Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 240936
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
336 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.../12Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH 12Z FRIDAY. BREEZY TO WINDY AT
MOST TERMINAL SITES TODAY INTO EARLY EVENING. ISOLATED SHOWERS AND
STORMS WILL OCCUR MAINLY IN THE SOUTH AND EAST PORTION OF THE
REGION. THIS INCLUDES KRKS AND KCPR TERMINAL SITES. A COLD FRONT
PUSHES INTO NORTHERN WY AROUND 01Z FRIDAY AND MOVES SOUTH TO
CENTRAL WY BETWEEN 06Z AND 08Z.

&&

.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.

&&

$$

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









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