Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 222058
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
258 PM MDT WED OCT 22 2014

.SHORT TERM...TONIGHT THROUGH THURSDAY

A DRY STABLE CONFLUENT FLOW HAS ENSUED OVER THE AREA AS TUESDAYS
TROUGH EXITS THE AREA AND A FLATTENING RIDGE MOVES IN FROM THE
WEST. THE TREND THROUGH THU WILL BE FOR INCREASING WESTERLY FLOW
AS THE GRADIENT TIGHTENS WITH THE FLATTENING RIDGE AND THE CLOSED
LOW OVER THE GULF OF ALASKA CHURNS OUT ANOTHER CLOSED LOW EAST
ACROSS CANADA AND SLINGS A VIGOROUS SHORTWAVE TOWARD THE NORTHERN
ROCKIES...AND AT THE SAME TIME A RIDGE BUILDS INTO THE SOUTHERN
ROCKIES FROM THE SOUTHWEST. INCREASING WEST WINDS WILL RESPOND TO
THIS SET UP... ESPECIALLY ALONG THE EAST SLOPE OF THE CONTINENTAL
DIVIDE AND ALONG THE SOUTHERN WIND CORRIDOR. IN ADDITION...WEST
WINDS WILL LIKELY INCREASE SIGNIFICANTLY IN THE AREA NORTH OF CODY
BY LATE THU AFTERNOON...PRIMARILY AROUND CLARK AS A POTENTIAL MTN
WAVE...ALBEIT RELATIVELY WEAK...DEVELOPS. A FROUDE NUMBER OF 1 BY
00Z FRI IN THAT AREA AS WELL AS A PROGGED CRITICAL LAYER ABOVE THE
ABSAROKA MTNS REFLECTS THIS NOTION. IN ADDITION...THE WEST
SOUTHWEST DIFLUENT FLOW WILL RESULT IN ISOLD RAIN/SNOW SHOWERS IN
THE FAR NW MTNS LATE THU. SOUTHWEST WEST WINDS HAVE ALREADY KICKED
IN ALONG THE SOUTHERN WIND CORRIDOR FROM THE GREEN MTNS TO KCPR.
OTHERWISE...EXPECT DRY WEATHER THROUGH THU. TEMPERATURES WILL BE
AROUND 10 DEGREES WARMER EVERYWHERE THU AS THE COOL AIR BEHIND
WEDNESDAYS TROUGH EXITS TO THE EAST.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

POTENTIAL MOUNTAIN WAVE EVENT TO START THIS PERIOD IN THE CODY
FOOTHILLS AS POTENTIALLY FAVORABLE MOUNTAIN TOP CONDITIONS COMBINE
WITH APPROACHING RIGHT FRONT QUAD OF 150KT+ UPPER JET AND MODERATE
GAP FLOW SIGNATURE. NAM12 IS PICKING UP A PERIOD OF UPSTREAM
MOUNTAIN TOP INVERSION AFTER MIDNIGHT THURSDAY NIGHT WHILE THE WRF
CROSS SECTION IS SHOWING A PERIOD IN THE EVENING THURSDAY OF
POTENTIAL FLOW REVERSAL OR AT LEAST POTENTIAL FOR WAVE INDUCED
CRITICAL LAYER. FROUDE CALCULATIONS FOR THURSDAY NIGHT ARE PRETTY
CONSISTENT IN THE 1 RANGE. WRF BOUNDARY LEVEL WINDS ARE NOT OVERLY
IMPRESSIVE ON THE FLATS BUT GET OVER 50KTS NEAR THE STEEP TERRAIN.
POTENTIAL IS GREAT ENOUGH TO AT LEAST GET THE WATCH OUT AS THERE ARE
ENOUGH FEATURES THAT COULD CAUSE THIS TO BE A DECENT EVENT. THE LOW
END WOULD PROBABLY PRODUCE NEAR OR AT HIGH WINDS FOR THE GAPS AND
WEST SIDE OF CLARK WHILE THE HIGH END WOULD RESULT IN A WAVE
BREAKING MOUNTAIN WAVE EVENT WITH WINDS WELL OVER 60 MPH WITH
POTENTIAL FOR 80 MPH PLUS. MOIST PLUME APPROACHES ABOUT THE SAME
TIME WITH OUR APPROACHING FRONTAL BOUNDARY WHICH WILL PROBABLY CLIP
THE NWRN CORNER WITH A LITTLE LIGHT PCPN THURSDAY NIGHT INTO FRIDAY
MORNING BEFORE RIDGING PUSHES IT NORTH INTO MT. SHALLOW FRONTAL
BOUNDARY STILL EXPECTED TO SIT ACROSS THE NORTH FRIDAY FOR A SLIGHT
TEMPERING OF TEMPERATURES COMPARED TO AREAS JUST TO THE SOUTH.
SATURDAY LOOKS WARM AND DRY WITH INCREASING SW WIND.

ERN PACIFIC TROUGH THEN OPENS UP AND MOVES INLAND ACROSS US SUNDAY
INTO MONDAY WITH MODELS VARYING ON TIMING AND STRENGTH OF SECONDARY
BACK SIDE SYSTEM SUNDAY NIGHT/MON MRNG. AIRMASS STILL LOOKS COLD
ENOUGH FOR POTENTIAL LIGHT SNOW IN CENTRAL WYO LATER SUNDAY NIGHT
INTO MONDAY MORNING WHERE PCPN FALLS. DECENT SHOT OF RAIN CHANGING
TO SNOW IN THE MOUNTAINS WITH THIS SYSTEM WITH A COUPLE TO SEVERAL
INCHES QUITE POSSIBLE IN THE MOUNTAINS. BRIEF RIDGING WITH
TEMPERATURES RECOVERING SOME TUESDAY BEFORE POTENTIAL SEWD MOVING
SHORTWAVE MOVES ACROSS LATER TUESDAY NIGHT INTO WEDNESDAY. MODELS
STRUGGLING WITH THE PATTERN CHANGE AND MOVEMENT OF SEVERAL KEY UPPER
LOWS OVER ASIA BUT IT DOES APPEAR THAT SIGNIFICANT CHANGES COULD BE
IN THE OFFING JUST BEYOND THE MEDIUM RANGE PERIOD. HOW IT ALL
EVOLVES AND THE EXACT TIMING IS STILL UNCERTAIN...MOST LIKELY
BETWEEN HALLOWEEN AND THE FIRST COUPLE DAYS OF NOVEMBER. NOTHING
CERTAIN YET.

&&

.AVIATION.../00Z ISSUANCE/
VFR CONDITIONS WILL OCCUR TONIGHT WITH MAINLY SKC SKIES. EXPECT
INCREASING MID/HIGH LEVEL CLOUDINESS AND STRENGTHENING MOUNTAIN
TOP WINDS WITH POSSIBLY SOME LLWS ON THE LEE SIDE OF MOUNTAIN
RANGES ALONG THE CONTINENTAL DIVIDE DEVELOPING AFTER 06Z TONIGHT. HOWEVER
NOT ENOUGH CONFIDENCE OR MAGNITUDE TO INCLUDE AT KCOD OR KLND AT
THIS TIME. WEST SOUTHWEST WINDS WILL INCREASE FROM KRKS TO KCPR BY
18Z THURSDAY. WEST WINDS WILL INCREASE FROM KCOD NORTH TO CLARK BY
00Z FRIDAY.

&&

.FIRE WEATHER...
TEMPERATURES REBOUND A BIT ON THURSDAY AS HIGH PRESSURE BUILDS IN FROM
THE SOUTH BUT IT WILL BE ANOTHER BREEZY DAY IN SPOTS WITH
SOUTHWEST WINDS OF 15 TO 25 MPH COMMON BETWEEN ROCK SPRINGS AND
CASPER AND OVER THE HIGHER ELEVATIONS. ON THURSDAY NIGHT WEST
WINDS WILL INCREASE SIGNIFICANTLY IN THE AREA AROUND CLARK NORTH
OF CODY.SOUTHWEST FLOW RETURNS ON FRIDAY WITH DRIER AND WARMER
CONDITIONS REMAINING. THERE COULD BE A FEW GUSTS OVER 25 MPH IN
THE AFTERNOON BETWEEN RAWLINS AND SOUTHERN CASPER DISPATCH BUT
MOST AREAS WILL HAVE RELATIVELY LIGHT WINDS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM THURSDAY EVENING THROUGH FRIDAY MORNING
WYZ003.

&&

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...LIPSON
FIRE WEATHER...LIPSON







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