTRL PLAINS WITH THE SFC PORTION OF THE LOW NOW OVR MO. LONG
TRAJECTORY FEED OF MOISTURE FEEDS UP ACROSS THE MS VALLEY...THEN WWD
ACROSS SD/NE...TAILING OFF INTO ERN AND SRN WY/NRN CO. MOST PRECIP
WITHIN THE FA IS CURRENTLY LOCATED OVR CNTRL/SRN WY...FALLING OFF
QUICKLY TO THE NORTH.

TODAY THRU THIS EVENING...THE UPR LOW STALLS OUT...ONLY MAKING IT
AS FAR E AS THE MO VALLEY BY AROUND MIDNIGHT...WITH THE SFC PORTION
OF THE SYSTEM TRACKING TO IL. GENERALLY...THIS SLOW PROGRESSION EWD
WILL ALSO SLOWLY TAKE THE MOISTURE WITH IT...WITH THE MORE
STRATIFORM PRECIP E OF THE DIVIDE FALLING OFF IN PARALLEL. COLD AIR
ALOFT W OF THE DIVIDE...HOWEVER...WILL ALLOW FOR SOME -SHRA/ISO -
TSRA THIS AFTERNOON/EARLY EVENING...WITH THE WRN/SRN MOUNTAINS
REAPING THE BENEFITS FROM THIS ISOLATED TO SCATTERED PRECIP.

HAVE DECIDED TO CANCEL THE ADVISORIES FOR ALL ZONES EXCEPT ZONE 15
(ERN WIND RIVER MOUNTAINS)...AS THE BETTER PRECIP/SNOW CAME THROUGH
MID MORNING...BEFORE MIXING WITH OR TURNING TO ALL RAIN BELOW 5500
FEET BY LATE MORNING. ADDITIONALLY...QPF TRENDS ARE FAVORING THE THE
TERRAIN FORCED AREAS WITH A NE ASPECT. ALSO ACCUMULATING SNOW SEEMS
TO BE MOSTLY RELEGATED TO ELEVATIONS ABOVE 6000 TO 6200 FEET THIS
AFTERNOON. SO...EVEN AS SNOW ELEVATIONS FALL THROUGH THE AFTERNOON
AND INTO THE EVENING...SO WILL THE PRECIP WITH MUCH LESS CHANCE TO
ACCUMULATE. OTHERWISE...SIGNIFICANT SNOWFALL TOTALS WILL GENERALLY
LIE BETWEEN 3 AND 9 INCHES ACROSS THE ERN WIND RIVER MOUNTAINS...2
TO 7 INCHES OVER/CLOSE TO CASPER MOUNTAIN...2 TO 6 INCHES IN THE SRN
ABSAROKAS...AND PERHAPS AN INCH TO 2 INCHES OVR PORTIONS OF NATRONA
AND FREMONT COUNTIES.

SUNDAY WILL BE HIGHLIGHTED BY A FOLDING RIDGE AND DRYING ACROSS THE
FA FROM N TO S THROUGH THE DAY...WITH ONLY A FEW LINGERING MORNING
SHOWERS GIVING WAY TO A SPURIOUS SHOWER OR TWO...MAINLY IN THE
BIGHORN...LARAMIE...OR MEDICINE BOW MOUNTAINS. WARM UP
BEGINS...WITH HIGHS REACHING INTO THE 40S TO MID 50S ACROSS THE
LOWER ELEVATIONS...WITH 30S AND 40S IN THE MOUNTAINS.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

MOISTURE AND NORTHEASTERLY UPSLOPE FLOW WILL TAPER OFF ON SUNDAY
NIGHT 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 THURSDAY.
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.  SHOWERS
EXPECTED TO BECOME SCATTERED OVER THE WESTERN MOUNTAINS WITH
ISOLATED THUNDERSTORMS DUE TO HEATING.  SHOULD HAVE ENOUGH RESIDUAL
MOISTURE ON THE GROUND TO EVAPORATE AND PROVIDE NEEDED MOISTURE FOR
CONVECTION. 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.  TEMPERATURES EXPECTED TO COOL
SIGNIFICANTLY ON SATURDAY AS SHOWERS BECOME MORE WIDESPREAD AND
EAST TO NORTHEAST UPSLOPE FLOW DEEPENS AND MOISTENS.  SNOW LEVEL
SHOULD START OUT AROUND 9000 FEET WITH A RAIN SNOW MIX DOWN TO 7500
FEET.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. ISOLATED RAIN OR
SNOW SHOWERS WILL END BY 12Z. PATCHY LOW CLOUDS OR FOG WILL FORM IN
PLACES OVERNIGHT WITH MVFR/IFR CONDITIONS UNTIL 17Z.

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. SOME LOW CLOUDS OR
FOG WILL FORM IN PLACES OVERNIGHT INTO SUNDAY MORNING WITH MVFR/IFR
CONDITIONS UNTIL 17Z.

&&

.FIRE WEATHER...

TODAY...LOW FIRE DANGER FOR ALL LOCATIONS CONTINUES WITH HIGH
MINIMUM RH VALUES ONLY BOTTOMING OUT IN THE MID 40S TO MID 80S
(PERCENT) ACROSS THE ENTIRE REGION. THERE WILL BE CHANCES FOR
ISOLATED TO SCATTERED SHOWERS OR AN ISOLATED THUNDERSTORM OR TWO
ACROSS THE SOUTH AND SOUTHWEST WY THIS AFTERNOON. MUCH BETTER
CHANCES FOR RAIN AND OR SNOW WILL OCCUR EAST OF THE DIVIDE...
ESPECIALLY ACROSS CENTRAL WYOMING TODAY  THROUGH THIS EVENING.
PRECIPITATION ENDS ACROSS WYOMING SUNDAY...HOWEVER FIRE DANGER WILL
REMAIN LOW FOR THE MOST PART AS LOTS OF RESIDUAL MOISTURE REMAINS
ACROSS MUCH OF THE STATE AND GREEN UP BEGINS. WINDS...HOWEVER...WILL
BE QUITE GUSTY ACROSS THE SOUTHERN PORTION OF WYOMING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR WYZ015.

&&

$$

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


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