472
FXUS65 KRIW 200445
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1045 PM MDT WED JUN 19 2019
SHORT TERM
THIS AFTERNOON THROUGH SATURDAY
SCATTERED SHOWERS AND THUNDERSTORMS HAVE STARTED THIS AFTERNOON
ACROSS NORTHWEST WY IN ADVANCE OF THE LEFT FRONT QUAD OF THE
UPPER LEVEL JET MOVING IN FAST FLOW OVER A LOW-LEVEL BOUNDARY
ALONG THE MT/WY BORDER. STRONG TO POSSIBLY SEVERE STORMS ARE
POSSIBLE LATE THIS AFTERNOON INTO THE EVENING HOURS FROM NORTH OF
CODY ESE INTO NORTHERN JOHNSON COUNTY. THESE STORMS ARE LIKELY TO
PRODUCE STRONG WIND AND POSSIBLY LARGE HAIL. THE SOUTHERN TWO-
THIRDS OF THE AREA WILL CONTINUE WITH WARMER DRIER AIR AND STRONG
WINDS WITH GUSTS UP TO 40 MPH. AS THE STORMINESS MOVES EASTWARD
TONIGHT, THE SURFACE WIND SHOULD SHIFT TO THE NORTH THROUGH MUCH
OF THE BIGHORN BASIN AND FROM JOHNSON INTO NATRONA COUNTY. A LARGE
SCALE TROUGH WILL MOVE FROM SOUTHERN BRITISH COLUMBIA INTO THE
NORTHERN ROCKIES THURSDAY, CONTINUING THE DRY SOUTHWEST FLOW INTO
THE SOUTHERN HALF OF THE FORECAST AREA. COOLER AIR WILL APPROACH
NORTHWEST WY BY THURSDAY EVENING, BRINGING 0C 700MB TEMPS TO YNP.
ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE THURSDAY AFTERNOON
AND EVENING NOT ONLY ACROSS THE FAR NORTHWEST MOUNTAINS, BUT ALSO
SWEETWATER COUNTY OFF THE UINTAS. THE GFS IS INDICATING MORE
SHOWERS ACTIVITY ACROSS SOUTHERN WY THURSDAY EVENING. A MID- AND
LOW- LEVEL COLD FRONT SHOULD THEN PUSH SOUTHEAST ACROSS THE AREA
FROM THURSDAY NIGHT INTO FRIDAY MORNING, WITH 700MB TEMPS COLDER
THAN -4C MOVING INTO NORTHWEST WY. THE LINGERING PRECIPITATION
OVER THAT AREA WILL LIKELY BRING SNOW TO THE HIGHER ELEVATIONS OF
YNP BY FRIDAY MORNING. THE REST OF THE AREA WILL SEE BREEZY
NORTHWEST WIND OVERNIGHT.
AN OVERALL TROUGH WILL REMAIN OVER THE NORTHERN ROCKIES WITH
EMBEDDED SHORTWAVE TROUGHS ROTATING AROUND THE FLOW. THIS PATTERN
WILL LIKELY KEEP BREEZY AND DRIER SOUTHWEST WIND THROUGH THE
SOUTHERN HALF OF THE AREA, AND BREEZY WEST WIND AND SCATTERED
SHOWERS AND THUNDERSTORMS TO THE NORTHERN HALF. FRIDAY WILL
CERTAINLY FEEL MUCH COOLER OVER THE STATE WITH AFTERNOON
TEMPERATURES ABOUT 15 DEGREES BELOW NORMAL. AS A STRONGER EMBEDDED
TROUGH MOVING INTO THE GREAT BASIN SATURDAY, THE OVERALL TROUGH
AXIS MOVES OVER THE AREA TO KEEP THE COOLER MOISTER AIR AROUND THE
AREA. ISOLATED TO SCATTERED SHOWERS ARE LIKELY AGAIN OVER WESTERN
AND CENTRAL WY WITH GENERALLY NORTH SURFACE WIND.
LONG TERM
SATURDAY NIGHT THROUGH WEDNESDAY
THE REMNANTS OF THE PINWHEELING UPPER LOW WILL FINALLY EXIT THE
REGION SATURDAY NIGHT. HOWEVER, THERE WILL BE ENOUGH INSTABILITY
IN THE AREA FOR WIDESPREAD SHOWERS AND THUNDERSTORMS SUNDAY. THE
REST OF THE FORECAST PERIOD WILL BE MARKED BY A SLOWLY BUILDING
RIDGE OF HIGH PRESSURE. THIS WILL BE DUE TO ANOTHER DIGGING UPPER
LOW OFF THE PACNW COAST MONDAY AND TUESDAY. AT THE SAME TIME, A
HIGH CENTER LINKED TO THE RIDGE WILL CONTINUE TO STRENGTHEN. BY
TUESDAY, THIS WILL BLOCK THE UPPER LOW AND CAUSE IT TO STAGNATE AS
THE RIDGE AXIS BUILDS OVER SOUTHERN CANADA.
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE
EVERY DAY, WITH THE BEST CHANCES OCCURRING OVER NORTHWEST PORTIONS
OF THE FORECAST AREA. THE HOTTEST TEMPERATURES OF THE YEAR SO FAR
COULD OCCUR BY WEDNESDAY, WITH HIGHS IN THE 90S FOR PLACES EAST OF
THE DIVIDE AND SWEETWATER COUNTY. WARM, GUSTY SOUTHWEST WINDS WILL
OCCUR ACROSS THE SOUTH AND THE WIND CORRIDOR TUESDAY AND
WEDNESDAY. RELATIVE HUMIDITY VALUES WOULD APPROACH CRITICAL VALUES
IN THIS PATTERN AS WELL. ALL OF THESE COMBINED FACTORS COULD LEAD
TO ELEVATED FIRE CONDITIONS, DESPITE THE RECENT WET WEATHER AND
CONTINUED GREEN UP CONDITIONS.
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1022 PM MDT WED JUN 19 2019
SHOWER ACTIVITY IS FADING FAST ACROSS NORTHERN WYOMING THIS
EVENING. A COUPLE SHOWERS MAY STILL BRIEFLY PASS WRL IN THE NEXT
COUPLE HOURS, BUT IMPACTS WILL BE MINIMAL. WINDS WILL REMAIN GUSTY
IN PLACES FOR A FEW MORE HOURS BEFORE FINALLY RELAXING DOWN TO
AROUND 5KTS. WINDS WILL AGAIN RAMP UP DURING THE MORNING TOMORROW,
WITH MOST SITES LIKELY TO SEE SUSTAINED WINDS AT 25KTS WITH
FREQUENT GUSTS REACHING 40KTS. THERE WILL BE A SMALL CHANCE FOR
SHOWERS NEAR COD/WRL DURING THE AFTERNOON, BUT CHANCES CURRENTLY
ARE TOO LOW TO NOTE IN TAFS. GUSTY WINDS WILL CONTINUE THROUGH AT
LEAST 06Z FOR AREAS GENERALLY WEST OF THE DIVIDE.
FIRE WEATHER
STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS NORTHERN
WYOMING LATE THIS AFTERNOON AND EVENING. STRONG TO POSSIBLY
DAMAGING WINDS AND LARGE HAIL WILL BE THE MAIN THREATS. ISOLATED
THUNDERSTORMS WILL ALSO BE POSSIBLE LATE THIS AFTERNOON ACROSS
CENTRAL PORTIONS. OTHERWISE, DRIER AND WARMER WEATHER WILL OCCUR
OVER THE SOUTHERN HALF OF THE FORECAST AREA THIS AFTERNOON. GUSTY
TO STRONG WINDS HAVE DEVELOPED THIS AFTERNOON OVER THESE AREAS,
AND WILL CONTINUE THROUGH MUCH OF THE EVENING. CRITICAL RH VALUES
WILL BE POSSIBLE OVER ZONE 279 THIS AFTERNOON. RH VALUES IN THE
UPPER TEENS WILL ALSO OCCUR IN THE SURROUNDING ZONES, INCLUDING
ZONE 283. MIXING AND SMOKE DISPERSAL WILL BE EXCELLENT TODAY, DUE
TO THE HIGH WINDS. AN APPROACHING LARGE SCALE SYSTEM IN THE
NORTHERN ROCKIES THURSDAY INTO FRIDAY WILL BRING MORE WINDY DRIER
AIR, A CHANCE OF SHOWERS BOTH NORTH AND SOUTH, BUT COOLER
TEMPERATURES TO THE AREA. A COLD FRONT SHOULD PUSH THROUGH
THURSDAY NIGHT.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...MCDONALD
LONG TERM...LAVOIE
AVIATION...STRAUB
FIRE WEATHER...LAVOIE/MCDONALD
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