FXUS65 KRIW 252250
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
350 PM MST WED NOV 25 2009
.SHORT TERM...TONIGHT THROUGH SATURDAY
LARGE RIDGE ACROSS THE WESTERN U.S. WILL MOVE EASTWARD TONIGHT WITH
CLEAR SKIES EXPECTED ACROSS ALL OF WESTERN AND CENTRAL WYOMING. WITH
STRONG SFC HIGH PRESSURE BUILDING ACROSS THE REGION TONIGHT AND VERY
DRY AIR MASS IN PLACE ACROSS THE REGION...LOW TEMPERATURES THURSDAY
MORNING WILL BE BELOW NORMAL ACROSS THE NORTHERN TWO-THIRDS OF THE
REGION. LOWS THURSDAY MORNING IN THE WESTERN VALLEYS WILL RANGE FROM
AROUND 5 BELOW ZERO TO AROUND 10 F AND LOWS IN THE BASINS EAST OF
THE DIVIDED WILL BE SLIGHTLY BELOW NORMAL. A WEAK SURFACE PRESSURE
GRADIENT BETWEEN STRONG HIGH PRESSURE CENTERED IN SOUTHERN ID AND
LOWER PRESSURE IN THE CENTRAL AND NORTHERN PLAINS WILL CREATE
SOUTHWEST WINDS STRONG ENOUGH TO MIX THE BOUNDARY LAYER ACROSS
SOUTHERN WY AND NATRONA COUNTY TONIGHT...WHERE LOW TEMPERATURES
THURSDAY MORNING WILL BE ABOVE NORMAL. RIDGE AXIS WILL CREST ACROSS
WESTERN WY FRIDAY WITH STRONG INVERSIONS IN PLACE ACROSS THE LOWER
ELEVATIONS OF WESTERN W...THE WIND RIVER BASIN AND THE BIG HORN
BASIN...WHERE HIGHS WILL BE NEAR TO SLIGHTLY ABOVE NORMAL. A LEE SFC
TROUGH ACROSS EASTERN WY AND THE WESTERN HIGH PLAINS WILL PRODUCE
SOUTHWEST WINDS WITH GUSTS UP TO 35 MPH THURSDAY AFTERNOON FROM
EASTERN SWEETWATER COUNTY NORTHEASTWARD INTO NATRONA COUNTY.
INVERSIONS WILL BE SHALLOW ACROSS SOUTHERN WY AND EASTERN CENTRAL WY
THURSDAY MORNING AND WILL MIX OUT DURING THE MORNING. THIS WILL
ALLOW HIGH TEMPERATURES THURSDAY ACROSS SOUTHERN WY...NATRONA
COUNTY AND JOHNSON COUNTY TO BE WELL ABOVE NORMAL IN THE 40S IN
SWEETWATER COUNTY...THE 50S IN NATRONA COUNTY AND IN THE 50S TO NEAR
60 IN JOHNSON COUNTY.
PAC TROUGH WILL ENTER THE WEST COAST FRIDAY...AND THE GFS...NAM AND
ECMWF CONTINUE TO SHOW THE TROUGH SPLITTING INTO 3 SHORTWAVES AS IT
MOVES INLAND. STRONG THERMAL GRADIENT WILL DEVELOP FRIDAY AFTERNOON
ACROSS ID/SOUTHERN MT AHEAD OF THE TROUGH. THIS STRONG THERMAL
GRADIENT AND TIGHTENING H85 HEIGHT FIELD CROSS WY WILL PRODUCE
GUSTY SOUTHWEST WINDS FROM EASTERN SWEETWATER COUNTY TO EASTERN
NATRONA COUNTY WITH GUSTS UP TO AROUND 40 MPH EXPECTED. THE
INVERSIONS ACROSS THE REMAINDER OF THE LOW LYING AREAS IN CENTRAL
AND WESTERN WY WILL BE BROKEN BY FRIDAY LATE MORNING AND EARLY
AFTERNOON...AS LIGHT WINDS REACH THE SURFACE. AS A RESULT OF GOOD
MIXING AND UNSEASONABLY WARM TEMPERATURES ALOFT...H7 TEMPERATURES
BETWEEN MINUS 2 C AND 2 C...ON FRIDAY...HIGH TEMPERATURES WILL BE 10
TO 16 F ABOVE NORMAL ACROSS THE REGION. WEAK SHORTWAVE WILL CROSS WY
FRIDAY NIGHT AND SATURDAY...BRINGING MUCH COLDER AIR MASS TO WY.
COLD FRONT WILL CROSS WESTERN WY FRIDAY LATE AFTERNOON AND EVENING
AND MOVE ACROSS THE STATE FRIDAY NIGHT. DUE TO THE SPLIT NATURE OF
THE LARGER SCALE TROUGH CROSSING THE WESTERN UNITED
STATES...MOISTURE WILL BE LACKING WITH THE SHORTWAVE WHICH WILL
CROSS WY. LIGHT TO MODERATE SNOWFALL IS EXPECTED WEST OF THE DIVIDE
WITH ACCUMULATIONS UP TO 6 INCHES POSSIBLE IN THE HIGHER ELEVATIONS
OF THE NORTHWEST MOUNTAINS. AS THE COLD FRONT CROSSES THE
DIVIDE...THE SHORTWAVE IS PROJECTED TO SHEAR FRIDAY NIGHT. SOME
LIGHT ACCUMULATIONS OF SNOW ARE POSSIBLE FRIDAY NIGHT EAST OF THE
DIVIDE. HIGHS SATURDAY WILL BE SLIGHTLY BELOW NORMAL ACROSS THE
REGION BEHIND THE COLD FRONT. UPPER LEVEL TROUGH WILL CROSS WESTERN
AND CENTRAL WY SATURDAY WITH CHANCES OF SNOW IN THE HIGHER
ELEVATIONS AND SLIGHT CHANCES IN THE LOWER ELEVATIONS.
.LONG TERM...XXX THROUGH XXX
MEDIUM RANGE MODELS ARE IN DECENT AGREEMENT IN DIGGING A SHORTWAVE
TROUGH SOUTHEAST OUT OF BRITISH COLUMBIA/PACIFIC
NORTHWEST...SOUTHEAST ACROSS IDAHO ON SATURDAY AND THEN QUICKLY
SOUTH INTO UTAH/ARIZONA SATURDAY NIGHT...WITH DEEP NORTHERLY FLOW
OVER THE AREA ON SUNDAY. THIS SYSTEM PASSING TO OUR WEST...SHOULD
GIVE A DECENT SHOT AT SOME SNOW WEST OF THE DIVIDE SATURDAY/SATURDAY
EVENING...BEFORE DRIER CONDITIONS PREVAIL. HAVE KEPT SLIGHT POPS
GOING EAST OF THE DIVIDE SATURDAY...TO RESPECT THE ECMWF SOLUTION
THAT HAS MORE MOISTURE LEFT OVER FROM THE INITIAL TROUGH...AND THE
WEAK UPSLOPE FLOW THAT DEVELOPS EAST OF THE DIVIDE SATURDAY. HOWEVER
THE BULK OF THE SNOW IS EXPECTED WEST OF THE DIVIDE. TOTAL SNOW
SHOULD BE IN THE 2-5 INCH RANGE IN THE MOUNTAINS...WITH 1-2 IN THE
FAR WESTERN VALLEYS BY SATURDAY EVENING. A RIDGE IN THE A EASTERN
PACIFIC WILL PUSH EAST INTO WEST/ROCKIES SUNDAY NIGHT/MONDAY. THIS
WILL RESULT IN MAINLY DRY CONDITIONS AND A WARMING TREND. A TROUGH
OVER THE GULF OF ALASKA SUNDAY...IS PROJECTED TO PUSH EAST SOUTHEAST
INTO BRITISH COLUMBIA/PACIFIC NORTHWEST ON MONDAY. THIS TROUGH WILL
CONTINUE EAST SOUTHEAST FLATTENING THE RIDGE MONDAY NIGHT AND
TUESDAY. THE ASSOCIATED COLD FRONT WITH THIS TROUGH SHOULD MOVE
ACROSS THE AREA MONDAY NIGHT/TUESDAY. THE 00Z ECMWF IS INDICATING
MORE ENERGY AFFECTING THE FORECAST AREA THEN THE GFS. HAVE MAINLY
CHANCE MTN POPS AND SLIGHT VALLEY POPS TO HANDLE THIS SYSTEM FOR
NOW. TEMPERATURES ARE EXPECTED TO BE SEASONAL TO SLIGHTLY BELOW
AVERAGE SATURDAY AND SUNDAY...WITH TEMPERATURES REBOUNDING TO ABOVE
AVERAGE ON MONDAY AND THEN BELOW AVERAGE TEMPERATURES RETURN BY
WEDNESDAY...AND POSSIBLY ON TUESDAY DEPENDING UPON TIMING OF THE
COLD FRONT WITH THE SYSTEM ON TUESDAY.
&&
.AVIATION...
VFR CONDITIONS WILL PREVAIL OVER WESTERN AND CENTRAL WYOMING
TONIGHT AND THANKSGIVING MORNING. THE ONE EXCEPTION WILL REMAIN IN
THE JACKSON VALLEY WHERE STRONG TEMPERATURE INVERSIONS AND THE
ASSOCIATED LOW BKN-OVC STRATUS CLOUD DECK WILL REDEVELOP AFTER
SUNSET. THE LOW STRATUS CLOUD COVER IS EXPECTED TO GRADUALLY
DISSIPATE AFTER 18Z THURSDAY.
&&
.FIRE WEATHER...
HIGH PRESSURE AT THE SURFACE AND ALOFT WILL MOVE FROM THE NORTHERN
INTERMOUNTAIN WEST ACROSS WYOMING THURSDAY THROUGH FRIDAY. DEEP
INVERSIONS WILL FORM TONIGHT ACROSS THE LOWER ELEVATIONS OF WESTERN
WYOMING...THE WIND RIVER BASIN AND THE BIG HORN BASIN AND PERSIST
THROUGH FRIDAY MORNING. WEAK SURFACE LOW PRESSURE IN THE WESTERN
HIGH PLAINS AND STRONG HIGH PRESSURE ACROSS IDAHO/WESTERN WYOMING
WILL PRODUCE GUSTY SOUTHWEST WINDS THURSDAY AFTERNOON FROM EASTERN
SWEETWATER COUNTY TO NATRONA COUNTY. WEAK INVERSIONS ACROSS SOUTHERN
AND EASTERN CENTRAL WYOMING TONIGHT WILL LIFT QUICKLY THURSDAY
MORNING. INVERSIONS ARE NOT EXPECTED ACROSS SOUTHERN WYOMING AND
NATRONA COUNTY FRIDAY MORNING...BUT WILL STILL BE FAIRLY STRONG IN
THE LOWER ELEVATIONS ACROSS THE REMINDER OF THE REGION. STRONGER
WINDS ALOFT WILL BREAK THE INVERSIONS FRIDAY ACROSS THE ENTIRE AREA
WITH LIGHT WINDS DEVELOPING IN THE BASINS BY FRIDAY AFTERNOON. HIGHS
FRIDAY WILL BE ABOVE NORMAL ACROSS THE ENTIRE REGION WITH LOW
DAYTIME RELATIVE HUMIDITY. A WEAK LOW PRESSURE SYSTEM AND A STRONG
COLD FRONT WILL CROSS WYOMING FRIDAY NIGHT AND SATURDAY. LIGHT TO
MODERATE SNOW ACCUMULATIONS ARE EXPECTED N WESTERN WYOMING FRIDAY
NIGHT AND SATURDAY WITH VERY LIGHT TO LIGHT ACCUMULATIONS EXPECTED
ACROSS CENTRAL WYOMING.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...SMITH
LONG TERM...WM
AVIATION...CHURCH
FIRE WEATHER...SMITH
