010
FXUS65 KRIW 280819
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
219 AM MDT FRI MAR 28 2025
KEY MESSAGES
- SHOWERS WILL BE POSSIBLE (40%) THIS AFTERNOON OVER
NORTHWESTERN AND SOUTHERN PORTIONS. AN ISOLATED THUNDERSTORM
CANNOT BE RULED OUT. AFTERNOON HIGHS WILL BE 10 TO 15 DEGREES
COOLER, BUT STILL SLIGHTLY ABOVE NORMAL.
- SHOWERS WILL SPREAD TO JOHNSON/NATRONA COUNTIES THROUGH THE
NIGHT, WITH PRECIPITATION AMOUNTS OF 0.25" TO 0.50" POSSIBLE
THROUGH MIDDAY SATURDAY.
- PRECIPITATION CHANCES BECOME WIDESPREAD ACROSS THE FORECAST
AREA SATURDAY AFTERNOON, WITH RAIN AND/OR SNOW SHOWERS
POSSIBLE. RAIN WILL CHANGE OVER TO SNOW THROUGH THE NIGHT,
BECOMING FOCUSED OVER NORTHERN PORTIONS AND AREAS EAST OF THE
DIVIDE.
- A WETTER AND COOLER WEATHER PATTERN WILL REMAIN IN PLACE
THROUGH THE FIRST HALF OF THE WEEK NEXT WEEK.
DISCUSSION
ISSUED AT 208 AM MDT FRI MAR 28 2025
RAIN SHOWERS MOVED OVER YELLOWSTONE NP EARLY THIS MORNING, WITH THE
EXPECTED COLD FRONT LAGGING A COUPLE OF HOURS BEHIND. RAIN TO
RAIN/SNOW SHOWERS WILL OCCUR OVER FAR WESTERN PORTIONS FROM THE
INCOMING BAND OF PRECIPITATION FROM ID THROUGH 12Z. WINDS WILL TURN
WEST-NORTHWEST IN THE WAKE OF THE FRONT AS IT PROGRESSES EASTWARD
THIS MORNING, WITH GUSTS OF 35 TO 45 MPH OCCURRING BETWEEN 08Z AND
13Z. THESE WINDS WILL BE DECREASING TOWARD THE END OF THIS TIMEFRAME
AND THE COLD FRONT EXITING THE CWA BY 15Z.
TEMPERATURES WILL BE 10 TO 15 DEGREES COOLER TODAY, AS A RESULT OF
THE FRONT, WITH HIGHS RETURNING TO THE 50S AND 60S. WINDS WILL NOT
BE AS STRONG AS YESTERDAY EITHER. A SHORTWAVE TROUGH FROM AN UPPER
LOW SITTING OFF THE PACNW COAST WILL APPROACH THE REGION TODAY,
BRINGING THE CHANCE FOR WIDELY SCATTERED SHOWERS BACK TO THE CWA.
THE BEST CHANCES (30-50%) LOOK TO BE OVER FAR NORTHWESTERN PORTIONS
AND THE WIND CORRIDOR. THERE COULD BE ENOUGH INSTABILITY WITH THE
SHOWERS OVER YELLOWSTONE AND THE JACKSON VALLEY FOR A THUNDERSTORM
TO OCCUR. THE SHOWERS OVER THE WIND CORRIDOR WILL SPREAD INTO
JOHNSON COUNTY THROUGH THE EVENING, WITH A 40-70% CHANCE FOR SHOWERS
TO OCCUR IN THIS AREA (JOHNSON/NATRONA COUNTIES) AS WELL AS FAR
EASTERN SWEETWATER COUNTY FROM 04Z-09Z. THIS WILL BE DUE TO A
MIDLEVEL LOW THAT WILL MOVE OVER EASTERN SWEETWATER COUNTY TO
SOUTHERN NATRONA COUNTY DURING THIS TIME. PRECIPITATION WILL BECOME
CONFINED TO JOHNSON/NATRONA COUNTIES AFTER 09Z, WITH PRECIPITATION
AMOUNTS OF 0.3" TO 0.5" POSSIBLE THROUGH 18Z. THIS WILL BE DUE TO
FAVORABLE, PERSISTENT UPSLOPE FLOW AS THE MIDLEVEL LOW STALLS. SNOW
LEVELS LOOK TO DROP TO 7000FT TONIGHT, WHICH WILL LEAD TO A FEW
INCHES OF SNOW OVER THE BIGHORNS FROM THIS EVENT TONIGHT.
PRECIPITATION CHANCES WILL CONTINUE TO BE WIDESPREAD ACROSS THE CWA
SATURDAY, AS THE UPPER LOW MOVES ONSHORE AND OVER THE PACNW,
WEAKENING AND FILLING AS IT PROGRESSES EASTWARD. THE BEST CHANCES
WILL OCCUR BY LATE AFTERNOON WITH CHANCES FOR ISOLATED THUNDERSTORMS
BEING MORE WIDESPREAD AS WELL. THIS WILL BE DUE TO STEEP LOW LEVEL
LAPSE RATES. ALSO, THERE COULD BE RAIN AND/OR SNOW SHOWERS OCCURRING
SATURDAY AFTERNOON SO TECHNICALLY THERE COULD BE THUNDER SNOW. THE
MOST LIKELY LOCATION OF THIS OCCURRING WOULD BE OVER SOUTHERN
FREMONT COUNTY, FROM SOUTH PASS/RED CANYON TO JEFFREY CITY. APART
FROM THE REDUCTION IN VISIBILITY, THE MAIN IMPACT FROM ANY SNOW
SHOWER WILL BE SNOW AND WILL BE CONFINED TO GRASSY AREAS.
PRECIPITATION WILL CONTINUE THROUGH SATURDAY NIGHT WITH SNOW
OCCURRING FOR MOST AREAS BY 06Z SUNDAY. THE MAIN LOW WILL TAKE A
SIMILAR TRACK AS TONIGHT, MOVING ACROSS SWEETWATER COUNTY TOWARD
SOUTHERN NATRONA COUNTY BETWEEN 00Z AND 06Z SUNDAY. ANY SNOW
ACCUMULATION IN THE LOWER ELEVATIONS WILL OCCUR OVERNIGHT, WITH THE
BETTER ACCUMULATIONS STAYING IN GRASSY AREAS. CONFIDENCE FOR HIGHER
SNOWFALL TOTALS (8 TO 12 INCHES) ARE IN THE BIGHORNS AND THE
SOUTHERN END OF THE ABSAROKAS, WHILE THE TIMING FOR GOOD UPSLOPE
FLOW OVER THE EAST SLOPES OF THE WIND RIVER MOUNTAINS IS SUSPECT AT
THIS TIME. THERE COULD BE A VERY SHALLOW LAYER (SFC-750MB)
COMPONENT, WITH BACKING WINDS TO THE NORTHWEST AT 700MB. OTHERWISE,
SNOWFALL AMOUNTS IN THE MOUNTAINS WILL RANGE BETWEEN 3 TO 6 INCHES.
PRECIPITATION WILL END FROM THE SOUTHWEST TO THE NORTHEAST THROUGH
THE DAY SUNDAY AS THE LOW EXITS EASTWARD. A TRANSITORY RIDGE WILL BE
IN PLACE BY SUNDAY NIGHT, AS ANOTHER UPPER LOW MAKES ITS WAY TO THE
PACNW. THIS WILL KEEP PACIFIC MOISTURE STREAMING OVER THE REGION AND
COULD RESULT IN ISOLATED RAIN SHOWERS OVER WESTERN AND SOUTHERN
PORTIONS AND SNOW IN THE WESTERN MOUNTAINS. THIS WOULD LIKELY
CONTINUE AND BECOME MORE WIDESPREAD INTO TUESDAY.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 951 PM MDT THU MAR 27 2025
VFR CONDITIONS PREVAIL FOR MOST THE PERIOD FOR MOST TERMINALS.
WITH THE COLD FRONT, EXPECT A 1 TO 4 HOUR PERIOD OF RAIN/SNOW
SHOWERS. MOST LIKELY CHANCES (3 OUT OF 5) FOR PREVAILING LIGHT
RAIN OR SNOW IS AT KJAC. SHOWERS ARE ALSO POSSIBLE AT KBPI AND
KPNA (2 OUT OF 5) AND KCOD AND KWRL (1 OUT OF 4) WITH THE
FRONT.
WINDS WILL BECOME WESTERLY TO NORTHWESTERLY, BUT RETURN TO
TYPICAL NIGHTTIME DRAINAGE FLOWS 2 TO 4 HOURS AFTER THE FRONTAL
PASSAGE. SOUTHWEST WINDS WILL INCREASE AGAIN FRIDAY LATE MORNING
AND EARLY AFTERNOON FOR MANY TERMINALS. THE NEXT SYSTEM WILL
BRING A CHANCE (AROUND 1 IN 3) OF SHOWERS AND LOWERED CEILINGS
AND POSSIBLE MVFR AND POSSIBLE IFR CONDITIONS ROUGHLY ALONG AND
EAST OF A KRKS TO KRIW TO KWRL LINE (ABOUT A 1 IN 3 CHANCE) AFTER
02Z SATURDAY.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON SMOKE, ICING, AND TURBULENCE.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...LAVOIE
AVIATION...HATTINGS
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