Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281032
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
332 AM MST WED JAN 28 2015

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

WRN CONUS FLAT RIDGE WITH AXIS E OF ERN BORDER OF WY...TRANSLATING
SLOWLY EWD. OPEN WAVE MOVING THRU THE RIDGE AND ACROSS THE
INTERMOUNTAIN STATES...WITH LIGHT RAIN...RAIN SNOW MIX AND LIGHT
SNOW BEING REPORTED IN RATHER SCATTERED FASHION JUST WEST OF THE CWA
ATTM. KEMMERER IS THE FIRST OT SHOW SIGNS OF WET SNOW EARLY THIS
MORNING. SFC SHOWS HI P OVR THE WRN CWA...WITH LOW P OFF TO THE N
AND E.

BEGINNING OF FCST HAS RELATIVELY WARM...FOR THIS TIME OF YEAR...UPR
EMBEDDED WAVE MAKING A RIGHT TURN AND HEADING ACROSS THE FA FROM W
TO E THRU THE REST OF TODAY...CONTINUING E AND S OUT OF THE FA
DURING THE EVENING PERIOD. WWA OUT FOR WRN ZONES 12 13 AND 23 THRU
THE MORNING HOURS AS THE INITIAL PUSH OF THE UPR DISTURBANCE AND
ASSOCIATED MOISTURE RUNS INTO THE WRN MOUNTAINS. ELSEWHERE...THE
QUICK MOVING NATURE OF THIS DISTURBANCE...AND LESS LIFTING
TERRAIN...TOGETHER WITH RATHER WARM LOW/MID LEVELS...STARTING OUR
NEAR -2C AT H7 AND DECREASING TO ONLY -4 TO -5 THRU THE
PRECIP/DAYTIME PERIOD TODAY...WILL PRECLUDE WINTER WEATHER ADVISORY
CONDITIONS ACROSS THE REST OF THE FA. PRECIP FALLING DURING THE DAY
IN MANY LOCATIONS WILL START AS  RAIN...THEN RAIN/SNOW MIX...OR WET
SNOW. THE MIXED NATURE OF THE PRECIP...IN ADDITION TO FAST MOVEMENT
OF THE SYSTEM THRU THE CWA...NOT MUCH ACCUMULATION IS EXPECTED E OF
THE DIVIDE. ONE PROBLEM THAT MAY ARISE HERE AND THERE WILL BE THE
POSSIBILITY OF FREEZING DRIZZLE OCCURRING INSTEAD OF SNOW. THE SIGNAL
IS THERE BUT NOT STRONG ENOUGH TO PINPOINT THE EXACT LOCATIONS.
TOTAL SNOW ACCUMULATIONS FROM TUE OVERNIGHT THROUGH THE REST OF
TODAY WILL RANGE FROM 2-5 INCHES FOR MOST MOUNTAIN LOCATIONS...WITH
5 TO 8 INCHES FROM THE TETONS INTO THE SWRN PORTION OF
YELLOWSTONE...WHILE THE WRN VALLEYS WILL SEE QUITE A MIX OF PRECIP
TYPES WITH ACCUMULATING SNOW BETWEEN 1 AND 4 INCHES. E OF THE DIVIDE
WILL SEE MUCH LESS ACCUMULATION AS THE BETTER PORTION OF THE STORM
MOVES THRU DURING THE RELATIVELY WARM DAYTIME PERIOD... PRODUCING AN
INCH OR LESS OVR THE LOWER ELEVATIONS...WITH THE BIGHORN MOUNTAINS
GENERALLY SEEING LESS THAN 3 INCHES AT ANY LOCATION.

TONIGHT THRU THURSDAY NIGHT...IMPROVING CONDITIONS EVERYWHERE BUT A
LITTLE COOLER THAN PREVIOUS DAYS...AND MORE SEASONAL. A BIT MORE
WIDESPREAD PATCHY FOG AROUND THE FA TONIGHT AND EARLY
THURSDAY...THEN AGAIN FRIDAY MORNING. ADDITIONALLY...THU
NIGHT...CLOUDS BEGIN TO MOVE INTO THE SRN/SWRN ZONES ONCE AGAIN AS
MOISTURE FROM THE SWRN CONUS GETS DIRECTED INTO THE REGION AROUND A
MEXICO HIGH...AND INCOMING WRN CONUS LOW/TROF...WITHOUT MUCH
CONSEQUENCE. THIS CONDITION WILL CONTINUE THRU THE END OF THE
FCST.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

A SHORTWAVE TROUGH DIVING SOUTHEAST OUT OF SW CANADA WILL IMPACT THE
AREA SATURDAY AND SATURDAY NIGHT. THE ASSOCIATED COLD FRONT IS
EXPECTED TO PUSH SOUTH ACROSS THE AREA SATURDAY AFTERNOON AND
EVENING. THE SNOWFALL WITH THIS STORM SYSTEM SHOULD MAINLY AFFECT
AREAS ALONG AND EAST OF THE DIVIDE. MODELS CONTINUE TO INDICATE SOME
UPSLOPE FLOW DEVELOPING EARLY SATURDAY EVENING IN WAKE OF THE FRONT.
HAVE TRENDED POPS UP...ESPECIALLY OVER THE BIGHORN MTS. THIS IS A
QUICK SYSTEM AND SNOWFALL AMOUNTS LOOK TO BE ON THE LIGHT /SUB
ADVISORY/ SIDE. A COLD NORTHWEST FLOW CONTINUES SUNDAY WITH A
CONTINUED CHANCE OF SNOW...MAINLY OVER THE NORTHWEST/NORTHERN
MOUNTAINS. MODELS HAVE TRENDED DRIER FOR SUNDAY...WITH THE NEXT
SYSTEM NOW PROJECTED TO IMPACT AREAS FARTHER NORTHEAST ACROSS THE
PLAINS/UPPER MIDWEST.

GLOBAL MODELS ARE IN DECENT AGREEMENT WITH A WEST COAST RIDGE
QUICKLY BREAKING DOWN SUNDAY NIGHT...WITH ONE OR TWO LOW AMPLITUDE
PACIFIC SYSTEMS IMPACTING THE AREA MONDAY AND TUESDAY IN A STRONG
ZONAL FLOW. THIS PATTERN GIVES THE WEST A DECENT CHANCE OF
SNOWFALL...WHILE AREAS EAST OF THE DIVIDE SEE DOWNSLOPING AND
GENERALLY DRY CONDITIONS. THE 00Z ECMWF HAS TRENDED TOWARD THE GFS
SOLUTION FROM 24 HOURS AGO. HAVE INCREASED POPS OUT WEST WITH AN
EMPHASIS ON MONDAY/MONDAY NIGHT. TEMPERATURES WILL BE TRICKY
MONDAY ESPECIALLY EAST OF THE DIVIDE AS THE CANADIAN AIR MASS FROM
THIS WEEKEND BEGINS TO MODIFY.

BOTH THE 00Z ECMWF AND GFS SHOW THE PATTERN AMPLIFYING WEDNESDAY
WITH RIDGING DEVELOPING OVER THE WEST COAST AND A TROUGH OVER THE
CENTRAL U.S. HOWEVER...THE ECMWF HAS A STRONG ARCTIC COLD FRONT
RIGHT ON THE WYOMING/MONTANA BORDER WHILE THE GFS IS FARTHER EAST.
THIS WILL BE SOMETHING TO KEEP AN EYE ON...OVER THE NEXT FEW
DAYS.

&&

.AVIATION.../12Z ISSUANCE/

A WEATHER SYSTEM WILL MOVE THROUGH WYOMING TODAY AND EXIT THE AREA
AROUND 00Z THIS EVENING. AREAS OF SNOW WILL OCCUR IN THE WEST UNTIL
20Z...THEN COME TO AN END BY 00Z. EXPECT MVFR TO IFR CONDITIONS AT
TIMES THROUGH 20Z...THEN VFR CONDITIONS WILL PREVAIL BY 00Z AND THEN
VFR CONDITIONS WILL PREVAIL IN THE WEST THROUGH TONIGHT.

EAST OF THE CONTINENTAL DIVIDE AREAS OF SNOW...POSSIBLY MIXED WITH
RAIN WILL OCCUR OVER THE REGION TODAY. EXPECT MVFR TO IFR CONDITIONS
AT TIMES AS THE PRECIPITATION BECOMES ALL SNOW. CONDITIONS WILL
IMPROVE IN THE NORTH AFTER 19Z AS THE SNOW ENDS...THEN IMPROVING IN
THE CENTRAL BETWEEN 22Z AND 00Z. VFR CONDITIONS WILL PREVAIL AFTER
00Z EAST OF THE DIVIDE.

PLEASE SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

&&

.FIRE WEATHER...

FIRE DANGER IS LOW FOR ALL AREAS...AND WILL REMAIN SO THROUGH THE
NEXT WEEK. OTHERWISE...A QUICK HITTING RELATIVELY WARM WINTER
WEATHER SYSTEM WILL ROLL THROUGH WYOMING TODAY...OFFERING BETTER
MIXING AND SMOKE DISPERSION ACROSS THE FORECAST AREA...EXCEPT FOR
THE CENTRAL AND NORTHERN BASINS WHICH WILL REMAIN IN THE POOR
CATEGORY. THIS DISTURBANCE WILL BRING ALSO BRING PRECIPITATION FIRST
INTO THE WEST AND NORTHWEST ZONES...THEN EAST ACROSS THE REST OF THE
FORECAST AREA THROUGH THE DAY TODAY.  MOST LOCATIONS...SAVE THE
SOUTHERN ZONES...WILL STAND A CHANCE OF SOME MEASURABLE
PRECIPITATION...HOWEVER AMOUNTS WILL GENERALLY REMAIN BELOW A TENTH
OF AN INCH FOR MOST LOCATIONS EXCEPT FOR THE HIGHER MOUNTAINS ACROSS
THE WEST WHICH COULD SEE TWICE THAT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 11 AM MST THIS MORNING
WYZ012-013-023.

&&

$$

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






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