Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 261803
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1203 PM MDT SUN OCT 26 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

IMAGERY SHOWS RIDGING MIGRATING EWD AND SETTLING OVER THE PLAINS
STATES WITH TROF STILL LOCATED TO THE WEST WITH ITS AXIS JUST COMING
INTO THE PAC COAST. 100 KT JET ORIENTED N/S NOW LOCATED JUST TO THE
WEST OF WY FROM NRN NV UP THRU WRN MT. AT THE SFC...HIGH PRESSURE
TOT HE E OVR THE PLAINS WITH DEVELOPING LOW PRESSURE TO THE WEST OVR
ID WITH A MODEST BUT BUILDING PRESSURE GRAD IN BETWEEN OVR WY. SFC
BOUNDARY REPRESENTED BY WEAK LEE TROF/DEVELOPING SLOW MOVING
FRONT...JUST E OF THE BIGHORN MOUNTAINS...THEN LOOSELY DROPPING INTO THE
BIGHORN BASIN TO THE WEST.

AS THE WRN TROF EXPANDS ACROSS THE REGION...UPR LVL FLOW OUT OF THE
S OR SW WILL INCREASE THIS MORNING AS THE JET MOVES OVR THE WRN FA.
WARM LL TEMPS WITH GOOD LAPSE RATES UP THRU 600 MB IN THE LEE OF THE
MOUNTAINS WILL DRAMATICALLY INCREASE THE THERMAL GRAD AND START TO
INCREASE THE WEAK P GRAD ALREADY IN PLACE. SFC TO MID LVL FLOW
INCREASES AND BECOMES QUITE UNI-DIRECTIONAL THRU ABOUT
650MB...BEFORE WINDS BEGIN TO BACK ABOVE THIS IN RESPONSE TO
DEVELOPING UPR FRONT AND CAA. WITH REGARD TO THE STRONG WINDS
EXPECTED  THROUGH THE MORNING HRS...LOCAL/REGIONAL MAX WIND SPEEDS
WILL OCCUR NEAR H7...AT SOME 50 TO 60 KTS...WITH INCREASING WARMING
AND STABILITY ABOVE THIS AND ABOUT 150MB DEEP. THIS SHOULD BE ENOUGH
TO CREATE A WAVE BREAKING SITUATION JUST TO THE LEE OF THE MOUNTAIN
PEAKS...FURTHER SQUEEZING AND THEN INCREASING THE WIND SPEEDS THRU
THIS LAYER...WHILE HELPING TO PIN WINDS MORE NEAR SFC. THIS SET-UP
WILL INCREASE WINDS DRAMATICALLY OVER/NEAR THE LEE PORTIONS OF THE
MAJOR MOUNTAIN RANGES...WITH PERHAPS SOME OCCASIONAL SPILL INTO THE
LOWER ELEVATIONS ADJACENT TO THESE MOUNTAINS. THE NORTHERN ABSAROKAS
AND ADJACENT CODY FOOTHILLS LOOK TO BE LOCATED IN THE MOST FAVORABLE
POSITION FOR STRONGER MOUNTAIN WAVE PRODUCTION...PEAKING BETWEEN 09Z
AND 15Z. THE HIGH WIND WATCH HAS THEREFORE BEEN CONVERTED TO A
WARNING WHICH WILL START AT 12AM LOCAL THIS MORNING AND LAST THRU 12
NOON. ADDITIONALLY...WINDS ACROSS THE USUAL SRN/SERN WIND
CORRIDOR...FROM AROUND SOUTH PASS...E/NE THRU SERN FREMONT...ALL OF
NATRONA...AND INTO SRN JOHNSON COUNTIES...WILL ALSO SEE A GOOD
INCREASE IN WINDS THIS MORNING...LASTING THRU MOST OF THE DAY ON
SUNDAY. THIS IS DUE TO THE INCREASING UNI-DIRECTIONAL WIND PROFILE
TOGETHER WITH DECENT LOW TO MID LVL INSTABILITY AND...MOST
IMPORTANTLY HERE...AN EVER TIGHTEN P GRAD AS LOWER PRESSURE FROM THE
NORTH/FRONT IMPINGES ON HIGHER PRESSURE TO THE SOUTH. STRONG WIND
GUSTS UP TO 55 MPH MAY BE POSSIBLE THIS MORNING ACROSS THE HILLS OF
THE AREA. WINDS WILL BE STRONGEST OVER SOUTH PASS...EAST TO BEAVER
RIM AND ALONG OUTER DRIVE AND ON TO THE SOUTH SIDE OF CASPER. WINDS
OF 20 TO 35 MPH WITH GUSTS 40 TO 50 MPH WILL AFFECT THE BROADEST
REGION IN THIS AREA BY NOON...LASTING UNTIL AROUND SUNSET.

OTHERWISE...AS THE UPR LVLS TRANSITION INTO A MORE SOUTHWEST UPR
FLOW PATTERN TODAY WITH THE EXPANSION OF THE TROF...A MODEST
INCREASE IN MOISTURE IS EXPECTED ACROSS THE WRN AND NRN FA ALONG
WITH INCREASING INSTABILITY...VORTICITY AND LIFT. STRONG DOWNSLOPING
ON THE ONE HAND WILL BATTLE THE COLD FRONT TRYING TO PUSH INTO THE
AREA ON THE OTHER THROUGH THE DAY...ALLOWING -SHRA/-SHSN AND ONE OR
TWO -TSRA TO DEVELOP AND SPREAD ACROSS MAINLY PORTIONS OF THE WRN FA
THRU THE DAY....THEN INTO THE NORTHERN ZONES BEHIND THE FRONT LATE
AFTERNOON AND OVERNIGHT THEN THRU THE DAY MONDAY. CAPE VALUES ACROSS
THE WEST...NORTHWEST AND NORTH WILL RANGE FROM 50 TO 100 J/KG AT
TIMES...ENOUGH TO POSSIBLY GET A FEW STRIKES OF LIGHTNING FROM.
ATTM...LIMITED MOISTURE WILL KEEP THE SNOW ON THE LOWER END OF THE
ACCUMULATION SCALE...MAXING OUT AT LESS THAN 6 INCHES OVER THE
HIGHEST PEAKS FOR THE MOST PART OVR A 30 HR PERIOD THRU MON MORNING.
AGAIN...DOWNSLOPING FLOW ACROSS MOST OF THE LOWER ELEVATIONS SOUTH
OF THE FRONT WILL KEEP PRECIP AWAY DURING THE SAME PERIOD OF
TIME...WITH ONLY VERY LIGHT PRECIP FOUND NORTH OF THE FRONT IN THE
BIGHORN BASIN AND PERHAPS JOHNSON COUNTY. MOSTLY COOL BREEZY AND DRY
ACROSS THE SRN HALF OF THE CWA MONDAY...WITH SOME DECREASING
MOUNTAIN AND FRONTAL SNOW/RAIN NORTH. TUESDAY WILL SEE IMPROVING AND
WARMING CONDITIONS FOR MOST LOCATIONS WITH LESS WIND...MORE SUN AND
NO PRECIP EXPECTED THRU THE DAY...WITH PERHAPS A SLIGHT CHANCE FOR
FLURRIES IN THE NORTHWEST LATER TUE NIGHT AS NW FLOW BRINGS A SLIGHT
INCREASE IN MOISTURE TO THE NRN MOUNTAINS...ALONG WITH AN INCREASE
IN OVERNIGHT WINDS IN THE SAME AREA.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

THE WEDNESDAY WEATHER SYSTEM IS TRENDING WEAKER AND FARTHER NORTH
WITH THE GFS/ECMWF 00Z RUNS. THIS WOULD TRANSLATE INTO LESS PRECIP
ACROSS THE SOUTH AND CENTRAL WITH SCATTERED SHOWERS OVER THE NORTH.
THE MOUNTAINS OF THE NORTH WOULD ALSO SEE BETTER SHOWER COVERAGE
THAN THE CENTRAL MOUNTAINS. THE SHOWERS WILL END LATE EVENING
WEDNESDAY. DRY WEATHER FOR THURSDAY AND FRIDAY WITH UPPER RIDGE NEAR
AND THEN OVER THE AREA. THE FLOW ALOFT BECOMES SOUTHWEST FRIDAY
NIGHT AS THE NEXT STORM SYSTEM MOVES INTO THE WESTERN U.S. AND
ELONGATES. HALLOWEEN NIGHT WEATHER DOES NOT LOOK SPOOKY AT THIS
POINT WITH MILD TEMPS. SATURDAY LOOKS DRY WITH BREEZY AREAS AS THE
WEATHER SYSTEM MOVES INTO THE GREAT BASIN BY 00Z SUNDAY. WILL KEEP
IT DRY EAST OF THE DIVIDE SATURDAY. WEST OF THE DIVIDE...THE GFS
BRINGS IN A FEW SHOWERS BY 18Z AND THEN BETTER COVERAGE BY 00Z SUN.
THE ECMWF IS SLOWER WITH ONLY ISOLATED AFTERNOON SHOWERS. FOR NOW
WILL SPLIT THE DIFFERENCE KEEPING IT MAINLY DRY SAT MORNING. THEN
ISOLATED SHOWERS IN THE AFTERNOON. THE WEATHER SYSTEM IS FORECAST TO
MOVE INTO WESTERN WY SAT NIGHT AND THEN THROUGH THE AREA NEXT
SUNDAY. GFS A LITTLE FASTER THAN THE ECMWF MODEL. THUS A CHANCE OF
RAIN SHOWERS AND ISOLATED STORMS IN THE WEST SATURDAY NIGHT AND
MAINLY SNOW SHOWERS NEXT SUNDAY. IN THE EAST...A CHANCE OF SHOWERS
AND ISOLD STORMS SUNDAY. AS FOR HIGH TEMPS...COOL ON WED...THEN
GRADUAL WARMING THURS AND FRI. SATURDAY STILL LOOKS MILD EAST OF THE
DIVIDE WITH SLIGHTLY COOLER HIGHS WEST OF THE DIVIDE DUE TO MORE
CLOUDS AND ISOLATED SHOWER ACTIVITY. NEXT SUNDAY WILL BE MUCH COOLER
IF THE 700MB TEMP FORECAST VERIFIES A WEEK OUT. GUIDANCE SEEMS TOO
WARM BASED ON THE THAT 700MB TEMP FORECAST...SO I ONLY COOLED HIGHS
DOWN A LITTLE SINCE IT IS A WEEK AWAY. STAY TUNED FOR UPDATES.

&&

.AVIATION.../18Z ISSUANCE/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

CONTINUED SHOWERS WILL LEAVE SOME MOUNTAIN OBSCURATION ACROSS THE
AREA TODAY...WITH GUSTY WIND CONTINUING. VCSH INCLUDED AT MANY
TERMINALS LEAVING A POTENTIAL FOR PERIODS OF MVFR CONDITIONS WITH
VFR CONDITIONS ANTICIPATED OTHERWISE. MOUNTAIN PASSES ARE
ANTICIPATED TO HAVE AREAS OF MODERATE TURBULENCE TODAY DUE TO
INCREASED HIGH LEVEL WIND. SHOWER ACTIVITY WILL INCREASE ACROSS
THE AREA AS WELL... PROVIDING A DECENT ENVIRONMENT FOR INCREASED
ICING...ESPECIALLY ACROSS THE NORTHWEST.

EAST OF THE DIVIDE...KCPR/KCOD/KLND/KRIW/KWRL ROUTES

GUSTY WIND WILL CONTINUE TODAY AT THE MAJORITY OF TERMINALS...WITH
SOME AIRPORTS NOT SEEING THE ONSET OF STRONGER WIND UNTIL AROUND
20Z. PERIODS OF SHOWER ACTIVITY WILL BEGIN THIS EVENING. THE MOIST
AND SHOWERY ENVIRONMENT MAY RESULT IN SOME INCREASED ICING
POTENTIAL... MAINLY ACROSS THE NORTHERN HALF OF THE AREA. BRIEF
PERIODS OF MVFR CONDITIONS WILL REMAIN POSSIBLE SHOULD SHOWERS
IMPACT AREA TERMINALS. ADDITIONALLY...CONTINUED GUSTY WIND WILL
BRING AREAS OF LIGHT TO MODERATE TURBULENCE THROUGH THE FORECAST
PERIOD.

&&

.FIRE WEATHER...

FIRE DANGER WILL TEND ON THE LOWER SIDE TODAY AS LOWER TEMPERATURES
IN ADDITION TO SOME MOISTURE AND CLOUDINESS INVADE THE FORECAST AREA
AND MINIMUM RH VALUES RISE...RANGING ABOVE 20 PERCENT FOR MOST
LOCATIONS. PRECIPITATION WILL ALSO BE POSSIBLE ACROSS THE WESTERN
AND NORTHERN DISPATCH ZONES THROUGH MONDAY MORNING. HOWEVER...WINDS
WILL INCREASE OUT OF THE SOUTHWEST AT 20 TO 30 MPH WITH GUSTS OF 35
TO TO 50 MPH AT TIMES ACROSS THE LOWER ELEVATIONS OF THE SOUTHERN
AND EASTERN ZONES. THE MOUNTAINS WILL SEE EVEN STRONGER
WINDS...PARTICULARLY NEAR RIDGE TOP LEVEL...BLOWING 30 TO 40 MPH
WITH GUSTS 50 TO 65 MPH AT TIMES. STRONGEST WINDS THROUGH THE
MORNING HOURS WILL BE HAD OVER THE ABSAROKA MOUNTAINS AND THE
ADJACENT CODY FOOTHILLS. MONDAY...RH VALUES WILL RISE EVEN
MORE...FURTHER DECREASING FIRE DANGER AS WINDS ALSO DECREASE IN
STRENGTH.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...AR
AVIATION...BRANHAM
FIRE WEATHER...BRAUN





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