Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 300521
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1121 PM MDT WED APR 29 2015

.SHORT TERM...TONIGHT THROUGH THURSDAY (ISSUED AT 223 PM MDT)

RIDGE AXIS SHIFTING EAST OF THE AREA AS SHORTWAVE AND COLD FRONT
APPROACH FROM THE WEST. EARLY THIS AFTERNOON THE COLD FRONT EXTENDED
FROM NWRN MT INTO CENTRAL ID. THIS COLD FRONT WILL CONTINUE MOVING
EWD AND ENTER OUR NWRN ZONES THIS EVENING AND ENTER INTO OUR CENTRAL
ZONES THURSDAY MORNING WITH SOME GUSTY NORTH WIND. AHEAD OF IT...WE
STILL EXPECT GUSTY WEST WIND ALONG THE LEE OF THE MTNS TONIGHT.
AN ISOLATED SHOWER OR PERHAPS A BRIEF TSTM IS STILL POSSIBLE IN THE
NW CORNER THIS EVENING. GENERALLY ISOLATED SHOWERS WILL OCCUR WITH
THE FRONTAL PASSAGE LATER TONIGHT INTO THURSDAY MORNING...MAINLY
OVER THE MOUNTAINS AND HIGHER TERRAIN. A FEW BUILDUPS ARE EXPECTED
THURSDAY AFTERNOON BUT INSTABILITY STILL LOOKS LIMITED WITH 100-200
J/KG IN THE MODIFIED SOUNDINGS. COULD EVEN BE TOO COOL BEHIND THE
FRONT TO BREAK THE CAP AND TOO DRY AHEAD OF IT TO PRODUCE MUCH.
ALTHOUGH...RIGHT ENTRANCE REGION OF A LITTLE JET STREAK MAY PROVIDE
SOME SUPPORT. STILL LOOKS LIKE IDEA OF JUST ISOLD LOOKS GOOD WITH
ANY TSTMS PROBABLY CONFINED TO AREA WHERE THE FRONT INTERSECTS THE
MOUNTAINS. NARROW WIND OF MORE SHOWERS IS CERTAINLY POSSIBLE
WHERE THE FRONT...TERRAIN AND JET STREAK ALL INTERACT. OTHERWISE...
COOLER BEHIND THE COLD FRONT BY 10-15 DEGREES...60S MAINLY INSTEAD
OF 70S TO LOWER 80S.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

A WEAK WAVE OF LOW PRESSURE WILL MOVE THROUGH THE AREA WEDNESDAY
NIGHT...WITH A FEW SHOWERS AND THUNDERSTORMS LINGERING INTO THE
EVENING. WITH THE DEPARTURE OF THIS SYSTEM...ZONAL FLOW WILL BEGIN
TO BUILD OVER THE AREA...WITH INCREASING DRY CONDITIONS EXPECTED.
SOUTHERN WYOMING MAY SEE VERY ISOLATED ACTIVITY AS MOISTURE PUSHES
ACROSS COLORADO...BUT COVERAGE SHOULD NOT BE SIGNIFICANT.

THESE DRY CONDITIONS WILL PERSIST THROUGH SATURDAY AFTERNOON. BY
SATURDAY EVENING...A SLIGHT SOUTHWEST TURN WILL OCCUR IN THE FLOW
PATTERN...JUST ENOUGH TO PERMIT INCREASED MOISTURE OVER THE FORECAST
AREA. SHOWER ACTIVITY WILL BE POSSIBLE...ESPECIALLY AGAIN ACROSS
SOUTHERN AND SOUTHWESTERN WYOMING...WITH STRONGER ZONAL FLOW
REMAINING ACROSS THE NORTHERN PORTION OF THE FORECAST AREA. THE NEXT
MORE SIGNIFICANT PUSH OF MOISTURE WILL MOVE OVER WESTERN AND CENTRAL
WYOMING SUNDAY NIGHT AND INTO MONDAY...BUT IS EXPECTED TO WEAKEN
THROUGH MONDAY MORNING AND AFTERNOON.

A DIGGING TROUGH OFF THE COAST OF CALIFORNIA WILL HELP TO FURTHER
PULL THE FLOW TO BECOME MORE SOUTHWEST EARLY TUESDAY MORNING...WITH
ANOTHER PUSH OF MOISTURE EXPECTED OVER THE STATE. SHOWERS AND
ASSOCIATED THUNDERSTORMS WILL REMAIN POSSIBLE THROUGH TUESDAY
AFTERNOON WITH THIS SYSTEM.

MODEL VARIANCES LEAVE A LOT OF DEBATE IN THE FORECAST PERIODS BEYOND
TUESDAY. THE GFS IS THE MORE PESSIMISTIC MODEL WITH WIDESPREAD
PRECIPITATION INDICATED THROUGH WEDNESDAY EVENING. THE ECMWF
MEANWHILE MOVES THE MORE OFFENDING SYSTEM THROUGH TO THE CENTRAL
PLAINS WEDNESDAY...WITH DRYING CONDITIONS POSSIBLE OVER MUCH OF
WYOMING THROUGH WEDNESDAY EVENING.

TEMPERATURES WILL REMAIN GENERALLY MILD THROUGH THE FORECAST
PERIOD...WITH SLIGHT COOL DOWNS ANTICIPATED WITH THE PERIODIC
ARRIVAL OF MOISTURE.

&&

.AVIATION.../06Z ISSUANCE/

A COLD FRONT WILL MOVE INTO THE WEST AND NORTH OVERNIGHT AND THEN
PUSH SOUTHWARD DURING THE DAY THURSDAY. A NORTH TO NORTHWEST WIND
WILL OCCUR BEHIND THE FRONT. ISOLATED SHOWERS WILL OCCUR OVER THE
NORTH WITH THE FRONTAL PASSAGE AND THRU 18Z. LOCAL MVFR CONDITIONS
MAY OCCUR IN THE NORTH AS WELL UNTIL 18Z. ISOLATED TO WIDELY
SCATTERED SHOWERS WILL SPREAD SOUTH INTO CENTRAL WY AFTER 18Z
THURSDAY THROUGH 01Z FRIDAY. A THUNDERSTORM OR TWO CANNOT BE RULED
OUT. IN FAR SOUTHERN WY ISOLATED SHOWERS AND STORMS ARE POSSIBLE...
BUT NOT IMPACTING KRKS AIRPORT. THE COLD FRONT PUSHES INTO SOUTHERN
WY AFTER 01Z FRIDAY WITH THE WIND TURNING TO THE EAST OR NORTHEAST.
ANY LINGERING SHOWERS WILL END BY 03Z FRIDAY WITH VFR CONDITIONS
PREVAILING.

&&

.FIRE WEATHER...

ISOLATED EARLY EVENING THUNDERSTORMS ARE POSSIBLE IN THE NORTHWEST
CORNER OF THE STATE. A COLD FRONT ON THURSDAY WILL PRODUCE MORE WIND
BUT ALSO COOLER TEMPERATURES...MORE CLOUD COVER AND HUMIDITY. VERY
WARM AND DRY CONDITIONS WILL RETURN FRIDAY WITH RELATIVELY LIGHT
WINDS KEEPING FIRE DANGER UNDER CONTROL. THERE WILL ALSO BE A
CHANCE ON THURSDAY FOR MAINLY MOUNTAIN DERIVED/MAINTAINED ISOLATED
TO WIDELY SCATTERED SHOWERS WITH PERHAPS A SHORT-LIVED
THUNDERSTORM OR TWO WITH LITTLE LIGHTNING. THE WEEKEND WILL
GRADUALLY SEE MOISTURE MOVING UP FROM THE SOUTH LEADING TO
ISOLATED THUNDERSTORMS IN THE FAR SOUTH SATURDAY AND JUST ABOUT
EVERYWHERE ON SUNDAY. SATURDAY WILL BE QUITE WARM AND DRY WITH
RH`S IN THE TEENS ACROSS AREAS EAST OF THE DIVIDE.

&&

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

&&

$$

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










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