Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 250611
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1210 AM MDT SAT APR 25 2015

.SHORT TERM...TONIGHT THROUGH SATURDAY

GENTLE RIDGING OVR WY...WITH PRE-TROF DIVERGENCE BEGINNING TO SPREAD
INTO THE SWRN PORTION OF THE STATE WITH A WEAK DISTURBANCE...JUST
AHEAD OF ANOTHER SW (OVR NRN NV ATTM) TROF EJECTING OUT AHEAD OF
MAIN TROF ORIENTED ALONG THE W CST...WITH CLOSED LOW CENTERED OVR
SRN BC. SFC SHOWS BROAD AREA OF LOW P AND A WEAK TROF E OF THE
ROCKIES AND OVR THE HIGH PLAINS OF WY...CO...AND INTO WRN SD AND NE.
FRONTS STRETCH FROM SWRN SD TO NERN WY AND ON UP INTO CNTRL
MT...WITH A COLD FRONT EXTENDING FROM CNTRL MT TO THE SW AND INTO
NV.

CURRENTLY BEST LIFT AND INSTABILITY OCCURRING OVR THE SWRN FA...WITH
SHOWERS AND ISOLATED THUNDER BEGINNING ONCE AGAIN ACROSS SRN LINCOLN
AND WRN SWEETWATER COUNTIES. COVERAGE OF STORMS WILL INCREASE THIS
AFTERNOON WITH LOW-TOPPED -TSRA MIXING WITH SCATTERED SHRA.
GENERALLY A LITTLE LOWER BUOYANCY TODAY...WITH CAPE VALUES REMAINING
BELOW 400 J/KG. ALSO...MOST UNSTABLE AXIS WILL BE LOCATED E OF THE
FA. STRONGER STORMS OF THE DAY LIKELY IN NORTHERN JOHNSON COUNTY.
HOWEVER...BETTER MOISTURE OVR THE SWRN FA WILL CONTINUE FEED THIS
AREA THRU THE AFTERNOON AND INTO THIS EVENING. THE DEW POINT SPREAD
DOES NOT LOOK AS GOOD AS YESTERDAY FOR MOST LOCATIONS...WITH GUST
POTENTIAL HOPEFULLY REMAINING ON THE LOWER SIDE AT LESS THAN 30 MPH.
THE NEXT DISTURBANCE ARRIVES LATER THIS EVENING...INCREASING SHOWERS
WITH SNOWFALL BEGINNING ABOVE 10000 FT BY MID EVENING...DECREASING
TO AROUND 7500 FEET AFTER MID-NIGHT. AFTER A RESPITE FROM MOST
PRECIP THRU THE REST OF THE MORNING HRS FOR MOST LOCATIONS SAVE THE
SW AND NW FA...THE FIRST OF A COUPLE OF FRONTS WILL BEGIN TO PUSH
SWD SAT MORNING E OF THE DIVIDE...AS MODERATELY MOIST MID/UPR FLOW
STARTS TO OVER-RIDE THE FRONT FROM THE SOUTH AND BETTER MID/UPR
DYNAMICS FEED INTO THE REGION ALONG WITH A WEAK JET STREAK BY SAT
AFTERNOON. AT THE SAME TIME...THERE ARE HINTS AT SOME FORM OF
CYCLOGENESIS GOING ON ACROSS SERN WY...WHICH MAY EFFECT THE ERN CWA
LATER. OTHERWISE...WIDELY SCATTERED TO SCATTERED AREAS OF PRECIP
WITH RAIN SHOWERS AND ISOLATED THUNDER WILL OCCUR AGAIN ACROSS MOST
OF THE SRN HALF OF THE FA...IN ADDITION TO THOSE OVR THE WRN
MOUNTAINS. WHILE MOISTURE WILL BE DECENT OVERALL...WARM TEMPS TO
BEGIN WITH AND THE TIME IT TAKES TO LOWER TEMPS AND SLOW LEVELS WILL
KEEP OVERNIGHT CONVECTIVE MOUNTAIN SNOWFALL RANGING FROM 1 TO 3
INCHES WITH ISOLATED PEAKS ABOVE 95000 FEET RECEIVING 4 TO 5
INCHES. SATURDAY. ONLY ANOTHER INCH OR SO WILL BE ADDED TO THIS
TOTAL THRU THE DAY.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

A DIGGING TROUGH STARTS OFF THE FORECAST PERIOD...WITH
PRECIPITATION SPREADING ACROSS MUCH OF CENTRAL AND WESTERN
WYOMING. MODELS INDICATE SOME MODEST INSTABILITY SATURDAY
EVENING...WITH PERHAPS AN ISOLATED THUNDERSTORM OR TWO LINGERING
INTO THE EVENING HOURS. PRECIPITATION ASSOCIATED WITH THIS TROUGH
WILL LINGER ACROSS THE STATE AS THE SYSTEM PROGRESSES EASTWARD ON
SUNDAY...WITH MOST ACTIVITY EXPECTED TO BE FOUND OVER THE EASTERN
HALF OF THE STATE.

CONDITIONS WILL BEGIN TO IMPROVE MONDAY AFTERNOON AND ESPECIALLY
MONDAY NIGHT AS A RIDGE WORKS TO BUILD OVER THE AREA. THE RIDGE
WILL CONTINUE TO AMPLIFY TUESDAY WITH WIDESPREAD DRY CONDITIONS
EXPECTED ACROSS THE FORECAST AREA.

DRY CONDITIONS WILL GENERALLY PERSIST THROUGH WEDNESDAY...THOUGH A
WEAK DISTURBANCE ACROSS NORTHWESTERN WYOMING MAY INTRODUCE A FEW
SHOWERS ACROSS THE IMPACTED AREA. SHOWER COVERAGE WILL INCREASE
THURSDAY...AS CONTINUED MOISTURE AND INSTABILITY REMAINS OVER
PORTIONS OF WESTERN WYOMING. SOME THUNDERSTORM ACTIVITY WILL BE
POSSIBLE. MODELS AT THIS TIME VARY CONCERNING THE PLACEMENT OF THE
OFFENDING LOW PRESSURE SYSTEM...AND CONSEQUENTLY THE COVERAGE OF
ASSOCIATED SHOWER ACTIVITY. THE ECMWF SPREADS PRECIPITATION ACROSS
MUCH OF THE FORECAST AREA BY FRIDAY AFTERNOON. THE
GFS...MEANWHILE...REMAINS MORE CONSERVATIVE...WITH SHOWERS
PRIMARILY OVER THE NORTHWESTERN CORNER OF THE STATE.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

ISOLATED CONVECTION WILL LINGER THROUGH EARLY MORNING HOURS MAINLY
OVER THE MOUNTAINS. OTHERWISE...A COLD FRONT WILL SLIDE INTO
NORTHERN WYOMING BETWEEN 09Z AND 12Z AND PUSH THROUGH MUCH OF THE
BIG HORN BASIN AND JOHNSON COUNTY BY 15-18Z. THE FRONT IS THEN
EXPECTED TO REACH THE DIVIDE BETWEEN 21Z AND 00Z. IN WAKE OF THIS
COLD FRONT EXPECT SOME BREEZY NORTHERLY WINDS AND SOME MVFR
CEILINGS. THERE ALSO COULD BE A FEW THUNDERSTORMS SATURDAY
AFTERNOON/EVENING...BUT THE MAIN IMPACT FROM THIS COLD FRONT AND
UPPER LEVEL SYSTEM WILL OCCUR AFTER 03Z SUNDAY. WIDESPREAD AND
PERSISTENT MVFR/IFR CONDITIONS IN VALLEY RAIN AND MOUNTAIN SNOW ARE
EXPECTED TO DEVELOP AFTER 03Z SUNDAY ESPECIALLY ACROSS THE WIND
RIVER BASIN INCLUDING KLND AND KRIW. ALTHOUGH LESS PRECIPITATION IS
EXPECTED FARTHER NORTH AND EAST...AREAS WITH MVFR CEILINGS ARE
EXPECTED. THERE COULD BE SOME MOUNTAIN OBSCURATION SATURDAY
MORNING...BUT WIDESPREAD MOUNTAIN OBSCURATIONS ARE EXPECTED SATURDAY
NIGHT. LIFR CONDITIONS ARE LIKELY ON ROUTES OVER THE WIND RIVER
MOUNTAINS DUE TO SNOW AND CLOUDS AFTER 03Z.

PLEASE SEE THE AVIATION WEATHER CENTER FOR THE LATEST INFORMATION ON
ICING FORECASTS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDELY SCATTERED SHOWERS WILL GRADUALLY DISSIPATE OR LIFT AWAY FROM
THE AREA EARLY THIS MORNING. THEN THERE COULD BE PATCHY FOG IN A FEW
AREAS...BUT CLOUD COVER SHOULD LIMIT COVERAGE. ANY FOG/LOW CLOUDS
ARE EXPECTED TO IMPROVE BETWEEN 14Z AND 16Z WITH MAINLY DRY AND VFR
CONDITIONS THROUGH EARLY SATURDAY AFTERNOON. AFTER 20Z...WIDELY
SCATTERED SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ARE EXPECTED TO
DEVELOP ACROSS THE ENTIRE AREA...WITH MORE COVERAGE TOWARDS 00Z. AS
A STORM SYSTEM APPROACHES FROM THE WEST THIS EVENING...A WIDESPREAD
AREA OF VALLEY RAIN/MOUNTAIN SNOW SHOULD DEVELOP ACROSS THE UPPER
GREEN RIVER BASIN AFTER 03Z SUNDAY...IMPACTING KBPI AND KPNA
TERMINALS WITH PERSISTENT IFR/MVFR CONDITIONS. THIS ACTIVITY IS
EXPECTED TO HAVE LESS OF AN IMPACT FOR KJAC...BUT PERIODS OF MVFR
CONDITIONS CANNOT BE RULED OUT. ALSO THE VALLEY RAIN COULD CHANGE TO
SNOW AFTER 06Z SUNDAY AS MORE COLD AIR WORKS INTO THE AREA. LIFR
CONDITIONS ARE LIKELY ON ROUTES OVER THE WIND RIVER MOUNTAINS DUE TO
SNOW AND CLOUDS AFTER 03Z SUNDAY.

PLEASE SEE THE AVIATION WEATHER CENTER FOR THE LATEST INFORMATION ON
ICING FORECASTS.

&&

.FIRE WEATHER...

FIRE DANGER RELATIVELY LOW TODAY...REMAINING LOW
THROUGH THE WEEKEND AS SEASONALLY COOL AND AND MOIST WEATHER TAKES
OVER THE NEXT SEVERAL DAYS. WIDELY SCATTERED TO SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS WILL OCCUR THIS AFTERNOON AND
EVENING...THEN AGAIN LATE SATURDAY. BETTER CHANCES FOR A WETTING
RAIN OR SNOW WILL BE ON SUNDAY FOR MOST AREAS AS THE MAIN
DISTURBANCE ROLLS OVER THE FORECAST AREA. A WARMING AND DRYING TREND
BEGINS ON MONDAY AND COULD LAST THE ENTIRE WEEK.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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









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