FXUS65 KRIW 140957
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
257 AM MST MON DEC 14 2009

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
PATCHES OF LIGHT SNOW ARE STILL FOUND OVER PORTIONS OF WESTERN 
WYOMING THIS MORNING. HOWEVER...MOST AREAS ARE VERY LIGHT AND 
VIEWING WEBCAMS SHOW MINIMAL BLOWING SNOW IMPACTING THE AREAS. WITH 
THESE IMPROVED CONDITIONS...HAVE DECIDED TO CANCEL REMAINING 
PORTIONS OF WINTER WEATHER HIGHLIGHTS. 

LIGHT SNOW WILL CONTINUE TODAY...THOUGH ACCUMULATIONS ARE EXPECTED 
TO BE GENERALLY LIGHT. SNOWFALL WILL THEN TAPER OFF THIS EVENING 
ACROSS MUCH OF THE AREA...WITH ONLY SHOWERS LINGERING OVER THE 
WESTERN MOUNTAINS AS MOISTURE REMAINS OVER THE WEST. WIND MAY 
ELEVATE THIS EVENING OVER THE LEE SIDE OF THE ABSAROKA 
MOUNTAINS...AND STRONGER WIND MAY CONSEQUENTLY IMPACT ADJACENT 
VALLEYS OVERNIGHT. SIGNATURES FOR MOUNTAIN WAVE ACTIVITY ARE WEAK 
WITH A MINIMAL TEMPERATURE GRADIENT NOTED BETWEEN THE CODY FOOTHILLS 
AND THE EASTERN SIDE OF YELLOWSTONE NATIONAL PARK. CROSS SECTIONS 
AROUND THE CLARK AREA DO SHOW A WEAK INVERSION WITH ELEVATED 
WIND...BUT THE SIGNATURE IS NOT IMPRESSIVE FOR A STRONG EVENT. 

SNOWFALL WILL CONTINUE ACROSS THE WESTERN MOUNTAINS THROUGH 
WEDNESDAY EVENING. THE ARCTIC FRONT WILL LEAVE COOLER TEMPERATURES 
OVER THE NORTHERN BASINS TODAY...WITH SLIGHTLY WARMER TEMPERATURES 
EXPECTED ELSEWHERE. THIS FRONT WILL LOSE ITS INFLUENCE ON TUESDAY 
WITH ALL AREAS SEEING WARMER TEMPERATURES WITH A WEAK NORTHWEST FLOW 
AND WEAK RIDGING PATTERN. MODELS DO SHOW INCREASED POTENTIAL FOR 
STRONG WIND OVER THE CODY FOOTHILLS AND ABSAROKA MOUNTAINS FOR 
TUESDAY NIGHT AND INTO WEDNESDAY MORNING. MODELS DEMONSTRATE BETWEEN 
A 5 AND 10 DEGREE CELSIUS TEMPERATURE GRADIENT...WITH A MORE DEFINED 
SIGNATURE ON CROSS SECTIONS FOR A POTENTIAL WAVE. HAVE INCREASED 
WIND IN FAVORED LOCATIONS TO REFLECT THIS POTENTIAL WAVE EVENT. THIS 
SITUATION WILL CONTINUE TO BE MONITORED OVER THE NEXT COUPLE SHIFTS. 
THE TEMPERATURES GRADIENT AND INCREASED WIND WEAKEN BY WEDNESDAY 
AFTERNOON. 
 
.LONG TERM...THURSDAY THROUGH MONDAY
THE ECMWF SHOWS A TROUGH MOVING ACROSS THE AREA THURSDAY INTO 
THURSDAY NIGHT. ECMWF IS SHARPER WITH THE TROUGH THAN THE 
OPERATIONAL GFS AND CANADIAN MODEL...AND PREFERRED DUE ITS 
CONSISTENCY. THUS INCREASING CHANCE OF SNOW FOR THE MOUNTAINS AND 
WEST THURSDAY...AND THEN EAST OF THE DIVIDE ON THURSDAY NIGHT. THE 
ECMWF KEEPS A NORTHERLY FLOW OVER THE AREA FRIDAY WITH THE 
POSSIBILITY OF SNOW SHOWERS LINGERING MUCH OF THE DAY. THE 
GFS/CANADIAN ARE DRIER SINCE THEY EXIT THE SYSTEM INTO THE PLAINS 
QUICKER. WILL KEEP SOME MOUNTAIN LIGHT SNOW GOING ON FRIDAY. AN 
UPPER RIDGE IS FORECAST OVER THE WESTERN U.S. SATURDAY AND SUNDAY. 
THE ECMWF AND SOME GFSENSEMBLE MEMBERS ARE MORE AMPLIFIED WITH THE 
RIDGE THAN THE 00Z OPERATIONAL GFS. LEANING TOWARD THE MORE 
AMPLIFIED SOLUTION WITH A NNW FLOW OVER THE AREA SAT AND SUN. THIS 
WOULD LEAD TO MOSTLY DRY WEATHER SAT AND SUN OVER MOST OF THE AREA. 
HAVE KEPT LOW PRECIP CHANCES OVER THE NW MTS FOR NOW WHICH IS A 
REDUCTION IN COVERAGE FROM LAST NIGHT THINKING. WILL SEE HOW THINGS 
LOOK TONIGHT AND MAY NEED TO LOWER PRECIP CHANCES EVEN MORE. NEXT 
MONDAY MAY SEE AN INCREASE IN MOISTURE INTO THE NW MTS WITH DRY 
WEATHER ELSEWHERE. TEMP FORECAST WILL BE A CHALLENGE DURING THE 
EXTENDED. COOLER HIGHS THURS AND FRI WITH A SLIGHT MODERATION SAT. 
BACKDOOR COLD FRONT SAT NIGHT INTO SUNDAY FOR THE EAST ZONES WOULD 
LEAD TO SLIGHTLY COOLER HIGHS THERE ON SUNDAY...WITH LITTLE CHANGE 
IN HIGHS CENTRAL AND WEST. THEN SLIGHTLY WARMER HIGHS NEXT MONDAY.

&&

.AVIATION...
LIGHT SNOW WILL CONTINUE OVER THE WESTERN AND NORTHERN 
MOUNTAINS...WITH VALLEYS SEEING VERY LIGHT SNOW/FLURRIES...WITH THE 
BEST CHANCE OF LIGHT SNOW AT KJAC...MAINLY BEFORE 18Z.  SOME BLOWING 
SNOW COULD REDUCE VISIBILITIES AT KRKS AND KJAC TODAY...WHERE WINDS 
WILL BE RELATIVELY STRONG OUT OF THE WEST...SOUTH RESPECTIVELY.  
IFR/MVFR CEILINGS ARE EXPECTED TO PERSIST FOR MUCH OF TODAY OVER THE 
BIG HORN BASIN AND JOHNSON COUNTY...WITH IMPROVING CONDITIONS 
EXPECTED LATE THIS AFTERNOON INTO THE EVENING.  WITH THE RECENT 
SNOWFALL OUT WEST...FOG IS A POSSIBLITY TONIGHT. 

&&

.FIRE WEATHER...
LIGHT SNOWFALL WILL CONTINUE TODAY. INCREASED WIND WILL CONTINUE TO 
BRING AREAS OF BLOWING SNOW TODAY. INCREASED WIND IS EXPECTED OVER 
THE WIND RIVER AND ABSAROKA MOUNTAIN RANGES AND ADJACENT 
VALLEYS...ALONG THE WIND CORRIDOR BETWEEN ROCK SPRINGS AND CASPER. 
SNOWFALL WILL TAPER OFF EAST OF THE DIVIDE THIS EVENING...WITH 
LINGERING SNOWFALL EXPECTED OVER THE WESTERN MOUNTAINS AND VALLEYS. 
TEMPERATURES WILL WARM OVER THE NEXT COUPLE OF DAYS. 

&&

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

&&

$$

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