Area Forecast Discussion
Issued by NWS Riverton, WY

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210
FXUS65 KRIW 100923
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
223 AM MST WED FEB 10 2016

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

SOUTHWEST WINDS IN THE CASPER AREA AND WNW WINDS AROUND CLARK ARE
ALREADY RESPONDING TO THE INCREASING SFC PRESSURE GRADIENT AS A SFC
LEE ENHANCED TROUGH ESTABLISHES ITSELF. THE SFC GRADIENT WILL ONLY
TIGHTEN AS A SFC LOW TRACKS SOUTHEAST ACROSS EASTERN MT AND THE
NORTHERN PLAINS TODAY. THIS SFC WX FEATURE IS ASCT WITH A VORT LOBE
TRACKING SOUTHEAST WITHIN THE FRONT OF THE PROMINENT RIDGE OVER THE
WESTERN UNITED STATES. IN ADDITION...THERE WILL BE A 9 TO 10C SFC
TEMP GRADIENT BETWEEN YNP AND THE CODY FOOTHILLS WHICH WILL ENHANCE
GAP FLOW ALONG THE CLARKS FORK CANYON AS WELL AS ALONG BOTH FORKS OF
THE SHOSHONE RIVER. AN SPS HAS BEEN ISSUED FOR TODAY FOR THE CODY
FOOTHILLS. DO NOT EXPECT MORE THAN BORDERLINE HIGH WINDS IN THE
CLARK AREA TODAY. 700MB WINDS ARE NOT PROGGED BY THE NAM TO BE MUCH
MORE THAN 35 KNOTS SO EVEN THE ABSAROKA MTNS/CHIEF JOSEPH WILL NOT
BLOW THAT HARD. THE RED DESERT TO CASPER AREA WILL HAVE A DECENT
GRADIENT WIND TODAY OF 25 TO 35 MPH WITH GUSTS OF 45 MPH. NOT
CONCERNED ABOUT BLOWING SNOW IN THAT AREA AS MUCH OF THE SNOW HAS
CRUSTED OVER FROM TUESDAYS RELATIVELY MILD TEMPS AND TEMPS WILL BE
EVEN WARMER TODAY. IN FACT...HIGH TEMPS TODAY WILL REACH NEAR RECORD
LEVELS WITH H7 TEMPS AT AROUND THE 3C MARK AT 18Z TODAY OVER THE
SOUTHERN HALF OF WY. HIGHS COULD APPROACH 60 IN BYG/COD TODAY BUT
WILL BE A BIT COOLER AROUND CPR WHERE SNOW COVER EXISTS...ESP JUST
WEST OF CASPER WHERE THE SNOW COVER APPEARS TO BE DEEPER/MORE
CONTINUOUS...SO 40S TO LOW 50S WOULD BE MORE REALISTIC THERE. THE
TRAPPED BASINS/VALLEYS WILL REMAIN IN THE 30S AND 40S THIS AFTERNOON
BUT THE BIG HORN BASINS WILL AGAIN REACH THE 50S WHERE LACK OF SNOW
COVER EXISTS. FOR THURSDAY...WINDS WILL BE LIGHTER WITH SLIGHTLY
COOLER TEMPS. THE BIGGER COOL DOWN BEHIND TODAYS SYSTEM WILL REMAIN
WELL TO OUR NORTHEAST OVER THE NORTHERN PLAINS. FRIDAY WILL FEATURE
A CONTINUATION OF MILD AND DRY WEATHER ALONG WITH BASIN AND VALLEY
INVERSIONS. WILL KEEP LATE NIGHT AND MORNING PATCHY FOG IN THE
VALLEYS AND BASINS THROUGH THE WEEK. SOME FOG WAS OBSERVED LAST
NIGHT...AND NOW WITH THE MELTING SNOW AROUND THE AREA...THAT TREND
TOWARD FOGGY MORNINGS IN THESE AREAS SHOULD CONTINUE.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
LONGWAVE RIDGE HOLDS OVER THE FAR WESTERN U.S. THROUGH EARLY NEXT
WEEK BEFORE SOME BRIEF WEAKENING EARLY NEXT WEEK. THE RIDGE WILL
LIKELY START REBUILDING AGAIN AT THE END OF THE MEDIUM RANGE
PERIOD. EXCEPT FOR THE GFS...THE MODELS HAVE TRENDED WEAKER AND
FURTHER NORTH WITH OUR SATURDAY/SAT NGT SYSTEM AS IT MOVES THROUGH
THE MEAN LONGWAVE RIDGE...AS EXPECTED LAST NIGHT. KEEPING POPS
CONFINED TO THE FAR WEST AND FAR NORTH AS THIS SYSTEM MOVES
THROUGH. SOME DECENT WINDS WILL LIKELY BLOW JUST AHEAD OF AND WITH
FRONTAL PASSAGE WITH THIS SYSTEM. DECENT MIXING EAST OF THE DIVIDE
EXPECTED SATURDAY. THE BETTER PCPN CHANCES MAY ACTUALLY BE SUNDAY
INTO MONDAY ACROSS THE FAR NW AS WARM ADVECTION/UPGLIDE DEVELOPS
IN THE NW FLOW. MOSTLY SNOW...EXCEPT A MIXTURE POSSIBLE MON AFTN
IN THE WRN VALLEYS. AFTER A LITTLE COOLDOWN SUNDAY...TEMPERATURES
WILL BEGIN WARMING AGAIN TO ABOVE TO WELL ABOVE NORMAL FOR MID
FEBRUARY WITH 40S AND 50S EAST OF THE DIVIDE WITH 30S AND EVEN A
FEW 40S WEST. STRONG ENOUGH FLOW THAT WILL SEE WINDY PERIODS OVER
THE PEAKS...LEE SLOPES...WIND CORRIDOR AND CODY FOOTHILLS AT
TIMES. ECMWF HAS A SHORTWAVE DROPPING SE ON TUE SIMILAR TO THE SAT
ONE THAT THE OTHER MODELS DO NOT SHOW. HARD TO TELL WHERE THIS
SYSTEM ORIGINATES. WITH RIDGE AXIS WEAKENED FOR A DAY OR
TWO...IT`S POSSIBLE A SHORTWAVE COULD COME ON THE COAST AND MOVE
SE TOWARDS US BUT HARD TO PICK THIS WAVE UP. WILL JUST KEEP IN
SOME SLGT CHANCES ACROSS THE NRN MTNS FOR NOW AND SEE HOW
EVERYTHING LOOKS TONIGHT. ANOTHER SHORTWAVE MAY TRY AND MOVE
THROUGH THE REBUILDING LONGWAVE RIDGE RIGHT AT THE END OF THE
MEDIUM RANGE PERIOD. A CHANCE OF SNOW WILL RETURN TO THE FAR WRN
MTNS...POSSIBLY MIXED WITH RAIN IN THE VALLEYS. ENOUGH PRESSURE
GRADIENT AND WINDS ALOFT FOR THE BASINS TO MIX OUT AND THAT
COMBINED WITH WARM MID LEVELS LEADING TO PLENTY OF 50S FOR MANY
AREAS EAST OF THE DIVIDE WITH MID 30S TO MID 40S WEST.

&&

.AVIATION.../12Z ISSUANCE/

FOG AND LOW CLOUDS WILL ONCE AGAIN IMPACT THE FAR WESTERN VALLEYS
THIS MORNING. WILL CONTINUE TO MONITOR TRENDS IN SATELLITE
IMAGERY...LOCAL WEBCAMS AND KJAC OBSERVATIONS TO DECIDE HOW HARD TO
HIT THE KJAC TERMINAL RIGHT AT 12Z ISSUANCE. THE FOG/LOW CLOUDS ONCE
THEY FORM WILL PROBABLY NOT SCATTER OUT/LIFT UNTIL EARLY THIS
AFTERNOON. OTHERWISE...VFR CONDITIONS ARE EXPECTED WITH ONLY
INCREASING HIGH CLOUDS TODAY. THE BASINS AND VALLEYS WILL SEE FAIRLY
LIGHT WINDS THROUGH THE PERIOD WHILE MOUNTAINS...FOOTHILLS AND WIND
CORRIDOR FROM KRKS TO KCPR WILL BE BREEZY TO WINDY AT TIMES.

&&

.FIRE WEATHER...

STEEP TEMPERATURE INVERSIONS...ESPECIALLY IN THE WESTERN VALLEYS
WILL LEAD TO VERY POOR SMOKE DISPERSION THIS WEEK. WINDS...HOWEVER...WILL
BE ON THE BREEZY SIDE ACROSS THE USUAL WIND PRONE AREA OF CENTRAL
WYOMING. TODAY...AREAS IN AND ADJACENT TO THE ABSAROKA MOUNTAINS
COULD SEE A FEW GUSTS OVER 50 MPH NEAR THE CANYONS. IT WILL BE
FAIRLY WINDY FROM THE RED DESERT TO CASPER TODAY AS WELL...WHICH
WILL IMPROVE SMOKE DISPERSION IN THESE AREAS. NO MAJOR SNOW STORMS
OR WIDESPREAD STRONG WIND EVENTS ARE ON THE HORIZON...

&&

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

&&

$$

SHORT TERM...LIPSON
LONG TERM...PS
AVIATION...WM
FIRE WEATHER...LIPSON



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