Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 231938
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
131 PM MDT MON MAR 23 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN APPROACHING WAVE OF LOW PRESSURE WILL INCREASE SOUTHWEST FLOW
OVER THE FORECAST AREA TODAY. THIS WILL HELP TO BRING COOLER
TEMPERATURES ACROSS MUCH OF THE FORECAST AREA. AS THE SOUTHWEST FLOW
BECOMES MORE PREVALENT DURING THE LATE MORNING AND EARLY AFTERNOON
HOURS...IT WILL USHER ADDITIONAL MOISTURE ACROSS THE AREA TO
INTRODUCE SHOWER ACTIVITY. MODELS CONTINUE TO INDICATE
DESTABILIZATION OF THE ATMOSPHERE THIS AFTERNOON...WITH SOME
ISOLATED THUNDERSTORMS POSSIBLE DURING THE AFTERNOON HOURS. ACTIVITY
MAY BEGIN WEST OF THE DIVIDE DURING THE LATE MORNING AND EARLY
AFTERNOON HOURS...BUT INSTABILITY ALSO INCREASES EAST OF THE DIVIDE
DURING THE LATE AFTERNOON HOURS...BRINGING SOME OPPORTUNITY FOR
ISOLATED THUNDERSTORMS. SHOULD THUNDERSTORMS DEVELOP...GUSTY WIND
WILL BE THE PRIMARY THREAT. THUNDERSTORM ACTIVITY WILL WEAKEN
THROUGH THE EVENING HOURS AS THE ATMOSPHERE STABILIZES.

THE FLOW WILL TURN MORE NORTHWESTERLY AS THE WAVE PASSES LATE
TONIGHT. PUSHES OF MOISTURE WILL CONTINUE IN THE NORTHWEST FLOW
THROUGH MUCH OF THE FORECAST PERIOD...ESPECIALLY DURING THE
AFTERNOON HOURS. TEMPERATURES WILL GENERALLY CONTINUE TO COOL ACROSS
THE AREA WITH INCREASED CLOUD COVER AND CONTINUED SHOWER ACTIVITY.
CONVECTIVE PARAMETERS DO NOT SHOW STRONG ENOUGH VALUES TO WARRANT
THE INCLUSION OF ADDITIONAL THUNDERSTORM ACTIVITY...THOUGH THEY MAY
BE ADDED LATER AS CONFIDENCE INCREASES. THIS FLOW PATTERN
WILL...HOWEVER...PERMIT FOR THE DEVELOPMENT FOR STRONGER WIND ACROSS
SOUTHERN WYOMING. THE I-80 CORRIDOR LOOKS ESPECIALLY SUSCEPTIBLE TO
THESE STRONGER WINDS WHICH WILL BEGIN TUESDAY AFTERNOON AND GO
THROUGH TUESDAY EVENING.

DRIER CONDITIONS ANTICIPATED ACROSS THE AREA BY LATE WEDNESDAY NIGHT
AS THE FLOW TURNS MORE NORTHERLY AND ONLY HAS ACCESS TO MINIMAL
MOISTURE. A FEW SHOWERS WILL STILL BE POSSIBLE ACROSS THE FAR
NORTH...BUT MOST OF THE AREA WILL BE DRY

.LONG TERM...THURSDAY THROUGH MONDAY

A CANADIAN CLIPPER...PROPAGATING THROUGH NORTHWEST FLOW...WILL BRING
THE LAST OF A SERIES OF DISTURBANCES ACROSS THE REGION THURSDAY.
BACK DOOR COLD FRONT LOOKS TO ACCOMPANY THIS DISTURBANCE...WHICH
LOOKS TO MAINLY IMPACT NORTHERN AND EASTERN PORTIONS OF THE CWA. A
STRONG POLAR JET STREAK OF WELL OVER 100 KNOTS WILL ALSO ACCOMPANY
THIS DISTURBANCE. THE FAVORED LEFT EXIT REGION OF THIS JET WILL BE
POSITIONED OVER JOHNSON COUNTY THURSDAY MORNING. THIS COMBINED WITH
ANOTHER PUSH OF COLD AIR...WITH 700 MB TEMPS AROUND -10...COULD
BRING SOME MORNING SNOW TO JOHNSON COUNTY. A QUICK 1 TO 2 INCHES MAY
BE POSSIBLE ACROSS LOWER ELEVATIONS THURSDAY MORNING...BEFORE SNOW
TRANSITIONS TO RAIN BY LATE MORNING OR EARLY AFTERNOON. THESE STRONG
UPPER LEVEL WINDS COULD ALSO BRING SOME GUSTY WINDS FROM JOHNSON
THROUGH NATRONA COUNTY THURSDAY. JET MAX AND UPPER LEVEL DISTURBANCE
PUSHES EASTWARD THURSDAY NIGHT...LEAVING IN ITS WAKE A FEW LINGERING
LIGHT RAIN AND SNOW SHOWERS...AND COOLER TEMPS FOR THURSDAY NIGHT
INTO FRIDAY MORNING.

RELATIVELY DRY NORTHWEST FLOW WILL THEN REBOUND TEMPS BACK INTO THE 60S
ON FRIDAY AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS THE WEST. THIS
RIDGE THEN MOVES OVERHEAD SATURDAY...BRINGING VERY WARM AND DRY
CONDITIONS. MOST AREAS EAST OF THE DIVIDE COULD SEE HIGH TEMPS IN
THE 70S FOR SATURDAY. RIDGE BEGINS TO FLATTEN SATURDAY
AFTERNOON...AS A SHORTWAVE TROUGH EXTENDS INTO CANADA. THIS INCREASED
PRESSURE GRADIENT...AND WESTERLY FLOW...COULD BRING A FEW BREEZY
AREAS SATURDAY AFTERNOON. WITH LOW RH EXPECTED...SATURDAY WILL HAVE
TO BE MONITORED FOR POTENTIAL FIRE WEATHER DANGER. THE MENTIONED
CANADIAN TROUGH CLIPS THE NORTHERN PLAINS SUNDAY...AND COULD
BRING A WEAK COLD FRONT ACROSS THE REGION. MOISTURE WILL BE LIMITED
WITH THIS SYSTEM...BRINGING ONLY SLIGHT CHANCES FOR ISOLATED TO
WIDELY SCATTERED RAIN SHOWERS.

WHILE THIS WEAK FRONT PUSHES THROUGH SUNDAY...AN UPPER LOW WILL MOVE
ON THE WESTERN US SHORES SUNDAY...AND HEAD EAST ACROSS CA AND
NV...AND STALL SUNDAYS FRONT. AS THIS LOW CONTINUES ITS EASTWARD PUSH
ACROSS UT AND CO...IT COULD SEND A FEW WEAK DISTURBANCES WITH
LIMITED MOISTURE INTO THE CWA SUNDAY NIGHT THROUGH MONDAY. KEPT AT
LEAST A SLIGHT CHANCE OF SHOWERS WITH THIS DISTURBANCE FOR A FEW
AREAS ACROSS WESTERN AND CENTRAL PORTIONS. LIMITED INSTABILITY
COMBINED WITH A PASSAGE OF ANOTHER WEAK FRONT...COULD PRODUCE AN
ISOLATED THUNDERSTORM ON MONDAY...ESPECIALLY ACROSS THE
WEST...ALTHOUGH CONFIDENCE IS NOT HIGH ENOUGH TO PLACE AS WX TYPE IN
FORECAST AT THIS TIME.

&&

.AVIATION.../18Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH THE
PERIOD. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE
EAST OF THE DIVIDE THROUGH 01Z. WIND GUSTS TO 30 KNOTS WILL BE
POSSIBLE NEAR ANY SHOWERS OR STORMS. ISOLATED SHOWERS WILL OCCUR
AFTER 01Z TUE THROUGH 12Z TUE. IN THE MOUNTAINS...SNOW WILL BE
LIKELY BY 20Z WITH MVFR TO IFR CONDITIONS OCCURRING THROUGH 04Z TUE.
THEN SCATTERED SNOW SHOWERS WILL OCCUR THROUGH 12Z TUE. EXPECT
FREQUENT MOUNTAIN OBSCURATION AFTER 20Z THROUGH 12Z TUE.

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

A SWATH OF HEAVY SNOW SHOWERS WITH ISOLATED THUNDERSTORMS WILL IMPACT
THE FAR WEST THROUGH AT LEAST 21Z. IFR CONDS ARE EXPECTED ALONG THIS
NORTHEAST MOVING CLOUD MASS THAT AS OF 19Z EXTENDED FROM YELLOWSTONE
NATIONAL PARK SOUTHEAST TO NEAR SOUTH PASS. THE FAR WEST WILL SEE
SOME IMPROVEMENT AFTER THIS PASSES BUT SCATTERED SNOW SHOWERS WILL
CONTINUE AROUND THE MOUNTAINS THROUGH THE NIGHT WITH FQT MTN
OBSCURATION. STRONG WIND WILL ALSO BE NOTED AT TIMES. PATCHY FOG
WILL DEVELOP TONIGHT...ESPECIALLY AROUND KJAC AND THE FAR WEST VALLEYS
IN GENERAL.

&&

.FIRE WEATHER...

AN APPROACHING WAVE OF LOW PRESSURE WILL RETURN SHOWERS ACROSS THE
WEST THIS AFTERNOON...WITH SOME THUNDERSTORM ACTIVITY POSSIBLE.
THESE SHOWERS MAY SPREAD EAST OF THE CONTINENTAL DIVIDE DURING THE
LATTER HALF OF THE AFTERNOON. GUSTY AND ERRATIC WIND WILL BE THE
PRIMARY THREAT WITH ANY THUNDERSTORM ACTIVITY THIS AFTERNOON...WITH
STORMS EXPECTED TO END DURING THE EARLY EVENING HOURS. PUSHES OF
MOISTURE SOME SHOWER ACTIVITY WILL REMAIN POSSIBLE FOR THE NEXT FEW
DAYS...THOUGH TODAY LOOKS THE MOST IDEAL FOR ANY THUNDERSTORM
ACTIVITY. THE NEXT CONCERN WILL BE TUESDAY AFTERNOON AND
EVENING...WHEN STRONG WINDS WILL BE POSSIBLE ACROSS THE I-80
CORRIDOR.

&&

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

&&

$$

SHORT TERM...BRANHAM
LONG TERM...ANGLIN
AVIATION...PS
FIRE WEATHER...BRANHAM








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