824
FXUS65 KBOI 252017
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
217 PM MDT MON AUG 25 2025
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 0.25–0.75 INCHES ARE EXPECTED ACROSS MUCH OF
SOUTHEAST OREGON AND SOUTHWEST IDAHO THROUGH FRIDAY MORNING,
WITH 1–2 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 30–60% 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.
AVIATION
ISOLATED THUNDERSTORMS ARE DEVELOPING THIS AFTERNOON AND
WILL LAST THROUGH THIS EVENING, CAPABLE OF PRODUCING OUTFLOW GUSTS
UP TO 40 KT AND LOCALLY HEAVY RAINFALL. SCATTERED SHOWERS CONTINUE
WITH LIGHT TO MODERATE RAINFALL. SOME REDUCTION IN VISIBILITY DUE TO
SMOKE AND MOUNTAIN OBSCURATION CONTINUES. SURFACE WINDS: VARIABLE 5-
15 KT. WINDS ALOFT AT 10KFT MSL: GENERALLY NE 5-15 KT.
KBOI...VFR, SOME HAZINESS FROM SMOKE CONTINUES TO REDUCE VISIBILITY.
LIGHT SHOWERS AND VIRGA ARE EXPECTED TODAY, WITH A 10% CHANCE OF
THUNDER THIS EVENING. GUSTY WINDS FROM DISTANT STORMS ARE MORE
LIKELY, WITH SPEEDS UP TO 40 KT. SURFACE WINDS 5-15 KT OUT OF THE SE
WITH GUSTS UP TO 25 KT, BECOMING E 5-10 KT THIS EVENING.
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
SHORT TERM...JDS
LONG TERM....JDS
AVIATION.....JM
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