Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 132038
AFDRIW

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

.SHORT TERM...TONIGHT THROUGH TUESDAY

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.../00Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH 00Z WEDNESDAY. S-SW SFC WINDS
AROUND 15KTS WILL PREVAIL THIS EVENING WITH SOUTH SOUTHWEST SFC WINDS
INCREASING TO 25 TO 35 WITH GUSTS OF 50 TO 60 KTS BY NOON TUESDAY
OVER AND NEAR THE EAST SLOPES OF THE MOUNTAINS AND THROUGH THE
WIND CORRIDOR FROM ROCK SPRINGS TO CASPER.  AREAS OF LOW LEVEL WIND
SHEAR CAN BE EXPECTED...ESPECAILLY IN THE FOOTHILLS OF THE MOUNTAINS.

&&

.FIRE WEATHER...

  ...FIRE WEATHER WATCH FOR STRONG WINDS AND LOW RELATIVE HUMIDITY
TUESDAY...

A FIRE WEATHER WATCH IS IN EFFECT FOR TUESDAY AFTERNOON AND
EVENING. 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 GENRALLY 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 WATCH FROM TUESDAY MORNING THROUGH TUESDAY AFTERNOON
WYZ015-019-027>030.

FIRE WEATHER WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY
EVENING WYZ275-276-280>283.

&&

$$

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








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