Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 271716
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1016 AM MST TUE JAN 27 2015

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

WRN CONUS RIDGE WITH AXIS NEAR/ALONG WRN BORDER OF WY...TRANSLATING
SLOWLY EWD. OLD BAJA COL IS NOW OPENING AND HEADING THIS DIRECTION.
SFC SHOWS HI P OVR THE WRN CWA...WITH LOW P OFF TO THE N AND E.

BEGINNING OF FCST HAS SOME PATCHY FOG OVR SMALL PORTIONS OF THE
CNTRL/NRN BASINS AND WRN VALLEYS. OTHERWISE...MOSTLY SKIES WITH
PLENTY OF SUNSHINE AND UNSEASONABLY WARM TEMP WILL RULE THE DAY ONCE
AGAIN EXCEPT FOR THE SWRN FA WHERE CLOUDS FROM THE SW CONUS
COL/DISTURBANCE WILL START TO INFILTRATE THE REGION BY MID-DAY. BY
LATE AFTERNOON/EVENING...WRN WY WILL BE THE FIRST TO FEEL THE
PRESENCE OF THE OLD COL...WITH INCREASING MOISTURE/CLOUD AND THE
BEGINNINGS OF PRECIPITATION. MOST OF THE PRECIP WILL START OUT AS
LIQUID BELOW 8000 FT BEFORE MIXING WITH SNOW IN THE
EVENING...BECOMING ALL LIGHT SNOW IN THE EARLY MORNING HRS ACROSS
THE WEST. ADDITIONALLY...THRU TODAY THE SFC P FIELD WILL BECOME
BETTER SUITED FOR PRODUCING GUSTY SW WINDS...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 WARM(ING) LL TEMPS...WILL ALLOW MODERATELY WINDS ALOFT TO HELP
INCREASE THE SFC WINDS ADIABATICALLY. THERE MAY BE AN ISOLATED AREA
OR TWO THAT WILL BLOW AT/NEAR WARNING CRITERIA...SUCH AS OUTER DRIVE
IN NATRONA COUNTY... HOWEVER MOST LOCATIONS STILL LOOK TO REMAIN
BELOW WARNING LEVELS. BUT THIS WILL BE SOMETHING TO WATCH.

OVERNIGHT TONIGHT AND INTO WED MORNING...AS THE UPR WAVE CONTINUES
INTO THE REGION...POP CHANCES RISE ACCORDINGLY THRU THE OVERNIGHT
PERIOD THRU THE DAY WED. HOWEVER...THE FLEETING NATURE OF THIS
DISTURBANCE AND RATHER WARM UPR LEVELS...STARTING OUR NEAR -2C AT H7
AND DECREASING TO ONLY -4ISH THRU WED AM...LOOKS TO PRECLUDE HIGH
QPF OR SNOWFALL THRU THE EVE WED...REMAINING BELOW ADVISORY CRITERIA
FOR THE MOST PART IN BOTH THE MOUNTAINS AND VALLEYS. THE UPR WAVE
ITSELF WILL MAKE A RIGHT TURN ACROSS WY...WITH H7 WINDS TURNING TO
THE NW BY MID-DAY WED...BRINGING SOME CHANCES FOR RAIN...RAIN/SNOW
MIX...OR WET SNOW...TO THE CNTRL AND NRN BASINS BY MID-DAY
WED...CONTINUING E AND S OUT OF THE FA DURING THE EVENING PERIOD. AS
MUCH IN THE WAY OF LIQUID OR MIXED PRECIP PRESENTS ITSELF...IN
ADDITION TO FAST MOVEMENT OF THE SYSTEM IN AND OUT OF THE CWA...NOT
MUCH ACCUMULATION IS EXPECTED E OF THE DIVIDE. TOTAL SNOW
ACCUMULATIONS THROUGH THE DAY WED LOOK TO REMAIN BELOW 3-4 INCHES
FOR MOST MOUNTAIN LOCATIONS...WITH 6 INCHES HARD TO COME BY EXCEPT
AN ISOLATED AREA OR TWO. THE WRN VALLEYS WILL SEE QUITE A MIX OF
PRECIP TYPES WITH ACCUMULATING SNOW AOB 2 INCHES AT MOST. E OF THE
DIVIDE WILL SEE MUCH LESS AS THE BEST PORTION OF THE STORM COMES
THRU DURING THE RELATIVELY WARM DAYTIME PERIOD ON WED...PRODUCING
PERHAPS A HALF AN INCH AROUND THE REGION OVR THE LOWER
ELEVATIONS...WITH THE BIGHORNS GENERALLY GETTING LESS THAN 3 INCHES
AT ANY LOCATION.

THURSDAY...IMPROVING CONDITIONS EVERYWHERE BUT SOMEWHAT COOLER THAN
PREVIOUS DAYS...MORE SEASONAL. A BIT MORE WIDESPREAD PATCHY FOG
AROUND THE FA EARLY...ESPECIALLY E OF THE DIVIDE. THU NIGHT...CLOUDS
BEGIN TO ENCROACH ON THE SWRN/WRN ZONES ONCE AGAIN WELL AHEAD OF THE
NEXT BROAD EPAC TROF DRAGGING SOME SW CONUS MOISTURE INTO THE REGION
OVERNIGHT...WITHOUT MUCH CONSEQUENCE.

.LONG TERM...FRIDAY THROUGH TUESDAY

ON FRIDAY...THE EXTREME NORTHERN EXTENT OF THE PRECIPITATION SHIELD
ASSOCIATED WITH AN UPPER LOW OVER THE DESERT SOUTHWEST/NORTHERN BAJA
COULD IMPACT THE SOUTHERN PORTIONS OF THE FORECAST AREA. IN THE
END IT WILL PROBABLY BE MORE OF A CLOUD SHIELD ACROSS THE SOUTH.
THIS UPPER LOW WILL GRADUALLY SHIFT EAST SOUTHEAST ACROSS THE
SOUTHERN ROCKIES/NORTHERN MEXICO OVER THE WEEKEND AND HAVE VERY
LITTLE OR NO SENSIBLE WEATHER IMPACT ACROSS THE FORECAST AREA
AFTER FRIDAY. ATTENTION THEN TURNS TO THE NORTHERN STREAM WHICH WILL
BE ACTIVE THIS WEEKEND INTO EARLY NEXT WEEK.

GLOBAL MODELS SHOW A SHORTWAVE TROUGH DIVING SOUTHEAST OUT OF SW
CANADA INTO THE NORTHERN ROCKIES/PLAINS LATE FRIDAY NIGHT AND
SATURDAY.  THE ASSOCIATED COLD FRONT IS EXPECTED TO PUSH SOUTH
ACROSS THE AREA LATE FRIDAY NIGHT/SATURDAY MORNING. THE BEST CHANCE
OF SNOWFALL WITH THIS SYSTEM WILL BE ACROSS THE NORTHERN
MOUNTAINS...ESPECIALLY THE BIGHORN MTS SATURDAY. THE GFS AND ECMWF
ARE ALSO HINTING AT UPSLOPE CONDITIONS DEVELOPING EAST OF THE DIVIDE
SATURDAY/SATURDAY EVENING. WILL HAVE SOME SLIGHT POPS IN THE LOWER
ELEVATIONS EAST OF THE DIVIDE TO ACCOUNT FOR THIS. IN THE
END...SNOWFALL AMOUNTS APPEAR TO BE ON THE LIGHT SIDE WITH THIS
SYSTEM. MODELS SHOW ANOTHER SYSTEM DIVING SOUTH OUT OF CANADA LATE
SUNDAY/SUNDAY NIGHT GIVING ANOTHER SHOT FOR SOME SNOWFALL AND A
REINFORCING SHOT OF CANADIAN AIR. HAVE TRENDED TEMPERATURES COOLER
FOR THIS WEEKEND. IN WAKE OF THE SYSTEM SUNDAY...A MOIST NORTHWEST
FLOW AND YET ANOTHER DISTURBANCE ARE POSSIBLE MONDAY KEEPING CHANCES
OF SNOWFALL GOING ACROSS THE WEST AND NORTH. THIS WILL ALSO KEEP
TEMPERATURES SEASONAL TO SLIGHTLY BELOW AVERAGE MONDAY. MODELS
DIVERGE SIGNIFICANTLY TUESDAY WITH THE GFS SHOWING THE FLOW BECOMING
MORE WESTERLY WITH AN APPROACHING LOW AMPLITUDE PACIFIC
SYSTEM...WHILE THE ECMWF KEEP THE NORTHWEST FLOW. FOR NOW WILL HAVE
SOME SLIGHT POPS WEST...DRY EAST WITH A SLIGHT WARMING TREND.

&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS WILL OCCUR EAST OF THE CONTINENTAL DIVIDE THROUGH 12Z
WEDNESDAY.

AREAS OF FOG OR LOW CLOUDS WILL OCCUR IN THE FAR WEST VALLEYS
INCLUDING THE AFTON AND JACKSON AIRPORTS. MVFR TO LIFR CONDITIONS
CAN BE EXPECTED UNTIL 20Z. OTHERWISE...VFR CONDITIONS WILL PREVAIL
WEST OF THE CONTINENTAL DIVIDE THROUGH 00Z. AFTER 00Z AREAS OF SNOW
WILL OCCUR IN THE MOUNTAINS WITH A MIX OR RAIN OR SNOW IN THE
WESTERN VALLEYS. EXPECT SOME MVFR CONDITIONS THROUGH 12Z WED IN THE
WESTERN VALLEYS INCLUDING THE KJAC AIRPORT. SHOWERS WILL SPREAD EAST
OF THE DIVIDE AFTER 12Z WEDNESDAY.

&&

.FIRE WEATHER...

FIRE DANGER REMAINS LOW FOR MOST AREAS. ANOTHER DAY OF POOR
MIXING/AND RELATIVELY LOW INVERSION HEIGHTS NORTH OF A ROCK SPRINGS
TO CASPER. ALONG AND SOUTH OF THIS LINE...EXPECT GUSTY SW WINDS OF
15 TO 35 MPH. POOR SMOKE DISPERSION IS ALSO FORECAST MOST OF THE
FORECAST AREA TODAY...BUT WILL IMPROVE QUITE A BIT ON WEDNESDAY AS A
QUICK HITTING WARM WINTER WEATHER SYSTEM ROLLS THROUGH WYOMING.
TONIGHT...INCREASED MOISTURE ACCOMPANYING THE UPPER LEVEL WINTER
DISTURBANCE WILL BRING PRECIPITATION INTO THE WEST THEN NORTHWEST
ZONES...TURNING EASTWARD ACROSS THE REST OF THE FORECAST AREA ON
WEDNESDAY. EVERYONE WILL STAND A CHANCE OF SOME MEASURABLE
PRECIPITATION...HOWEVER AMOUNTS WILL GENERALLY REMAIN BELOW A TENTH
OF AN INCH FOR MOST ANY LOCATION.

&&

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

&&

$$

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









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