Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 210908
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
308 AM MDT THU MAY 21 2015

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

THE ACTIVE WEATHER PATTERN LOOKS TO CONTINUE INTO THE FIRST PART OF
THE HOLIDAY WEEKEND. AS OF RIGHT...WE STILL GAVE A FEW LIGHT SHOWERS
MAINLY WEST OF THE DIVIDE BUT NOTHING OF CONSEQUENCE. THIS LOOKS TO
BE ON OF THE QUIETEST TIMES OF THE SHORT TERM FORECAST PERIOD.
THINGS WILL BECOME MORE ACTIVE THIS AFTERNOON AS ANOTHER SHORTWAVE
APPROACHES THE AREA FROM THE SOUTH AND WEST AND BRINGS ANOTHER ROUND
OF SHOWERS AND THUNDERSTORMS. MUCH LIKE YESTERDAY...THE VAST
MAJORITY OF THESE LOOK TO STAY WEST OF THE DIVIDE. ALSO...WITH MORE
SOUTHERLY FLOW AND MORE SUNSHINE THAN YESTERDAY...TEMPERATURES
SHOULD WARM UP CLOSER TO NORMAL LEVELS...BUT STILL RATHER CHILLY FOR
THIS TIME OF YEAR. A FEW OF THESE STORMS COULD SNEAK EAST OF THE
DIVIDE...BUT MOST AREAS EAST OF THE DIVIDE SHOULD REMAIN MAINLY DRY
MOST OF THE TIME. MOST SHOWERS SHOULD WANE AFTER MIDNIGHT ALTHOUGH A
FEW COULD LINGER AS A DEEPER PUSH OF MOISTURE MOVES TOWARDS THE
AREA.

THE AFOREMENTIONED PUSH OF MOISTURE WILL BEGIN TO PUSH NORTHWARD
ACROSS THE AREA IN THE MORNING...BUT THE BEST CHANCE OF RAIN WILL BE
DURING THE AFTERNOON. AS OF THIS TIME...THE BEST CHANCE OF SHOWERS
WILL BE ACROSS CENTRAL PORTIONS OF THE AREA WITH LESSER CHANCES
FURTHER NORTH. AS FOR THE CHANCE OF ANY STRONGER STORMS...THE BEST
CHANCE WOULD BE FURTHER NORTH WHERE THE START OF THE RAIN WOULD BE
LATER AND THERE COULD BE SOME MORNING SUNSHINE THAT COULD
DESTABILIZE THINGS SOMEWHAT. BY LATER FRIDAY NIGHT...AN INTERESTING
SCENARIO AS BOTH THE NAM AND THE GFS SHOW A DRY SLOT TRYING TO WORK
INTO THE AREA...ALTHOUGH THE NAM IS MORE PRONOUNCED WITH IT THAT THE
GFS IS.

AND THIS LEADS US TO THE QUESTION OF SATURDAY. IF THE MODELS ARE TO
BE BELIEVED...MUCH OF SATURDAY MORNING COULD BE DRY EAST OF THE
DIVIDE...ESPECIALLY THE FURTHER EAST YOU GO. THERE COULD EVEN BE
SOME CLEARING. AND THIS LEADS TO THE POSSIBILITY OF MORE CONVECTIVE
PRECIPITATION RATHER THAN STRATIFORM. AGAIN...IT DEPENDS OF THE
MODEL. THE GFS IS COOLER BUT STILL HAS NEGATIVE LIFTED INDICES AND
UP TO 300 J/KG OF CAPE IN HE AFTERNOON. MEANWHILE...THE
NAM..ALTHOUGH IT TENDS TO OVERDO INSTABILITY A BIT...IT IS SHOWING
AROUND 1000 J/KG OF CAPE OVER PORTIONS OF THE AREA ALONG WITH LIFTED
INDICES DROPPING TO AS LOW AS -5. THE NEW STORM PREDICTION CENTER DAY
3 OUTLOOK BRINGS A MARGINAL AREA INTO SOUTHEASTERN WYOMING AS
WELL. THERE IS ALSO A DECENT JET NEAR THE AREA AND WITH THE LOW
NEAR BY THERE WILL BE SOME DIRECTIONAL SHEAR AROUND. AGAIN...THE
BIG X FACTOR WILL BE HOW MUCH SUNSHINE AND DESTABILIZATION THERE
IS. SOMETHING TO WATCH. BY SATURDAY NIGHT...AGAIN THE QUESTION IS
WHETHER OR NOT THE S WORD WILL ENTER THE FORECAST AGAIN. THIS
SYSTEM STILL LOOKS WARMER THAN THE LAST ONE. THE GFS IS THE
COLDEST WITH -1 CELSIUS AT 700 MILLIBARS WHICH WOULD BRING SNOW
LEVELS DOWN TO AROUND 8000 FEET. THE NAM IS WARMER WITH LEVELS
CLOSER TO 9000 FEET. THE GFS WAS CLOSER LAST TIME THOUGH.
CONTINUITY HAD THIS REPRESENTED FAIRLY WELL SO WE MADE FEW
CHANGES.

.LONG TERM...SUNDAY THROUGH THURSDAY

SUNDAY WILL SEE THE WEATHER SYSTEM MOVE SLOWLY INTO EASTERN WY BY
00Z MONDAY. RAIN WILL BE MORE LIKELY IN THE EASTERN ZONES SUNDAY
WITH SCATTERED RAIN SHOWERS ELSEWHERE. THE WEATHER SYSTEM MOVES OUT
SUNDAY NIGHT WITH SHOWER ACTIVITY DECREASING. MONDAY LOOKS DRIER
CENTRAL AND EAST WITH A WEST FLOW ALOFT. SHOULD SEE SLIGHT CHANCE
FOR SHOWERS AND STORMS OVER MUCH OF THE REGION MON AFTERNOON AND
EVENING. FLOW ALOFT TURNS TO THE WEST SOUTHWEST FOR TUESDAY. DO NOT
SEE A WEATHER DISTURBANCE IN THE FLOW ON TUE BUT THERE IS ENOUGH
MOISTURE AND INSTABILITY FOR CONVECTION TO FIRE UP IN THE WEST AND
SOUTHWEST. ONLY ISOLATED ACTIVITY FOR THE REST OF THE AREA. WEDNESDAY
AND THURSDAY WILL SEE A SOUTHWEST FLOW ALOFT PER THE GFS MODEL
WITH A DECENT WEATHER DISTURBANCE ON THURS PM AND NIGHT. THEN A
POTENTIAL WEATHER DISTURBANCE AGAIN NEXT THURSDAY. THE ECMWF MODEL
IS A TAD DIFFERENT NEXT WED AND THURS WITH LESS POTENT WEATHER
SYSTEMS IN THE FLOW. WILL KEEP THE SCATTERED SHOWERS AND ISOLATED
STORMS IN THE FORECAST BOTH DAYS. AS FOR TEMPS...A COOL DAY ON
SUNDAY THEN WARMING UP A FEW DEGREES FOR MON AND TUE. THEN MAYBE A
LITTLE COOLER WED AND NEXT THURS DUE TO MORE CLOUDS AND MORE
COVERAGE OF SHOWERS/STORMS.


&&

.AVIATION.../12Z ISSUANCE/

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

VFR CEILINGS WILL PREVAIL THROUGH THE FORECAST PERIOD. CLOUD DECK
PERSISTS AT KCPR THIS MORNING WITH DEFORMATION AXIS LINGERING AND
MOIST LOWER ATMOSPHERE IN PLACE. MOUNTAIN TOP OBSCURATIONS WILL
PERSIST THROUGH ABOUT 15Z TODAY...ESPECIALLY FROM KLND EAST TO
VICINITY OF KCPR. EXPECT LESS CLOUD COVER FOR A CHUNK OF TODAY WHICH
WILL AID MIXING AND LIFT CEILINGS. THE NEXT IN A SERIES OF
SHORTWAVES WILL APPROACH SOUTHWEST WYOMING THURSDAY AFTERNOON.
FAVORABLE INSTABILITY AND DYNAMICS WILL BE OVER SOUTHWEST WYOMING.
ISOLATED THUNDERSTORMS WILL MAINLY BE CONFINED TO THE HIGHER TERRAIN
AFTER 21Z/THU AND IS EXPECTED TO DISSIPATE WITH THE SETTING SUN.
HAVE LINGERED VCSH INTO THE 06Z-08Z/FRI TIME FRAME ACROSS CENTRAL
WYOMING...WITH LITTLE IF ANY SHOWER ACTIVITY IMPACTING KWRL OR KCOD.

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

WEAK SHOWERS HAVE DISSIPATED ACROSS THE FAR WEST EARLY THIS MORNING.
EXPECT CEILINGS AND VISIBILITIES TO REMAIN VFR IN THE WESTERN BASINS
AND VALLEYS THROUGH THE FORECAST PERIOD. MOUNTAIN OBSCURATIONS...
ESPECIALLY ABOVE ABOUT 9K-10K FEET WILL BE WIDESPREAD UNTIL ABOUT
15Z TODAY BEFORE SHORTWAVE ENERGY WANES ACROSS THE FAR WEST. THE
NEXT IN A SERIES OF SHORTWAVES WILL ROTATE NORTH THURSDAY AFTERNOON.
SHOWERS WILL BE MOST NUMEROUS OVER THE HIGHER TERRAIN...WITH
DEVELOPMENT OCCURRING BETWEEN 18Z-20Z TODAY. LIFTED INDICIES AND
CAPE ARE SUFFICIENT TO GENERATE WIDELY SCATTERED THUNDERSTORMS AFTER
21Z THIS AFTERNOON. SIMILAR TO LAST NIGHT...THE SHOWERS AND STORMS
WILL CONTINUE UNTIL ABOUT 04Z/FRI WITH SOME SHOWERS LINGERING UNTIL
WELL AFTER 06Z/FRI. CLOUD HEIGHTS OVERNIGHT THURSDAY INTO FRIDAY
WILL BE LOWER...ALBEIT LIKELY STILL VFR...AS A RESULT OF THE
INCREASED LOW-LEVEL MOISTURE ACROSS SOUTHWEST WYOMING.

&&

.FIRE WEATHER...

FIRE DANGER RELATIVELY LOW AS SEASONAL TO COOL AND RELATIVELY MOIST
CONDITIONS PERSIST. A WEAK UPPER LEVEL DISTURBANCE WILL BRING
ISOLATED CONVECTION MAINLY WEST OF THE DIVIDE TODAY. DEEPER MOISTURE
WILL MOVE TOWARD THE AREA FOR FRIDAY AND BRING ANOTHER CHANCE OF A
WETTING RAIN FROM FRIDAY INTO FRIDAY NIGHT. THERE WILL BE A CHANCE
OF SHOWERS AND THUNDERSTORMS THAT WILL PERSIST INTO SATURDAY AS
WELL.

&&

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

&&

$$

SHORT TERM...HATTINGS
LONG TERM...AR
AVIATION...CNJ
FIRE WEATHER...HATTINGS







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