757
FXUS65 KRIW 201021
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
421 AM MDT SUN OCT 20 2019
SHORT TERM
(TODAY THROUGH TUESDAY)
ISSUED AT 415 AM MDT SUN OCT 20 2019
SATELLITE IMAGERY EARLY THIS MORNING SHOWS THE UPPER LOW OVER THE
CENTRAL/SOUTHERN BIGHORN MOUNTAINS. RADAR IMAGERY EARLY THIS
MORNING SHOWS PERSISTENT SNOW SHOWERS IN THE NORTHWEST FLOW ACROSS
WESTERN WYOMING, WHILE AN AREA OF RAIN AND SNOW EXPANDING IN
COVERAGE NEAR THE UPPER LOW. THERE WAS EVEN A LIGHTNING STRIKE OR
TWO ACROSS NORTHEAST FREMONT COUNTY AROUND 2 AM. THIS UPPER LOW IS
PROGGED TO PUSH INTO THE NEBRASKA PANHANDLE BY 18Z, AND THEN TO
NORTH-CENTRAL NEBRASKA BY 00Z MONDAY.
THE ACTIVITY OVER THE WEST WILL CONTINUE TO DECREASE IN COVERAGE
AND INTENSITY AS THE MORNING PROGRESSES. NO CHANGES TO WINTER
HIGHLIGHTS OVER THE WEST.
THE BEST DYNAMICS WILL BE OVER THE FAR EASTERN SECTIONS OF THE
FORECAST AREA ASSOCIATED WITH THE UPPER LOW BEFORE IT AND THE
DYNAMICS PULL AWAY AROUND MIDDAY. IN THE AFTERNOON, DESPITE THE
BULK OF THE DYNAMICS PUSHING AWAY, MODELS CONTINUE TO SHOW
INSTABILITY ISOLATED TO SCATTERED SNOW SHOWERS PUSHING SOUTHEAST
ACROSS THE AREA MAINLY EAST OF THE DIVIDE. THE HIGH RESOLUTION
MODELS CONTINUE TO IMPACT THE CASPER AREA WITH THIS SHOWER
ACTIVITY. SNOW COULD BE HEAVY IN THESE SHOWERS. DESPITE
TEMPERATURES IN THE MID TO UPPER 30S EARLY THIS MORNING, EXPECT
ANY RAIN TO CHANGE QUICKLY TO SNOW FROM DYNAMICAL COOLING AND A
LOW WET-BULB ZERO TEMPS. THUS WITH SNOWFALL, POSSIBLY HEAVY AT
TIMES, IN COMBINATION WITH STRONG WIND HAVE ELECTED TO ISSUE A
WINTER WEATHER ADVISORY UNTIL 6 PM TODAY FOR JOHNSON AND NATRONA
COUNTIES. ONCE THE PRECIPITATION CHANGES TO SNOW, EXPECT ALL SNOW
THROUGH THE EVENT. ROAD IMPACTS REMAIN IN QUESTION DUE TEMPS IN
THE 30S, BUT SUSPECT THE RATE OF THE SNOWFALL THIS MORNING SHOULD
MAKE BECOME SLICK THIS MORNING, BEFORE LIKELY IMPROVING IN THE
AFTERNOON. HOWEVER, THE HEAVY SNOW SHOWERS THIS AFTERNOON COULD
RESULT IN WET ROADS QUICKLY BECOME SLICK AND SNOW COVERED AGAIN.
THE HIGH WIND WARNING REMAINS IN EFFECT FOR JOHNSON COUNTY.
TONIGHT, MODELS SHOW A SHORTWAVE IN THE STRONG NORTHWEST FLOW
PULLING ACROSS THE AREA. THERE IS ALSO SOME UPPER JET FORCING
WHICH WILL ALLOW FOR WIDESPREAD SNOWFALL OVER THE FAR
WEST/NORTHWEST LAST TONIGHT INTO MONDAY MORNING. SNOW
ACCUMULATIONS SHOULD BE LIGHT, BUT MAIN CONCERN IN THIS PATTERN IS
FOR GRAND TARGHEE AND POSSIBLY THE ALPINE AREA GETTING HEAVIER
SNOW THAN WHAT MODEL PRECIPITATION AMOUNTS WOULD SUGGEST.
BY MIDDAY MONDAY INTO THE AFTERNOON, THE FORECAST AREA BEGINS TO
BE ON THE ANTI-CYCLONIC SIDE OF THE UPPER FLOW WHICH SHOULD
DECREASE THE COVERAGE OF SNOW SIGNIFICANTLY.
TUESDAY, PERSISTENT MOIST NORTHWEST FLOW WILL CONTINUE PERIODS OF
SNOW OVER THE NORTHWEST.
LONG TERM
(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 415 AM MDT SUN OCT 20 2019
A COLD FRONT WILL MOVE INTO THE STATE ON WEDNESDAY. WITH THIS
SYSTEM, THE SHOWERS IN THE NORTHWEST WILL PUSH EAST OF THE DIVIDE,
SPREADING FURTHER SOUTH INTO PORTIONS OF CENTRAL WYOMING. THE
SHOWERS WILL BE IN THE REGION THROUGH THURSDAY. GUSTY WINDS WILL
ALSO ACCOMPANY THIS NEXT SYSTEM ACROSS MUCH OF THE AREA. THURSDAY
LOOKS TO BE THE COLDEST MORNING WITH THE MODELS SHOWING H7
TEMPERATURES AT -8 TO -14 C FOR SURFACE TEMPS IN THE TEENS AND LOW
TO MID 20S. THE SHOWERS WILL DIMINISH LATER IN THE DAY FOR DRIER
CONDITIONS.
FRIDAY WILL SEE SIMILAR MORNING LOWS, HOWEVER IT WILL BE A FAIRLY
DRY DAY. MODELS ARE INDICATING A NEW SYSTEM MOVING INTO THE NORTH ON
SATURDAY, BUT IT THERE IS TOO MUCH UNCERTAINTY THIS EARLY IN THE
FORECAST PERIOD.
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 415 AM MDT SUN OCT 20 2019
WEST OF THE CONTINENTAL DIVIDE...KRKS, KJAC, KBPI, KPNA TERMINAL
SITES.
TODAY WILL SEE SCATTERED SNOW SHOWERS IN NW WY WITH ISOLATED SNOW
SHOWERS ELSEWHERE. A GUSTY WIND WILL BE COMMON AT THE TERMINAL
SITES, DIMINISHING THIS EVENING. SNOW SHOWERS WILL INCREASE IN
COVERAGE OVER THE WEST AFTER 03Z, CONTINUING THROUGH 12Z MONDAY. THE
TERMINAL SITES WILL HAVE VFR CONDITIONS. KJAC MAY SEE MVFR
CONDITIONS AT TIMES DUE TO REDUCED VISIBILITY AND LOWER CEILINGS.
MOUNTAINS WILL BE OBSCURED AT TIMES.
EAST OF THE CONTINENTAL DIVIDE...KCPR, KLND, KRIW, KCOD, KWRL
TERMINAL SITES.
AT 12Z, AREAS OF SNOW WILL OCCUR ALONG AND EAST OF A LINE FROM KCOD
TO KRIW TO KCPR. HERE MVFR CONDITIONS WILL PREVAIL WITH LOCAL IFR
CONDITIONS. THIS AREA OF SNOW WILL CONTINUE THROUGH 21Z BEFORE
DECREASING BY 00Z. EXPECT MOUNTAINS TO BE FREQUENTLY OBSCURED TODAY.
A GUSTY WIND WILL BE COMMON TODAY, DECREASING THIS EVENING. VERY
WINDY CONDITIONS WILL OCCUR AT KBYG AIRPORT TODAY WITH WIND GUSTS AS
HIGH AS 50 KNOTS.
AFTER 00Z, SCATTERED SNOW SHOWERS WILL OCCUR WITH LOCAL MVFR
CONDITIONS THROUGH 06Z MONDAY, THEN DECREASING SNOW SHOWERS AFTER
06Z.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
FIRE WEATHER
ISSUED AT 415 AM MDT SUN OCT 20 2019
UNSEASONABLY COLD AND BLUSTERY TODAY AND MONDAY. THE SNOW WILL END
ACROSS MUCH OF THE WEST BY MIDDAY, BUT SOME SIGNIFICANT SNOWFALL
AND STRONG WIND IS EXPECTED ACROSS JOHNSON AND NATRONA COUNTIES
TODAY. THE SNOW OVER THE EAST WILL END BY EARLY EVENING, BUT
ANOTHER ROUND OF SNOW WILL IMPACT THE WEST BEGINNING AROUND
MIDNIGHT LASTING THROUGH MONDAY MORNING. HOWEVER ACCUMULATIONS
WILL BE LIGHTER THAN WHAT OCCURRED WITH THE PAST SYSTEM. ANOTHER
STRONG STORM SYSTEM WILL IMPACT THE AREA TUESDAY NIGHT AND
WEDNESDAY WITH THE BULK OF THE SNOWFALL ACROSS NORTHERN AND
CENTRAL WYOMING.
RIW WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL NOON MDT TODAY FOR WYZ001-002-
013>015-023-024-027.
WINTER STORM WARNING UNTIL NOON MDT TODAY FOR WYZ012.
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ010-
011-020-022.
HIGH WIND WARNING UNTIL 6 PM MDT THIS EVENING FOR WYZ010.
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ008-
009.
SHORT TERM...MURRELL
LONG TERM...SWANSON
AVIATION...ROSS
FIRE WEATHER...MURRELL
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