Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 021000
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
400 AM MDT WED SEP 2 2015

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

A FEW WEAK SHOWERS PERSIST ACROSS WESTERN WYOMING THIS
MORNING...WITH LITTLE TO NO CONSEQUENCE. THE STORY CONTINUES TO BE
CRITICAL FIRE BEHAVIOR. TEMPERATURES WILL AGAIN BE ABLE TO WARM
TODAY UNDER PERSISTENT LOW RELATIVE HUMIDITY. A TIGHTENING PRESSURE
GRADIENT WILL AGAIN RESULT IN GUSTY SOUTHWEST WIND.

GENERALLY DRY CONDITIONS EXPECTED THROUGH THE EVENING...WITH A WEAK
PUSH OF MOISTURE NOTED AFTER MIDNIGHT. THIS PUSH MAY GENERATE
SHOWERS AND THUNDERSTORMS...ESPECIALLY OVER THE WESTERN MOUNTAINS.
SOUTHWEST FLOW TO INCREASE THROUGH THE DAY ON THURSDAY...AS A WAVE
OF LOW PRESSURE MOVES OVER THE PACIFIC NORTHWEST. THIS SOUTHWEST
FLOW WILL PICK UP ANOTHER ROUND OF MOISTURE...WITH SHOWERS AND
THUNDERSTORMS POSSIBLE ACROSS MUCH OF THE FORECAST AREA BY THURSDAY
AFTERNOON AND EVENING. EVEN WITH THIS PUSH OF MOISTURE... SOME AREAS
WILL CONTINUE TO EXPERIENCE DRY...WINDY...AND WARM CONDITIONS. THIS
WILL KEEP EXTREME FIRE BEHAVIOR ACROSS MOST OF THE AREA EAST OF THE
CONTINENTAL DIVIDE THROUGH THURSDAY EVENING.

FIRE WEATHER WILL FINALLY SEE SOME REPRIEVE FRIDAY. THE PACIFIC
NORTHWEST WAVE WILL CONTINUE TO DIG SOUTH THROUGH THE
AFTERNOON...PUSHING ANOTHER ROUND OF MOISTURE INTO THE STATE. THIS
SYSTEM AND ITS ASSOCIATED MOISTURE AND CLOUD COVER WILL HELP TO
REBOUND RELATIVE HUMIDITY ACROSS THE AREA. GUSTY WIND WILL STILL BE
A THREAT ON FRIDAY...THOUGH THE REMAINDER OF FIRE WEATHER ELEMENTS
ARE NOT ANTICIPATED TO BE CRITICAL. THE PACIFIC SYSTEM WILL DIG NEAR
THE DESERT SOUTHWEST BY EARLY SATURDAY MORNING...WITH SHOWERS
REMAINING OVER THE AREA.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

A STRONG AND UNSEASONABLY COLD UPPER LOW OVER THE NORTHERN GREAT
BASIN SATURDAY IS EXPECTED TO EJECT NORTHEAST ACROSS THE NORTHERN
ROCKIES SATURDAY NIGHT/SUNDAY MORNING. THE ASSOCIATED STRONG COLD
FRONT IS EXPECTED TO PUSH QUICKLY FROM WEST TO EAST ACROSS THE
FORECAST AREA SATURDAY NIGHT/SUNDAY MORNING...WITH THE 00Z ECMWF
ABOUT 6 HOURS QUICKER THAN THE GFS. AHEAD OF THE FRONT ON
SATURDAY...EXPECT MILD TO WARM TEMPERATURES AND BREEZY
SOUTH/SOUTHWEST WINDS. AREAS EAST OF THE DIVIDE WILL NEED TO BE
MONITORED FOR CRITICAL FIRE WEATHER CONDITIONS. HOWEVER RIGHT
NOW...MIN RH IS NOT FORECAST TO REACH CRITICAL CRITERIA.
DIFFLUENT FLOW AHEAD OF THE SYSTEM SHOULD RESULT IN ISOLATED TO
SCATTERED CONVECTION DEVELOPING WEST OF THE DIVIDE SATURDAY
AFTERNOON...BUT WITH LITTLE OR NO ACTIVITY EAST. A BETTER CHANCE
OF CONVECTION WILL OCCUR ALONG THE FRONTAL BOUNDARY/STRONG
BAROCLINIC ZONE...AS WELL AS NEAR THE TRACK OF THE UPPER LOW
SATURDAY NIGHT/SUNDAY MORNING. THE BEST SHOT OF PRECIPITATION WITH
THIS SYSTEM WILL BE OVER THE NORTHWEST PORTION OF THE FORECAST
AREA SATURDAY NIGHT...WITH SOME MOUNTAIN SNOW ACCUMULATIONS
POSSIBLE. 700 MB TEMPERATURES ARE PROGGED TO BE AROUND -3C BY
AROUND 12Z SUNDAY MORNING OVER THE EXTREME WEST/NORTHWEST WHICH
WOULD CORRELATE WITH SNOW LEVELS DROPPING DOWN TO AROUND 7000
FEET. HAVE NOT BROUGHT SNOW LEVELS DOWN THAT FAR...AND MODELS SHOW
THE BULK OF THE PRECIPITATION EXITING THE AREA BY THE TIME THE
COLDEST AIR ARRIVES EARLY SUNDAY MORNING.

A MAINLY DRY WEST/NORTHWEST FLOW IS EXPECTED MONDAY THROUGH
WEDNESDAY WITH SEASONAL TO SLIGHTLY BELOW AVERAGE TEMPERATURES.
THE ECMWF HINTS AT A WEAK SYSTEM AND ASSOCIATED COLD FRONT
IMPACTING THE AREA IN THE TUESDAY/WEDNESDAY TIME FRAME. HAVE
ELECTED TO KEEP THE FORECAST DRY FOR NOW...BUT LATER SHIFTS MIGHT
NEED TO ADD SOME POPS ESPECIALLY OVER THE NORTHERN MOUNTAINS IF
THE ECMWF SOLUTION COMES TO FRUITION.

&&

.AVIATION.../00Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. BREEZY TO WINDY
CONDITIONS WILL OCCUR AT MANY TERMINAL SITES TODAY FROM LATE MORNING
THROUGH LATE AFTERNOON. AFTER 00Z ISOLATED SHOWERS OR STORMS ARE
POSSIBLE ACROSS FAR WEST AND SOUTHWEST WY THROUGH 12Z THURS. OUTFLOW
WIND GUSTS TO 35 KNOTS WILL BE POSSIBLE NEAR STORMS.

&&

.FIRE WEATHER...

CRITICAL FIRE WEATHER CONDITIONS WILL REMAIN OVER THE AREA FOR THE
NEXT COUPLE DAYS. AN APPROACHING SYSTEM WILL KEEP INCREASED
SOUTHWEST WIND ACROSS CENTRAL AND WESTERN WYOMING. MEANWHILE...DRY
CONDITIONS WILL ALSO PERSIST WITH LOW RELATIVE HUMIDITY EXPECTED
WITH WARM TEMPERATURES. THIS WILL KEEP JUSTIFICATION FOR THE RED
FLAG WARNING THROUGH THURSDAY EVENING. CONDITIONS WILL FINALLY RELAX
LATE THURSDAY AS AN APPROACHING NORTHWEST SYSTEM WILL PUSH MORE
MOISTURE OVER THE AREA TO HELP ALLEVIATE THE LOW HUMIDITY. GUSTY
WINDS...HOWEVER...ARE ANTICIPATED TO REMAIN FOR THE NEXT COUPLE
DAYS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 9 PM MDT THURSDAY FOR WYZ275>277-279>283-
285-287-289-300-414>416.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...AR
FIRE WEATHER...BRANHAM


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