Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

000
FXUS65 KRIW 181048
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
348 AM MST TUE NOV 18 2014

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

WV IMAGERY SHOWS LONGWAVE TROF ACROSS MOST OF THE CONUS...SAVE THE
WEST COAST UNDER AN AMPLIFIED RIDGE...WITH CENTER OF CLOSED LOW
ROTATING AROUND THE NRN GREAT LAKES AND ANOTHER SWIFT MOVING SW/JET
STREAK OVR SWRN CANADA MOVING S INTO NRN INTERMOUNTAIN REGION. AT
THE SFC...LEFT OVER STATIONARY FRONT STILL EXTENDS ACROSS NERN WY...
UP THRU CNTRL MT. SFC COLD POOL CONTINUES OVR THE FA TO THE WEST OF
THE STATIONARY FRONT UNDER MOSTLY CLEAR SKIES AND CONTINUING HIGH
PRESSURE...WITH A BULLSEYE ONCE AGAIN OVR THE BIGHORN BASIN.

MODEST WARM ADVECTION CONTINUES ACROSS MOST OF THE CWA WITH SLOW
WARMING THRU THE FCST PERIOD. OTHERWISE...THE FCST WILL BE MOSTLY
DRY THRU THE DAY WED WITH THE EXCEPTION OF LIGHT SNOW ACROSS THE
HIGHER PEAKS OF THE BIGHORN MOUNTAINS ACCOMPANYING A FLY-BY ANOTHER
CLIPPER FRONT LATER TODAY. BRISK NW WINDS WILL ONCE AGAIN PUSH INTO
NRN JOHNSON COUNTY TODAY...WITH INCREASED WEST WIND AHEAD OF THE
FRONT BETWEEN SWEETWATER AND NATRONA COUNTIES.
ADDITIONALLY...INCREASING NWRLY MID/UPR LVL WIND ASSOCIATED WITH THE
APPROACHING JET STREAK MOVING OUT OF CANADA TODAY WILL REACT WITH AN
INCREASING THERMO/OMEGA GRAD BETWEEN THE FOOTHILLS AND MOUNTAINS OF
NRN AND CNTRL WY TO GIVE QUITE GUSTY SFC WIND CONDITIONS THIS
AFTERNOON FROM AROUND NOON TO THE EARLY EVENING PERIOD OVR THE WRN
WIND RIVER MOUNTAINS TO THE NORTH OVR THE ABSAROKA CHAIN. MOUNTAIN
WAVE PRODUCTION LOOKS TO REMAIN RELATIVELY LOW AS WIND DIRECTION IS
NOT IDEAL. HOWEVER...SOME AREAS COULD APPROACH MIN WARNING
CONDITIONS FOR AN HR OR TWO OVR/NEAR THE USUAL SUSPECTS INCLUDING
CHIEF JOSEPH AND CLARK AT THE LOWER ELEVATIONS. WINDS WILL BE CONDUCIVE IN
THIS CASE IN GETTING INTO CODY...BLOWING 20 TO 30 MPH WITH GUSTS TO
40 MPH POSSIBLE. SAME THING FOR THE DUBOIS/CROWHEART AREA IN
WESTERN FREMONT COUNTY. THE SNOWPACK TODAY SHOULD BE MORE MORE
STABLE AND ICE CRUSTED AND NOT NEARLY AS DRY AND LOOSE AS THE
PREVIOUS FEW DAYS...FOREGOING THE NEED FOR ANOTHER WSW/BLOWING
SNOW SITUATION. HOWEVER...AS ALLUDED TO WITH THE WIND FCST
ABOVE...THE HIGHER MOUNTAIN PEAKS MAY EXPERIENCE BLOWING SNOW
CONDITIONS THIS AFTERNOON.

WED...THE STRONGER JET FLOW SUBSIDES ALONG WITH THE GUSTIER SFC
WINDS OF TODAY AS WEST COAST RIDGE APPROACHES THE STATE FROM THE
WEST. ALSO...A MODEST INFLUX OF MID LVL MOISTURE WILL TOP THE RIDGE
AND BEGIN TO INFILTRATE THE REGION...OFFERING UP A LOW END CHC
FOR SOME ISOLATED MAINLY TERRAIN FORCED LIGHT SNOW ACROSS THE
WRN/NWRN MOUNTAINS WED NIGHT.

THU...MODEST UPR RIDGING CONTINUES ACROSS WY...CHASED CLOSELY BY THE
NEXT SW TROF COMING FROM THE EPAC...BRINGING SOME INCREASED BUT
MODEST MOISTURE ALONG WITH IT. PRECIP CHANCES WILL INCREASE SOME
ACCORDINGLY ACROSS THE WRN FA AS MARGINAL DYNAMICS ADD TO THE
TERRAIN LIFTING...SQUEEZING OUT SOME LIGHT SNOW...ESPECIALLY LATER
IN THE AFTERNOON AND LASTING THRU THE EVENING PERIOD. ATTM...THIS
INITIAL DISTURBANCE (BEFORE THE WEEKEND VERSION) IS NOT ALL THAT
IMPRESSIVE LOOKING INASMUCH AS QPF OR SNOWFALL POTENTIAL THROUGH THE
END OF THIS FCST PERIOD AS DEEP MOISTURE AND COLD TEMPS ALONG WITH
IMPRESSIVE DYNAMICS APPEAR TO BE SOMEWHAT LACKING. THAT SAID...THE
WRN MOUNTAINS STILL COULD SEE WIDESPREAD 2 TO 4 INCHES OF NEW
SNOWFALL BY FRIDAY MORNING WITH THE HIGHER PEAKS RECEIVING 3 TO 6
INCHES. THE VALLEYS GENERALLY LOOK TO STAY IN THE HALF INCH TO 2
INCH CATEGORY.

.LONG TERM...FRIDAY THROUGH TUESDAY

A STRONG STORM SYSTEM POSSIBLE SATURDAY WITH SIGNIFICANT SNOW AND
WIND WEST...AND STRONG/HIGH WIND EAST.

FRIDAY LOOKS TO BE THE PROVERBIAL CALM BEFORE THE STORM...WITH SOME
LIGHT SNOW/FLURRIES OVER THE FAR WEST...WITH TEMPERATURES SEASONAL
TO SLIGHTLY BELOW AVERAGE. THE EXCEPTION COULD BE THE EASTERN
BIGHORN BASIN WHERE THE ARCTIC AIR MASS OVER THE PAST WEEK COULD
HANG TOUGH...WHERE TEMPS COULD REMAIN AROUND 10 DEGREES BELOW
AVERAGE. HOWEVER THIS IS THE FAR CRY FROM THE 30 TO 50 DEGREES
BELOW AVERAGE OVER THE PAST SEVERAL DAYS.

AHEAD OF THE STORM SYSTEM SATURDAY...MODELS ARE SHOWING A MOIST
ISENTROPIC UPGLIDE PATTERN DEVELOPING BETWEEN 06Z AND 12Z. THIS
SHOULD RESULT IN WIDESPREAD SNOWFALL DEVELOPING OVER THE FAR WEST
AFTER MIDNIGHT FRIDAY NIGHT. THE QUICK MOVING SHORTWAVE TROUGH AND
THE ASSOCIATED PACIFIC COLD FRONT IN THE FAST WESTERLY FLOW IS
EXPECTED TO PUSH ACROSS THE FORECAST AREA SATURDAY AFTERNOON AND
EVENING. THE SYNOPTIC LIFT ASSOCIATED WITH THE SHORTWAVE AND
BAROCLINIC ZONE/FRONT COULD BE ENHANCED BY THE LEFT FRONT QUAD OF A
150+ KT UPPER JET SATURDAY. WINTER HIGHLIGHTS APPEAR MORE LIKELY
OVER PORTIONS OF THE WEST FROM LATE FRIDAY NIGHT THROUGH SUNDAY TIME
FRAME...WITH THE MAIN IMPACT PROBABLY SATURDAY. TO COMPLICATE
MATTERS A BIT...MODELS ARE HINTING ENOUGH WARM AIR COULD BE PULLED
NORTHWARD TO HAVE THE SNOW CHANGE TO RAIN MIDDAY SATURDAY ACROSS THE
WESTERN VALLEYS ESPECIALLY STAR VALLEY. HOWEVER THIS WOULD BE SHORT
LIVED...WITH A CHANGE BACK TO SNOW IN WAKE OF THE COLD FRONT
SATURDAY AFTERNOON. WHILE SIGNIFICANT SNOWFALL/WIND COULD BE
OCCURRING OVER THE WEST SATURDAY...A STRONG SURFACE PRESSURE
GRADIENT AND 700MB WEST WINDS AROUND 50 KTS WILL PROBABLY RESULT
IN VERY STRONG TO HIGH WIND ESPECIALLY IN RKS TO CPR WIND CORRIDOR
SATURDAY. COULD ALSO SEE SOME STRONG WIND IN THE CODY FOOTHILLS
LATE FRIDAY NIGHT INTO SATURDAY WITH SOME MOUNTAIN WAVE POTENTIAL
AND STRONG GAP FLOW FROM A STRONG TEMP GRADIENT BETWEEN
YELLOWSTONE AND THE CODY FOOTHILLS. STRONG DOWNSLOPING SATURDAY
EAST OF THE DIVIDE WILL KEEP THOSE AREAS MAINLY DRY...BUT COULD
SEE SOME PRECIPITATION ALONG AND IN WAKE OF THE FRONT.

ALTHOUGH THE MAIN SYSTEM WILL BE EAST OF THE AREA SUNDAY...THE
FORECAST AREA WILL REMAIN ON THE CYCLONIC SIDE OF THE JET WITH A
RELATIVELY UNSTABLE ATMOSPHERE FOR NOVEMBER. THIS SHOULD RESULT IN
ISOLATED TO SCATTERED SNOW SHOWERS...WITH MORE SNOW SHOWER ACTIVITY
OVER THE NORTHWEST AND NORTHERN MOUNTAINS WHICH FAVOR A MOIST
NORTHWEST FLOW. THIS PATTERN CONTINUES INTO MONDAY...BUT WITH A
MORE STABLE ENVIRONMENT FOR MONDAY. THUS WILL DECREASE POPS A
BIT...BUT STILL KEEP CHANCE POPS FOR THE NORTHWEST/NORTHERN
MOUNTAINS.

A RELATIVELY MOIST NORTHWEST FLOW CONTINUES TUESDAY...BUT THE AREA
WILL BE ON THE ANTICYCLONIC SIDE OF THE UPPER JET WHICH SHOULD
RESULT IN EVEN LESS SNOW SHOWER ACTIVITY.

DUE TO THE PACIFIC NATURE OF THIS SYSTEM...THE AIR MASS IN WAKE OF
THIS COLD FRONT SATURDAY/SATURDAY NIGHT WILL NOT BE NEARLY AS COLD
AS THE ARCTIC AIR MASS THAT HAS IMPACTED THE REGION FOR THE PAST
WEEK.

&&

.AVIATION.../12Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH TONIGHT IN MOST AREAS. IN THE
FAR WEST VALLEYS AND BASINS LOW CLOUDS AND PATCHY FOG WILL PERSIST
THIS MORNING WITH MVFR TO IFR CONDITIONS EXPECTED. THE FOG WILL LIFT
BY 19Z WITH THE LOW CLOUDS DISSIPATING BY 21Z IN THE WEST.

LOW LYING AREAS IN CENTRAL WYOMING WILL ALSO SEE AREAS OF LOW CLOUDS
AND PATCHY FOG...ESPECIALLY IN LOW LYING AREAS IN THE BIGHORN BASIN
AND AROUND BOYSEN RESERVOIR NORTH OF RIVERTON. EXPECT LOCAL MVFR TO
IFR CONDITIONS WITH CONDITIONS IMPROVING BY 19Z.

BREEZY TO WINDY CONDITIONS WILL OCCUR TODAY INTO THIS EVENING IN THE
FAVORED WIND LOCATIONS...INCLUDING KCOD...KCPR AND KRKS.

&&

.FIRE WEATHER...

FIRE DANGER LOW AND REMAINING LOW THROUGH THE REST OF THE WORK WEEK
AS SNOW COVER OR MINIMUM RH VALUES STAY WELL ABOVE CRITICAL LEVELS.
HOWEVER...BRISK WEST TO NORTHWEST WINDS WILL BE PREVALENT TODAY
ACROSS THE EASTERN ZONES AND OVER THE NORTHERN AND CENTRAL MOUNTAINS AS
ANOTHER CLIPPER FRONT APPROACHES NORTHEASTERN WYOMING THIS
AFTERNOON. INVERSIONS WILL LIFT SOME TODAY...BUT NOT BREAK FOR MOST
LOCATIONS...REMAINING AT OR BELOW 1500 FEET FOR MOST LOCATIONS IN
THE MIDDLE OF THE DAY...AND A FEW LOCATIONS NOT RISING MORE THAN A
FEW HUNDRED FEET. WINDS WILL DECREASE TONIGHT WITH A NICE DAY ON
TAP FOR WEDNESDAY. CLOUDS AND MOISTURE BEGIN TO INCREASE ACROSS
THE WEST WEDNESDAY NIGHT WITH LIGHT AREAS OF SNOW INCREASING OVER
THE WESTERN FORECAST ZONES ON THURSDAY...LASTING ON AND OFF AGAIN
THROUGH THE WEEKEND.


&&

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

&&

$$

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







USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.