Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 140514
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1114 PM MDT MON APR 13 2015

UPDATE...FOR 06Z AVIATION DISCUSSION AND TO UPGRADE THE HIGH WIND
WATCHES TO WARNINGS AND THE FIRE WEATHER WATCH TO RED FLAG WARNING.

.SHORT TERM...TONIGHT THROUGH TUESDAY (ISSUED AT 238 PM MDT)

A HIGH WIND WATCH IS IN EFFECT FOR TUESDAY AND TUESDAY EVENING
FOR SOUTHERN LINCOLN AND SWEETWATER COUNTIES.  ALSO FOR THE EAST
SLOPES OF THE WIND RIVER MOUNTAINS AND THE GREEN AND RATTLESNAKE
MOUNTAINS. SOUTH TO SOUTHWEST WINDS OF 40 MPH WITH GUSTS TO 60 MPH
ARE EXPECTED. THE MOUNTAINS MAY SEE 50 MPH WINDS WITH GUSTS TO 75 MPH.
TO THE NORTH AND EAST A FIRE WEATHER WATCH IS IN EFFECT ON TUESDAY
UNTIL 6 PM MDT...OVER FREMONT...NATRONA...JOHNSON COUNTIES AND
THE BIGHORN BASIN. SOUTH TO SOUTHWEST WINDS OF 20 TO 30 MPH WITH
GUSTS TO 50 MPH AND LOW RELATIVE HUMIDITY AROUND 10 PERCENT WILL
COMBINE WITH CRITICALLY DRY FUELS FOR CONDITIONS FAVORABLE FOR
HARD TO CONTROL FIRES WITH RAPID RATES OF SPREAD.

OVERNIGHT TONIGHT TEMPERATURES WILL WARM WITH MOSTLY CLEAR CONDITIONS.
A PACIFIC COLD FRONT WILL APPROACH THE WEST ON TUESDAY WITH INCREASING
CLOUD IN THE MORNING. SHOWERS WILL INCREASE ACROSS THE WEST AND
NORTH WITH ISOLATED THUNDERSTORMS WITH STRONG GUSTY WINDS AND SMALL
HAIL DEVELOPING IN THE AFTERNOON. TEMPERATURES WILL BE VERY WARM
AHEAD OF THE COLD FRONT.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY

AS WE ENTER THE LONG TERM. WE WILL TAKE A DROP. A DROP LIKE ON THE
SCARIEST ROLLER COASTER AT CEDAR POINT...OR WHAT WE CALL IN WYOMING
APRIL. A STRONG COLD FRONT AMPLE MOISTURE WILL MOVE WEST TO EAST
ACROSS THE STATE ON TUESDAY NIGHT AND USHER IN MUCH COOLER AIR. 700
MILLIBAR TEMPERATURES WILL FALL AS MUCH AS 17 DEGREES CELSIUS...OR
30 DEGREES FOR THOSE OF YOU WHO ARE MORE IMPERIALLY ORIENTED. IN
OTHER WORDS IT WILL BE COMPLETELY DIFFERENT WHEN YOU WAKE UP
WEDNESDAY MORNING THEN WHEN YOU GO TO BED TUESDAY NIGHT...AT LEAST
FOR MOST AREAS. THERE IS ENOUGH ENERGY FOR A FEW THUNDERSTORMS ON
TUESDAY EVENING AHEAD OF THE FRONT. AFTER THAT...PRECIPITATION
CHANGES OVER TO SNOW AS TEMPERATURES CRASH LATE AT NIGHT AND EARLY
WEDNESDAY MORNING. THE STEADIEST AND HEAVIEST SNOW FOR MOST AREAS
STILL LOOKS TO BE WEDNESDAY MORNING INTO EARLY AFTERNOON WHEN THERE
WILL BE SOME INTERACTION WITH THE RIGHT REAR QUAD OF A PASSING JET
STREAK TO PROVIDE SOME EXTRA DYNAMICS. AFTER THAT...IT TURNS INTO
MORE OF A NORTHEASTERLY UPSLOPE EVENT AS 700 MILLIBAR FLOW TURNS
THAT WAY AS LEE CYCLOGENESIS OCCURS OVER COLORADO. THIS LOOKS TO
CONTINUE INTO WEDNESDAY AFTERNOON AND EVEN WEDNESDAY NIGHT. IN
ADDITION...STRONG COLD ADVECTION WILL LEAD TO GUSTY WINDS MUCH OF
WEDNESDAY...ESPECIALLY IN THE FAVORED AREAS LIKE THE NORTHERN BIG
HORN BASIN...SOUTH OF THE OWL CREEK RANGE AND ACROSS JOHNSON COUNTY.
THIS WILL LIKELY LEAD TO BLOWING AND DRIFTING SNOW AND DIFFICULT
TRAVEL CONDITIONS. AS FOR AMOUNTS...CONTINUITY LOOKED REASONABLE SO
WE ONLY MADE MINOR TWEAKS. AT THIS POINT...IT LOOKS LIKE MORE
ADVISORY...ESPECIALLY DURING THE DAY SINCE THE RECENT WARM
WEATHER...WARM GROUND TEMPERATURES AND HIGH SUN ANGLE WOULD LIKELY
MELT A LOT OF SNOW THAT FALLS ON PAVED SURFACES UNLESS IT IS VERY
HEAVY.

AN ADDITIONAL CONCERN FOR WEDNESDAY NIGHT IS THE MODELS ARE SHOWING
DEVELOPMENT OF A HEAVIER BAND OF SNOW SOMEWHERE IN CENTRAL OR
EASTERN WYOMING AS THE LOW DEEPENS IN THE LEE OF THE ROCKIES. THE
MODELS ARE ALL OVER THE PLACE WITH THE PLACEMENT THOUGH. FOR
NOW...WE BUMPED SNOW AMOUNTS IN THE EAST A BIT BUT WILL NOT GO
HIGHER UNTIL MODELS COME INTO MORE CONSENSUS SINCE THIS MESOSCALE
BANDING IS HARD TO PINPOINT.

SNOW SHOULD END FROM NORTHWEST TO SOUTHEAST FROM WEDNESDAY NIGHT
INTO THURSDAY MORNING...BUT THE HEAVY SNOW SHOULD BE OVER BY
THURSDAY MORNING. RIDGING SHOULD THEN BUILD OVER THE AREA FROM
THURSDAY AFTERNOON THROUGH FRIDAY WITH FRIDAY LOOKING LIKE A FAIRLY
NICE DAY. THE NEXT SYSTEM THEN LOOKS TO MOVE IN FOR THE WEEKEND. AS
EXPECTED...MODELS DIVERGE ON THE DETAILS AND TIMING OF THE SYSTEM.
AT THIS POINT...MOST AREAS SHOULD BE DRY MOST OF THE TIME FOR
SATURDAY...ESPECIALLY ACROSS THE SOUTHERN TWO THIRDS OF THE AREA
WITH SUNDAY COOLER AND MORE UNSETTLED.WITH MOST OF THE ATTENTION ON
THE WEDNESDAY SYSTEM AND A LACK OF MODEL CONSISTENCY...WE LET
CONTINUITY RIDE UNTIL WE GET CLOSER TO THE WEEKEND TO SEE IF DETAILS
BECOME CLEARER.

&&

.AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS WILL PREVAIL THROUGH TUESDAY EVENING. EXPECT A GUSTY
SOUTH TO SOUTHWEST WIND AT ALL THE TERMINAL SITES MONDAY AHEAD OF AN
APPROACHING WEATHER SYSTEM. AS THE COLD FRONT PASSES AFTER 00Z THE
WIND WILL BECOME WEST OR NORTHWEST AND GUSTY. ISOLATED SHOWERS WILL
OCCUR TOWARD 00Z. THEN SHOWERS WILL BECOME MORE NUMEROUS AFTER 03Z
WITH RAIN SHOWERS CHANGING TO SNOW SHOWERS TOWARD 06Z.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR CONDITIONS WILL PREVAIL THROUGH 21Z TUESDAY. SHOWERS WILL DEVELOP
AFTER 18Z OVER THE WEST WITH ISOLATED THUNDERSTORMS. THE COLD FRONT
WILL MOVE INTO THE WEST AROUND 00Z USHERING IN COLDER AIR AND
CHANGING RAIN SHOWERS TO SNOW BY 03Z. THEN SNOW SHOWERS WILL OCCUR
THROUGH 06Z WED. EXPECT AREAS OF MVFR CONDITIONS TO DEVELOP AFTER
00Z.  MVFR TO IFR CONDITIONS WILL BECOME MORE WIDESPREAD BY 06Z WED.
PLEASE SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

&&

.FIRE WEATHER...

STRONG WINDS WILL COMBINE WITH LOW RELATIVE HUMIDITY AND CRITICALLY
DRY FUELS TO PRODUCE CONDITIONS FAVORABLE FOR RAPID FIRE GROWTH.
THESE CONDITIONS WILL BE PRODUCED BY STRONG SOUTH TO SOUTHWEST WINDS
AHEAD OF A PACIFIC COLD FRONT.  TONIGHT WILL BE MOSTLY CLEAR AND
BREEZY WITH GENERALLY POOR RELATIVE HUMIDITY.  CLOUDS WILL INCREASE
IN THE WEST WITH SOME MOUNTAIN SHOWERS WITH ISOLATED THUNDERSTORMS
IN THE MOUNTAINS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

HIGH WIND WARNING FROM TUESDAY MORNING THROUGH TUESDAY AFTERNOON
WYZ015-019-020-027>030.

RED FLAG WARNING FROM TUESDAY AFTERNOON THROUGH TUESDAY EVENING
WYZ275-280>283.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...HATTINGS
AVIATION...AR
FIRE WEATHER...C.BAKER










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