Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 270520 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED FOR AVIATION
NATIONAL WEATHER SERVICE RIVERTON WY
1120 PM MDT SUN JUL 26 2015

.UPDATE...

FIRE ZONE 283...WHICH INCLUDES MOST OF THE LOWLANDS OF FREMONT
COUNTY HAS BEEN ADDED TO THE RED FLAG WARNING FOR MONDAY NOW THAT
THE VEGETATION HAS BEEN DECLARED CRITICALLY DRY AND READY TO
CARRY FIRE BY OUR LAND MANAGEMENT PARTNERS.

&&

.PREV DISCUSSION... /ISSUED 145 PM MDT SUN JUL 26 2015/

.SHORT TERM...TONIGHT THROUGH MONDAY

WV IMAGERY SHOWING CONTINUING LOW AMPLITUDE TROF RIDGE TROF PATTERN
ACROSS THE CONUS WITH CNTRL HIGH LOCATED OVR TX/NM. MINOR
DISTURBANCE CURRENTLY MAKING ITS WAY OUT OF NRN WY INTO SERN
MT...WHILE LARGE WCST UPR TROF IS STARTING TO KICK EWD. SFC HAS WEAK
MOSTLY DRY COLD FRONT ACROSS NWRN WY WITH OTHERWISE WEAK SFC P GRAD
ACROSS THE STATE.

RED FLAG CONDITIONS WILL EXIST ACROSS FIRE WX ZONES 280...281 AND
300...NATRONA COUNTY AND SRN JOHNSON COUNTY BOTH TODAY AND MONDAY AS
HAINES VALUES RANGE BETWEEN 5 AND 6 ALONG WITH LOW RH VALUES. MIN RH
VALUES WILL LIKELY DROP AND HOVER IN THE LOWER/MID TEENS...WITH
WINDS GUSTING FROM 15 TO NEAR 25 MPH AT TIMES....TO 40 MPH ON MONDAY
WHICH WILL BE THE MOST EXTREME FIRE WX DAY.

THIS AFTERNOON AND TONIGHT...RIDGING...DRYING AND GOOD CAPPING IN
CONTROL ACROSS MOST OF THE FA WITH ONLY ISOLATED SHOWERS OR THUNDER
POSSIBLE OVR THE HIGHER TERRAIN AND ADJACENT FOOTHILLS/BIGHORN BASIN
IN THE NW/N. SHOWERS AND STORMS SHOULD DIE OFF QUICKLY EARLY THIS
EVENING. NOT MUCH MOVEMENT FROM THE AFOREMENTIONED FRONT
TODAY/TONIGHT.

MONDAY...BUILDING LOW P AND STRENGTHENING OF FROM WILL TAKE PLACE
ACROSS NCNTRL TO SWRN WY...EVENTUALLY BEING PUSHED ACROSS THE FA
WITH THE APPROACH OF THE LARGE UPR TROF HEADED EWD ACROSS THE NW/NRN
TIER OF STATES. AS CYCLOGENSIS TAKES PLACE FROM NCNTRL WY INTO SERN
MT AND THE WRN DAKOTAS DURING THE DAY...THE SFC P GRAD WILL INCREASE
RAPIDLY ALONG WITH A GREAT INCREASE IN WIND SPEED ALOFT. SFC WINDS
WILL ACCORDINGLY INCREASE QUICKLY BY LATE MORNING AS RELATIVELY
STRONG WINDS ARE BROUGHT TO THE SFC ADIABATICALLY FROM ALOFT AND
COMBINE WITH THE INCREASING P GRAD TO GIVE A BROAD AREA OF W TO SW
SFC WINDS INCREASING TO 20 TO 30 MPH WITH GUSTS AS HIGH AS 45 MPH AT
TIMES ACROSS THE SRN AND SERN ZONES. THIS WILL GREATLY AND QUICKLY
INCREASE THE FIRE DANGER INTO THE EXTREME CATEGORY OVER AREAS OF THE
SERN FA WHERE FUELS ARE CONSIDERED CRITICAL. OTHERWISE AND
ELSEWHERE...ANOTHER DRY DAY ACROSS MOST OF THE FA EXCEPT FOR THE
W/NW ZONES IN THE AFTERNOON AS SOME MODEST MOISTURE IS INJECTED INTO
THE REGION FROM AROUND THE BASE OF THE UPR TROF...THEN EVENTUALLY
OVR CODY FOOTHILLS AND BIGHORN BASIN BY LATE AFTERNOON. INCREASING
AND HIGH SHEAR TO AS MUCH AS 50 KTS THRU 6 KM...AND MODEST ML CAPE
RANGING FROM 250 TO 800 J/KG WILL YIELD A FEW STRONG/BORDERLINE
SEVERE STORMS ALONG AND NORTH OF A JACKSON TO CODY LINE WHERE BRIEF
HEAVY RAIN...SMALL/MARGINAL SEVERE HAIL...AND GUSTY WINDS TO 45 MPH
WILL BE POSSIBLE. LATER...AS ISOLATED THUNDERSTORMS MOVE EWD OVR THE
BIGHORN BASIN...STRONGER WINDS WILL BE THE MAIN THREAT.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

SOUTHWEST FLOW WILL DOMINATE THE WEATHER ACROSS WESTERN AND CENTRAL
WYOMING THROUGH TUESDAY AHEAD OF AN UNSEASONMABLY STRONG PACIFIC
LOW PRESSURE TROUGH THAT WILL BE MOVING INTO THE PACIFIC NORTHWEST.
MOISTURE WILL BE LIMITED TO THE NORTHWEST AND FAR NORTH WHERE
SCATTERED MOUNTAIN SHOWERS AND ISOLATED THUNDERSTORMS WILL BE A
THREAT TUESDAY AFTERNOON AND EVENING WITH A FEW SHOWERS LINGERING
OVER THE HIGHER MOUNTAINS THROUGH THE NIGHT AND INTO THE MORNING
HOURS. TEMPERATURES WILL COOL AS THE PACIFIC TROUGH MOVES ACROSS
SOUTHERN CANADA AND MONTANA CLIPPING NORTHERN WYOMING MONDAY NIGHT
DRIVING A COLD FRONT SOUTH MONDAY NIGHT AND TUESDAY.  THE COLD FRONT
WILL BRING COOLER TEMPERATURES AND HIGHER HUMIDITY WITH WINDS
SHIFTING TO THE NORTHEAST.  THE SOUTH WILL REMAIN WINDY ON TUESDAY
WITH LOW RELATIVE HUMIDITY BEFORE THE COLD FRONT PUSHES SOUTH
THROUGH THE AREA.  COOLER AND DRY WEATHER WILL THEN BE IN PLACE
WEDNESDAY...WITH A GRADUAL WARMING TREND THROUGH SATURDAY WITH DRY
CONDITIONS PREVAILING.  WINDS MAY PICK UP ON FRIDAY AND VERY LOW
RELATIVE HUMIDITY IN THE AFTERNOON.  FRIDAY NIGHT AND SATURDAY...
THE HIGH PRESSURE RIDGE WILL PICK UP SUBTROPICAL MOISTURE ADVECTING
IT NORTH AND THE EAST INTO WESTERN AND SOUTHERN WYOMING BRINGING AN
INCREASED CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS IN THE
WESTERN MOUNTAINS AND THE SOUTHWEST.

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH THE
FORECAST PERIOD. A FEW LIGHT SHOWERS MAY EFFECT AREAS BETWEEN KRKS
AND KCPR THROUGH 12Z. SOUTHWEST WINDS WILL PICK UP TO THE
BREEZY/WINDY CATEGORIES ACROSS THE SOUTHERN AND SOUTHEASTERN
FORECAST AREAS FROM MID TO LATE MORNING ON MONDAY...WITH INCREASING
CHANCES FOR ISOLATED TO WIDELY SCATTERED SHOWER AND THUNDERSTORMS
MAINLY NORTH OF A KAFO TO KWRL LINE AFTER 18Z.

.FIRE WEATHER...

...ZONE 283 HAS JOINED ZONES 280 281 285 AND 300 IN THE RED FLAG
WARNING FOR MONDAY...

HOT...DRY...BREEZY AND UNSTABLE ACROSS MUCH OF THE STATE
TODAY...WITH CONDITIONS EXPECTED TO BE MORE EXTREME ON MONDAY AHEAD
OF A DRY COLD FRONTAL PASSAGE. ALL ZONES WITH CRITICALLY DRY
FUELS...MAINLY NATRONA AND JOHNSON COUNTIES...HAVE A RED FLAG
WARNING IN EFFECT THE REST OF TODAY THROUGH MONDAY EVENING.
ADDITIONALLY...ENHANCED FIRE DANGER EXISTS ACROSS MUCH OF THE REST
OF THE STATE...EVEN IN AREAS THAT ARE NOT UNDER A RED FLAG WARNING.
IT IS NOT SAFE TO BURN OR DO ANYTHING THAT MAY EMIT SPARKS OUTDOORS
TODAY OR MONDAY. WINDS SHOULD QUICKLY DIE OFF MONDAY EVENING TO LESS
THAN CRITICAL AFTER THE PASSAGE OF THE COLD FRONT.

A SMALL POTENTIAL FOR FIRE STARTS WILL EXIST DUE TO LIGHTNING
STRIKES ACROSS THOSE AREAS WHERE THUNDERSTORMS EXIST...MAINLY ACROSS
THE NORTHWEST TODAY...NORTHWEST AND NORTH TOMORROW. SOME OF THESE
STORMS COULD ALSO PRODUCE STRONG DOWNBURST WINDS THAT TRAVEL FAR
FROM THE PARENT STORM...ESPECIALLY THROUGH FROM THE EASTERN EDGE OF
THE NORTHWESTERN MOUNTAINS AND INTO THE BIGHORN BASIN.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 10 PM MDT MONDAY FOR WYZ280-281-285-300.

RED FLAG WARNING FROM 10 AM TO 10 PM MDT MONDAY FOR WYZ283.

&&

$$

SHORT TERM...BRAUN
LONG TERM...C.BAKER
AVIATION...HATTINGS
FIRE WEATHER...BRAUN



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