Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 190941
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
341 AM MDT SAT APR 19 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

WV IMAGERY STILL SHOWS PROGRESSIVE/FAST MOVING NRN BRANCH OF POLAR
FLOW ATOP SOMEWHAT SLOWER SRN BRANCH OF SUB-TROPICAL FLOW STRETCHING
ACROSS THE ENTIRE CONUS. THERE ARE NO LESS THAN 5 ACTIVE UPR LOWS
ENCOMPASSING THE CONUS...WITH EACH TRYING TO STEAL SOME THUNDER FROM
THE OTHER...KEEP ALL IN CHECK FOR THE MOST PART. HERE...UPR TROF
THRU WITH A COUPLE OF MOSTLY DRY FRONTS DRAPED ACROSS THE SRN AND
NRN FA. BENIGN HIGH PRESSURE WITH WEAK GRADIENT SLOWLY INFILTRATING
FROM THE NW...REIGNING IN THE WINDS FOR A WHILE ANYWAY.

GENERALLY...TODAY WILL BE SLIGHTLY COOLER THAN FRIDAY...WITH HIGH
TEMPS STILL REACHING INTO THE MIDDLE AND UPPER 60S FOR MOST OF THE
LOWER ELEVATIONS. OTHERWISE...NEARLY STATIONARY FRONT SET UP NEAR/
NORTH OF THE WY/CO BORDER IN OUR SRN MOST ZONES WILL AID IN RENEWED
CONVECTIVE DEVELOPMENT BY MID DAY IN A LARGELY DRY ADIABATIC
ATMOSPHERE. THIS AREA MAY LIFT FAR ENOUGH NORTH THAT SOME ACTIVITY
MAY PRESENT ITSELF OVR SRN NATRONA COUNTY TOO. WON`T HELP MUCH
HOWEVER AS CONVECTIVE MODE WILL HAVE LITTLE MOISTURE TO WORK
WITH...YIELDING MOSTLY DRY SHOWERS/STORMS WITH GUSTY WINDS.

SUNDAY WILL BE NICE OVERALL. THE AFTERNOON WILL OFFER LOW END
CHANCES FOR ISOLATED TO WIDELY SCATTERED SHOWERS WITH SOME THUNDER
AS A WEAK UPR LVL DISTURBANCE AND SFC FRONT RACE THROUGH THE FA.
TIMING AND MARGINALLY AVAILABLE MOISTURE WILL LIMIT THE CONVECTIVE
AREA TO OUR SRN AND SERN ZONES. HOWEVER...THIS WILL BE ANOTHER CASE
OF HIGH BASED SHOWERS/FEW STORMS WITH LITTLE RAIN...AND MORE GUSTY
WINDS. MONDAY THRU MOST OF THE DAY...UPR RIDGE AND STABLE ATMOSPHERE
IN PLACE. BY EVENING HOWEVER...RIDGE AXIS STARTS TO HEAD OUT WHILE
TROF FROM THE WEST BEGINS TO MOVE IN WITH PVA STARTING AS PART OF
POLAR JET...CURRENTLY HOVERING OVR THE EPAC REGION W OF
WA/OR...WORKS ITS WAY INTO THE WRN MOUNTAINS WITH A LITTLE MOISTURE.
THIS WILL HERALD THE BEGINNING OF NEW CYCLOGENESIS IN THE PAC NW
STATES THAT WILL AFFECT OUR CWA IN SOME RESPECT THROUGH THE MIDDLE
OF NEXT WEEK.

.LONG TERM...TUESDAY THROUGH SATURDAY

UPPER LOW ALONG THE EASTERN END OF THE ALEUTIANS EARLY THIS MORNING
WILL DIG INTO THE EASTERN PACIFIC AND MOVE ONTO THE WEST COAST
TUESDAY MORNING...WITH UPPER TROUGH LIFTING ACROSS THE ROCKIES ON
WEDNESDAY.  ASSOCIATED SURFACE COLD FRONT WILL SLOWLY MOVE EAST
ACROSS IDAHO TUESDAY...INTO THE WEST TUESDAY AFTERNOON...AND ACROSS
CENTRAL WYOMING TUESDAY NIGHT.  ECMWF AND GFS SPREAD INCREASES AS
THE UPPER TROUGH CROSSES THE DIVIDE...THE ECMWF REMAINS QUICKER
BUILDING A RIDGE IN BEHIND THE TROUGH ON THURSDAY WHILE THE GFS
KEEPS A COOL UNSETTLED NW FLOW OVER THE AREA...BEFORE BUILDING THE
RIDGE IN THURSDAY NIGHT.  OPERATIONAL ECMWF IS SLIGHTLY FASTER THAN
THE EC ENSEMBLE MEAN WHILE THE GFS OPERATIONAL IS SLIGHTLY SLOWER
AND DEEPER THAN ITS ENSEMBLE MEAN.  SPLITTING THE DIFFERENCE WOULD
PUT THE UPPER TROUGH AXIS ROUGHLY ALONG 100W BY 00Z FRIDAY AND THE
UPSTREAM RIDGE ALONG 115W...WITH THIS RIDGE TRANSLATING THE AREA ON
FRIDAY AS NEXT PACIFIC TROUGH PUSHES ONTO THE WEST COAST.

FOR SENSIBLE WEATHER...

ON TUESDAY...VERY MILD AND WINDY CONDITIONS WILL DEVELOP ACROSS
CENTRAL AREAS AS PACIFIC COLD FRONT PUSHES ACROSS IDAHO WITH
INCREASING CHANCES OF SHOWERS AND THUNDERSTORMS ACROSS THE
WEST...SHOWERS AND ISOLATED STORMS SPREADING EAST LATE IN THE DAY.
SNOW LEVELS WILL REMAIN QUITE HIGH TUESDAY AHEAD OF THE
FRONT...GENERALLY AROUND 10KFT AND UP. RAPID SNOW MELT AND
SIGNIFICANT RISES IN CREEKS AND STREAMS WILL BE A CONCERN WITH THE
WARM TEMPERATURES...ESPECIALLY WITH THE POTENTIAL FOR RAIN NEAR
AND BELOW 10KFT.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...COLD FRONT WILL PUSH ACROSS THE
AREA SPREADING SHOWERS AND ISOLATED THUNDERSTORMS EAST OF THE DIVIDE
WITH SNOW LEVELS LOWERING TO THE VALLEY FLOORS IN THE WEST.  WNW
MOIST CYCLONIC FLOW ON BACKSIDE OF TROUGH LOOKS TO BRING SIGNIFICANT
SNOW ACCUMULATIONS FROM TETON...TOGWOTEE PASS NORTH TO YNP AND
THE BEARTOOTH PASS AREA WEDNESDAY AND WEDNESDAY NIGHT. GUSTY
DOWNSLOPE WEST WINDS WILL HINDER PRECIPITATION EAST OF THE DIVIDE
BEHIND THE COLD FRONT ON WEDNESDAY WITH THE BEST CHANCES OF RAIN
OR A RAIN AND SNOW MIX ACROSS THE NORTH AND SWEETWATER COUNTY.
HOWEVER...COLDER AND UNSTABLE NW FLOW PREVAIL BEHIND THE SYSTEM
WEDNESDAY NIGHT WITH SIGNIFICANT SNOW POSSIBLE IN THE BIGHORN
RANGE WITH POSSIBLY SOME HEAVIER CONVECTIVE SNOWBANDS FORMING IN
THE CENTRAL BASINS.

THURSDAY...FORECAST MAINTAINS CHANCES OF SNOW SHOWERS IN THE
NORTHERN MOUNTAINS WITH SLIGHT CHANCES OF RAIN/SNOW SHOWERS ACROSS
THE LOWER ELEVATIONS OF THE NORTH.  GUSTY W-NW WINDS AND SEASONABLY
COOL CONDITIONS OTHERWISE.

FRIDAY AND SATURDAY...WARMING TREND WITH BACKING SW FLOW AHEAD OF
NEXT PACIFIC TROUGH WITH INCREASING CHANCES OF SHOWERS IN THE
WEST...SLIGHT CHANCES OF SHOWERS EAST OF THE DIVIDE ON SATURDAY.


&&

.AVIATION.../12Z ISSUANCE/

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

THE EXTENT OF STRATUS IN WAKE OF A COLD FRONT OVER NATRONA
COUNTY...POSSIBLY IMPACTING KCPR...REMAINS IN QUESTION EARLY THIS
MORNING. WHETHER OR NOT TO KEEP THE BKN020 FOR KCPR WILL BE DECIDED
CLOSE TO THE 12Z TAF ISSUANCE TIME. HOWEVER...WHAT STRATUS DOES FORM
SHOULD LIFT OR SCATTER OUT BY AROUND 15Z. OTHERWISE...VFR CONDITIONS
WITH ONLY FEW-SCT HIGH CLOUDS AND MAINLY LIGHT WINDS ARE EXPECTED
THROUGH THE FORECAST PERIOD.

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

PATCHY FOG COULD OCCUR IN THE FAR WESTERN VALLEYS THIS MORNING WHERE
RAIN OCCURRED FRIDAY. OTHERWISE...THE MAIN AVIATION CONCERN WILL BE
THE POSSIBILITY OF ISOLATED CONVECTION SOUTH OF INTERSTATE 80. THIS
ACTIVITY SHOULD REMAIN SOUTH OF THE KRKS TERMINAL...BUT THE TERMINAL
COULD SEE SOME OUTFLOW WINDS FROM THE ACTIVITY. OTHERWISE...VFR
CONDITIONS AND LIGHT WINDS ARE EXPECTED.

&&

.FIRE WEATHER...

TODAY...HIGH TEMPERATURES WILL BE WARM AND SEASONAL...WITH
MUCH LIGHTER WINDS THAN ON FRIDAY. ISOLATED CHANCES FOR MOSTLY DRY
SHOWERS OR AN ISOLATED THUNDERSTORM WILL BE POSSIBLE SOUTH OF A ROCK
SPRINGS TO CASPER LINE.  SUNDAY WILL BE SIMILAR IN MANY
RESPECTS...WITH HIGH TEMPERATURES A FEW DEGREES WARMER AND SLIGHT
CHANCES FOR SHOWERS A JUST BIT FURTHER NORTH. WINDS WILL BEGIN TO
SLOWLY INCREASE MONDAY NIGHT AS WILL CHANCES FOR PRECIPITATION IN
THE WESTERN MOUNTAIN ZONES...AS THE NEXT UPPER LEVEL DISTURBANCE
APPROACHES FROM THE WEST...HERALDING THE BEGINNING OF A COUPLE OF
DAYS OF PRECIPITATION OUT WEST. SIGNIFICANT MOUNTAIN SNOWS WILL BE
POSSIBLE STARTING TUESDAY NIGHT. OTHERWISE...WARM AND DRY ACROSS THE
CENTRAL AND SOUTHERN DISPATCH ZONES THROUGH TUESDAY NIGHT...WITH
WINDY CONDITIONS COMMENCING ACROSS ALL ZONES FROM TUESDAY NIGHT AND
LASTING THROUGH THURSDAY. THERE WILL BE SOME ENHANCED FIRE
DANGER...ESPECIALLY ON TUESDAY...AS THE WARMEST TEMPERATURE OF THE
SEASON COMBINE WITH THE STRONG WINDS. COOLER TEMPERATURES BOTH
WEDNESDAY AND THURSDAY WILL THEN MODERATE THE DANGER TO SOME
EXTENT.

&&

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

$$

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








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