000
FXUS65 KRIW 142059
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
159 PM MST WED NOV 14 2007

.SHORT TERM...TONIGHT THROUGH SATURDAY
VERY DRY COOL AIRMASS OVER AREA TODAY WITH NORTHWEST FLOW ALOFT.
1035 MB SURFACE HIGH PRESSURE CENTERED OVER NW WYOMING THIS
AFTERNOON WILL SLIDE SE ACROSS WYOMING THIS EVENING AS UPPER RIDGE
BUILDS IN. THICK CIRRUS SHIELD WILL ACCOMPANY THIS RIDGE JUST EAST
OF ITS AXIS WITH CRAS IMAGERY SHOWING NW HALF OF WY UNDER
EXTENSIVE HIGH CLOUD COVER BY 12Z THURSDAY. LEE TROUGH STRENGTHENS
THURSDAY MORNING WITH SW WINDS PICKING UP THROUGH CPR AREA AND
CENTRAL WIND CORRIDOR. THICKENING HIGH CLOUDS AND LATE NIGHT
BREEZY AREAS WILL MODERATE TEMPERATURES TOWARD THE HIGH END OF MOS
GUIDANCE. STRONG WARM ADVECTION WILL BRING A RETURN TO ABOVE
NORMAL TEMPERATURES THURSDAY WITH MOST AREAS RUNNING AROUND 10F
ABOVE SEASONAL AVERAGES. SHORTWAVE OFF THE NW COAST NEAR 48N/135W
AT 20Z WILL MOVE OVER RIDGE ACROSS CENTRAL CANADA 00Z
FRIDAY...FLATTENING RIDGE AND BRINGING SOME WEAK ISENTROPIC
UPGLIDE AND FAVORABLE OROGRAPHIC LIFT INTO THE NORTHWEST THURSDAY
NIGHT. SHORTWAVE WILL TAKE A NE DIVE INTO THE NORTHERN PLAINS
FRIDAY MORNING DRIVING A WEAK COLD FRONT ACROSS NE WYOMING.
HOWEVER FRONT WILL HAVE LITTLE AFFECT ON TEMPERATURES AS MILD
PACIFIC AIRMASS PREVAILS ALONG WITH ANOTHER UNSEASONABLY WARM DAY
WITH MOST BASIN HIGHS IN THE 50S. STRONG 160 KNOT JET APPROACHES
THE NW COAST SATURDAY WITH BACKING WAA FLOW...AND INCREASING
ISENTROPIC UPGLIDE OVER THE WEST FRIDAY NIGHT AND SATURDAY
MORNING. BEST COVERAGE OF PRECIPITATION IN THE WEST SHOULD OCCUR
06Z-18Z SATURDAY AHEAD OF H7 THERMAL RIDGE AXIS WITH WEAK COLD
ADVECTION AND A DECREASE IN PRECIPITATION COVERAGE SATURDAY
AFTERNOON. SNOW LEVELS WILL REMAIN NEAR 8000 FEET SATURDAY MORNING
AND PRECIPITATION IS EXPECTED TO BE RELATIVELY LIGHT WITH 2 TO 5
INCHES OF SNOWFALL POSSIBLE SATURDAY MORNING OVER THE TETON RANGE
AND NORTHWEST MOUNTAINS. WINDY AND MILD CONDITIONS WILL PREVAIL
EAST OF THE DIVIDE SATURDAY BUT THE PROBABILITY OF ANOTHER HIGH
WIND EVENT IS LOW.


.LONG TERM...SUNDAY THROUGH WEDNESDAY
ACTIVE PATTERN TAKING SHAPE DURING THE EXTENDED PERIOD WITH A
STRONG PROBABILITY THAT WINTER LIKE WEATHER WILL FINALLY SETTLE IN
ACROSS THE CENTRAL AND WESTERN WYOMING. STILL PLENTY OF ROOM FOR
ERROR IN THE DETAILS WITH COMPLEX SCENARIO DEVELOPING BOTH OVER THE
WEEKEND AND INTO THE MIDDLE OF NEXT WEEK. THE MODELS ARE TAKING
THE COLD TROUGH OVER SWRN AK AND VERY SLOWLY MOVES IT TOWARD THE
COAST LATE IN THE WEEKEND...AFTER IT SLOWS AND ALLOWS SEVERAL
SHORTWAVES TO ROTATE AROUND IT WHILE IT SITS OF THE BC COAST THIS
WEEKEND. THE RIDGE IS FORECAST TO FLATTEN AHEAD OF THIS SYSTEM AS
A 150-160KT JET MAX MOVES INTO THE PACNW AND TOWARDS THE WY/MT
AREA SAT NIGHT AND SUNDAY. THE EURO IS MOST BULLISH WITH THE
OROGRAPHIC PCPN IN THE WRN MTNS THIS WEEKEND WHILE THE GFS HAS A
DECENT SHOT MAINLY ON SATURDAY. HAVE BEGUN TO HIT SATURDAY HARDER
AND WILL FOCUS ON SUNDAY TONIGHT IF THE TRENDS CONTINUE. MAIN
FOCUS THEN EARLY NEXT WEEK IS DEVELOPMENT OF A LARGE COLD
TROUGH...THE AFOREMENTIONED AK/PACNW TROUGH...THAT IS FORECAST TO
DIG INTO THE GREAT BASIN MONDAY AND TUESDAY WITH A REINFORCING
SHOT OF ENERGY COMING DOWN FROM THE NORTH TUESDAY INTO WEDNESDAY.
PATTERN HOLDS HOPE FOR MUCH OF THE AREA WITH POSSIBLE JET STREAK
DYNAMICS IN THE SERN HALF OF THE AREA AND STRONG UPSLOPE EAST OF
THE DIVIDE WITH POSSIBLE ISENTROPIC ASCENT IN THE SOUTH. HAVE HIT
THE ENTIRE AREA WITH CHANCE POPS AS THE COLD PUSHES SOUTH ACROSS
THE AREA AND HAVE CONTINUED THAT IN ALL BUT THE NWRN CORNER
THROUGH WEDNESDAY ALONG WITH COLDER AND COLDER AFTERNOON HIGHS.
WILL CONTINUE THIS TREND TONIGHT IF THINGS CONTINUE TO EVOLVE AS EXPECTED.

&&

.AVIATION...
STRONG HIGH PRESSURE AT THE SURFACE AND ALOFT WILL PRODUCE VFR
CONDITIONS TONIGHT THROUGH THURSDAY EVENING. WINDS TONIGHT WILL
BECOME LIGHT AND VARIABLE WITHIN ONE HOUR OF SUNSET. A WEAK WARM
FRONT WILL MOVE ACROSS EASTERN MONTANA THURSDAY...AS HIGH PRESSURE
MOVES EAST OF WYOMING INTO THE NORTHERN PLAINS. THE HIGHER WINDS
ALOFT ASSOCIATED WITH THE FRONT WILL HAVE LITTLE EFFECT ON
INCREASING WIND SPEEDS ABOVE 10 KNOTS AT THE MAJORITY OF TAF SITES
THURSDAY AFTERNOON...DUE TO A STRONG INVERSION IN THE LOWER LAYERS
OF THE ATMOSPHERE. HOWEVER...THE SFC PRESSURE GRADIENT WILL INCREASE
JUST ENOUGH OVER KJAC AND KCPR TO CAUSE HIGHER WINDS ALOFT TO MIX
DOWN TO THE SURFACE AROUND 11 AM MST AT KCPR AND AROUND 1 PM MST AT
KJAC. EXPECT WIND GUSTS AT KJAC TO BETWEEN 15 AND 20 KT AFTER 1 PM
AND TO BETWEEN 25 AND 20 KT AT KCPR AFTER 11 AM.

&&

.FIRE WEATHER...
A VERY DRY AND COOL AIRMASS WILL GIVE WAY TO INCREASING HIGH
CLOUDS AND A WARMER AIRMASS ALOFT TONIGHT AND THURSDAY. A LEE TROUGH
WILL BRING BREEZY TO WINDY CONDITIONS ACROSS THE LOWER ELEVATIONS
OF NATRONA COUNTY AND ALONG THE EAST SLOPES OF THE DIVIDE LATE
TONIGHT AND THURSDAY. UNSEASONABLY WARM TEMPERATURES WILL RETURN
TO THE AREA THURSDAY AND FRIDAY WITH ACCUMULATING SNOWFALL
RETURNING TO THE WESTERN MOUNTAINS ABOVE 8000 FEET FRIDAY NIGHT
AND SATURDAY MORNING.

&&

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

$$

SHORT TERM...AEM
LONG TERM...SKRBAC
AVIATION...SMITH
FIRE WEATHER...AEM

----------------------------------------------------------------------

000
FXUS65 KRIW 302247
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
347 PM MST FRI NOV 30 2007

.SHORT TERM...TONIGHT THROUGH MONDAY
INTERESTING SYSTEM DEVELOPING FOR TONIGHT AND SATURDAY AS VERY
HIGH PW AIR...IN EXCESS OF 200 PERCENT OF NORMAL...IS HEADED NORTH
FROM UT AND AZ INTO SRN WYOMING OVERNIGHT. THIS WILL COMBINE WITH
ENTRENCHED COLDER AIR OVER CENTRAL WYOMING. JET STREAK DYNAMICS
AND ISENTROPIC LIFT WILL BOTH PROVIDE SUPPORT IN THIS STORM. MOIST
ISENTROPIC UPGLIDE DEVELOPS QUICKLY THIS EVENING ACROSS THE SOUTH
AND LIFTS NWD OVERNIGHT. FRONT HAS WASHED OUT IN THE FAR SOUTH
WHICH SHOULD MAKE FOR AN INTERESTING BOUNDARY ACROSS THE GREEN
MOUNTAINS AND RATTLESNAKE RANGE AREA SATURDAY MORNING. RIGHT
ENTRANCE REGION OF MOVING NWD ACROSS IDAHO WILL PROVIDE FIRST SHOT
OF RIGHT ENTRANCE REGION DYNAMICS TO SWEETWATER COUNTY LATER THIS
EVENING WITH POSSIBLE DUAL JET STRUCTURE COUPLET DEVELOPING ACROSS
MUCH OF THE AREA SATURDAY MORNING TO PROVIDE THE BEST SHOT OF SNOWFALL.
RAPID DEVELOP OF THE SURFACE LOW IS EXPECTED OVER NCNTRL CO
SATURDAY MORNING TO AID IN WRAPAROUND PCPN BACK TO AT LEAST CPR
BEFORE MOVING OFF TO THE NORTH. NAM INTENSITY SEEMS THE MOST REASONABLE.
SCENARIO IS STILL COMPLEX WITH MULTIPLE PIECES TO THIS STORM
COMBINED WITH EXACT LOCATION OF FRONTAL BOUNDARY. AS OF 3 PM...RKS
HAD RISEN TO AROUND 40 DEGREES WITH STRONG SW WINDS. PLENTY OF
RAIN AND SNOW HEADING QUICKLY N FROM UT THOUGH SO IT SHOULD JUST
BE A MATTER OF TIME FOR SNOW TO DEVELOP AS TEMPERATURES SHOULD DROP
QUICKLY AGAIN AFTER DARK. SECONDARY SHORTWAVE THAT BOTTOMS OUT NR
SFO IS THEN EXPECTED TO MOVE EAST ACROSS EITHER CO OR SRN WY
SATURDAY EVENING. NAM HAS THIS FURTHER SOUTH WITH NO IMPACT ACROSS
THE AREA WHILE THE GFS AND CRAS IMAGERY SHOWING ANOTHER ROUND OF
CLOUDS AND LIKELY SNOW SHOWERS MOVING QUICKLY ACROSS FROM WEST TO
EAST. HAVE EDGED THE FORECAST THIS WAY FOR NOW BUT MORE ROOM TO
ADJUST IF THIS SOLUTION LOOKS BETTER TONIGHT.

MAIN CONCERN AFTER THIS STORM IS THE WIND THEN FOR SUNDAY AND
MONDAY. HAVE CONTINUED TO TREND TOWARDS STRONG WINDS DURING THIS
PERIOD ACROSS THE WIND CORRIDOR...MTNS...LANDER FOOTHILLS AND
ESPECIALLY THE CODY FOOTHILLS. IT IS QUITE LIKELY THAT SOME HIGH
WIND WATCHES WILL BE NEEDED WITHIN THE NEXT 24-36 HOURS FOR THIS
UPCOMING RAPID PATTERN CHANGE. TEMPERATURES SHOULD ALSO RAPIDLY
REBOUND SUNDAY INTO MONDAY EVEN WITH SNOW COVER.

.LONG TERM...MONDAY NIGHT THROUGH FRIDAY
AT THE BEGINNING OF THE LONG TERM...A RIDGE WILL BE OVER THE
ROCKIES...WITH MAINLY DRY WEATHER AND ABOVE AVERAGE TEMPERATURES.
700 MB TEMPERATURES ARE EXPECTED TO RANGE GENERALLY BETWEEN 0 AND
+5 DEG CELSIUS THROUGH TUESDAY...WITH TEMPS SOME 5 TO 10 DEGREES
ABOVE AVERAGE. A DECENT PRESSURE GRADIENT AND STRONG 700MB FLOW
SHOULD RESULT IN WINDY CONDITIONS IN FAVORED AREAS. MONDAY APPEARS
TO BE THE DRIEST DAY WHEN THE RIDGE WILL BE THE STRONGEST WITH
ONLY A SLIGHT CHANCE OF SOME MOUNTAIN SNOW SHOWERS. BY
TUESDAY...THE RIDGE IS EXPECTED TO FLATTEN OUT...WITH THE WEST
BEGINNING TO BE IMPACTED BY A DEEP MOIST WESTERLY FLOW. THE LATTER
HALF OF THE EXTENDED WILL BECOME PROGRESSIVE WITH AT LEAST A
COUPLE OF DISTURBANCES/SHORTWAVE TROUGHS. WEDNESDAY AND WEDNESDAY
NIGHT...BOTH THE GFS AND ECMWF INDICATE A WEAK SHORTWAVE TROUGH
PUSHING EAST SOUTHEAST ACROSS THE NORTHERN AND CENTRAL
ROCKIES...WITH THE GFS FARTHER NORTH AT THIS TIME. AN ASSOCIATED
COLD FRONT IS EXPECTED TO MOVE THROUGH THE AREA
WEDNESDAY/WEDNESDAY NIGHT...RETURNING TEMPERATURES BACK TO
SEASONAL LEVELS. WILL HAVE CHANCE POPS OUT WEST...BUT ONLY SLIGHT
POPS EAST OF THE DIVIDE FOR NOW. BEYOND WEDNESDAY...THERE IS
CONSIDERABLE SPREAD IN THE GFS ENSEMBLES WITH THE NEXT TROUGH THAT
COULD AFFECT THE AREA FRIDAY.

&&

.AVIATION...
AN APPROACHING DISTURBANCE WILL LEAVE SOME LOW CLOUD COVER AND 
ASSOCIATED MVFR CONDITIONS ACROSS AREA AIRPORTS TODAY. KLND IS 
EXPECTED TO BE IN AND OUT OF SNOW SHOWERS...WHICH MAY CREATE A FEW 
PERIODS OF IFR CONDITIONS. THE STRONGER STORM WILL MOVE INTO 
SOUTHERN WYOMING AFTER 03Z THIS EVENING...BRINGING ADDITIONAL MVFR 
CONDITIONS. SNOW SHOWERS SHOULD START THERE BEFORE 06Z...WITH 
PERIODS OF IFR CONDITIONS EXPECTED. SNOW SHOWERS TO MOVE INTO THE 
KCPR AREA AS WELL DURING THE LATE AFTERNOON...WITH SNOW SHOWERS 
STARTING BETWEEN 04Z AND 05Z. PROMINENT SNOW SHOWERS WILL BE 
SOUTHEAST OF A LINE FROM KCPR TO KRKS THROUGH 00Z SUNDAY...WITH 
ADDITIONAL SHOWER ACTIVITY ANTICIPATED FROM KBYG TO KEVW. 

&&

.FIRE WEATHER...
ANOTHER STORM SYSTEM WILL BRING SNOW TO MUCH OF CENTRAL AND
SOUTHERN WYOMING TONIGHT INTO SATURDAY. THE PATTERN WILL QUICKLY
TRANSITION THEN SUNDAY AND MONDAY INTO WARMER AND VERY WINDY
CONDITIONS. 

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
SNOW ADVISORY FROM 2 AM TO 5 PM MST SATURDAY FOR WYZ020-022.

SNOW ADVISORY FROM 8 PM THIS EVENING TO 5 PM MST SATURDAY FOR 
WYZ028>030.

SNOW ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST SATURDAY FOR 
WYZ019.

&&

$$

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

----------------------------------------------------------------------

000
FXUS65 KRIW 160230
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
830 PM MDT THU MAY 15 2008

.UPDATE...

AREA OF MID TO HIGH LEVEL WARM ADVECTION CLOUD COVER HAS SPREAD
WESTWARD TO THE DIVIDE...AND HAVE INCREASED CLOUD COVER EAST OF
THE DIVIDE AS FAR SOUTH AS SOUTHERN NATRONA COUNTY AND THE GREEN
AND RATTLESNAKE RANGES THROUGH 06Z. CRAS CLOUD COVER...18Z GFS AND
00Z NAM PROJECT THAT CLOUDS WILL LINGER ACROSS THE NORTHEASTERN
BIGHORN BASIN EASTWARD ACROSS JOHNSON COUNTY THROUGH 15Z
FRIDAY...SO INCREASED LOW TEMPERATURES FRIDAY MORNING ACROSS THIS
REGION BY 3 TO 5 F.

ZONE FORECAST UPDATE WILL BE OUT BEFORE 8:45 PM.

&&

.PREV DISCUSSION... /ISSUED 332 PM MDT THU MAY 15 2008/ 

SHORT TERM...TONIGHT THROUGH SUNDAY
LINGERING SHOWER ACTIVITY CONTINUES TO CLEAR OUT OF THE CWA THIS
AFTERNOON...WITH SOME LEFTOVER MID LEVEL CLOUDS STILL PRESENT
ACROSS CENTRAL AND WESTERN WYOMING. CLOUD COVER WILL CONTINUE TO
DISSIPATE THIS EVENING AS HIGH PRESSURE RIDGE BECOMES DOMINANT
WEATHER FEATURE. RIDGE AXIS REMAINS NEARLY STATIONARY OVER THE
WEST COAST...THOUGH IS MOVING SLOWLY INLAND. A FEW ISOLATED
SHOWERS WILL CONTINUE OVER THE BIG HORN MOUNTAINS THROUGH THIS
EVENING DUE TO UPSLOPE CONDITIONS. A JET STREAK MOVING THROUGH THE
AREA WILL KEEP SOME STRONGER NORTH WINDS ACROSS THE AREA THROUGH
THE OVERNIGHT HOURS.

FRIDAY WILL BE THE FIRST OFFICIAL DAY IN THE RIDGING PATTERN WITH
CLEARING CONDITIONS AND WARMING TEMPERATURES. H7 TEMPERATURES OVER
THE WEST COAST AT 12Z TODAY RANGED FROM 10 TO 13 DEGREES CELSIUS.
THIS THERMAL RIDGE WILL CONTINUE TO ADVANCE TOWARDS THE STATE
FRIDAY WITH H7 TEMPERATURES WARMING TO 5 TO 7 DEGREES CELSIUS BY
FRIDAY AFTERNOON...ALLOWING SURFACE TEMPERATURES TO REACH INTO THE
LOW 70S. H7 TEMPERATURES CONTINUE TO WARM THROUGH THE
WEEKEND...WITH VALUES APPROACHING THE 13 DEGREE MARK BY SUNDAY.
WANT TO SEE THESE TEMPERATURES EVOLVE OUT WEST BEFORE BELIEVING THE
POTENTIAL FOR UPPER 80S ACROSS THE SOUTH AND EAST SUNDAY...HAVE
BUMPED UP TEMPERATURES A COUPLE DEGREES INTO THE LOW TO MID 80S
FOR NOW. WINDS WEAKEN UNDER THE RIDGE ON FRIDAY AFTERNOON...WITH
GENERALLY LIGHT WINDS CONTINUING THROUGH SUNDAY. WARMER
TEMPERATURES WILL CAUSE CONTINUED SNOWMELT THROUGH THE
WEEKEND...CAUSING SMALL STREAMS TO RISE. THIS SITUATION WILL
CONTINUE TO BE CLOSELY MONITORED FOR ANY FLOODING
POTENTIAL.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY
EXTENDED FORECAST BASED MOSTLY ON THE ECMWF MODEL TONIGHT AS THE
GFS CONTINUES ITS OWN COURSE OF THE PAST FEW NIGHTS. SOME OF THE
GFS ENSEMBLE MEMBERS SUPPORT A TROUGH COMING INTO THE ROCKIES
WHICH MAY LEAD ONE TO HOPE THE GFS WILL COME AROUND TO THE ECMWF
IN THE COMING DAYS. DRY AND WARM SUNDAY WITH UPPER RIDGE IN
CONTROL. MONDAY LOOKS MOSTLY DRY ASIDE FROM ISOLATED AFTERNOON AND
EVENING SHOWERS OR STORMS IN THE NW MTS. STILL WARM ON MONDAY AND
HAVE RAISED THE HIGHS A FEW DEGREES. THE FLOW ALOFT TURNS SW ON
TUESDAY AHEAD OF THE TROUGH. BREEZY TO WINDY WITH THE FRONT
NEARING THE WEST AT 00Z WED. ANOTHER WARM DAY ON TUESDAY. WILL
LEAVE LOW CHANCE OF AFTERNOON AND EVENING SHOWERS AND STORMS IN
THE MTS AND THE FAR WEST FOR NOW. LOOKS MOSTLY DRY TUE PM EAST OF
THE DIVIDE WITH ISOLATED ACTIVITY TUE NIGHT. TROUGH IMPACTS THE
ROCKIES WED AND THU WITH UNSETTLED WEATHER EXPECTED. A CHANCE OF
SHOWERS AND STORMS WED INTO WED NIGHT WITH A CHANCE OF SHOWERS ON
THU. TEMPS TO COOL DOWN WED AND THU.

AVIATION...
HIGH PRESSURE BEGINS TO BUILD OVER THE REGION TONIGHT AND FRIDAY. 
THE AIRMASS DRIES OUT WITH A MOSTLY CLEAR SKY. IN FACT...IT SHOULD 
BE GENERALLY CLEAR WITH LIGHT SURFACE WINDS THROUGH THE UPCOMING 
WEEKEND. AS A RESULT...VFR CONDITIONS WILL PREVAIL ACROSS CENTRAL 
AND WESTERN WYOMING THIS FORECAST PERIOD.

FIRE WEATHER...
LINGERING SNOW SHOWERS WILL BE FOUND OVER THE BIG HORN MOUNTAINS
THIS EVENING...WITH THE REMAINDER OF THE AREA CLEARING OUT UNDER A
RIDGE OF HIGH PRESSURE. THIS RIDGE WILL BECOME THE DOMINANT
WEATHER FEATURE THROUGH THE WEEKEND...ALLOWING SKY CONDITIONS TO
BECOME MOSTLY CLEAR. HIGH TEMPERATURES WILL REACH INTO THE LOW 70S
ACROSS THE EASTERN BASINS FRIDAY WITH VALUES IN THE UPPER 50S
ACROSS THE HIGHER ELEVATION. CONTINUED WARMING EXPECTED SATURDAY
AND SUNDAY...WITH LOW TO MID 80S ANTICIPATED OVER THE
BASINS...WITH MID 60S POSSIBLE OVER THE MOUNTAINS. HUMIDITIES
WILL CONTINUE TO DECREASE THROUGH THE WEEKEND...WITH MANY LOWER
ELEVATION AREAS SEEING VALUES IN THE TEENS BY SUNDAY. WINDS WILL
BE GENERALLY LIGHT FROM FRIDAY AFTERNOON ON.

&&

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

&&

$$

UPDATE...SMITH
SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...KPL
FIRE WEATHER...BRANHAM

----------------------------------------------------------------------

000
FXUS65 KRIW 222156
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
356 PM MDT SUN JUN 22 2008

.SHORT TERM...TONIGHT THROUGH WEDNESDAY
A PERSISTENT EXTENSIVE BATCH OF ALTOSTRATUS CLOUDS ASSOCIATED WITH
THE VIGOROUS SHORTWAVE THAT BROUGHT ALL THAT LIGHTNING TO NORTHERN
CALIFORNIA YESTERDAY KEPT HIGH TEMPERATURES DOWN INTO THE UPPER
70S TO LOW 80S SO FAR IN CENTRAL WYOMING TODAY. THE CRAS SATELLITE
MODEL ACTUALLY HAD FORECAST THIS FEATURE FAIRLY WELL. WHERE THERE
HAS BEEN MORE SOLAR INSULATION TO THE WEST THERE ARE CONVECTIVE
CELLS FORMING OVER EASTERN IDAHO THAT ARE TRACKING NORTHEAST
POISED FOR NORTHWEST WY. OTHER THUNDERSTORMS ARE ROLLING OFF THE
UINTAS INTO SOUTHWEST SWEETWATER COUNTY WHERE CAPES ARE 2400 J/KG.
A WEAK BOUNDARY WILL PUSH SOUTH BEHIND THIS WEATHER FEATURE THIS
EVENING AND WILL ACT AS A FOCUS FOR ADDITIONAL THUNDERSTORM
ACTIVITY THIS EVENING AS THIS BOUNDARY MOVES SOUTH. ANY ISOLATED
THUNDERSTORM DEVELOPMENT WILL LAG BEHIND OVER CENTRAL COMPARED TO
THE OTHER AREAS BECAUSE OF THE ABSENCE OF FULL AFTERNOON HEATING
THERE. SPC HAS INDICATED OUR NORTHERN CWA TO BE IN A SLIGHT RISK
THIS EVENING WHERE CAPES ARE SLATED TO BE 1200J/KG. THE NEXT
SHORTWAVE IN THE FLOW NOW OVER EASTERN WASHINGTON AND OREGON
WOULD AFFECT WY AFTER MIDNIGHT TONIGHT. THIS FEATURE WILL KEEP
SCATTERED THUNDERSTORMS GOING PAST MIDNIGHT TONIGHT ACROSS
NORTHERN WY. THE NAM 20 DISPLAYS A HALF INCH OF PRECIP OVER YNP
BETWEEN 06Z AND 12Z TONIGHT. ANOTHER SECONDARY SURFACE BOUNDARY
BEHIND THIS FEATURE IS PROGGED TO SLIDE SOUTH ACROSS AREAS EAST OF
THE DIVIDE MONDAY MORNING BEHIND THIS SECOND SHORT WAVE. HIGHER
DEW POINTS IN THE 40S WILL FILTER SOUTH BEHIND THIS BOUNDARY.
THIS WILL SET UP NATRONA AND JOHNSON COUNTIES TO BE THE BEST
CANDIDATES FOR LATE DAY T STORMS MONDAY. AN INFLUX OF BOUNDARY
LEVEL MOISTURE IS EXPECTED TO INVADE FORM THE EAST LATE MONDAY
NIGHT SO KEPT CONVECTIVE ACTIVITY GOING ALL NIGHT IN OUR NORTHEAST
ZONES MONDAY NIGHT. YET ANOTHER SHORT WAVE TRACKS ACROSS THE AREA
TUESDAY WITH THE BEST CAPES OF 1000J/KG REMAINING OVER JOHNSON CO
WHERE THE STRONGEST T STORMS WILL BE. EXPECT LESS ACTIVITY
WEDNESDAY WITH THE LACK OF ANY IDENTIFIABLE FEATURE MOVING THROUGH
BUT KEPT WIDELY SCATTERED POPS IN JOHNSON COUNTY WHERE 1000 PLUS
CAPES WILL REMAIN. HIGH TEMPS SHOULD SOAR INTO THE LOW 90S IN
MANY AREAS TUESDAY AND WEDNESDAY WHEN 700MB TEMPS INCREASE. WENT
WITH A GFS/NAM BLEND FOR HIGH TEMPS ON THESE DAYS SINCE THE GFS
INDICATES 18C AND THE NAM 14C AT 70MB.

.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY
PROGRESSIVE NORTHERN STREAM CONTINUES WEDNESDAY AND THURSDAY NEAR
U.S/CANADIAN BORDER BEFORE WEAKENING AND MIGRATING NORTHWARD
FRIDAY THROUGH NEXT WEEKEND. THOUGH JET ENERGY WILL REMAIN WELL
NORTH OF THE AREA THROUGHOUT THE PERIOD...MEAN FRONTAL/DRYLINE
POSITION WILL REMAIN NEAR THE MONTANA/WYOMING BORDER AND ACROSS
THE EASTERN BIG HORN BASIN TO NEAR THE NATRONA/CONVERSE COUNTY
LINE WEDNESDAY AND THURSDAY REINFORCED BY SHORTWAVE PASSAGES TO
THE NORTH BOTH WEDNESDAY AND THURSDAY NIGHTS. THE BEST CHANCES
FOR THUNDERSTORMS WILL REMAIN OVER AND ADJACENT TO THE BIG HORN
MOUNTAINS WEDNESDAY AND THURSDAY. THURSDAY NIGHT SHORTWAVE WILL BE
THE LAST IN A SERIES BEFORE HOT UPPER HIGH OVER THE SOUTHERN
ROCKIES EXPANDS NORTHWARD WHILE UPPER RIDGE BUILDS IN FROM EASTERN
PACIFIC ACROSS WESTERN U.S. PUSHING THE WESTERLIES WELL NORTH INTO
CANADA. THUS...FRIDAY THROUGH SUNDAY WILL BE CHARACTERIZED BY
MOSTLY DRY UNSEASONABLY WARM CONDITIONS WITH LIGHT WIND WITH
POSSIBLY A FEW AIRMASS THUNDERSTORMS DEVELOPING OVER THE OWL CREEK
AND BIG HORN MOUNTAINS DURING THE HEAT OF THE DAY. MODERATE TO
SEVERE DROUGHT CONDITIONS ACROSS SOUTHWEST WYOMING ARE EXPECTED TO
PERSIST AND EXPAND WITH LITTLE OR NO CHANCE OF SIGNIFICANT
PRECIPITATION THROUGH THE REST OF JUNE. FIRE DANGER WILL ALSO BE
ON THE INCREASE IN THE SOUTHWEST HALF OF THE STATE WHERE LITTLE
RAIN HAS BEEN RECEIVED SINCE THE FIRST WEEK OF JUNE WITH FINER
FUELS IN GREENUP EXPECTED TO CURE OUT OVER THE NEXT SEVERAL DAYS.

&&

.AVIATION...
A WEAK UPPER LEVEL DISTURBANCE WILL MOVE ACROSS NORTHERN WY THIS
EVENING. ADEQUATE LOW AND MID LEVEL MOISTURE AND A SLIGHTLY UNSTABLE
AIRMASS ACROSS THE CODY FOOTHILLS...THE NORTHERN BIGHORN BASIN...THE
BIGHORN MOUNTAINS...JOHNSON COUNTY AND NATRONA COUNTY WILL ALLOW
ISOLATED THUNDERSTORMS TO CONTINUE THROUGH AROUND 02Z AND ISOLATED
SHOWER ACTIVITY TO CONTINUE THROUGH AROUND 06Z. INCLUDED A VICINITY
THUNDERSTORM AT KCOD AND KCPR EARLY THIS EVENING AND VICINITY
SHOWERS THROUGH MIDNIGHT. OTHERWISE...VFR CONDITIONS WILL PREVAIL
TONIGHT WITH WINDS BECOMING LIGHT AFTER MIDNIGHT. A COLD FRONT WILL
MOVE FROM NORTHEASTERN WYOMING TO THE DIVIDE MONDAY...AND WINDS EAST
OF THE DIVIDE WILL SHIFT TO THE NORTH TO NORTHWEST IN THE EARLY
AFTERNOON. A STRAY SHOWER OR THUNDERSTORM COULD FORM ACROSS NORTH
CENTRAL AND EAST CENTRAL WYOMING IN THE AFTERNOON. WINDS WEST OF THE
DIVIDE MONDAY WILL BE WEST AT 10 TO 15 KT WITH GUSTS TO AROUND 25 KT
AT KRKS.

&&

.FIRE WEATHER...
N EASTBOUND WEAK UPPER LEVEL DISTURBANCE WILL PRODUCE
A FEW THUNDERSTORMS MAINLY IN NORTHERN WYOMING THIS EVENING. THESE STORMS
WILL HAVE A TENDENCY TO PROPAGATE SOUTH AS COOL FRONT PUSHES SOUTH ACROSS
WYOMING THIS EVENING. ANOTHER WEAK UPPER LEVEL DISTURBANCE IN THE FLOW WILL
PUSH EAST ACROSS WYOMING AFTER MIDNIGHT TONIGHT WHICH WILL PROLONG THE
THUNDERSTORM ACTIVITY ACROSS NORTHERN WYOMING TONIGHT. AS MUCH AS ONE QUARTER
OF AN INCH OR PRECIPITATION COULD FALL OVER MANY AREAS OF YELLOWSTONE PARK
TONIGHT. ANOTHER SURFACE BOUNDARY WILL PUSH SOUTH BEHIND THIS DISTURBANCE WITH
HIGHER DEW POINTS FILTERING BEHIND THIS BOUNDARY. TEMPERATURES SHOULD STILL
BE WARMER IN MANY AREAS MONDAY WITH THE LACK OF HIGH AND MID LEVEL CLOUDS IN THE
AREA ALLOWING FOR MORE SOLAR INSULATION. MORE LATE DAY THUNDERSTORMS ARE
EXPECTED MAINLY IN NORTHERN AND EASTERN ZONES LATE MONDAY. AN INFLUX OF LOW LEVEL
MOISTURE FROM THE EAST WILL LIKELY PROLONG SCATTERED THUNDERSTORM ACTIVITY
THROUGH MOST OF THE NIGHT MONDAY NIGHT...MAINLY ACROSS THE NORTHERN AND
EASTERN ZONES. ANOTHER UPPER LEVEL DISTURBANCE WILL TRACK ACROSS THE AREA
TUESDAY FOR MORE LATE DAY THUNDERSTORMS... AGAIN MAINLY ACROSS NORTHERN AND
EASTERN ZONES. LATE DAY WIDELY SCATTERED THUNDERSTORMS WILL BE LIMITED TO
PORTIONS OF YELLOWSTONE PARK...THE NORTHERN ABSAROKA MOUNTAINS...NATRONA AND
JOHNSON COUNTY WEDNESDAY. THE MINIMUM RELATIVE HUMIDITY WILL BE IN THE LOWER
TEENS IN SWEETWATER COUNTY MONDAY WITH LOWER TEENS SPREADING NORTH TO THE
WIND RIVER BASIN ON TUESDAY AND WEDNESDAY. SOUTHWEST WINDS OF 10 TO 15 MPH
WILL BE COMMON WEST OF THE DIVIDE WITH MORE VARIABLE WIND DIRECTION EXPECTED
EAST OF THE DIVIDE WITH MORE FREQUENT SURFACE BOUNDARIES MOVING THROUGH THOSE
AREAS.


&&

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

$$

SHORT TERM...LIPSON
LONG TERM...AEM
AVIATION...SMITH
FIRE WEATHER...LIPSON