Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 251010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN JAN 25 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

NW FLOW CONTINUES OVR WY WITH RIDGE WEST AND TROF EAST. SMALL SW OVR
WRN MT AND ANOTHER FURTHER UPSTREAM ACROSS SRN BC...BOTH HEADED THIS
WAY. N/S JET ACROSS ERN WY...NOSING INTO THE FRONT RANGE OF CO.
AND...AS ADVERTISED FOR THE LAST SEVERAL DAYS...A NEARLY COL OVR THE
EPAC WEST OF BAJA...WHICH STILL LOOKS TO HAVE CONSEQUENCES ACROSS
PORTIONS OF WY BY MID WEEK. SFC SHOWS HI P WEST WITH A DECENT
LOWERING P GRAD TO THE EAST...PROVIDING SOME MIXED AREAS WITH GUSTY
WINDS...ESPECIALLY ACROSS THE SRN FCST ZONES.

BEGINNING OF FCST HAS SOME AREAS OF PATCHY FOG IN THE USUAL SPOTS.
SOME MODEST MOISTURE STILL HANGING AROUND THE NRN/NWRN CWA WILL
TRANSLATE S AND EAST TODAY. THIS TOGETHER WITH THE DISTURBANCES
MENTIONED ABOVE WILL KEEP SOME LOW END POPS AROUND THE WRN AND NRN
ZONES THRU AT LEAST MID-DAY...WITHOUT MUCH IN THE WAY OF SUBSTANCE.

MONDAY...SKIES CLEAR...INVERSIONS SET BACK IN FOR ANOTHER MORNING
STARTING WITH PATCHY FOG...BUT CLEARING/SUNNY SKIES OTHERWISE...
UNDER AN INCREASING INFLUENCE OF THE WRN RIDGE OF HI P. THIS WILL
VIRTUALLY ELIMINATE NW FLOW BY MON NIGHT. TUE WILL BE ANOTHER SUNNY
DAY ACROSS MOST OF THE FA EXCEPT FOR THE SWRN ZONES WHICH WILL HAVE
INCREASING CLOUDS THRU THE DAY AS THE BAJA COL IS KICKED THIS
DIRECTION. ADDITIONALLY...THRU THE DAY ON TUE...SFC P FIELD WILL
BECOME BETTER SUITED FOR PRODUCING GUSTY SW WIND...WITH ADDITIONAL
HELP IN THIS CASE FROM ALOFT AS UPR RIDGE ORIENTS ITSELF FAR ENOUGH
E TO TO ALLOW NEARLY UNIDIRECTIONAL SW FLOW THRU MID LVLS. THIS
TOGETHER WITH WARMING LL TEMPS...WILL ALLOW MODERATELY STRONGER
WINDS ALOFT TO INCREASE THE SFC WINDS ADIABATICALLY.

TUE NIGHT INTO WED MORNING...AS THE COL FROM BAJA HEADS THIS
DIRECTION...IT WILL QUICKLY BECOME AN OPEN WAVE BUT STILL BE ABLE TO
BRING SOME MOISTURE WITH IT...BRUSHING THE WRN TO NWRN FCST AREA
THRU THE OVERNIGHT PERIOD. AS THIS HAS BEEN FCST FOR SOME TIME
NOW...AND ASSUMING THE UPSTREAM KICKER ARRIVES WITHIN THE CRITICAL
DISTANCE BY MONDAY AFTERNOON...POP CHANCES WILL RISE ACCORDINGLY
THRU THE OVERNIGHT PERIOD TUE. HOWEVER...THE FLEETING NATURE OF THIS
DISTURBANCE CURRENTLY LOOKS TO PRECLUDE TOO MUCH QPF OR SNOWFALL
THRU THE END OF THIS FCST PERIOD...REMAINING BELOW ADVISORY CRITERIA
FOR THE MOST PART.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
SYNOPSIS...COOLER CONDITIONS WITH SOME RAIN AND SNOW SHOWERS WILL
SPREAD EAST OF THE DIVIDE WEDNESDAY.  GENERALLY DRY AND SEASONABLY
MILD CONDITIONS WILL PREVAIL ACROSS MOST AREAS THURSDAY THROUGH
SUNDAY.  THE ONE EXCEPTION WILL BE CHANCES OF RAIN AND SNOW SHOWERS
PUSHING NORTH INTO SOUTHERN WYOMING ON FRIDAY BEFORE BEING
SUPPRESSED FURTHER SOUTH OVER THE WEEKEND.


DISCUSSION...BOTH GFS AND ECMWF HAVE SHORTWAVE TROUGH...REMNANTS OF
BAJA UPPER LOW...PUSHING EAST OUT OF SOUTHEAST WYOMING INTO THE
CENTRAL HIGH PLAINS 12Z-18Z WED...WITH CLIPPER IN NORTHERN STREAM
DIVING SE INTO THE NORTHERN HIGH PLAINS.  THE NORTHERN STREAM
CLIPPER WILL DRIVE A CANADIAN COLD FRONT SOUTH ACROSS THE AREA
DURING THE DAY WEDNESDAY.  GFS AND ECMWF BOTH SHOW FETCH OF
SUB-TROPICAL MOISTURE LINGERING OVER AREA BEHIND SOUTHERN STREAM
SYSTEM TO INTERACT WITH CANADIAN COLD FRONT THROUGH THE DAY.
OVERALL....RAIN AND SNOW SHOWER COVERAGE SHOULD BE SPOTTY OVER THE
LOWER ELEVATIONS THROUGH THE DAY BUT WE COULD SEE MORE ORGANIZED
BANDING ACROSS CENTRAL WYOMING IN UNSTABLE NW FLOW...ESPECIALLY
DOWNWIND OF THE OWL CREEK MTNS AND SOUTHERN BIGHORN RANGE.

GFS KEEPS BROAD TROUGH FROM BAJA REGION INTO THE EASTERN GREAT BASIN
ON WEDNESDAY NIGHT AND THURSDAY...CONTINUING TO FEED SUB-TROPICAL
MOISTURE INTO SOUTHERN AND CENTRAL WYOMING.  ECMWF SHOWS SHARPER
DEFORMATION AREA KEEPING THIS MOISTURE TO OUR SOUTH AS BROAD RIDGE
BUILDS ACROSS THE NORTHERN ROCKIES WITH WARM AIR ADVECTION ACROSS WYOMING.
FORECAST IS WEIGHTED TOWARD ECMWF`S DRIER SCENARIO.

BOTH GFS AND ECMWF SHOW OVERALL AGREEMENT BRINGING SUB-TROPICAL
MOISTURE PLUME INTO SOUTHERN WYOMING ON FRIDAY WITH BROAD TROUGH
OVER THE SW U.S.  THIS MAY BRING SOME RAIN AND SNOW SHOWERS UP TO
AROUND INTERSTATE 80 ON FRIDAY BEFORE UPPER LOW CLOSES OFF OVER BAJA
CALIFORNIA ON SATURDAY WITH MOISTURE PLUME GETTING SUPPRESSED
FURTHER SOUTH OF WYOMING OVER THE WEEKEND.    OVERALL MODEL TREND
WITH NORTHERN STREAM FRIDAY THROUGH THE WEEKEND HAS BEEN TOWARD
BROADER RIDGE OVER THE NORTHERN ROCKIES...THUS KEEPING ARCTIC
INTRUSIONS FURTHER EAST ACROSS THE NORTHERN PLAINS AND GREAT LAKES
REGION.  SEASONABLY MILD AND DRY CONDITIONS EXPECTED FOR MOST OF THE
AREA OVER SUPERBOWL WEEKEND.


&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL OVER MOST OF THE TODAY. SOME SNOW
SHOWERS WILL OCCUR OVER THE NORTHERN MOUNTAINS UNTIL 18Z WITH LOCAL
MVFR CONDITIONS. IN THE FAR WEST FROM YELLOWSTONE PARK TO KEMMERER
AREAS OF MVFR AND IFR CONDITIONS WILL OCCUR UNTIL 19Z. THEN VFR
CONDITIONS WILL PREVAIL OVER THE FAR WEST AFTER 19Z. GUSTY WIND WILL
OCCUR AT KRKS AND KCPR AIRPORTS THROUGH MOST OF THE DAY WITH THE
WIND DECREASING AT KRKS BY 02Z WHILE CONTINUING TO BE WINDY AT KCPR.

&&

.FIRE WEATHER...

FIRE DANGER REMAINS LOW FOR MOST AREAS...WITH RH VALUES REMAINING
ABOVE 50 PERCENT FOR LOCATIONS BELOW 7000 FEET...TO 25 PERCENT OR
LOWER ABOVE TIMBERLINE WHERE ROCKS AND SNOW ABOUND. MIXING/INVERSION
HEIGHTS WILL REMAIN ON THE LOWER SIDE...1000 TO 1500 FEET AT MOST...
THROUGH AT LEAST TUESDAY FOR MOST LOCATIONS SOUTH OF A ROCK SPRINGS
TO CASPER LINE. POOR SMOKE DISPERSION IS ALSO FORECAST THROUGH THE SAME
PERIOD. SIGNIFICANT PRECIPITATION IS NOT EXPECTED ANYWHERE OVER THE
FORECAST AREA UNTIL TUESDAY NIGHT WHEN INCREASED MOISTURE FOLLOWING
AN UPPER LEVEL DISTURBANCE HEADS INTO THE WEST AND NORTHWEST.

&&

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

$$

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









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