355
FXUS65 KBOI 180555
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1155 PM MDT THU SEP 17 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- UPPER LOW PRESSURE APPROACHING FROM NE CALIFORNIA WILL BRING
SHOWERS, SCATTERED STRONG THUNDERSTORMS, AND COOLER
TEMPERATURES THROUGH FRIDAY.
- STRONGEST THUNDERSTORMS IN CENTRAL IDAHO WITH GUSTY OUTFLOW
WINDS, HAIL, AND BRIEF HEAVY RAIN.
- GRADUAL WARMING AND DRYING TREND BEGINNING SATURDAY AND
CONTINUING THROUGH AT LEAST TUESDAY.
SHORT TERM /THROUGH SATURDAY NIGHT/
ISSUED 302 PM MDT THU SEP 17 2026
SOUTHWESTERLY FLOW AHEAD OF THE APPROACHING UPPER LOW WILL KEEP
TEMPERATURES WARM ACROSS THE REGION TODAY, WITH DRY AIR
PREVENTING STORM FORMATION OVER THE TREASURE VALLEY AND OWYHEE
MOUNTAINS IN IDAHO AND MALHEUR COUNTY IN OREGON. OTHERWISE,
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO RETURN THIS AFTERNOON
THROUGH EVENING OVER EASTERN OR AND THE WEST-CENTRAL ID
MOUNTAINS. LATEST SATELLITE IMAGERY SHOWS SOME CLEARING AND
CUMULUS BUILDUP OVER THE AFOREMENTIONED AREAS, ALIGNING WITH THE
EXPECTED INSTABILITY FOR THIS EVENING. GUSTY OUTFLOW WINDS UP
TO 50-60 MPH, SMALL HAIL, AND BRIEF HEAVY RAIN ARE THE MAIN
CONCERNS. ABUNDANT LIGHTNING IS ALSO LIKELY WITH THESE SCATTERED
STORMS IN THE AFTERNOON, AND FAST STORM MOTION WILL ALSO KEEP
RAINFALL AMOUNTS LOW, ESPECIALLY OVER SOUTHEAST OREGON. THIS
WILL INCREASE THE RISK FOR LIGHTNING IGNITIONS, PROMPTING THE
RED FLAG WARNING FOR SCATTERED LIGHTNING THROUGH 9 PM MDT THIS
EVENING. CONDITIONS WILL COOL 5-10 DEGREES FRIDAY AS THE LOW
PRESSURE SYSTEM MOVES OVERHEAD. SCATTERED SHOWERS AND ISOLATED
AFTERNOON THUNDERSTORMS WILL OCCUR AGAIN FRIDAY, WITH INCREASED
COVERAGE OVER THE TREASURE VALLEY AND MALHEUR COUNTY. SHOWERS
WILL THEN TAPER OFF OVER THE EASTERNMOST PORTIONS OF THE CWA ON
SATURDAY WITH HIGH PRESSURE BUILDING BACK IN OVER THE REGION.
LONG TERM /SUNDAY THROUGH THURSDAY/
ISSUED 302 PM MDT THU SEP 17 2026
HIGH PRESSURE REBUILDING OVER THE REGION WILL RETURN A SLIGHT
WARMING AND DRYING TREND SUNDAY THROUGH MONDAY, WITH PEAK
DAYTIME TEMPERATURES EXPECTED TO HOVER IN THE LOWER 80S FOR THE
TREASURE VALLEY AREA. LATE MONDAY THROUGH TUESDAY, THE AREA WILL
BE SANDWICHED BETWEEN A SHORTWAVE TROUGH STEERING ACROSS THE
LOWER GREAT BASIN AND A LONGWAVE PACIFIC TROUGH MOVING INTO THE
NORTHWEST COAST. THIS PATTERN WILL KEEP US IN MODERATED ZONAL
FLOW ALOFT ON TUESDAY, WITH SEASONABLE CONDITIONS AND A CHANCE
OF SHOWERS NEAR THE ID-NV BORDER. COME WEDNESDAY, THE AREA WILL
COME UNDER A STRONG SOUTHWEST FLOW AHEAD OF THE APPROACHING
PACIFIC TROUGH, CONTINUING DRY CONDITIONS AND TEMPERATURES 5 TO
10 DEGREES ABOVE NORMAL THROUGH THURSDAY.
AVIATION /06Z FRIDAY THROUGH SATURDAY/
ISSUED 1155 PM MDT THU SEP 17 2026
GENERALLY VFR. AREAS OF FOG OVERNIGHT RESULTING IN AREAS OF
IFR/LIFR, PRIMARILY IN E-OREGON. ISOLATED SHOWERS AND LIGHTNING
OVERNIGHT, BECOMING ISOLATED TO SCATTERED FRI/PM. OUTFLOWS OF AROUND
35 KT POSSIBLE OUT OF STRONGER STORMS. SURFACE WINDS OUTSIDE OF
STORMS: SW-NW 6-12 KT OVERNIGHT. THEN W-NW 5-15 KT WITH GUSTS TO 20-
25 KT FRI/PM. WINDS ALOFT AT 10KFT MSL: VARIABLE 5-15 KT.
KBOI...VFR. A SLIGHT CHANCE OF RAIN SHOWERS FRI/AM. ISOLATED TO
SCATTERED RAIN SHOWERS FRI/PM WITH A 10% CHANCE OF LIGHTNING AT THE
TERMINAL. FOOTHILLS WILL BE FAVORED FOR SHOWERS (60% CHANCE) AND
THUNDER (20% CHANCE). SURFACE WINDS: NW 5-15 KT.
WEEKEND OUTLOOK...BRIEF MVFR AND MOUNTAIN OBSCURATION IN LINGERING
SHOWERS NEAR KTWF-KJER ON SATURDAY, WITH SHOWERS TAPERING OFF BY
MIDDAY. EXPECT VFR CONDITIONS OTHERWISE THROUGH SUNDAY WITH VARIABLE
WINDS LESS THAN 10 KT OVERNIGHT AND IN HIGH TERRAIN AND NW 5-15 KT
IN VALLEYS DURING THE AFTERNOON.
BOI WATCHES/WARNINGS/ADVISORIES
ID...FIRE WEATHER WATCH FROM 3 AM MDT FRIDAY THROUGH FRIDAY EVENING
FOR IDZ403-421-423-424-426.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
AVIATION.....NF
SHORT TERM...JY/LC
LONG TERM....JY
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