Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 200550
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1149 PM MDT FRI SEP 19 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY

THE TROUGH/COLD FRONT IS EXITING THE AREA ATTM WITH LINGERING
SHOWERS MOVING OFF TO THE EAST OF NATRONA AND SWEETWATER COUNTIES.
THE VALLEY FOG IN FAR WESTERN WY THAT DEVELOPED AFTER THURSDAY
EVENINGS RAINFALL FINALLY DISSIPATED BY 12 NOON TODAY. HIGH PRESSURE
WILL BE BUILDING IN FROM THE WEST THROUGH SATURDAY. WE CAN LOOK
FORWARD TO COOLER WEATHER AND PRECIPITATION FREE WEATHER THROUGH
SATURDAY.  HIGH TEMPERATURES WILL BE ABOUT 15 DEGREES COOLER
SATURDAY OVER WHAT THEY WERE THURSDAY EAST OF THE DIVIDE BUT NOT
MUCH CHANGE IN TEMPERATURE IS EXPECTED WEST OF THE DIVIDE. WINDS
WILL BE RELATIVELY LIGHT THROUGH SATURDAY.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

WHILE THERE WAS REMARKABLE AGREEMENT AMONG THE LR MODELS
EARLIER...SINCE THE NEW EURO HAS COME IN...THAT IS NOT TRUE ANYMORE
IN/BY DAY 7...PRETTY GOOD OTHERWISE.

AT THE BEGINNING OF THE FCST PERIOD...CONUS UNDER A RIDGE/TROF
PATTERN FROM WEST OT EAST WITH A SIGNIFICANT COL JUST STARTING TO
GET KICKED INTO THE SW CONUS BY WAY OF SRN CALIFORNIA AS THE
APPROACH OF UPSTREAM SW ALLOWS UPR LVL WESTERLIES TO ONCE AGAIN FLOW
OVR AND AROUND THE COL. THIS ALSO SHOWS UP WELL IN THE PVA
FIELDS...GOING FROM A SPOKED PATTERN TO BIMODAL WITH PVA LEADING
NVA. AT THE SAME TIME...WRN RIDGE AXIS WILL BE ORIENTED ACROSS THE
WRN FA AND OFF TO THE CONUS NW...WITH BROAD AREA OF HIGH PRESSURE AT
THE SFC...DEEPENING TO THE E. DRY SAT AND HALF OF SUN BEFORE
MOISTURE RETURNS TO THE REGION FROM THE SW AS EX-COL CONTINUES
TOWARD WY AND WRN RIDGE EXPANDS EWD ALONG WITH THE SFC
HIGH...ALLOWING DESERT SOUTHWEST HEAT LOW TO SQUEEZE SOME TROPICAL
MOISTURE...AND PERHAPS EVEN INCLUDING SOME FROM TC POLO...UP FROM
MEXICO AND THRU THE SRN AND CNTRL ROCKIES. THE MAIN MOISTURE FEED
LOOKS TO INFILTRATE THE SWRN QUAD OF THE FA BY SUN
AFTERNOON...RESULTING IN SCATTERED SHOWERS AND STORMS. INSTABILITY
AND SHEAR LOOK REMAIN IN CHECK FOR MOST AREAS W OF THE DIVIDE.
HOWEVER...A COUPLE OF STRONGER STORMS SHOULD BE EXPECTED OVER THE
FAR SW PORTION OF THE FA WHERE BOTH SHEAR AND AVAILABLE
ENERGY...SUNLIGHT LIMITED...MAY PRODUCE SOME SMALL HAIL APPROACHING
AN INCH...WITH STRONG OUTFLOW A SECONDARY CONSIDERATION.
MONDAY...THE TROF UNDER RIDGE CONTINUES ACROSS THE REGION WITH SOME
MOISTURE ALSO CONTINUING ACROSS THE FA...BUT THE MAIN BLOB NOW
GETTING SHUNTED TO THE SOUTH AND/OR EAST AHEAD OF THE SYSTEM AND
INTO THE CNTRL PLAINS. TWO MOISTURE MAXIMUMS WILL BE AROUND THE CWA
AND THE UPR LOW...ONE RETURNING INTO THE NERN FA AND THE JOHNSON
COUNTY AREA...THE OTHER ACROSS THE WEST ON THE BACKSIDE OF THE
LOW...MUCH OF THIS MOISTURE MID/UPR LVL. THE WRN MOUNTAINS LOOK TO
BENEFIT THE MOST FROM THIS SYSTEM THRU TUES MORNING...SHIFTING EWD
THRU THE REST OF THE DAY AND THEN OUT OF THE FA TUE
NIGHT.

AS TROF EXITS THE AREA OVERNIGHT TUE...RIDGING RETURNS TO THE
FORECAST AREA ALONG WITH WARMING AND MOSTLY SUNNY/DRY SKIES THROUGH
THURSDAY. FRI...AS MENTIONED ABOVE...HERALDS THE APPROACH OF THE
NEXT PAC TROF. GOOD CONTINUITY BETWEEN MDLS NOW ENDS WITH NOW VASTLY
DIFFERING SOLUTIONS. WHILE THE GFS HAS MOSTLY STAYED THE COURSE IN
DEVELOPING A LARGE CLOSED LOW TROF WITH COLDER AIR DIGGING FURTHER
SWD...THE EURO HAS NOW DECIDED NOT TO DIG AND INSTEAD RATHER
BENIGNLY BRING AN EVER BROADENING TROF ACROSS THE CONUS NW...KEEPING
MOST MOISTURE AND PRECIP TO THE N OF THE FA. BOTH
SOLUTIONS...ALTHOUGH DIFFERING...SEEM PREDICATED ON THE DEVELOPMENT
AND PLACEMENT OF THE EPAC HIGH...WITH THE EURO ALLOWING IT TO
PENETRATE MUCH FURTHER EWD AND INTO THE CNTRL CONUS...IN EFFECT
MEETING UP WITH THE ERN CONUS HIGH. THE GFS MAINTAINS A DIVISION
BETWEEN THE TWO WITH A LARGE FLAT RIDGE OVERRUNNING THE CONUS AND
THE TROF/LOW BECOMING NEARLY CUT-OFF OVER THE INTERMOUNTAIN WEST.
WILL TAKE SOME TIME TO SEE WHICH SOLUTION BECOMES MORE CLEAR OR IF
THE EURO RETURNS TO WHAT IT AND THE GFS HAVE BEEN SAYING OVER THE
PAST COUPLE OF DAYS. BOTTOM LONE...SMALL POPS IN DAY 7 FOR MAINLY
THE WEST...FAR BELOW WHAT THE GFS WANTS...BUT MUCH MORE THAN THE
EURO.

&&

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL ACROSS WESTERN AND CENTRAL WYOMING
THROUGH 06Z SUNDAY.  NORTHEAST SURFACE WINDS OF 10 TO 15 KTS WITH
GUSTS TO 25 KTS WILL BE ENCOUNTERED VICINITY KCPR AND KRKS.

&&

.FIRE WEATHER...

DRIER CONDITIONS WILL MOVE INTO THE AREA AND LINGER THROUGH SUNDAY
MORNING. TEMPERATURES WILL COOL OVER THE NEXT SEVERAL DAYS UNDER
THE CURRENT WEATHER PATTERN...WITH INCREASED HUMIDITY OVER THE
AREA. FIRE WEATHER CONCERNS SHOULD BE ON THE LOW SIDE THE NEXT FEW
DAYS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...LIPSON
LONG TERM...BRAUN
AVIATION...CMB
FIRE WEATHER...LIPSON









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