923
FXUS65 KBOI 040820 CCA
AFDBOI
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE BOISE ID
218 AM MDT FRI SEP 4 2026
KEY MESSAGES
- SHOWERS AND THUNDERSTORMS WITH LOCAL HEAVY RAINS TODAY.
- AREAS OF VALLEY FOG EARLY SATURDAY MORNING.
- TEMPERATURES 10 TO 20 DEGREES BELOW NORMAL TODAY, THEN AROUND 10
DEGREES BELOW NORMAL SATURDAY AND SUNDAY.
- WARMING NEXT WEEK, WITH AN INCREASING CHANCE OF THUNDERSTORMS
WEDNESDAY AFTERNOON THROUGH FRIDAY.
SHORT TERM /THROUGH SUNDAY NIGHT/
AT 1 AM MDT RADAR SHOWED MODERATE TO HEAVY RAIN BAND EXTENDING
FROM WASHINGTON COUNTY/ID SSW-WARD THROUGH VALE, OR, INTO
CENTRAL MALHEUR COUNTY/OR. SINCE THEN THE BAND HAS SHIFTED
EASTWARD INTO ID AND HAS WEAKENED SINCE LATE EVENING WHEN IT
HAD HEAVIER RAIN IN EASTERN OR. RADAR SHOWED THE HEAVIEST RAIN
JUST WEST OF WEISER/ID AROUND MIDNIGHT MDT, AND A FLOOD ADVISORY
WAS ISSUED THERE FOR URBAN AND SMALL STREAM FLOODING UNTIL 3 AM
MDT. LATEST HI-RES MODELS SHOW THE RAIN BAND BECOMING STRONGER AGAIN
IN THE EASTERN PARTS OF BOISE AND VALLEY COUNTIES STARTING AROUND 3
AM MDT, AND ESPECIALLY THE WAPITI BURN SCAR. A FLASH FLOOD WATCH IS
IN EFFECT ON BURN SCARS THROUGH FRIDAY IN MOST OF OUR CWA (EXCEPT
SOUTH OF THE SNAKE BASIN), BUT GREATEST CONCERN IS ON THE WAPITI
BURN SCAR AS THE BAND SHOULD MOVE RIGHT OVERHEAD 4-5 AM MDT.
MEANWHILE, A COLD FRONT REACHED TWIN FALLS AND JEROME JUST BEFORE
MIDNIGHT WITH WESTERLY GUSTS TO 40 MPH. THE FRONT WILL CONTINUE EAST
TODAY WHILE COLDER AIR COMES IN FROM THE WEST. PRE-DAWN TEMPS WERE
IN THE 40S IN THE VALLEYS AND UPPER 30S IN THE MOUNTAINS, WITH SNOW
REPORTED ABOVE 5500 FEET IN EASTERN OR. THE COLD AIR AND PCPN WERE
DUE TO A DEEP UPPER LOW QUASI- STATIONARY ON THE OREGON COAST. THE
LOW IS FORECAST TO GRADUALLY FILL (I.E., WEAKEN) THROUGH SATURDAY
BEFORE MOVING INLAND SUNDAY AND THROUGH OUR NORTHERN ZONES SUNDAY
NIGHT. BACK TO TODAY, INSTABILITY WILL INCREASE THIS AFTERNOON
LEADING TO SCATTERED THUNDERSTORMS IN EASTERN OREGON LATE MORNING
THROUGH AFTERNOON, AND SOUTHWEST IDAHO (MAINLY OWYHEE COUNTY) BY MID-
AFTERNOON AND POSSIBLY THE TREASURE VALLEY LATE AFTERNOON. STRONGER
STORMS WILL FEATURE HEAVY RAIN AND HAIL. IMPROVING CONDITIONS WILL
TAKE PLACE OVERNIGHT THROUGH SATURDAY EVENING, BUT AREAS OF FOG WILL
FORM OVERNIGHT INTO SATURDAY MORNING AFTER TODAY'S RAIN. BECOMING
WETTER AGAIN SATURDAY NIGHT THROUGH SUNDAY NIGHT, WITH A CHANCE OF
THUNDERSTORMS SUNDAY AFTERNOON/ EVENING, AS THE UPPER LOW MOVES
THROUGH. TEMPS WILL STAY BELOW NORMAL THROUGH THE WEEKEND, BUT
SUNDAY SHOULD BE A COUPLE DEGREES WARMER THAN SATURDAY.
LONG TERM /MONDAY THROUGH FRIDAY/
HIGH PRESSURE ALOFT WILL REBUILD STARTING MONDAY AS THE UPPER
LOW EXITS THROUGH MONTANA INTO SOUTHERN CANADA. THE HIGHER
PRESSURE WILL BRING WARMER AIR BACK INTO OUR CWA THE REST OF
THE WEEK, WITH TEMPS RISING BACK TO NORMAL OR SEVERAL DEGREES
ABOVE WEDNESDAY AND BEYOND. THE NEXT UPPER LOW IS FORECAST TO
STAY OFF THE OREGON COAST, BUT LATEST MODELS (GFS MORE THAN
ECMWF) SHOW SOUTHWESTERLY FLOW ALOFT TAPPING INTO MOISTURE FROM
THE NEXT WESTWARD-MOVING HURRICANE IN THE PACIFIC SUBTROPICS.
WE THEREFORE HAVE A SLIGHT CHANCE OF THUNDERSTORMS IN THE
FORECAST AS EARLY AS WEDNESDAY AFTERNOON, BUT MORE LIKELY
THURSDAY AND FRIDAY.
AVIATION /06Z FRIDAY THROUGH SATURDAY/
ISSUED 1142 PM MDT THU SEP 3 2026
MOSTLY VFR. NUMEROUS RAIN SHOWERS THROUGH FRIDAY MORNING, THEN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FRIDAY AFTERNOON.
AREAS OF MVFR/IFR WITH HEAVIEST PRECIP. MOUNTAINS OBSCURED.
SNOW LEVELS 6.5K-7.5K FEET MSL IN E OREGON, AND 8K-9K FEET IN
W-CENTRAL ID. SURFACE WINDS: SW-NW 5-15 KT WITH AREAS OF 20-30
KT GUSTS, THEN VARIABLE 5-15 KT STARTING EARLY FRIDAY MORNING.
WINDS ALOFT AT 10KFT MSL: SW 15-25 KT.
KBOI...GENERALLY VFR. SHOWERS BRINGING MVFR AT TIMES, DECREASING
AFTER FRIDAY/10Z. THEN, A 20% CHANCE OF SHOWERS AND THUNDERSTORMS
FRIDAY AFTERNOON. SURFACE WINDS: NW 5-15 KT. GUSTS TO 20-25 KT
UNTIL EARLY FRIDAY MORNING, BECOMING LIGHT AND VARIABLE AS SHOWERS
EXIT MID-MORNING.
WEEKEND OUTLOOK...MOSTLY VFR. SCATTERED SHOWERS SATURDAY MORNING.
ACTIVITY DECREASING FROM SW TO NE LATE MORNING. THEN, SHOWERS
INCREASING AGAIN SUNDAY, WITH HIGHEST CHANCES (50-70%) OVER EAST
OREGON AND W-CENTRAL IDAHO. LOCALIZED MVFR/IFR AND MTN
OBSCURATION IN HEAVIEST PRECIP. PATCHY FOG/LOW STRATUS
DEVELOPMENT SATURDAY/ SUNDAY MORNINGS. SW-NW SURFACE WINDS 5-10
KT WITH PM GUSTS TO 20 KT.
BOI WATCHES/WARNINGS/ADVISORIES
ID...FLASH FLOOD WATCH THROUGH THIS EVENING FOR IDZ011-013.
OR...FLASH FLOOD WATCH THROUGH THIS EVENING FOR ORZ061>063.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
SHORT TERM...LC
LONG TERM....LC
AVIATION.....SH
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