Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 241501
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
901 AM MDT SUN MAY 24 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

UPDATED TO EXTEND FLASH FLOOD WATCH UNTIL MIDNIGHT TONIGHT.
ALSO ADDED ALL OF FREMONT AND HOT SPRINGS COUNTIES AND EASTERN
SWEETWATER COUNTY TO THE FLASH FLOOD WATCH.  RAINFALL OF AN INCH
TO 2.5 INCHES HAS ALREADY OCCURRED OVER MUCH OF THE WATCH AREA
OVER NIGHT AND THIS MORNING.

WV IMAGERY SHOWING LARGE UPR TROF CONTINUES ACROSS THE WRN CONUS
WITH CLOSED LOW OVR WRN CO/SRN WY...WITH NICE VORT LOBE ROTATING
ANTI-CLOCKWISE AROUND CNTRL CLOSED PORTION OF THE LOW INTO SCNTRL
WY. EMBEDDED SW ALSO ROTATING AROUND THE LOW...NOW STRETCHED
DIAGONALLY ACROSS WY FROM THE SW TO NCNTRL. SFC HAS GENERAL HIGH P
NORTH OVR MT...HIGH P SOUTH OVR CO/NM...WITH A WEAK LOW P
TROF/DEVELOPING FRONT IN BETWEEN AND ACROSS CNTRL WY.

EARLY MORNING FOG WILL CONTINUE TO BE POSSIBLE OVR MUCH OF THE FA
THRU TUE MORNING...ESPECIALLY E OF THE DIVIDE.  OTHERWISE...MAINLY
HYDROLOGIC CONCERNS AS UPR TROF MIGRATES EWD WHILE THE CNTRL UPR LOW
SLOWLY PULLS FROM CO/WY BORDER AREA INTO THE HIGH PLAINS BY THIS
EVENING. WEAK SFC CYCLOGENESIS TO TAKE PLACE FROM ERN/NERN CO INTO
SERN WY AND WRN NE. LOW TO MID LVL MOISTURE RETURN AROUND THE
DEVELOPING SFC LOW...WHILE MID/UPR MOISTURE ACCOMPANYING THE UPR
WAVE/CLOSED LOW DEEPENS MOISTURE E OF THE DIVIDE...WITH PWS RANGING
FROM 0.70 TO 0.80...WILL GIVE ANOTHER DAY OF PLENTIFUL
RAINFALL...AGAIN ESPECIALLY E OF THE DIVIDE. WIDESPREAD AREAS OF NEW
PRECIPITATION THRU SUNDAY EVENING WILL RANGE FROM .75 TO 1.25
INCHES...WITH SOME PREFERRED LOCATIONS ALONG THE E SIDE OF THE
BIGHORNS...NEAR/OVR THE SRN BIGHORNS...AND THE GREEN AND ERN
WIND RIVER MOUNTAINS...WHERE PRECIP WILL BE ENHANCED DUE TO TERRAIN
LIFT OR TERRAIN INDUCED CONVERGENCE. EVEN THE FOOTHILLS OF THE
WESTERN SIDE OF THE BIGHORNS WILL BE SUSCEPTABLE TO ENHANCED PRECIP
AS DEEP FLOW MOVES AROUND FROM THE NORTH. FLASH FLOODING WILL
CONTINUE TO BE A CONCERN FOR ANOTHER DAY E OF THE DIVIDE...AND HAVE
ADDED THE WESTERN BIGHORNS  AND WASHAKIE COUNTY TO THE CURRENT FLASH
FLOOD WATCH AREA. AREAS SATURATED MOST OVR THE PAST COUPLE OF DAYS
INCLUDE FREMONT COUNTY...PARTICULARLY WRN AND SRN PORTIONS...MOST OF
NATRONA COUNTY...THE SRN AND ERN PORTIONS OF WASHAKIE COUNTY...AND
AREAS IMMEDIATELY ADJACENT TO THESE COUNT AREAS. AGAIN...THIS SYSTEM
CONTINUES TO LOOK COMPARATIVELY WARM...WITH H7 TEMPS REMAINING
MOSTLY ABOVE -1 DEG C THRU THE ENTIRE FCST PERIOD...AND REALLY WELL
ABOVE ZERO FOR MOST OF THAT TIME. EXPECT...A TRACE TO AN INCH OR TWO
DURING THE COLDEST PORTION OF THE NIGHTS ABOVE 9500 FEET...WITH ONLY
THE HIGHEST ELEVATIONS RECEIVING AN ISOLATED 3 OR 4 INCHES BY MONDAY
MORNING. STORM MOVEMENT IMPROVES SLIGHTLY...EVENTUALLY BECOMING NRLY
AT 15 TO 20 MPH MOST LOCATIONS BY THE END OF THE TODAY EXCEPT FOR
JOHNSON COUNTY WHICH WILL KEEP MOVEMENT OUT OF THE E OT NE. SEVERE
WX WILL REMAIN MOSTLY WELL EAST TO SOUTHEAST OF FA WITH CONTINUED
RELATIVELY LOW SHEAR CONDITIONS. THE BEST CHANCES FOR SMALL HAIL UP
TO ONE HALF INCH AND PERHAPS A BOUNDARY LOCKED FUNNEL CLOUD WILL LAY
ACROSS THE FAR ERN FA...WITH A SMALLER CHANCE FOR SMALL HAIL NEAR
THE FAR WRN BORDER AREA WHERE SOME POSSIBLE INCREASED SUNSHINE MAY
ENHANCE A COUPLE OF STORMS.

TONIGHT THRU TUESDAY...SYSTEM PUSHES EWD INTO THE PLAINS WITH
TRANSITIONAL RIDGING TAKING PLACE ACROSS THE FAR WRN FA MONDAY WHILE
THE REST OF THE FA WILL BE UNDER THE INFLUENCE OF A SW ROTATING INTO
THE AREA FROM THE NE AROUND THE EXITING LOW...WITH MORE
SHOWER/THUNDER ACTIVITY...ALBEIT ON A LESSER BASIS. OTHERWISE...A
BIT WARMER AND MORE UNSTABLE WITH PERHAPS AN BETTER SPRINKLING OF
STRONGER THUNDERSTORMS MIXED IN WITH SHOWERS ON TUESDAY.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

GFS MODEL CONTINUES ITS TREND FROM PREVIOUS NIGHTS BY TAKING A
WEATHER SYSTEM FROM THE PACIFIC NW WEDNESDAY AND MOVING IT INTO
IDAHO THURSDAY. ON FRIDAY THE GFS TAKES A MORE SOUTHEAST TRACK
TOWARD SW WY OR NORTHERN UTAH AND THEN TO NW COLORADO BY FRIDAY
NIGHT. FROM THERE IT DRIFTS EAST THROUGH NORTHERN COLORADO SATURDAY
AND OUT OF THE AREA SATURDAY NIGHT. WITH MOISTURE PRESENT AND ANY
SUNSHINE THAT OCCURS...INSTABILITY WILL OCCUR AND THUS SHOWERS AND
THUNDERSTORMS WILL FORM IN THE AFTERNOON AND EVENING. LINGERING
SHOWERS DURING THE LATE NIGHT AND MORNING HOURS. NEXT SUNDAY LOOKS
LIKE A QUIETER DAY WITH ONLY ISOLATED SHOWERS OR STORMS IN NW WY IN
THE AFTERNOON. THE ECMWF MODEL IS SIMILAR WEDNESDAY THROUGH THURSDAY
BUT THEN THE ECMWF SPEEDS UP THE WEATHER SYSTEM MOVEMENT ON FRIDAY
AND TAKES IT OUT OF THE AREA BY SATURDAY MORNING. THEN IT HAS MOSTLY
DRY WEATHER FOR SATURDAY AND NEXT SUNDAY WITH ONLY ISOLATED SHOWERS
OR STORMS. WILL FOLLOW A MORE GFS SPEED FOR NOW AS MOST OF THESE
SYSTEMS HAVE BEEN SLOWER MOVING OUT OVER THE PAST MONTH. WILL PLAY
NEXT SATURDAY WITH A SLIGHT CHANCE OF SHOWERS AND ISOLATED STORMS
AND THEN ISOLATED MOUNTAIN ACTIVITY NEXT SUNDAY. AS FOR TEMPS...WED
HIGH TEMPS IN THE 60S TO LOWER 70S...THEN HIGHS THURSDAY ABOUT THE
SAME AS WED TO SLIGHTLY COOLER IN SOME PLACES. FRIDAY LOOKS A LITTLE
COOLER WITH MORE CLOUDS EXPECTED AS THE SYSTEM MOVES THROUGH THE
AREA. THEN A LITTLE WARMER SATURDAY AND EVEN WARMER NEXT SUNDAY TO
EXIT THE MONTH OF MAY.

.AVIATION.../18Z ISSUANCE/

WIDESPREAD MVFR TO IFR CONDITIONS AND MTN OBSCURATIONS...LCL IFR
CONDITIONS WITH NMRS -SHRA WILL CONTINUE ALONG AND EAST OF THE
DIVIDE THROUGH 18Z MONDAY. THESE CONDITIONS WILL NOT BE AS
WIDESPREAD WEST OF THE DIVIDE WHICH MAY SEE MORE FOG DEVELOPMENT
THROUGH THE MORNING HOURS.

THE UPPER LOW OVER WESTERN COLORADO WILL SLOWLY LIFT NE INTO EASTERN
WYOMING ON SUNDAY AND SUNDAY NIGHT...AND THERE WILL LIKELY BE SOME
LIFTING OF CIGS LATE IN THE AFTERNOON FOLLOWED BY RAPID
DEVELOPMENT OF SHOWERS AND THUNDERSTORMS THROUGH THE AFTERNOON AND
EARLY EVENING. WIDESPREAD MVFR -RA/AREAS OF IFR RA BR...MTN
OBSCURATIONS ON THE BACKSIDE OF THE UPPER LOW WILL FOLLOW AFTER
03Z SUNDAY ACROSS MOST OF THE AREA.

.FIRE WEATHER...

FIRE DANGER LOW AND WILL REMAIN LOW THROUGH TUESDAY AS
RELATIVELY COOL AND WET WEATHER REMAINS IN PLACE AS YET ANOTHER
VIGOROUS UPPER LEVEL SYSTEM ROTATES ACROSS THE REGION. WIDESPREAD
PRECIPITATION...WITH BETWEEN A HALF AN INCH AND AN INCH AND A
QUARTER EAST OF THE DIVIDE...AND LIGHT MOUNTAIN SNOW IS EXPECTED
TODAY AND TONIGHT...WITH EMBEDDED THUNDERSTORMS POSSIBLE EACH
AFTERNOON AND EARLY EVENING THROUGH TUESDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH THIS EVENING
WYZ005>011-015>020-022-030.

&&

$$

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





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