Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 251756
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1156 AM MDT FRI JUL 25 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

WV IMAGERY SHOWING FLAT UPR RIDGE W/ HIGH CENTERED OVR ERN NM. TROF
THAT HAS FLATTENED THE RIDGE IS RUNNING EWD ALONG THE MT/CA BORDER.
THE DIRTY PORTION OF THE RIDGE HAS NOW BEEN MAINLY PUSHED SWD INTO
NRN CO. AT THE SFC...LOW PRESS TO THE E IN WRN SD...HIGH PRESS W AND
OVR THE PAC NW. WEAK DRY SFC FRONT CUTTING RIGHT THRU WY FROM NE TO
SW. DEEP DRY AIR HAS MOVED INTO THE FA FROM THE SW/W TODAY. UPR HIGH
OVR SWRN CONUS REMAINS IN PLACE FOR THE MOST PART FOR THE NEXT FEW
DAYS...JUST SLOWLY TRENDING WWD THRU THE FCST PERIOD.

TODAY WILL BE COOLER...WITH A DEEP DRY ATMOSPHERE IN PLACE...WITH
VIRTUALLY NO CHANCE FOR ACTIVE CONVECTION EXCEPT FOR POSSIBLY NEAR
THE WY/CO BORDER REGION. MORE SIGNIFICANTLY...INCREASED FIRE DANGER
...INCLUDING RED FLAG WARNINGS...WILL CONTINUE ACROSS THE SRN AND
ERN ZONES THRU 9 PM TONIGHT. HOWEVER...WILL REMOVE THE CODY
FOOTHILLS (ZONE 276) FROM THE RED FLAG WARNINGS TODAY AS THIS AREA
BEHIND THE FRONT DOES NOT LOOK TO PRODUCE BOTH THE WINDS AND LOW RH
VALUES NEEDED. OTHERWISE...DAYTIME TEMPS WILL COOL INTO THE UPR 80S
AND LOWER 90S FOR MOST LOW ELEVATIONS SITES...60S AND 70 IN THE
MOUNTAINS. MIN RH VALUES WILL RANGE FROM THE SINGLE DIGITS TO THE
MID TEENS FOR MOST BASINS AND VALLEYS...20S IN THE MOUNTAINS. WINDS
BY MID TO LATE AFTERNOON WILL BLOW OUT OF THE WEST 15 TO 25 MPH FROM
CENTRAL TO SOUTHERN WYOMING...INCLUDING THE MOUNTAINS. THE STRONGEST
WINDS IN THE RED FLAG AREAS LOOK TO REMAIN UNDER AND SOUTH OF THE
DEVELOPING LOW IN SRN WY...MAINLY TARGETING THE SOUTH CENTRAL AND
SOUTHERN ZONES. MUCH OF FREMONT AND NATRONA COUNTIES WILL PROBABLY
NOT QUITE REACH THE WIND CRITERIA NEEDED FOR THE RFW...BECAUSE OF
POSITION RELATIVE TO THE DEVELOPING SFC LOW...BUT IT IS TOO CLOSE TO
NOT TO KEEP THE WARNING GOING AND THERE WILL CERTAINLY BE AT LEAST
ISOLATED AREAS THAT DO REACH THE MIN CRITERIA. STILL...ALL OTHER
LOCATIONS ACROSS THE FA WILL BE UNDER ENHANCED FIRE DANGER FOR ONE
REASON OR ANOTHER.

SAT AND SAT NIGHT...FLAT DRY ZONAL FLOW BEGINS THE TRANSITION TO DRY
NW FLOW. LEE SIDE LOW PRESSURE MOVES OFF INTO THE CNTRL
PLAINS...WITH ADDITIONAL COOLING FOLLOWING THE PASSAGE OF ANOTHER
COOL FRONT E OF THE DIVIDE...BUT SLIGHT WARMING W OF THE DIVIDE
WHERE THE FRONT WILL NOT BE A PRESENCE. THE SFC P GRAD SHOULD ALSO
RELAX FOR MOST LOCATIONS...WITH STRONGEST WINDS OF THE DAY ACROSS
MAINLY SWEETWATER COUNTY (FIRE ZONE 279) NEAREST LOW PRESSURE TO THE
S IN COLORADO. NOT GOING THE EXTEND THE RFW FOR ANY ZONES
ATTM...INCLUDING ZONE 279 AS IT LOOKS LIKE WINDS MAY REMAIN JUST
BELOW RFW CRITERIA...ALTHOUGH MIN RH VALUES WILL CERTAINLY BE LOW
AGAIN. THE COMBINATION OF THE TWO WILL MAY NOT BE THERE. WILL
MONITOR FURTHER OVR THE NEXT 24 HRS FOR A DECISION BEFORE EXPIRATION
LATER TONIGHT.

SUNDAY...UPR RIDGE ROTATES AND AMPLIFIES ABOVE THE
FA...TRANSITIONING FROM ZONAL TO NORTHWEST FLOW...THEN TO WEAK ZONAL
AS AXIS ALIGNS N/S THRU THE REGION WITH HEIGHTS AND TEMPS RISING.
WARMER WITH HIGHS WELL BACK INTO THE MID 80S TO NEAR 90. WITH SFC
HIGH P NOW E OF THE CWA AND LOWER P TO THE SW...AND ONLY A MODEST AT
BEST P GRAD AND WEAKENING UPR LVL FLOW AS THE RIDGE EXPANDS
AMPLIFIES AND ORIENTS OVERHEAD...WINDS WILL NOT BE AN ISSUE THIS
DAY. MAY BE A VERY SMALL CHANCE FOR SHRA/TSRA WHERE LOW MOISTURE
WILL ROTATE UP FROM THE SW IN WEAK RING O FIRE...OVR THE SW
MOUNTAINS.

.LONG TERM...MONDAY THROUGH FRIDAY

BLOCKING PATTERN SETS UP ACROSS NORTH AMERICA DURING THIS PERIOD
WITH HIGH AMPLITUDE RIDGE OVER THE WESTERN ATLANTIC KEEPING LONGWAVE
TROUGH OVER THE EASTERN U.S. WITH UPPER RIDGE OVER THE INTERMOUNTAIN
WEST...UPPER TROUGH ACROSS THE EASTERN PACIFIC.  LIKE AN L.A.
FREEWAY AT RUSH HOUR...LITTLE MOVEMENT WILL OCCUR WITH THESE
SYNOPTIC FEATURES.

HOWEVER...MONSOONAL MOISTURE`S PATH WILL BE UNIMPEDED AROUND THE
PERIPHERY OF THE RIDGE...MAKING A NORTHWARD SURGE ACROSS THE GREAT
BASIN INTO SW WYOMING ON SUNDAY NIGHT/MONDAY WHILE RETURN FLOW
AROUND SURFACE HIGH PRESSURE OVER THE HIGH PLAINS BRINGS GULF
MOISTURE INTO WYOMING FROM THE EAST...WITH THIS MOISTURE CONVERGING
ACROSS THE SOUTHERN TWO-THIRDS OF WYOMING BY TUESDAY WITH PWAT
VALUES OF 1 INCH OR GREATER.  SO ON MONDAY...INITIAL PLUME OF MAINLY
MID AND HIGH LEVEL MOISTURE WILL BRING AN INITIAL ROUND OF ISOLATED
TO WIDELY SCATTERED THUNDERSTORMS INTO THE SW MONDAY MORNING/EARLY
MONDAY AFTERNOON WITH THIS ACTIVITY EXPECTED TO SPREAD NORTH AND
EAST DURING THE LATE AFTERNOON AND EVENING.  AS LOWER LEVELS MOISTEN
UP ON TUESDAY EXPECT SCATTERED THUNDERSTORMS...SOME HEAVY RAIN
PRODUCERS...ACROSS THE SOUTH AND CENTRAL WITH LESS ACTIVITY ACROSS
THE NORTH WHERE THERE WILL BE LESS MOISTURE AND INSTABILITY TO WORK
WITH.  FORECAST TRENDS HIGH TEMPERATURES ON TUESDAY ACROSS THE SOUTH
SEVERAL DEGREES COOLER WITH EXPECTED CLOUD COVER AND CONVECTION
THROUGH THE DAY.

ON WEDNESDAY AND THURSDAY...BOTH GFS AND ECMWF SHOW SOME SUPPRESSION
OF THE GULF MOISTURE FEED FROM CENTRAL HIGH PLAINS WITH PLUME OF
MOISTURE SANDWICHED ALONG THE DIVIDE ALONG AND WEST OF THE DIVIDE
WITH LOW LEVEL UPSLOPE FLOW...NW FLOW ALOFT.  STORM MOTION WILL BE
SE...SO MOST ACTIVITY IS EXPECTED TO DEVELOP AND TRACK NEARLY
PARALLEL TO THE SOUTHERN ABSAROKA AND WIND RIVER RANGES.

MEDIUM-RANGE MODELS SHOW SOME DE-AMPLIFICATION...BROADENING OF FLOW
ACROSS THE CONUS FRIDAY.  THIS WILL BE A SLOW PROCESS THAT WILL
RESULT IN LITTLE OR NO CHANGE TO PATTERN OVER THE ROCKIES WITH PLUME
OF MOISTURE...THE "RING OF FIRE" OF CONVECTION LIKELY TO REMAIN OVER
THE GREAT BASIN AND ALONG THE WYOMING DIVIDE FRIDAY AND INTO THE
WEEKEND.

&&

.AVIATION.../18Z ISSUANCE/

GENERALLY VFR CONDITIONS WILL BE FOUND ACROSS THE FORECAST AREA
THROUGH THE FORECAST PERIOD. A FEW ISOLATED SHOWERS WILL BE
POSSIBLE SOUTHEAST OF A LINE FROM KRKS TO KCPR...MAINLY AFTER 19Z
TODAY. GUSTY WINDS WILL ALSO BE FOUND THROUGH THE DAY...ESPECIALLY
INCREASING AFTER 18Z THIS AFTERNOON. WIND SHOULD WEAKEN AFTER 03Z
THIS EVENING. VFR CONDITIONS WILL BE FOUND ACROSS THE AREA ON
SATURDAY UNDER THE PRESENCE OF HIGH PRESSURE. ANOTHER ROUND OF
GUSTY WIND WILL RETURN TO KRKS AFTER 18Z SATURDAY.

&&

.FIRE WEATHER...

A RED FLAG WARNING CONTINUES FOR PORTIONS OF CENTRAL AND SOUTHERN
WYOMING THROUGH TONIGHT...MAINLY FOR THE AFTERNOON AND EVENING
PERIODS. CRITICAL FIRE WEATHER CONDITIONS HAVE DEVELOPED ACROSS
THESE AREAS WHERE CRITICALLY DRY FUELS ALSO EXIST. ALTHOUGH HIGH
TEMPERATURES WILL DROP TODAY OVER THOSE THE PAST FEW DAYS...VERY
WARM TO HOT DAYTIME TEMPERATURES IN THE UPPER 80S AND LOWER 90S WILL
COMBINE WITH A DRYING ATMOSPHERE AND VERY LOW RH VALUES RANGING FROM
THE SINGLE DIGITS TO THE MID TEENS AND INCREASING WEST WINDS. MOST
OF THE ENHANCED FIRE WEATHER CONDITIONS WILL BE TIED TO ANOTHER
RELATIVELY STRONG SURFACE PRESSURE GRADIENT ACROSS THE SOUTHERN
FORECAST AREA THAT WILL ALSO COMBINE WITH DECENT MID/UPPER LEVEL
FLOW TO GIVE WESTERLY WIND GUSTS BETWEEN 25 AND 35 MPH IN THE
AFTERNOON AND EARLY EVENING ACROSS MOST OF THE WARNED AREA. SIMILAR
BUT WEAKENING CONDITIONS WILL BE PRESENT SATURDAY...ALTHOUGH HIGH
TEMPERATURES WILL BE SOMEWHAT COOLER AGAIN OVER THE WARNED AREAS
BEHIND ANOTHER DRY COOL FRONT...BUT WILL STILL REMAIN WARM AND DRY.
HOWEVER...BOTH THE SURFACE PRESSURE GRADIENT AND UPPER LEVEL FLOW
SHOULD WEAKEN JUST ENOUGH TO KEEP WINDS FROM REACHING RED FLAG
CONDITIONS...WHILE HAINES INDEX WILL GENERALLY FALL BETWEEN 4 AND 5.
FIRE DANGER WILL STILL BE ENHANCED...ESPECIALLY ACROSS ZONE
279.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING
WYZ279-280-283-285-287-300.

&&

$$

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




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