FXUS65 KRIW 231010
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST WED DEC 23 2009
.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
THE ARRIVAL OF THE SOUTHERLY PUSH OF MOISTURE HAS BEEN SLOW MOVING
THIS MORNING. SNOWFALL OCCURRING OVER SOUTHEASTERN WYOMING...WITH
LIGHT SNOW ALSO NOTED OVER THE GREEN MOUNTAINS AND RATTLESNAKE
RANGE...ALONG WITH CASPER MOUNTAIN AND THE LOWER ELEVATIONS OF
NATRONA COUNTY. MODELS CONTINUE TO INDICATE THE LOW CURRENTLY
LOCATED OVER THE DESERT SOUTHWEST WILL MOVE FURTHER SOUTHEAST
TONIGHT PULLING MOST OF ITS MOISTURE ALONG WITH IT. HOWEVER...A
SECONDARY AREA OF LOW PRESSURE WILL MOVE SOUTH OUT OF CANADA THIS
MORNING AND AFTERNOON.
THIS SECONDARY SYSTEM WILL HAVE A LARGER IMPACT ON THE AREA. JOHNSON
COUNTY WILL EXPERIENCE INCREASED WIND WITH THE ARRIVAL OF AN ARCTIC
FRONT EARLY THIS MORNING. IN ADDITION...SNOWFALL WILL DEVELOP OVER
MUCH OF NORTHERN WYOMING...THOUGH JOHNSON COUNTY IS EXPECTED TO SEE
THE HEAVIEST SNOWFALL RATES. WITH LIGHT SNOWFALL ANTICIPATED TO
BEGIN WITH THE FRONTAL PASSAGE THIS MORNING...A WINTER WEATHER
ADVISORY FOR SNOW AND BLOWING SNOW WAS ISSUED FOR THE LOWER
ELEVATIONS OF JOHNSON COUNTY FOR TODAY THROUGH THIS EVENING. WIND
WILL COMBINE WITH SNOWFALL TO BRING BLOWING SNOW AND ASSOCIATED VERY
LIMITED VISIBILITIES. STRONGER WIND IS EXPECTED TO DEVELOP THIS
AFTERNOON...AND TRAVELERS MAY EXPERIENCE PERIODS OF NEAR WHITEOUT
CONDITIONS WHEN TRAVELING ACROSS INTERSTATES 90 AND 25 THOUGH
JOHNSON COUNTY. BY LATE THIS EVENING...3 TO 5 INCHES OF SNOWFALL
WILL BE POSSIBLE ACROSS JOHNSON COUNTY...THOUGH WIND MAY POTENTIALLY
CAUSE SIGNIFICANT DRIFTING SNOWFALL.
AS THE FRONT MOVES FURTHER SOUTH...SNOWFALL WILL INCREASE ACROSS
NATRONA COUNTY THIS AFTERNOON AND WILL CONTINUE THROUGH THE EVENING
HOURS. THIS SNOWFALL WILL ALSO IMPACT CASPER MOUNTAIN THROUGHOUT THE
DAY. A WINTER WEATHER ADVISORY HAS ALSO BEEN ISSUED FOR THESE AREAS.
BY LATE THIS EVENING...SNOWFALL OF 2 TO 5 INCHES IS EXPECTED. SOME
WIND WILL BE PRESENT WHICH MAY CAUSE SOME LIMITED VISIBILITY...BUT
NOT TO THE EXTENT OF JOHNSON COUNTY. THE QUESTIONS MARKS WITH THIS
SYSTEM ARE THE WIND RIVER BASIN AND MOUNTAINS...ESPECIALLY THE
EASTERN SLOPES OF THE MOUNTAINS AND THE LANDER FOOTHILLS. CURRENT
FORECAST HAS AROUND 2 TO 4 INCHES OF SNOWFALL POSSIBLE IN THE LANDER
FOOTHILLS...BUT HAVE OPTED TO LEAVE THEM OUT OF THE CURRENT ADVISORY
SINCE SNOW IS SLOW TO PROGRESS AND LIKELY WILL NOT BECOME HEAVY OVER
THESE LOCATIONS UNTIL THIS AFTERNOON.
THE ARCTIC FRONT WILL LEAVE COOLER TEMPERATURES ACROSS THE
AREA...ESPECIALLY OVERNIGHT WHEN MANY AREAS WILL SEE SINGLE DIGITS
OR SUB ZERO OVERNIGHT LOWS. THE SYSTEM WHICH IS BRINGING MODERATE
SNOWFALL OVER THE EASTERN PORTIONS OF THE CWA WILL DIVE QUICKLY
SOUTH THURSDAY MORNING. MODELS CONTINUE TO END THE MAJORITY OF
SNOWFALL AFTER 12Z THURSDAY...THOUGH THE GFS DOES DEMONSTRATE SOME
WRAPAROUND MOISTURE ONCE THIS SYSTEM MOVES OVER SOUTHEASTERN
WYOMING. KEPT LINGERING LIGHT SNOWFALL OVER THE EASTERN ZONES
THROUGH 12Z FRIDAY FOR THIS POTENTIAL...BUT IT IS POSSIBLE THAT POPS
WILL NEED TO BE INCREASED FURTHER DEPENDING ON THE TRACK OF THE
SYSTEM.
CONDITIONS EXPECTED TO IMPROVE FRIDAY AFTERNOON AS THE AREA OF LOW
PRESSURE MOVES FURTHER INTO THE CENTRAL PLAINS. DRY CONDITIONS
EXPECTED FRIDAY AFTERNOON THROUGH FRIDAY EVENING WITH TEMPERATURES
EXPECTED TO WARM SLIGHTLY.
.LONG TERM...SATURDAY THROUGH WEDNESDAY
MEDIUM RANGE MODELS BEGIN IN REASONABLE AGREEMENT BUT BY THE END
OF THE PERIOD A WIDE RANGE OF SOLUTIONS EXIST. PATTERN IS VERY
COMPLEX AND VERY MUCH WINTER LIKE WITH THE MODELS CHANGING EACH
RUN. THE GFS RECHARGES THE RIDGE TO OUR WEST EARLY NEXT WEEK AND
ACTUALLY HAS A SHORTWAVE DROPPING DOWN FROM THE SOUTH ON TUESDAY.
THE ECMWF HAS MORE OF AN INFLUENCE FROM THE NEXT DESERT SW UPPER
LOW. THE GEM AT 144HRS IS PROBABLY CLOSER TO A WEAKER VERSION OF
THE ECMWF. THE UKMET HAS A STRONGER DESERT SW TROUGH LIKE THE
EURO. THE DESERT TROUGH SOLUTIONS HAVE MOST OF THE ENERGY TOO FAR
SOUTH FOR US BUT THE EURO DOES LIFT THE TROUGH NE TUESDAY NIGHT
ALLOWING A LITTLE BIT OF QPF INTO OUR FAR SRN ZONES. AT THE SAME
TIME...THE GFS HAS A LITTLE QPF DROPPING SOUTH WITH THE CLIPPER
TYPE SYSTEM. KEEPING A DRY FORECAST FOR NOW AS NEITHER SOLUTION
WOULD PRODUCE MUCH IF ANY SNOW ACROSS OUR AREA. WE MAY STILL BE
UNDER THE INFLUENCE OF THE MONSTER UPPER LOW BY SATURDAY WITH COLD
NLY FLOW BUT PCPN WILL LIKELY BE JUST EAST OF US BY THEN. WE
SHOULD THEN SEE A COUPLE DAYS OF WARMING ALOFT WITH STEEPENING
BASIN AND VALLEY INVERSIONS. HOLDING OFF ON ANY SIGNIFICANT FOG
YET AS RIDGE WEAKENS RATHER QUICKLY AND SOME CLOUD COVER MAY
HAMPER FORMATION. OTHERWISE...COLD PERIOD FOR THE TRAPPED BASIN
AND VALLEYS WITH SOME MODERATION WHERE BREEZES KICK UP. COULD BE A
COUPLE BITTER COLD MORNINGS OVER THE WEEKEND BEFORE SOME
MODERATION OCCURS.
&&
.AVIATION...
EAST OF THE CONTINENTAL DIVIDE...MVFR CONDITIONS WILL PREVAIL TODAY
WITH AREAS OF IFR CONDITIONS DUE TO LOW CEILINGS AND LOW VISIBILITY
IN SNOW. MORNING FOG MAY STILL BE AN ISSUE IN NORTHERN AND CENTRAL
WY AS WELL CREATING SOME IFR TO LIFR CONDITIONS. A STRONG COLD FRONT
WILL BE MOVING INTO NORTHERN WY BY 18Z AND THEN MOVING SOUTH IN THE
AFTERNOON. A NORTH WIND OF 15 TO 20 KNOTS WILL BE COMMON WITH GUSTS
OVER 30 KNOTS IN PLACES WITH THE COLD FRONT. MVFR CONDITIONS WILL
EXTEND BEYOND 00Z THU IN THIS AREA WITH LIGHT SNOW AND LOW CLOUDS.
WEST OF THE CONTINENTAL DIVIDE...VFR CONDITIONS WILL PREVAIL TODAY
WITH LOCAL MVFR CONDITIONS DUE TO LOW CLOUDS AND PATCHY LIGHT SNOW.
WINDY CONDITIONS WILL OCCUR IN SOUTHERN WY INCLUDING THE KRKS
AIRPORT TODAY WITH SPEEDS OF 20 TO 30 KNOTS EXPECTED...DECREASING IN
SPEED AFTER 00Z THURS.
&&
.FIRE WEATHER...
AN ARCTIC COLD FRONT WILL MOVE THROUGH MUCH OF THE FORECAST AREA
TODAY. THIS FRONT WILL BRING GUSTY WIND TO THE LOWER ELEVATIONS OF
JOHNSON COUNTY...ALONG WITH PERIODS OF MODERATE TO HEAVY SNOWFALL.
MUCH COOLER TEMPERATURES EXPECTED BEHIND THE FRONT...WHICH WILL
CONTINUES ITS SOUTHERLY PROGRESSION THROUGH THE STATE THROUGH THE
AFTERNOON AND EVENING HOURS. THE INCREASED WIND ACROSS JOHNSON
COUNTY WILL HELP TO INCREASE SMOKE DISPERSAL THIS AFTERNOON AND WILL
LINGER INTO THE EVENING HOURS. THERE WILL BE SLIGHTLY ELEVATED WIND
OVER NATRONA COUNTY THIS AFTERNOON AND EVENING...WHICH MAY ALSO HELP
TO ELEVATE SMOKE DISPERSAL. WIND ELSEWHERE ACROSS THE AREA IS
EXPECTED TO REMAIN GENERALLY LIGHT WITH THIS SYSTEM...AND THE
MOVEMENT OF AN AREA OF LOW PRESSURE TOWARDS THE STATE WILL LIMIT THE
EFFECTIVENESS OF SNOW DISPERSAL THROUGH THE EVENING HOURS. THIS AREA
OF LOW PRESSURE IS EXPECTED TO MOVE GENERALLY EAST OF THE AREA BY
FRIDAY AFTERNOON AS NORTHWEST FLOW ASSOCIATED WITH A RIDGE OF HIGH
PRESSURE MOVES OVER THE AREA BY FRIDAY AFTERNOON.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR WYZ010-
011-019-022.
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 11 PM MST
THIS EVENING FOR WYZ020.
&&
$$
SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...AR
FIRE WEATHER...BRANHAM
