National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS65 KRIW 230542
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1042 PM MST THU JAN 22 2015

.SHORT TERM...TONIGHT THROUGH FRIDAY

A WEAK FAST MOVING LOW PRESSURE TROUGH WILL SWEEP SOUTH ACROSS
THE AREA FRIDAY WITH LOCAL LIGHT SNOW OVER AND NEAR THE NORTHERN
AND WESTERN MOUNTAINS WITH VERY LIGHT ACCUMULATIONS EXPECTED.
OVERNIGHT SOME FOG AND LOW STRATUS IS EXPECTED TO FORM ALONG AND
NEAR THE RIVERS AND LAKES IN THE BASINS AND VALLEYS.  THIS WILL BE
HAMPERED BY INCREASED MID AND HIGH CLOUDS. LOCAL WINDY AREAS WILL
OCCUR OVER AND NEAR THE EAST SLOPES OF THE MOUNTAINS AND THROUGH THE
WIND CORRIDOR FROM ROCK SPRINGS TO CASPER. AS THE TROUGH PASSES
SOUTH THE WINDS WILL SHIFT TO THE NORTH AND GENERALLY DECREASE.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

WEAK FRONTAL BOUNDARY WILL EXIT SOUTHWARD FRIDAY EVENING...ENDING
ANY LINGERING PRECIPITATION BY 06Z SATURDAY. A BRIEF LULL IN
PRECIPITATION IS THEN EXPECTED OVERNIGHT FRIDAY NIGHT INTO EARLY
SATURDAY MORNING...AS DRY AIR MOVES ACROSS THE STATE. CLEAR SKIES
COULD LEAD TO AREAS OF PATCHY FOG SATURDAY MORNING...MAINLY ACROSS
THE WIND RIVER AND BIGHORN BASIN. A WEAK DISTURBANCE...COMBINED WITH
ANOTHER WEAK FRONTAL BOUNDARY...WILL BRING ANOTHER SHOT OF LIGHT
SNOW DURING THE DAY SATURDAY...MAINLY ACROSS THE NORTHERN AND
WESTERN MOUNTAINS. ECMWF HAS THE WEAK FRONTAL BOUNDARY DIPPING
SLIGHTLY FURTHER SOUTH THAN THE GFS...WHICH COULD BRING A BRIEF SHOT
OF LIGHT SNOW TO LOWER ELEVATIONS OF THE NORTH...AND TO THE EASTERN
CWA SATURDAY AFTERNOON AND EVENING. AN INCREASED GRADIENT WILL ALSO
BRING SOME GUSTY WINDS TO THE ABSAROKA MOUNTAINS AND THE CODY
FOOTHILLS ON SATURDAY. WINDS COULD ALSO INCREASE ACROSS THE WIND
CORRIDOR FROM ROCK SPRINGS TO CASPER ON SATURDAY. HIGH PRESSURE WILL
BUILD ACROSS THE REGION SATURDAY NIGHT...ENDING ANY LINGERING PRECIP
AND DIMINISHING WINDS.

SUNDAY THROUGH TUESDAY...A LARGE RIDGE OF HIGH PRESSURE WILL
POSITION ITSELF ACROSS ROCKY MOUNTAIN REGION DURING THIS TIME
PERIOD. MAINLY CLEAR SKIES AND NO PRECIP IS EXPECTED. MAIN FORECAST
CHALLENGE IS HOW WARM WILL IT GET. H7 TEMPS WILL CLIMB NEAR 5-6 C.
SURFACE TEMPS WILL REALLY DEPEND ON TWO FACTORS...SNOW COVER AND
MIXING. WITH LIGHT WINDS EXPECTED UNDER THE RIDGE...FULLY MIXING OUT
WILL BE TOUGH TO COME BY...ESPECIALLY ACROSS THE WEST. CURRENT
NOHRSC SNOW COVER ANALYSIS SHOWS WHAT ONE MAY EXPECT FOR SNOW IN THE
MOUNTAINS AND WESTERN VALLEYS...WITH LITTLE SNOW COVER ACROSS THE
LOWER ELEVATIONS OF THE CWA. IF SATURDAYS DISTURBANCE PROVIDES
LITTLE NEW SNOW...AND GUSTY WINDS CAN PROVIDE ENOUGH WARM TEMPS TO
MELT SOME SNOW...THIS AIR MASS IS WARM AND DRY ENOUGH TO PRODUCE
HIGHS GENERALLY IN THE 40S...WITH SOME MID TO UPPER POSSIBLE 50S
NEAR THE CODY FOOTHILLS AND THE EASTERN FOOTHILLS OF THE BIGHORNS.

WEDNESDAY THROUGH THURSDAY...HIGH PRESSURE RIDGE CONTAINING WARM DRY
AIR...WILL BE PUSHED OUT BY A SHORTWAVE TROUGH OUT OF THE BAJA AREA.
SLIGHT DIFFERENCES REMAIN WITH THIS DISTURBANCE. GFS WAS A MORE
PROGRESSIVE WAVE...AS THE ECMWF HAS THE WAVE WASHING OUT IN WESTERLY
FLOW...THEN LINGERS THIS MOIST FLOW AS A RIDGE BUILDS TO THE
SOUTHWEST. EITHER SOLUTION BRINGS CHANCES FOR MAINLY SNOW ACROSS THE
WEST...WITH THE ECMWF SOLUTION BRINGING SOME SCATTERED LIGHT
SNOW/RAIN ACTIVITY DURING THE AFTERNOON AND EVENING ON WEDNESDAY
ACROSS THE SOUTH AND PORTIONS EAST OF THE DIVIDE. GUSTY WINDS WILL
ALSO BE POSSIBLE WITH THIS DISTURBANCE...ESPECIALLY ACROSS
SWEETWATER COUNTY UP THROUGH NATRONA COUNTY. MODELS THEN START TO
HINT TOWARDS AN ACTIVE END TO NEXT WEEK AS THE GFS BRINGS A LARGE
TROUGH ACROSS THE DESERT SW...AND PUSHES A COLD FRONT ACROSS THE
STATE. THE ECMWF SOLUTION KEEPS THIS TROUGH FURTHER SOUTHWEST OFF
THE CA COAST..BUT STILL DROPS A COLD FRONT AND STRONG JET ACROSS THE
REGION. EITHER SOLUTION CAUSED FOR SLIGHT CHANCES FOR LIGHT SNOW TO
BE PLACED IN FOR A FEW AREAS...ALTHOUGH THE MODELS MAY NEED A FEW
DAYS TO IRON OUT THE DETAILS...AND INSPIRE HIGHER CONFIDENCE.

&&

.AVIATION.../06Z ISSUANCE/

A QUICK MOVING SYSTEM WILL SLIDE SOUTHEAST ACROSS THE COWBOY STATE
FRIDAY WITH CONSIDERABLE CLOUDINESS AND ISOLATED TO LOCALLY
SCATTERED SNOW SHOWERS. CEILINGS IN THE LOWER ELEVATIONS ARE
EXPECTED TO RANGE BETWEEN 050-100 KFT AGL FOR MUCH OF THE DAY...WITH
BRIEF PERIODS OF MVFR/IFR CONDITIONS POSSIBLE IN SNOW SHOWERS. THE
EXCEPTION TO THIS RULE COULD BE THE JAC TERMINAL THIS MORNING...AND
HAVE DECIDED TO TEMPO MVFR CONDITIONS. MOUNTAINS WILL BE OBSCURED AT
TIMES. IMPROVING CONDITIONS ARE EXPECTED FROM NORTH TO SOUTH BETWEEN
20Z AND 02Z...WITH SKIES QUICKLY BECOMING MAINLY SKC IN MOST AREAS.
NOT OUT OF THE QUESTION...THAT THE FAR WESTERN VALLEYS COULD HANG
ONTO A STRATOCU DECK BETWEEN 025-050 KFT AGL. WHERE SNOWFALL DOES
OCCUR...THERE WILL BE AN INCREASED THREAT OF SOME FOG DEVELOPING.
HOWEVER A LIMITING FACTOR WILL BE INCREASING MID/HIGH LEVEL
CLOUDINESS AFTER 06Z AS ANOTHER FAST MOVING SYSTEM APPROACHES THE
REGION. THE BASINS AND VALLEYS WILL SEE FAIRLY LIGHT WINDS THROUGH
THE PERIOD WHILE THE LEE SIDE OF MOUNTAINS...FOOTHILLS AND WIND
CORRIDOR FROM KRKS TO KCPR WILL BE BREEZY TO WINDY AT TIMES.

&&

.FIRE WEATHER...

GENERALLY TYPICAL WINTER CONDITIONS WILL CONTINUE TONIGHT AND FRIDAY
WITH SOME LOCAL LIGHT SNOW COMING SOUTH ACROSS THE NORTH AND WEST
MOUNTAINS ON FRIDAY.  SOME WARMING WILL MOVE INTO THE WEST ON
SATURDAY WITH WARMING SPREADING EAST INTO MONDAY. THE LOWER AIR MASS
WILL REMAIN STABLE WITH LOW MIXING HEIGHTS AND POOR SMOKE DISPERSAL.

&&

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

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ANGLIN
AVIATION...WM
FIRE WEATHER...C.BAKER