370
FXUS65 KBOI 260301
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
901 PM MDT MON AUG 25 2025
DISCUSSION
EXTENSIVE CLOUD COVER CONTINUES TO IMPACT THE AREA
FROM THUNDERSTORMS ASSOCIATED WITH MONSOON MOISTURE TO THE
SOUTH. ISOLATED SHOWERS CONTINUE THIS EVENING, MAINLY ACROSS
EASTERN OR AND THE CENTRAL ID MOUNTAINS. THESE WILL TAPER OFF
WITH PARTIAL CLEARING OVERNIGHT. TUESDAY, SHOULD HAVE MORE
SUNNY BREAKS THAN TODAY, WHICH WILL AID IN THUNDERSTORM
DEVELOPMENT DURING THE AFTERNOON. THUNDERSTORMS ARE FORECAST TO
DEVELOP OVER THE HIGHER TERRAIN AND SLOWLY DRIFT NORTHWARD
THROUGH THE AFTERNOON AND EVENING. WHILE PRECIPITABLE WATER
REMAINS IN THE 99TH PERCENTILE FOR THIS TIME OF YEAR, MODELS
DIVERGE SIGNIFICANTLY ON WEDNESDAY, THE NAM/4KM NAM DEVELOPS A
DEEPER TROUGH OVER THE AREA THAN THE REST OF THE MODELS AND
SIGNIFICANTLY MORE PRECIPITATION THAN THE REST OF THE MODEL
ENSEMBLES. THE HRRR AND RRFS HIGH RESOLUTION MODELS FEATURE MUCH
LOWER PRECIPITATION AMOUNTS. THIS LINES UP WITH THE EC AND GFS
THAT ARE MUCH WEAKER WITH THE UPPER LEVEL TROUGH. FORECAST HAS
BEEN UPDATED TO LOWER TEMPERATURES ON WEDNESDAY.
AVIATION
ISOLATED SHOWERS/THUNDERSTORMS TONIGHT WILL BECOME
NUMEROUS BY TUESDAY AFTERNOON. OUTFLOW GUSTS TO 25-35 KT, HEAVY
RAIN, AND SMALL HAIL POSSIBLE. MVFR AND MTNS OBSCURED IN
MODERATE/HEAVY RAIN. VISIBILITY REDUCTIONS NEAR WILDFIRES. SURFACE
WINDS: VARIABLE UP TO 10 KT. WINDS ALOFT AT 10KFT MSL: VARIABLE 5-15
KT.
KBOI...VFR. SCATTERED SHOWERS/THUNDERSTORMS IN TREASURE VALLEY
TUESDAY AFTERNOON, WITH 40% CHANCE OF HITTING AIRPORT. OUTFLOW GUSTS
TO 25-35 KT GUSTS, MOD/HEAVY RAIN, AND SMALL HAIL POSSIBLE. THEN,
RAIN SHOWERS LIKELY (75% CHANCE) AT KBOI TUESDAY EVENING THROUGH
WEDNESDAY AFTERNOON. SHOWERS MAY BE HEAVY AT TIMES AND CREATE MVFR
VISIBILITY. SURFACE WINDS: VARIABLE AROUND 5 KT THIS EVENING,
BECOMING SE OVERNIGHT.
PREV DISCUSSION
SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT...MONSOONAL
MOISTURE WILL SURGE INTO THE REGION OVER THE NEXT THREE DAYS,
BRINGING ABNORMALLY HIGH MOISTURE CONTENT AND AN ELEVATED RISK
FOR EXCESSIVE RAINFALL AND FLASH FLOODING. A FLASH FLOOD WATCH
REMAINS IN EFFECT FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
EVENING.
AS OF 2 PM MDT, SHOWER ACTIVITY HAS INCREASED ALONG THE EASTERN
EDGE OF THE WEAK UPPER-LEVEL TROUGH JUST WEST OF THE FORECAST
AREA. THIS BAND OF SHOWERS EXTENDS FROM THE TREASURE VALLEY INTO
THE SOUTHERN SAWTOOTH MOUNTAINS AND WILL CONTINUE TO LIFT
NORTHWARD INTO THE CENTRAL IDAHO MOUNTAINS THROUGH THE EVENING.
UP TO A QUARTER OF AN INCH RAIN IS POSSIBLE WITH THIS BAND.
MEANWHILE, SLOW-MOVING THUNDERSTORMS HAVE ALREADY DEVELOPED
ALONG THE NEVADA BORDER WHERE SKIES HAVE CLEARED. THESE STORMS
WILL GRADUALLY SPREAD EAST-NORTHEAST INTO HARNEY AND MALHEUR
COUNTIES AND THE WESTERN MAGIC VALLEY LATER THIS AFTERNOON AND
EVENING WHERE BREAKS IN CLOUD COVER ALLOW FOR SURFACE HEATING.
EXPECT STORMS TO PRODUCE HEAVY RAINFALL ALONG WITH GUSTY OUTFLOW
WINDS UP TO 40 MPH.
MOISTURE WILL CONTINUE TO DEEPEN ACROSS THE AREA THROUGH
WEDNESDAY, WITH SHOWER AND THUNDERSTORM COVERAGE INCREASING. THE
MAIN CONCERN WILL BE EXCESSIVE RAINFALL, PARTICULARLY ON
WEDNESDAY WHEN INSTABILITY OVERLAPS WITH A SLOW-MOVING UPPER
TROUGH. PRECIPITABLE WATER VALUES CLIMB TO THE 97TH PERCENTILE
ACROSS SOUTHWEST IDAHO TUESDAY AND REACH THE 99TH PERCENTILE
WEDNESDAY. WHILE CLOUD COVER COULD LIMIT INSTABILITY AT TIMES,
THE POTENTIAL FOR HEAVY RAINFALL REMAINS ABOVE NORMAL. EFI
GUIDANCE FURTHER HIGHLIGHTS THE SIGNAL FOR UNUSUALLY HEAVY
RAINFALL OVER SOUTHWEST IDAHO AND SOUTHEAST OREGON.
RAINFALL TOTALS OF 0.25 TO 0.75 INCHES ARE EXPECTED ACROSS MUCH OF
SOUTHEAST OREGON AND SOUTHWEST IDAHO THROUGH FRIDAY MORNING, WITH 1
TO 2 INCHES POSSIBLE IN THE CENTRAL IDAHO MOUNTAINS, ESPECIALLY NEAR
MCCALL AND LOWMAN. WITH RAINFALL AMOUNTS NEAR OR ABOVE TYPICAL LATE-
AUGUST EXTREMES, THE RISK FOR LOCALIZED FLASH FLOODING WILL BE
HIGHEST IN BURN SCARS, STEEP TERRAIN, AND URBAN AREAS.
TEMPERATURES WILL TREND WELL BELOW NORMAL THROUGH THE PERIOD
UNDER WIDESPREAD CLOUDS, RAIN, AND TROUGH PASSAGE.
LONG TERM...THURSDAY THROUGH MONDAY...ENSEMBLE GUIDANCE NOW
FAVORS MONSOONAL MOISTURE LINGERING INTO THURSDAY, PARTICULARLY
ACROSS SOUTHWEST IDAHO WHERE THERE IS A 30 TO 60% CHANCE OF SHOWERS
AND THUNDERSTORMS. MEANWHILE, DRIER AIR WILL BEGIN TO SPREAD INTO
SOUTHEAST OREGON. IF THIS TREND HOLDS, THE FLASH FLOOD WATCH MAY
NEED TO BE EXTENDED INTO THURSDAY. MODELS REMAIN IN GOOD AGREEMENT
ON THE DEVELOPMENT OF AN UPPER RIDGE FRIDAY, WHICH WILL PERSIST INTO
EARLY NEXT WEEK, BRINGING DRY CONDITIONS AND A WARMING TREND WITH
TEMPERATURES RISING TO A FEW DEGREES ABOVE NORMAL.
BOI WATCHES/WARNINGS/ADVISORIES
ID...FLASH FLOOD WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
EVENING IDZ011>016-028>030-033.
OR...FLASH FLOOD WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
EVENING ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
DISCUSSION...KA
AVIATION.....SH
SHORT TERM...JDS
LONG TERM....JDS
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page