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000
FXUS65 KRIW 020558
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1057 PM MST SUN MAR 1 2015

UPDATE...UPDATED TO ADD 06Z AVIATION DISCUSSION BELOW.

.SHORT TERM...TONIGHT THROUGH MONDAY (ISSUED AT 151 PM)

AFTER COLLABORATING WITH MID TERM FORECASTER...CYS AND WYDOT MET HAVE
DELAYED WATCH FOR SWEETWATER UNTIL 00Z TUESDAY.  ALL WINTER HIGHLIGHTS
NOW IN MID TERM PERIOD. SOME STRATUS AND FLURRIES WILL LINGER
AROUND THE VALLEYS AND BASINS TONIGHT.  WARMING WILL OCCUR MAINLY ACROSS
THE SOUTH WHERE MID TO UPPER 30S HIGHS WILL BE POSSIBLE MONDAY
WHERE SOME SNOW...RAIN MIXED WITH SNOW WILL INCREASE THROUGH THE
AFTERNOON. LEAST WARMING WILL BE IN THE NORTH. CLOUDS WILL SPREAD
UP FROM THE SOUTH WHILE THE NORTH AND CENTRAL AREAS AWAIT THE
CANADIAN BLAST OF COLD AIR SNOW AND WIND THAT WILL MOVE IN MONDAY EVENING.
PLEASE REFER TO CYSWSWRIW FOR MORE DETAILS ON THE IMPENDING
WEATHER CHANGE.

.MID TERM...MONDAY NIGHT THROUGH WEDNESDAY

THE PERIOD BEGINS WITH A CORNUCOPIA OF WINTRY CONDITIONS FOR THE
AREA. THE MAIN SHOW WILL FIRST BE SEEDED BY A SYSTEM THAT WILL
IMPACT MOSTLY AREAS TO OUR SOUTH DURING THE SHORT TERM PERIOD...BUT
IT WILL KICK UP A RICHLY MOIST AIRMASS FOR THIS TIME OF YEAR INTO
CENTRAL AND SOUTHERN WYOMING. THIS WILL GIVE OUR SECOND SYSTEM
SOMETHING TO WORK WITH AS IT DROPS SOUTH OUT OF THE DRY ARCTIC
MONDAY NIGHT. THIS SECOND SYSTEM WILL HAVE A LITTLE BIT OF SUPPORT
UPSTAIRS AS IT IS ACCOMPANIED BY A CYCLONICALLY CURVING JET AND SOME
ROBUST QG FORCING. ALSO THE MODELS ARE SHOWING AN ORGANIZED
BAROCLINIC ZONE WITH THE FRONT AS IT DROPS SOUTH THROUGH THE STATE
MONDAY NIGHT INTO TUESDAY FOLLOWED BY A LONG PERIOD OF UPSLOPE FLOW
FOR AREAS EAST OF THE DIVIDE AS HIGH PRESSURE AT THE SURFACE FILTERS
IN BEHIND THE FRONT. SO THERE WILL BE SEVERAL FEATURES THAT WOULD
SUGGEST SOME AREAS OF SIGNIFICANT SNOW ACCUMULATION WITH THIS
SYSTEM. HOWEVER...IT IS A PRETTY COLD SYSTEM ALOFT SO ONCE THAT
FRONT PASSES BY THE MOISTURE AVAILABLE FOR HEAVY SNOW WILL BE
SQUEEZED OUT AND SHUNTED SOUTH AND EAST. ADDITIONALLY...THERE IS NOT
A LOT OF INSTABILITY ALONG AND BEHIND THE FRONT SO THAT WILL KEEP
MOST OF THE SNOW BANDING AND LOCAL ENHANCEMENTS SOUTH AND WEST OF
THE DIVIDE FOR MONDAY NIGHT INTO TUESDAY. HOWEVER...THE COMBINED
IMPACT OF THE SNOW...WIND...LOW WIND CHILLS AND EXPECTED AFFECTS ON
TRAVEL AND CALVING SEASON LEAD TO A LIBERAL ISSUANCE OF WINTER STORM
WATCHES AND ADVISORIES. MOST ELEMENTS WILL BE BORDERLINE BUT THE
COMBINED IMPACT CERTAINLY WARRANTS A HIGHLIGHT OF SOME SORT. WENT
AHEAD AND HIGHLIGHTED THE AREAS WHERE MORE SNOW IS EXPECTED WITH A
WATCH AND KEPT THE OTHERS AT AN ADVISORY. OPTED TO PUSH THE WATCH
FOR SWEETWATER FORWARD TO MONDAY TO HIGHLIGHT THE MORE SIGNIFICANT
IMPACT TO THE POPULATION CENTERS BUT THERE WILL CERTAINLY BE AT
LEAST SOME SNOW DURING THE DAY ON MONDAY FROM THE FIRST
SYSTEM...WHICH COULD BE HEAVY AT TIMES...ESPECIALLY SOUTH OF THE
INTERSTATE.

THINGS BEGIN TO WIND DOWN ON TUESDAY AFTERNOON AS IT CLEARS FROM
NORTH TO SOUTH...TUESDAY NIGHT COULD BE A COLD ONE WHEREVER IT DOES
CLEAR. THERE WILL BE SOME MILDER AIR JUST TO THE EAST IN A HURRY TO
MOVE IN HOWEVER...THIS WILL LIKELY LEAD TO SOME SHARP INVERSIONS AND
PATCHY FOG EARLY WEDNESDAY MORNING.

.LONG TERM WEDNESDAY NIGHT THROUGH SUNDAY

DRY NORTHWESTERLY FLOW...WITH A SFC HIGH OVER SOUTHERN WY...WILL
KEEP DRY CONDITIONS IN THE FORECAST TO END THE WORK WEEK. MAIN
FORECAST CHALLENGE WILL BE TEMPERATURES. TEMPS WILL REBOUND SLIGHTLY
FOR THURSDAY...HOWEVER...WITH FRESH SNOW STILL EXPECTED ON THE
GROUND...BELOW AVERAGE LOWS AND HIGHS CAN BE EXPECTED. TEMPS WILL
THEN MAKE A GRADUAL REBOUND THROUGH THE WEEKEND...WITH LOWS IN THE
TEENS AND 20S BY THE END OF THE WEEKEND...AND HIGHS IN THE 30S AND
40S.

STILL LOOKS TO BE ONLY ONE DISTURBANCE WORTH WATCHING FOR LATE IN
THE PERIOD. QUICK MOVING SHORTWAVE DROPS OUT OF CANADA FRIDAY NIGHT
INTO SATURDAY...WITH AN ENHANCED JET STREAK OF AROUND 75 KNOTS.
THIS DISTURBANCE WONT HAVE AN OVERLY ABUNDANT AMOUNT OF
MOISTURE...HOWEVER DEPENDING HOW THIS JET STREAK POSITIONS...AT LEAST
A FEW AREAS COULD SEE AREAS OF LIGHT SNOW...POSSIBLY MIXED WITH RAIN
AT TIMES. PLACED MAINLY SLIGHT CHANCE ACROSS AREAS WITH THE BEST
CHANCES FOR ANY PRECIP...WHICH AT THIS MOMENT APPEARS TO BE MAINLY
THE NORTHWESTERN MOUNTAINS...BIGHORN MOUNTAINS...AND THE LOWER
ELEVATIONS OF THE NORTHERN AND EASTERN CWA. THIS SHORTWAVE AND ITS
ASSOCIATED MOISTURE EXITS SATURDAY NIGHT...ALONG WITH ANY CHANCES
FOR PRECIP. NORTHWEST FLOW RETURNS ON SUNDAY...ALONG WITH A SLIGHT
WARMING TREND...POSSIBLY MAKING IT THE WARMEST DAY OF THE EXTENDED
FORECAST.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES
VFR CONDITIONS...FL SCT-BKN200-250 ACROSS THE SOUTH HALF OF
WY...WILL PREVAIL THROUGH 18Z.   A LOW PRESSURE SYSTEM LIFTING NE
ACROSS THE GREAT BASIN WILL PUSH SCT MVFR -SHRASN NORTH TO A VCNTY
KLND-KCPR LINE 21Z MON-00Z TUE.  CONDITIONS WILL THEN DETERIORATE
RAPIDLY AFTER 00Z TUE AS A COLD FRONT PUSHES DOWN FROM THE NORTH
BRINGING WIDESPREAD MVFR/IFR -SN AND MTN OBSCURATIONS ACROSS THE
AREA BY 4Z TUE.  THE HEAVIEST SNOWFALL AND AREAS OF LIFR CONDITIONS
WILL BE FOUND VCNTY AND SOUTH OF A KCPR-KLND LINE.  THESE CONDITIONS
WILL PERSIST THROUGH 12Z TUE.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES
AN UPPER LEVEL DISTURBANCE LIFTING ACROSS THE GREAT BASIN TONIGHT
WILL BRING AN INITIAL BAND OF MVFR/IFR -SN NORTH INTO SOUTHERN
WYOMING TO VCNTY AND SOUTH OF INTERSTATE 80 10Z-15Z MON.  THERE
SHOULD BE SOME IMPROVEMENT ACROSS THE SOUTH IN THE LATE
MORNING...AND THEN MORE WIDESPREAD PERSISTENT IFR SNOW IS EXPECTED
TO DEVELOP ACROSS SOUTHERN WYOMING AROUND 20Z MON AND PERSIST INTO
THE OVERNIGHT HOURS.  A CANADIAN COLD FRONT PUSHING DOWN FROM THE
NORTH WILL SPREAD SNOW SOUTH ALONG THE DIVIDE MONDAY
EVENING...FILLING WESTERN WYOMING WITH WIDESPREAD MVFR/IFR -SN BY
06Z TUES ALONG WITH MTNS BECOMING MOSTLY OBSCURED.


&&

.FIRE WEATHER...

COLD AIR WILL REMAIN OVER THE NORTH AND CENTRAL AREAS...WHILE
TEMPERATURES WARM ACROSS THE FAR SOUTH WITH LIGHT SNOW...TO A RAIN
SNOW MIX MOVES INTO SOUTHEAST SWEETWATER COUNTY THROUGH THE
AFTERNOON. LOW MIXING HEIGHTS AND POOR SMOKE DISPERSAL WILL PREVAIL
ACROSS CENTRAL AND NORTH WITH FAIR TO LOCALLY GOOD SMOKE DISPERSAL WILL
OCCUR ACROSS THE SOUTH BEFORE THE ONSET OF LOWER CLOUDS AND
PRECIPITATION.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY AFTERNOON
WYZ018>020-022-030.

WINTER WEATHER ADVISORY FROM 6 PM MONDAY TO 6 PM MST TUESDAY
WYZ002>011-015>017-028-029.

&&

$$

SHORT TERM...C.BAKER
MID TERM...ALLEN
LONG TERM...ANGLIN
AVIATION...AEM
FIRE WEATHER...C.BAKER