Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 142026
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
226 PM MDT THU AUG 14 2014

.SHORT TERM...REST OF THIS AFTERNOON THROUGH FRIDAY

THE MEXICAN LOW NEVER MADE IT NORTH OF COLORADO BUT THE VORT MAX
OUT AHEAD OF IT BECAME OUR PRIMARY MID LEVEL CIRCULATION WHICH HAS
BEEN OVER NORTHWEST WY MOVING INTO MONTANA AND APPEARS TO BE THE
CULPRIT FOR OUR PREDICTED AREA OF STRATIFORM RAINFALL THAT FELL
OVER THE EAST HALF OF THE CWA OVERNIGHT AND THIS MORNING. THIS
WOULD EXPLAIN THE PLACEMENT OF THIS NORTH TO SOUTH ORIENTED BAND
OF PRECIP OCCURRING AROUND 60 MILES FARTHER WEST THAN PREDICTED
WITH MANY AREAS SEEING .15 TO .30 OF AN INCHES OF RAINFALL FROM
THE WIND RIVER BASIN TO THE BIG HORN BASIN AND BIG HORN MTNS. SOME
LOW CLOUDS FORMED ALONG THE BACK EDGE OF THIS PRECIP BAND WHICH
HAS MORPHED INTO LOW BASED CUMULUS WHICH ARE COEXISTING WITH A
HIGHER BASE OF BUILDING CUMULUS ORIGINATING IN A MORE UNSTABLE
AIRMASS WHERE EARLIER CLEARING TOOK PLACE ALONG THE DIVIDE AND
AREAS TO THE WEST AND SOUTH OF THERE. THE TWO FAVORED AREAS THAT
WILL MOST LIKELY SEE CONVECTION THIS AFTERNOON AND EVENING APPEAR
TO BE IN THE SOUTHERN WARM SECTOR OF THE CIRCULATION ASSOCIATED WITH
THE NW WY LOW SUCH AS WHERE CONVECTION HAS ALREADY FORMED ACROSS
THE GREEN MTNS AND SOUTH PASS...JUST TO THE SOUTHWEST OF THE AREA
OF CLEARING IN OUR NORTHEAST CWA WHERE A SUBTLE SURFACE BOUNDARY
WILL LIKELY DEVELOP FROM DIFFERENTIAL HEATING AND ALSO IN THE
NORTHWEST QUARTER OF WYOMING CLOSER TO THE PAC NORTHWEST LOW WHERE
SOUTHWEST DIFLUENT FLOW WILL TAKE PLACE. RAINFALL SHOULD BE THE
PRIMARY INGREDIENT WITH ANY CONVECTION THIS AFTERNOON AND EVENING
WITH DEW POINTS UP IN THE 50S RESULTING IN PLENTY OF MOISTURE BUT
NOT ENOUGH SUN GETTING THROUGH FOR STRONG CONVECTION,. THE BEST
DYNAMICS SHOULD REMAIN TO THE NORTHWEST OF THE CWA.

FOR FRIDAY...WITH THE PAC NW LOW TRACKING TO THE NORTHERN IDAHO
PANHANDLE...OUR FLOW WILL VEER TO MORE WESTERLY USHERING IN DRIER
AIR WITH ANY T STORMS RESTRICTED TO MAINLY THE NORTHERN MTNS WHERE
THE BEST CAPES AND MOISTURE WILL BE. TEMPS WILL RUN ABOUT 5 TO 10
DEGREES WARMER FRIDAY WITH MORE SUN.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

AS PREVIOUSLY MENTIONED...THE PAC NW LOW WILL MOVE FRIDAY NIGHT
INTO SATURDAY FROM WESTERN WASHINGTON INTO SOUTHERN ALBERTA...THUS
PULLING MOISTURE AND DYNAMICS NORTHWARD INTO MT INSTEAD OF WY. A
FEW SHOWERS ARE POSSIBLE IN THE NW MOUNTAINS FRIDAY EVENING...WITH
CLEARING SKIES EXPECTED. ON SATURDAY...THE LOW CURVES BACK
SOUTHEAST TO EXTREME NE MT...BRINGING SOME MID LEVEL MOISTURE AND
INSTABILITY TO NE WYOMING. HAVE KEEP SLIGHT CHANCE OF CONVECTIVE
ACTIVITY MAINLY AROUND THE BIGHORN MOUNTAINS AND JOHNSON COUNTY.
TEMPS SAT WILL BE A COUPLE OF DEGREES WARMER THAN FRI. A WEAK COOL
PUSH IS EXPECTED TO MOVE INTO NE WY FROM MT SUN AFTERNOON AND SET
UP A BOUNDARY WHERE ISOLATED STORMS MAY INITIATE LATE DAY OR EARLY
EVENING. MONDAY LOOKS TO BE QUITE SIMILAR TO SUNDAY EXCEPT FOR
WEAK WINDS.

ON TUESDAY...THE MODEL GUIDANCE IS ADVERTISING SOME EMBEDDED
ENERGY TO MOVE THROUGH THE GREAT BASIN RIDGE. THE VORTICITY MAXES
SHOULD PROVIDE SOME INSTABILITY TO KICK OFF MORE THUNDERSTORMS
COMPARED TO THE PREVIOUS THREE DAYS. THE EMPHASIS APPEARS TO BE
OVER NORTHERN WY. BEGINNING ON WEDNESDAY...BOTH THE GFS AND ECMWF
ARE INDICATING A SIZABLE TROUGH TO PUSH SOUTHWARD OUT OF WESTERN
CANADA INTO THE NW US...THUS SQUEEZING THE UPPER LEVEL HIGH
PRESSURE FURTHER SOUTH AND SLIGHTLY STRENGTHENING THE WESTERLY
FLOW ACROSS THE STATE. AS A RESULT...WEST WINDS SHOULD INCREASE
BOTH WEDNESDAY AND THURSDAY. ISOLATED CONVECTION IS POSSIBLE ON
WEDNESDAY...BUT NEAR TO SLIGHTLY ABOVE NORMAL TEMPERATURES AND
DRIER CONDITIONS WILL RAISE SOME FIRE WEATHER CONCERNS. ON
THURSDAY...THE WESTERLY FLOW INCREASES AS THE TROUGH IN THE PAC NW
STRENGTHENS...AS PRECIPITATION CHANCES INCREASE STEADILY IN THE
FAR NW MOUNTAINS AROUND YNP. THE CURRENT MODEL GUIDANCE IS SHOWING
A VERY INTERESTING PATTERN FOR NEXT WEEKEND.

&&

.AVIATION.../00Z ISSUANCE/
THE AREA OF LINGERING STEADY RAINFALL IS EXITING JOHNSON COUNTY
MAKING WAY FOR RAPIDLY DEVELOPING CONVECTION FROM SOUTHWEST TO
NORTHEAST ACROSS WESTERN AND CENTRAL WY. THE CONVECTION WILL
LINGER INTO THE EVENING. FAVORED AREAS OF CONVECTION SHOULD TAKE
PLACE IN NORTHWEST WYOMING AND IN JOHNSON COUNTY INCLUDING KBYG.
THESE STORMS SHOULD PRODUCE MVFR/LOCAL IFR CONDITIONS AND MTN
OBSCURATIONS. DRIER WEATHER WITH ISOLATED TO WIDELY SCATTERED
THUNDERSTORMS ARE EXPECTED MAINLY IN THE NORTHERN MOUNTAINS FRIDAY
AFTERNOON.

&&

.FIRE WEATHER...
MONSOONAL MOISTURE AND AN UPPER LEVEL SYSTEM MOVING NORTH WILL BRING
A SCATTERING OF SHOWERS AND ISOLATED THUNDERSTORMS THROUGH THIS
EVENING. A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD OVER THE
AREA FOR FRIDAY AND SATURDAY AND BRING DRIER AND WARMER WEATHER.
HOWEVER...WINDS ARE EXPECTED TO REMAIN LIGHT TO MODERATE AND
RELATIVE HUMIDITY ABOVE CRITICAL LEVELS. AS A RESULT...WE EXPECT
MINIMAL FIRE CONCERNS THROUGH SATURDAY.

&&

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

&&

$$

SHORT TERM...LIPSON
LONG TERM...MCDONALD
AVIATION...LIPSON
FIRE WEATHER...LIPSON



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