HAMweather.com Area Forecast Discussion for County Warning Area RIW

Thu, 16 Feb 2012 06:55:15 GMT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1040 PM MST WED FEB 15 2012

.SHORT TERM...TONIGHT THROUGH SATURDAY
UPPER LOW WHICH CAUSED THE SNOW IN THE FAR WEST OVERNIGHT IS NOW
OVER SOUTHERN NEVADA WITH THE NORTHERN DEFORMATION AXIS STILL
PRODUCING AREAS OF LIGHT SNOW IN THE SOUTHWEST. ALSO WEAK MID
LEVEL DISTURBANCE WITH -30C COLD CORE IS MOVING INTO THE AREA
CAUSING BUILDING CUMULUS AND INCREASING LIGHT SNOW SHOWERS...
ESPECIALLY NEAR THE CENTRAL MOUNTAINS. A FEW SNOW SHOWERS ARE EVEN
DEVELOPING IN THE WIND RIVER BASIN...SOUTHERN JOHNSON...SOUTHERN
BIGHORN BASIN AND NATRONA COUNTY. WILL EXPAND THE SLIGHT CHANCES
TO INCLUDE ALL OF THIS AREA THROUGH 03Z EVEN THOUGH WEAK
INSTABILITY MAY QUICKLY DIMINISH AFTER SUNSET. WILL ALSO LINGER A
CHANCE OF SNOW ACROSS SRN SWEETWATER OVERNIGHT AS DEFORMATION AXIS
AND -30C COLD CORE TO THE NORTH MAY STILL INTERACT TO KEEP AT
LEAST SOME HIGHER TERRAIN SNOW SHOWERS OR FLURRIES AROUND. ON
THURSDAY...WEAK PASSING WAVE IN THE NORTHERN HIGH PLAINS SHOULD
HAVE LIMITED IMPACT ACROSS THE AREA OTHER THAN SOME BREEZY AREAS.
STRONGER SHORTWAVE APPROACHES THURSDAY EVENING IN THE NORTHWEST
AND SPREADS QUICKLY SE ACROSS THE AREA INTO FRIDAY MORNING. TREND
HAS BEEN STRONGER AND FURTHER WEST WITH THIS DISTURBANCE SINCE
YESTERDAY BUT WITH LIMITED MOISTURE. DISTURBANCES IN NW FLOW ARE
ALWAYS TRICKY AND WE'LL NEED TO WATCH THIS ONE CLOSELY. FOR
NOW...HAVE INCREASED POPS BACK TO LIKELY ACROSS THE NORTHWEST
MOUNTAINS THURSDAY NIGHT... EVENTUALLY SPREADING TO THE BIGHORNS.
ALSO ADDED SOME SLIGHT CHANCES FOR NOW ACROSS THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS AND ALSO THE DUBOIS TO CROWHEART AREA.
SHORTWAVE RIDGE THEN MOVES OVER EARLY SATURDAY AHEAD OF MORE
VIGOROUS TROUGH THAT WILL JUST BEGIN TO IMPACT THE FAR WEST BY
AFTERNOON. GFS IS SLOWER THAN THE NAM OR SREF IN BRINGING THE SNOW
BACK INTO THE WEST. TRIMMED BACK THE SATURDAY MORNING POPS BUT
KEPT THE HIGHER SATURDAY AFTERNOON POPS. SATURDAY COULD BE A
DECENT DAY EAST OF THE DIVIDE WITH HIGHS IN THE 40S IF THE MID TO
HIGH LEVEL CLOUDS DON'T GET TO THICK TO SOON. LEFT THE IDEA OF
PATCHY FOG IN THE FORECAST FOR TONIGHT ACROSS THE WEST... SOUTH
AND LOW LYING CENTRAL ZONES WITH LIGHT WINDS AND RESIDUAL
MOISTURE. MORE EXTENSIVE CLOUD COVER WILL LIKELY ELIMINATE OR
SEVERELY LIMIT FOG FRIDAY MORNING. FOG CHANCES MAY INCREASE AGAIN
SATURDAY MORNING.

LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY
THE RIDGE WILL CONTINUE TO EXIT STAGE EAST ON SATURDAY NIGHT AS A 
TROUGH MOVES INTO THE AREA FROM THE WEST. POPS WILL INCREASE ACROSS 
THE WEST WITH NORTHWEST FLOW DEVELOPING SATURDAY NIGHT AND INTO 
SUNDAY. MODELS CONTINUE TO DIVERGE A BIT ON THE DETAILS OF THE NEXT 
SYSTEM FOR LATER SUNDAY INTO THE FIRST PART OF NEXT WEEK. THE GFS 
SHOWS A CLOSED LOW DEVELOPING OVER THE EASTERN NEVADA BY 00Z SUNDAY 
BEFORE OPENING UP NEAR THE FOUR CORNERS AND BEGINNING TO SHEAR OUT 
ON MONDAY. THE EUROPEAN HAS MOVE OF AN OPEN WAVE SOLUTION WITH ANY 
UPPER LEVEL LOW CONTINUING TO MOVE NEAR THE US CANADIAN BORDER. BOTH 
MODELS DO COME BACK INTO AGREEMENT BY TUESDAY WITH WITH A TROUGH 
EXTENDING FROM THE DAKOTAS SOUTHWESTWARD INTO COLORADO AND NEW 
MEXICO. GIVEN THE MODELS SPLITS AND LACK OF RUN TO RUN 
CONTINUITY...FEW CHANGES WERE MADE TO THE GRIDS. DID UP POPS A BIT 
FOR SUNDAY NIGHT INTO THE FIRST PART OF MONDAY AS THIS LOOKS TO BE 
THE MOST ACTIVE PORTION OF THE FORECAST. WINDS MAY PICK UP TOWARD 
THE MIDDLE OF NEXT WEEK AS THE PRESSURE GRADIENT TIGHTENS BETWEEN 
LOW PRESSURE OVER CANADA AND HIGH PRESSURE OVER THE GREAT BASIN.

AVIATION.../06Z ISSUANCE/

LIGHT WINDS AND MOSTLY CLEAR SKIES WILL PREVAIL OVER MUCH OF THE 
REGION FOR THE REST OF TONIGHT. THE MAIN EXCEPTION WILL BE THE 
STRATUS IN STAR VALLEY...AFFECTING KAFO...WHERE IFR CONDITIONS WILL 
LIKELY CONTINUE THROUGH THURSDAY MORNING. ELSEWHERE...PATCHY FOG 
COULD FORM IN THE VALLEYS AND BASINS LATER TONIGHT...WITH THE BEST 
SHOT ACROSS THE WEST...WITH IFR/MVFR CONDITIONS IN THE FOG. ANY 
FOG/STRATUS IS EXPECTED TO LIFT BETWEEN 16Z AND 18Z. MID-HIGH LEVEL 
CLOUDS WILL BEGIN TO STREAM INTO THE AREA THURSDAY AFTERNOON AND 
EVENING. SCATTERED TO NUMEROUS MOUNTAIN SNOW SHOWERS ARE EXPECTED TO 
BEGIN TO BREAKOUT ACROSS THE NORTHWEST AND NORTH AFTER 00Z. THE KJAC 
TERMINAL COULD BE IMPACTED BY THESE SNOW SHOWERS ESPECIALLY AFTER 
04Z FRIDAY. 

FIRE WEATHER...
WINDS WILL INCREASE ACROSS THE WIND CORRIDOR AND CODY FOOTHILLS ON
THURSDAY WITH GENERALLY LIGHTER WINDS ELSEWHERE AND SOME SHALLOW
MORNING INVERSIONS. A NEW WEATHER SYSTEM WILL MOVE SOUTHEAST ACROSS
THE AREA THURSDAY NIGHT INTO FRIDAY MORNING WITH SOME LIGHT
MOUNTAIN SNOWFALL AND A CHANCE OF LIGHT SNOW NEAR THE MOUNTAINS
AND FAR NORTH. 

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