Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 270911
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
311 AM MDT MON OCT 27 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

IMAGERY SHOWS INFLUENCES OF RIDGING ENDING AS PRIMARY RIDGE
CONTINUES AN EWD TREK...WITH WRN UPR TROF HAVING ALSO MOVED E...NOW
CUTTING THRU WY FROM NCNTRL TO THE SW CORNER...CONTINUING TO COOL
OFF THE UPR LVLS...KEEPING ATMOSPHERE JUST ON THE UNSTABLE SIDE.
MODEST EPAC MOISTURE ALSO ACCOMPANYING THE TROF. LARGE LEE CYCLONE
NOW SPINNING UP OVR THE HIGH/CENTRAL PLAINS WITH NICE BAROCLINIC
LEAF SHOWING OVER THE SERN HALF OF WY UNDER THE LIFTING INFLUENCE OF
LEADING JET STREAK. HEAVIEST PRECIPITATION IS CO-LOCATED WITH THE
LEAF...JUST ON/AHEAD OF THE LEADING EDGE OF THE JET. OBS DEPICT SFC
COLD FRONT THRU AND SOUTH/EAST OF THE STATE WITH HIGH PRESSURE
BUILDING IN FROM THE WEST. A WEAK SECONDARY FRONT MAY ALSO BE
LOCATED NORTH NEAR/ALONG THE BORDER W/ MT. MAINLY LIGHT POST FRONTAL
AND CONVECTIVE PRECIP...BOTH LIQUID AND FROZEN...FALLING ACROSS THE
NWRN FA AND ALONG/NEAR/NORTH OF SECONDARY FRONTAL AREA NEAR BORDER.

UPR LVLS BEGIN TRANSITION TO NW FLOW AS UPR TROF TRANSLATES
EWD...FURTHER DRIVING SECOND FRONT/BOUNDARY THRU THE FA TODAY...MAINLY E
OF THE DIVIDE. SECOND UPR JET ASSOCIATED WITH THE WRN SIDE OF THE
TROF MARKS THE END OF THE EPAC MOISTURE AND THE BEGINNING OF A LARGE
RELATIVELY DRY AIR MASS WHICH SHOULD ARRIVE NEAR THE WRN BORDER OF
WY LATER THIS AFTERNOON...EFFECTIVELY ENDING PRECIP CHCS FROM W TO
THRU THE EVENING PERIOD. IN THE MEANTIME...LIGHT PRECIP WILL BE
FOUND THIS MORNING AND EARLY AFTERNOON NORTH OF THE
FRONT...OROGRAPHICALLY AND CONVECTIVELY FORCED OVR THE NRN AND CNTRL
MOUNTAINS...AND MORE SHALLOWLY FORCED POST FRONTALLY OVR THE LOWER
ELEVATIONS IN THE BIGHORN BASIN...EWD INTO JOHNSON AND NATRONA
COUNTIES. THE WIND RIVER BASIN SHOULD REMAIN MOSTLY PRECIP FREE.
EXPECT ANOTHER 1 TO 2 INCHES OF NEW SNOWFALL TODAY OVER THE HIGHER
REACHES OF THE MOUNTAINS...WHILE SNOW LEVELS FALL THIS MORNING TO
THE VALLEY/BASIN FLOORS...WITH BETWEEN A TRACE AND A HALF AN INCH
COMMON. OTHERWISE AND ELSEWHERE...IT WILL BE COOL BREEZY AND DRY
ACROSS MOST OF THE SRN HALF OF THE CWA. TONIGHT...CLEARING SKIES AND
BECOMING COLD ACROSS THE FA WITH TEENS IN THE MOUNTAINS AND LOWER
AND MID 20S OVER THE LOW ELEVATIONS.

TUE AND WED WILL SEE MODEST WARMING...WITH MORE SUN AND NO PRECIP
FOR THE MOST PART. BREEZY LATE AFTERNOON CONDITIONS WILL ALSO BE
PRESENT ACROSS THE USUAL SPOTS IN RESPONSE TO THE SFC WARMING UNDER
STILL RELATIVELY COOL UPR LVLS GIVING LAPSE RATES JUST STRONG ENOUGH
TO BRING DOWN SOME SLIGHTLY STRONGER 700 MB FLOW. THIS WILL BE
NOTHING LIKE THE WIND AS OF LATE...JUST ENOUGH TO LET EVERYONE KNOW
IT`S THERE. ADDITIONALLY...THE SOME LOW END MOISTURE AND
CLOUD...SEEN IN IMAGERY IN AND AHEAD OF THE NEXT RIDGE OVR THE
EPAC...WILL OFFER UP SLIGHT CHANCES FOR WIDELY SPACED VERY LIGHT
SNOW OR FLURRIES IN THE NORTHWEST...MAINLY ON WEDNESDAY. THIS WILL
OCCUR AS A FLEETING WEAK JET STREAK/VORT MAX RIDES THRU THE
FLATTENING RIDGE AND PROVIDES SOME ADDITIONAL LIFT TO THAT OF THE
TERRAIN...MAYBE SQUEEZING SOMETHING OUT HERE AND THERE. WINDS WILL
ALSO INCREASE SOME ON WEDNESDAY IN RESPONSE TO THE APPROACH OF THE
DISTURBANCE...WITH SOME MODEST MOUNTAIN WAVE ACTION EXPECTED OVER
THE CENTRAL AND NORTHERN MOUNTAINS.

.LONG TERM...THURSDAY THROUGH MONDAY

MILD END TO A ABNORMALLY WARM OCTOBER AS RIDGE AXIS MOVES OVERHEAD
THURSDAY INTO FRIDAY WITH WARMER DAYS BUT CHILLY TO COLD MORNINGS.
MODELS HAVE COME BACK AROUND TO A MORE PROGRESSIVE AND FASTER
ARRIVING TROUGH AGAIN FOR NEXT WEEKEND. THE MODELS HAVE STRUGGLED
MIGHTILY WITH THIS SYSTEM BUT THEY APPEAR TO AT LEAST BE SETTLING
ON A TROUGH MOVING EAST ACROSS THE AREA LATER SATURDAY THROUGH
SUNDAY (THE CURRENT HIGH LATITUDE SYSTEM OUT NEAR THE DATELINE). THE GFS
IS FASTEST AND FURTHER NORTH WITH THE MAJORITY OF THE ENERGY. THE
GEM HAS MUCH MORE ENERGY ON THE SOUTH END OF THE TROUGH OVER SRN
UT BY LATE SATURDAY WHILE THE ECMWF IS MIDDLE GROUND WITH THE
TROUGH BOTTOMING OUT OVER NV AND THEN LIFTING NE ACROSS US LATE
SATURDAY INTO SUNDAY. PCPN CHANCES INCREASE OUT WEST AS THE DAY
WEARS ON SATURDAY WITH A CHANCE SPREADING EAST OF THE DIVIDE
SATURDAY NIGHT...ESPECIALLY ACROSS THE NORTH AND WITH THE FRONT IN
THE SOUTH. WARM ENOUGH FOR RAIN DURING THE DAY AND EARLY EVENING
IN THE WRN VALLEYS BEFORE SNOW LEVELS LOWER TO THE VALLEY FLOOR
SATURDAY EVENING. TRACK IS STILL UNCERTAIN BUT ENOUGH COLD AIR
EAST OF THE DIVIDE TO SEE SOME RAIN CHANGING TO SNOW SATURDAY
NIGHT INTO SUNDAY ALONG THE TRACK OF THIS SYSTEM AND WITH THE
FRONT ACROSS THE I80 CORRIDOR/RED DESERT AREA. MODELS DIVERGE MORE
ON WHETHER WE GET A SHORTWAVE QUICKLY FOLLOWING THIS SYSTEM. THE
GFS SHEARS UP A SMALL PIECE OF ENERGY FROM THE NEXT TROUGH MOVING
TOWARDS THE COAST WITH ANOTHER SHOT OF PCPN IN THE WEST SUNDAY
NIGHT AND MAYBE A FEW SNOW SHOWERS EAST OF THE DIVIDE ON
MONDAY...MAINLY NEAR THE HIGHER TERRAIN. THE ECMWF HAS A SLOWER
AND WEAKER SHORTWAVE BRUSHING US ON MONDAY BUT WITH MOST OF THE
ENERGY NORTH IN MT.

&&

.AVIATION.../12Z ISSUANCE/

WEST OF THE DIVIDE KBPI/KJAC/KPNA/KRKS ROUTES
ISOLD TO SCT -SHSN WILL LINGER OVER THE AREA THROUGH MID TO LATE
MORNING WITH HIGHER MTN OBSCURATIONS AND AREAS OF MVFR
CIGS...ESPECIALLY VCNTY KJAC-KDUB OVER TOGWOTEE PASS.  SUBSIDENCE
AND DRYING WILL RESULT IN CLEARING ACROSS THE AREA MONDAY AFTERNOON
ALONG WITH W-NW WINDS 15-25KT ACROSS THE INTERSTATE 80.  WINDS WILL
DIMINISH MONDAY EVENING WITH VFR CONDITIONS PREVAILING THROUGH 12Z
TUESDAY.

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

ISOLD TO SCT -SHSN...MORE NUMEROUS OVER THE BIGHORN RANGE...WILL BE
ENCOUNTERED ALONG AND N-E OF A VCNTY KCOD-KWRL-KCPR LINE THROUGH 15Z
ALONG WITH LCL MVFR CONDITIONS...WHILE THE BIGHORN RANGE AND THE
DIVIDE REMAIN FQTLY OBSCURED.  RAPID CLEARING FROM W-E WILL OCCUR
LATE MONDAY MORNING/MONDAY AFTERNOON WITH W-NW WINDS AT 10-20KTS
PERSISTING VCNTY AND E OF A KBYG-KRIW LINE THROUGH THE AFTERNOON.
DIMINISHING WIND AND VFR...SKC-SCT250...CONDITIONS WILL FOLLOW
MONDAY NIGHT.

&&

.FIRE WEATHER...

FIRE DANGER WILL REMAIN RELATIVELY LOW TODAY AS COOL TEMPERATURES
COMBINE WITH MINIMUM RH VALUES RANGING ABOVE 25 PERCENT FOR MOST
LOCATIONS. LIGHT PRECIPITATION WILL CONTINUE TO BE POSSIBLE ACROSS
THE NORTHERN AND NORTHWESTERN MOUNTAINS...AND OVER PORTIONS OF THE
BIGHORN BASIN AND THE EASTERN DISPATCH ZONES. WINDS...ALTHOUGH
BREEZY AT TIMES...WILL NOT BE NEARLY AS STRONG AS THE PREVIOUS
COUPLE OF DAYS...WITH MOST GUSTS REMAINING UNDER 30 MPH FOR MOST
LOCATIONS. WARMER AND DRIER ON TUESDAY. THIS COMBINING WITH  BREEZY
CONDITIONS ACROSS THE SOUTHEASTERN DISPATCH ZONES WILL ENHANCE FIRE
DANGER A BIT.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...SKRBAC
AVIATION...AEM
FIRE WEATHER...BRAUN








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