Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 241716
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1116 AM MDT THU JUL 24 2014

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

WV IMAGERY SHOWING ROBUST UPR RIDGE...STILL SANDWICHED BETWEEN TWO
UPR TROFS AND CENTERED OVER CO AND EXTENDING ACROSS THE CWA TONIGHT
WITH THE DIRTY PORTION OF THE RIDGE CUTTING THROUGH WY AND UP INTO
ERN MT AND THE DAKOTAS. MOISTURE FROM THE NA MONSOON (LIKE FLOW) IS
NOW SET AND BEGINNING TO EVENTUALLY SPIN MOISTURE INTO THE REGION
FROM THE S CNTRL CONUS...PERHAPS BY THE BEGINNING OF NEXT WEEK. IN
THE MEANTIME HOWEVER...DEEP DRY AIR WILL START TO FEED INTO THE FA
FROM THE SW CONUS TODAY AS THE AXIS PORTION OF THE RIDGE ROTATES EWD
AND THE FLOW ALOFT BECOMES STRONGLY UNIDIRECTIONAL AND SW
ORIENTED.

UPR HIGH OVR SWRN CONUS STILL REMAINS IN PLACE FOR THE MOST PART.
HOWEVER...THE N/S AMPLIFICATION OF THE HIGH OVR WY WILL START TO
FLATTEN TODAY AND BEGIN THE SLOW PROGRESSION TO ZONAL AND FINALLY NW
FLOW THRU THE WEEKEND. AS THE WRN COASTAL TROF PUSHES ACROSS THE NRN
CONUS BORDER REGION W/ CA...DECREASING HEIGHTS OVR WY ALONG WITH
TEMPERATURES...STARTING TODAY WITH HIGH TEMPS COMING IN A FEW DEG
BELOW THOSE ON WEDNESDAY...WITH THE W AND NWRN CWA SEEING DROPS OF 5
TO 10 DEG. OTHERWISE...WEAK DISTURBANCES  EMBEDDED IN THE PERIPHERY
OF UPR HIGH THIS MORNING CONTINUE TO ROTATE CLOCKWISE ACROSS OR NEAR
THE FA...CONTINUING ISOLATED  CONVECTIVE CHANCES OVERNIGHT TONIGHT
WITH SMALL RAIN CORES...BUT  DRY LIGHTNING AND GUSTY ERRATIC WINDS
UP TO 55 MPH...OVR MAINLY THE SRN AND SWRN PORTION OF THE FORECAST
AREA...WITH A FEW OTHERS IN FREMONT AND JOHNSON COUNTIES. ANOTHER
DISTURBANCE WILL SWING THRU THE WRN TO NWRN FA LATER THIS MORNING
FROM OUT OF NRN UTAH...OFFERING MORE SMALL CHCS FOR PESKY EARLY
MORNING CONVECTION TO CONTINUE. THIS AFTERNOON...ANOTHER STRONGER
DISTURBANCE ROTATING AROUND THE NW CONUS LOW WILL COMBINE WITH SOME
MONSOONAL-ISH MOISTURE ACROSS S AND ERN WY...BRINGING YET ANOTHER
CHANCE FOR CONVECTION...MAINLY ACROSS THE SRN AND ERN PORTIONS OF
THE CWA...WITH THE USUAL LIGHTNING AND GUSTY WIND POSSIBLE FOR
ANOTHER DAY IN THIS AREA. A DEVELOPING LEE SIDE SFC LOW AND FRONT
SWINGING OUT OF MT AND STRENGTHENING OVR ERN WY WILL ALSO HELP FOCUS
CONVECTION OVR THE SAME REGION. HOWEVER...DRY AIR WILL BE WORKING
ITS WAY INTO THE FA THRU THE DAY FROM THE WEST...AND THIS WILL BE
THE LAST CHC FOR ANY PRECIP OR THUNDER THRU THE REST OF THIS FCST
PERIOD. FRIDAY WILL BE COOLER...WITH A DEEPER DRIER ATMOSPHERE AND
MORE STABLE TOO...WITH VIRTUALLY NO CHANCE FOR ACTIVE CONVECTION
EXCEPT FOR POSSIBLY NEAR THE WY/CO BORDER. MORE SIGNIFICANTLY FOR
BOTH TODAY AND FRIDAY IS THE INCREASED FIRE DANGER THAT WILL
CONTINUE ACROSS THE SRN AND ERN ZONES...WITH THE ADDITION OF THE
CODY FOOTHILLS. TODAY...HOT DAYTIME TEMPS IN THE 90S TO NEAR 100
AGAIN WILL COMBINE WITH LOW RH VALUES RANGING FROM THE UPR SINGLE
DIGITS TO THE MID TEENS AND INCREASING SW WINDS (AS MENTIONED ABOVE)
ACROSS AREAS THAT HAVE WHERE THE DRY FUEL STATUS IS NOW CRITICAL.
BOTH THE SURFACE PRESSURE FIELDS ALONG WITH INCREASED UPR FLOW IN
RESPONSE TO THE PASSING OF THE UPR WAVE AND DEVELOPING LEE LOW WILL
INCREASE THE LOCAL P GRAD AND ALSO BRING STRONGER FLOW DOWN TO THE
SFC FROM ALOFT ADIABATICALLY...GIVING WINDY CONDITIONS OVR THE
CENTRAL...SOUTHERN AND EASTERN FA. THE ADDITION OF A FEW ISOLATED
THUNDERSTORMS AS PREVIOUSLY MENTIONED WILL ALSO HELP TO EXACERBATE
THE SITUATION EVEN FURTHER TODAY. SIMILAR CONDITIONS WILL BE PRESENT
FRIDAY EVEN WITH COOLER HIGH TEMPS AROUND...WITHOUT THE CONVECTIVE
POTENTIAL HOWEVER. RED FLAG WARNING THEREFORE CONTINUES THROUGH FRI
EVENING FOR SRN CNTRL AND SERN FIRE ZONES...WITH THE ADDITION OF THE
CODY FOOTHILLS (STARTING TODAY AT NOON) AND ALSO RUN THRU FRI
EVENING.

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 A 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
SOMEWHAT OVR THE PREVIOUS TWO DAYS AS THE LOW P SYSTEM MOVES
OFF...DECREASING W TO NW WINDS TO JUST BELOW WHAT WOULD BE NEEDED FOR
FURTHER RED FLAG WARNING CONDITIONS. HOWEVER...FIRE DANGER WILL
CERTAINLY BE ENHANCED...ESPECIALLY ACROSS THE SRN FCST ZONES. WILL
CONTINUE TO MONITOR FOR POSSIBLE CHANGES.

.LONG TERM...SUNDAY THROUGH THURSDAY

UPPER LOW MOVING ACROSS THE NORTHERN ROCKIES TODAY WILL CARVE OUT A
LONGWAVE TROUGH ACROSS THE EASTERN U.S. EARLY NEXT WEEK...FORMING A
BLOCK OVER NORTH AMERICA WITH UPPER RIDGE CENTERED JUST WEST OF THE
DIVIDE AND UPPER TROUGH OVER THE EASTERN PACIFIC.  THIS WILL PUT
WYOMING UNDER THE INFLUENCE OF NW FLOW ALOFT.  SUB-TROPICAL MOISTURE
THAT WAS SUPPRESSED BY ZONAL FLOW WILL BEGIN TO DRIFT NORTHWARD
ACROSS THE GREAT BASIN ON SUNDAY WITH BOTH GFS AND ECMWF SHOWING
THIS MOISTURE PLUME AND EMBEDDED SUB-TROPICAL DISTURBANCES ROUNDING
THE TOP OF THE RIDGE AND PUSHING E-SE ACROSS WYOMING ON MONDAY.
THIS "RING OF FIRE" PATTERN WILL REMAIN OVER THE AREA THROUGH MUCH
OF NEXT WEEK.  THE LAST WEEK OF JULY IS TYPICALLY WHEN WYOMING SEES
A BRIEF SURGE NWD OF THE SW MONSOON OR THE VERY HIGH 55+ DEWPOINTS
PUSHING UP FROM THE GREAT BASIN.  HOWEVER...NW FLOW ALOFT WILL KEEP
THIS DEEPER LOW MOISTURE SUPPRESSED WELL TO OUR SOUTH.  HOWEVER...NW
FLOW WILL KEEP SFC HIGH PRESSURE OVER THE HIGH PLAINS AND AN
EASTERLY UPSLOPE FLOW EAST OF THE DIVIDE THROUGH THIS PERIOD ALONG
WITH AT LEAST SLIGHT INSTABILITY FOR CHANCES OF THUNDERSTORMS EACH
DAY...AND MORE THE WET THAN DRY VARIETY WITH EVEN A FEW STRONG TO
SEVERE STORMS POSSIBLE TUESDAY AND WEDNESDAY ACROSS CENTRAL WY.   NW
FLOW AND AFTERNOON CONVECTION WILL ALSO KEEP TEMPERATURES NEAR OR
SLIGHTLY BELOW NORMAL EAST OF THE DIVIDE THROUGH THE PERIOD WITH
HIGHS MOSTLY IN THE 80S WITH SOME LOWER 90S IN THE BIG HORN
BASIN...WHILE TEMPERATURES WEST OF THE DIVIDE WILL BE NEAR OR
SLIGHTLY ABOVE NORMAL WHERE HIGHS WILL BE MOSTLY FROM 75F TO 85F IN
THE WESTERN VALLEYS.

&&

.AVIATION.../18Z ISSUANCE/

ISOLATED HIGH BASED SHOWERS AND THUNDERSTORMS WITH OUTFLOW WINDS OF
40 TO 50 MPH WILL BE POSSIBLE THROUGH THE EVENING HOURS IN THE
SOUTHEAST PARTS OF THE AREA INCLUDING KRKS AND KCPR. ISOLATED
STRONGER STORMS ARE POSSIBLE IN JOHNSON COUNTY UNTIL 03Z. A COLD
FRONT WILL PUSH SOUTH INTO NORTHERN WYOMING AROUND 01Z FRIDAY AND
THEN MOVE SOUTH INTO CENTRAL WYOMING BETWEEN 06Z AND 08Z FRIDAY.
THE COLD FRONT WILL BE PUSHED EAST ON FRIDAY BY A DRY...HOT...
WESTERLY FLOW WITH DRY CONDITIONS FOR ALL BUT THE SOUTHEASTERN
CORNER OF SWEETWATER COUNTY WHERE ISOLATED THUNDERSTORMS ARE
POSSIBLE.

&&

.FIRE WEATHER...

A RED FLAG WARNING CONTINUES FOR PORTIONS OF NORTHERN...CENTRAL AND
SOUTHERN WYOMING THROUGH FRIDAY EVENING...MAINLY FOR THE AFTERNOON
AND EVENING PERIODS. CRITICAL FIRE WEATHER CONDITIONS HAVE DEVELOPED
ACROSS THESE AREAS WHERE CRITICALLY DRY FUELS ALSO EXIST. ANOTHER
DAY OF HOT DAYTIME TEMPERATURES IN THE 90S WILL COMBINE WITH A
DRYING ATMOSPHERE AND VERY LOW RH VALUES RANGING FROM THE UPR SINGLE
DIGITS TO THE MID TEENS AND INCREASING SOUTHWEST TO WEST WINDS.
ADDITIONALLY...THERE WILL BE A CONTINUED POSSIBILITY OF ISOLATED
THUNDER TODAY...FURTHER  REINFORCING HEIGHTEN FIRE
DANGER....ESPECIALLY ACROSS FIRE WEATHER ZONES 279...280 AND 300.
MUCH OF THE EXTREME FIRE WEATHER BEHAVIOR CONDITIONS WILL WILL BE
TIED TO A STRONGLY INCREASED SURFACE PRESSURE GRADIENT THAT WILL ALSO
COMBINE WITH STRONGER UPPER LEVEL FLOW TO GIVE WESTERLY WIND GUST
BETWEEN 25 AND 35 MPH IN THE AFTERNOON AND EARLY EVENING. SIMILAR
CONDITIONS WILL BE PRESENT FRIDAY...ALTHOUGH HIGH TEMPERATURES WILL
BE SOMEWHAT COOLER OVER THE WARNED AREAS. SATURDAY WILL COOL OFF
FURTHER BEHIND A DRY COOL FRONT...BUT WILL STILL REMAIN WARM AND
DRY. HOWEVER...AS THE LOW PRESSURE SYSTEM AND ITS FRONT MOVE OFF TO
THE EAST...THE SURFACE PRESSURE GRADIENT SHOULD RELAX JUST ENOUGH TO
KEEP WINDS FROM REACHING RED FLAG CONDITIONS...ALTHOUGH FIRE DANGER
WILL STILL BE ENHANCED...ESPECIALLY ACROSS ZONE 279.

&&

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

RED FLAG WARNING FROM NOON TODAY TO 9 PM MDT FRIDAY WYZ276.

&&

$$

UPDATE...SKRBAC
SHORT TERM...BRAUN
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...BRAUN








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