448
FXUS65 KBOI 011747
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1147 AM MDT TUE SEP 1 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- CONVECTIVE POTENTIAL INCREASES TODAY AND WEDNESDAY WITH
ISOLATED TO SCATTERED THUNDERSTORMS MAINLY ACROSS THE
MOUNTAINS OF CENTRAL IDAHO AND EASTERN OREGON.
- A STRONG LOW PRESSURE SYSTEM LATER THIS WEEK WILL BRING
COOLER AND WINDIER CONDITIONS WITH PERIODS OF SHOWERS AND
THUNDERSTORMS, ESPECIALLY TO OREGON AND WEST-CENTRAL IDAHO.
SHORT TERM /THROUGH THURSDAY NIGHT/
ISSUED 315 AM MDT TUE SEP 1 2026
AN ACTIVE AND PROGRESSIVE PATTERN WILL UNFOLD ACROSS SOUTHEAST OREGON
AND SOUTHWEST IDAHO THROUGH THE SHORT TERM PERIOD AS AN EXPANSIVE UPPER
LEVEL LOW PRESSURE SYSTEM MOVES TOWARD THE PACIFIC NORTHWEST COAST.
SOUTHWESTERLY FLOW ALOFT HAS BROUGHT INCREASING PACIFIC MOISTURE. THIS
COMBINED WITH AN APPROACHING SHORTWAVE, AT 2 AM MDT NEAR CENTRAL
CALIFORNIA, SHOULD INITIATE MOSTLY VIRGA SHOWERS ACROSS SOUTHWEST OREGON
THROUGH THE REMAINING MORNING HOURS. GIVEN THE VERY DRY BOUNDARY LAYER,
RAINFALL WILL BE LIMITED. HOWEVER, GUSTY OUTFLOW WINDS ARE POSSIBLE
WITH THE STRONGER SHOWERS. AS THE SHORTWAVE CONTINUES NORTH-NORTHEAST
TODAY, DYNAMIC LIFT COMBINED WITH DAYTIME HEATING WILL TRIGGER CONVECTIVE
DEVELOPMENT BY THIS AFTERNOON. THE HIGHEST THUNDERSTORM POTENTIAL WILL
REMAIN FOCUSED OVER THE HIGHER TERRAIN OF CENTRAL IDAHO AND THE WESTERN
MAGIC VALLEY. AGAIN, GIVEN THE DRY BOUNDARY LAYER, STORMS TODAY WILL
BE CAPABLE OF PRODUCING LOCALIZED GUSTY OUTFLOW WINDS UP TO 45 MPH
AND SMALL HAIL. VALLEYS IN SOUTHWEST IDAHO MAY END UP LARGELY DRY-SLOTTED,
THOUGH MID AND HIGH LEVEL CLOUDINESS WILL INCREASE. TEMPERATURES WILL
PEAK AROUND 5 DEGREES ABOVE SEASONAL NORMALS, WITH VALLEY HIGHS
TOUCHING THE UPPER 80S TO NEAR 90 DEGREES.
A BRIEF BREAK IS EXPECTED LATE TUESDAY EVENING BEFORE THE NEXT TROUGH
EJECTS NORTHEASTWARD FROM THE MAIN LOW CIRCULATION WEDNESDAY MORNING.
THIS NEGATIVELY TILTED TROUGH IS STRONGER THAN TODAY'S, WHICH SHOULD
BE ENOUGH FOR SOME ISOLATED SHOWERS AND THUNDERSTORMS WEDNESDAY MORNING,
THOUGH THE LACK OF SURFACE INSTABILITY WILL BE A LIMITING FACTOR.
BETTER INSTABILITY SHOULD EXIST ACROSS THE CENTRAL IDAHO MOUNTAINS EARLY
WEDNESDAY AFTERNOON, WHICH COULD ALLOW FOR INCREASED THUNDERSTORM COVERAGE
CAPABLE OF HEAVY RAIN AND SMALL HAIL. COOLER AIR WILL BEGIN TO NUDGE INTO
EASTERN OREGON, WHICH WILL LIMIT AFTERNOON THUNDERSTORM POTENTIAL THERE.
THE PRIMARY CHANGE IN THE WEATHER PATTERN ARRIVES LATE WEDNESDAY NIGHT
INTO THURSDAY AS A DEEPER UPPER LOW MOVES ONSHORE INTO THE PACIFIC
NORTHWEST. DYNAMIC FORCING INCREASES DRAMATICALLY THURSDAY INTO THURSDAY
NIGHT AS DEEP MOISTURE STREAMS INTO THE REGION FROM THE SOUTH AND
SOUTHWEST. EXPECT WIDESPREAD PRECIPITATION COVERAGE TO BUILD FROM WEST
TO EAST. PRECIPITABLE WATER VALUES WILL CLIMB INTO THE 70TH TO 75TH
PERCENTILE RANGE, SETTING THE STAGE FOR HEAVIER RAIN, ESPECIALLY
ACROSS SOUTHEAST OREGON AND THE CENTRAL IDAHO MOUNTAINS. THERE REMAINS
QUITE A BIT OF UNCERTAINTY WITH PRECIPITATION AMOUNTS THURSDAY, AS PWS
SHOWN IN THE MODELS DO NOT MATCH MODEL RAINFALL RATES GIVEN THE
SOUTHWEST FLOW PATTERN. THUNDERSTORMS EMBEDDED WITHIN THE BROADER
PRECIPITATION SHIELD THURSDAY AFTERNOON COULD ENHANCE LOCAL RAINFALL
RATES, BUT MODELS APPEAR TO BE OVERESTIMATING PRECIPITATION IN THIS
FALL PATTERN. HIGH TEMPERATURES ON THURSDAY WILL DROP SHARPLY, RUNNING
10 TO 15 DEGREES COOLER THAN WEDNESDAY.
LONG TERM /FRIDAY THROUGH TUESDAY/
ISSUED 315 AM MDT TUE SEP 1 2026
THE UPPER LEVEL LOW LOOKS TO STALL OR DRIFT SLOWLY ACROSS THE PACIFIC
NORTHWEST THROUGH FRIDAY BEFORE GRADUALLY WEAKENING OVER THE
WEEKEND.
A PROLONGED PERIOD OF RAINFALL THROUGH FRIDAY EVENING IS POSSIBLE AS
THE MAIN CORE OF UPPER DYNAMICS AND PLUME OF PACIFIC MOISTURE CROSS
SOUTHEAST OREGON AND SOUTHWEST IDAHO. SHOWERS AND EMBEDDED THUNDERSTORMS
WILL REMAIN WIDESPREAD. CLOSE TO HALF AN INCH OF RAINFALL IS POSSIBLE,
WITH LOCALLY HIGHER AMOUNTS THURSDAY THROUGH FRIDAY. PERSISTENT CLOUD
COVER AND PRECIPITATION WILL KEEP FRIDAY TEMPERATURES WELL BELOW NORMAL,
WITH VALLEY HIGHS ONLY IN THE UPPER 60S TO LOWER 70S.
FOR SATURDAY THROUGH TUESDAY, THE CLOSED LOW WILL TRANSITION INTO AN
OPEN TROUGH AND MOVE EASTWARD TOWARD THE NORTHERN ROCKIES. WHILE THE
HEAVIEST AND MOST WIDESPREAD RAIN WILL SHIFT EAST OF OUR AREA BY EARLY
SATURDAY, UNSETTLED CONDITIONS WILL PERSIST. SECONDARY SHORTWAVES
ROTATING THROUGH THE TROUGH WILL MAINTAIN DAILY CHANCES (20 TO 40
PERCENT) FOR AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS THROUGH EARLY
NEXT WEEK, PRIMARILY OVER MOUNTAINOUS TERRAIN. TEMPERATURES WILL BEGIN
A STEADY RECOVERY OVER THE WEEKEND AND INTO TUESDAY, THOUGH REMAINING
SLIGHTLY BELOW NORMAL FOR EARLY SEPTEMBER.
AVIATION /18Z TUESDAY THROUGH WEDNESDAY/
ISSUED 1133 AM MDT TUE SEP 1 2026
MID LEVEL MOISTURE STREAMING NORTHWARD ACROSS THE REGION AHEAD
OF AN APPROACHING TROUGH WILL SET THE STAGE FOR ISOLATED TO
SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THIS EVENING. GUSTY
WINDS WILL ACCOMPANY ANY STORMS THAT DEVELOP DUE TO DRY LOW
LEVELS. VFR CONDITIONS SHOULD BE DOMINANT, EXCEPT NEAR STRONGER
STORMS. ANOTHER ROUND OF SHOWERS WILL BE POSSIBLE OVERNIGHT,
WITH A STRONG SIGNAL OF PRECIPITATION AND POTENTIAL FOR MVFR/IFR
CONDITIONS MID TO LATE WEEK AS A TROUGH SETTLES OVER THE REGION.
SURFACE WINDS GENERALLY ESE 10-15 KT WITH HIGHER GUSTS, SHIFTING
TO THE SW/W AFTER 20Z. SW WIND BECOMING DOMINANT AFTER 12Z
WEDNESDAY. WINDS ALOFT AT 10KFT SSW 20-30 KT.
KBOI...VFR WITH ISOLATED SHOWERS AND THUNDERSTORMS POSSIBLE
THROUGH 00Z THIS EVENING. LITTLE PRECIPITATION EXPECTED, BUT
VARIABLE GUSTY WINDS AND A FEW LIGHTNING STRIKES ARE POSSIBLE
(15-20% CHANCE). SOUTHEAST SURFACE WINDS SHOULD DOMINATE, BUT
OUTFLOW WINDS FROM STORMS WILL MAKE FOR VARIABLE WINDS AT TIMES.
GUIDANCE SUGGESTS A TURN TO THE WSW AFTER 20Z, BUT STORM OUTFLOW
WILL COMPLICATE ANY SHIFT. SE WINDS TO RETURN OVERNIGHT, BEFORE
SW WINDS BEGIN TO DOMINATE BY LATE MORNING WEDNESDAY. ANOTHER
ROUND OF SHOWERS (VFR) POSSIBLE EARLY WEDNESDAY.
BOI WATCHES/WARNINGS/ADVISORIES
ID...OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
AVIATION.....MC
SHORT TERM...JDS
LONG TERM....JDS
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