222
FXUS65 KBOI 311207
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
607 AM MDT MON AUG 31 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- WARM TODAY AND TUESDAY.
- CHANCE OF THUNDERSTORMS IN S-CENTRAL ID MON, AND CENTRAL ID
TUE AFTERNOONS.
- A STRONG LOW PRESSURE SYSTEM EXPECTED LATER THIS WEEK WILL
BRING COOLER, WINDIER, AND WETTER CONDITIONS.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED 302 AM MDT MON AUG 31 2026
TRANSIENT UPPER LEVEL SHORTWAVE RIDGING BUILDS OVER THE REGION
TODAY, INITIATING A NOTABLE WARMING TREND ACROSS SOUTHEAST
OREGON AND SOUTHWEST IDAHO. HIGH TEMPERATURES TODAY WILL REBOUND
NEAR SEASONAL NORMALS, REACHING THE MID TO UPPER 80S IN LOWER
VALLEY LOCATIONS. THE RETURN OF SOUTHWESTERLY FLOW WILL ALLOW
FOR MOISTURE TO SPREAD NORTHWARD INTO SOUTH-CENTRAL IDAHO THIS
AFTERNOON AND EVENING. A WEAK SHORTWAVE TRAVERSING THE GREAT
BASIN THIS AFTERNOON WILL TRIGGER THUNDERSTORM DEVELOPMENT OVER
THE HIGHER TERRAIN SOUTH OF TWIN FALLS. OUTFLOW WINDS UP TO 40
MPH ARE POSSIBLE FROM THE STRONGEST STORMS.
BY TUESDAY, AN EXPANSIVE UPPER LEVEL LOW PRESSURE SYSTEM WILL
SETTLE ALONG THE PACIFIC NORTHWEST COAST. AS THE PRESSURE
GRADIENT TIGHTENS BETWEEN THIS APPROACHING TROUGH AND HIGH
PRESSURE TO OUR SOUTHEAST, SOUTHWESTERLY FLOW ALOFT WILL
STRENGTHEN SIGNIFICANTLY. THIS WARM ADVECTION PATTERN WILL PUSH
TUESDAY AFTERNOON MAXIMUMS AROUND 5 TO 10 DEGREES ABOVE NORMAL,
WITH VALLEY LOCATIONS CLIMBING INTO THE UPPER 80S TO NEAR 90
DEGREES. AFTERNOON SURFACE WINDS WILL ALSO BECOME BREEZY TO
LOCALLY GUSTY ON TUESDAY, PARTICULARLY ACROSS OPEN TERRAIN AND
HIGH ELEVATION ZONES. THIS COULD BE PROBLEMATIC FOR ONGOING
FIRES ACROSS THE BLM LANDS AS THE WINDS WILL COMBINE WITH LOW
HUMIDITIES.
SHORTWAVE ENERGY ROTATING AROUND THE PARENT TROUGH WILL SHIFT
INLAND TUESDAY NIGHT INTO WEDNESDAY. THIS WILL DRAW MONSOONAL
MOISTURE NORTHWARD INTO SOUTH-CENTRAL IDAHO WHILE PUSHING
DYNAMIC LIFT ACROSS SOUTHEAST OREGON AND THE WEST CENTRAL
MOUNTAINS. EXPECT SHOWER AND THUNDERSTORM CHANCES TO INCREASE
ACROSS EASTERN OREGON LATE TUESDAY NIGHT, SPREADING EASTWARD
INTO THE IDAHO MOUNTAINS ON WEDNESDAY. SOUTHWEST IDAHO VALLEYS
WILL LIKELY SIT WITHIN A DRY SLOT BETWEEN THE PRIMARY LOW CENTER
TO THE WEST AND DEEP MONSOONAL MOISTURE TO THE EAST, LIMITING
WIDESPREAD PRECIPITATION CHANCES FOR LOWER ELEVATIONS. HIGH
TEMPERATURES WILL BEGIN THEIR DOWNWARD TREND ON WEDNESDAY AS
CLOUD COVER INCREASES AND THE COOLER AIR MASS BEGINS TO IMPINGE
FROM THE WEST. THUNDERSTORMS WILL BE POSSIBLE AGAIN IN THE
MOUNTAINS OF CENTRAL IDAHO WEDNESDAY AFTERNOON AND EVENING.
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED 302 AM MDT MON AUG 31 2026
DETERMINISTIC AND ENSEMBLE CONSENSUS REMAINS STRONG FOR A DEEP
LONG-WAVE TROUGH AND CLOSED LOW PRESSURE SYSTEM TO STALL NEAR
THE OREGON AND WASHINGTON COASTLINE THROUGH MUCH OF THE LONG
TERM PERIOD. THIS POSITIONING KEEPS OUR FORECAST AREA SITUATED
IN PERSISTENT, MODERATELY UNSTABLE SOUTHWESTERLY FLOW ALOFT.
EMBEDDED SHORTWAVES WILL PERIODICALLY ORBIT THE MAIN LOW CENTER,
MAINTAINING PERSISTENT SHOWER AND THUNDERSTORM CHANCES THROUGH
THURSDAY AND FRIDAY, PARTICULARLY OVER SOUTHEAST OREGON AND THE
WEST CENTRAL IDAHO MOUNTAINS. SW IDAHO VALLEYS WILL REMAIN
SUSCEPTIBLE TO DRY SLOTTING, THOUGH ISOLATED ACTIVITY CANNOT BE
RULED OUT AS ATMOSPHERIC INSTABILITY PULSES EACH AFTERNOON.
A SUBSTANTIAL COOLING TREND WILL TAKE HOLD STARTING THURSDAY AS
LOWER HEIGHTS OVERSPREAD THE AREA. TEMPERATURES WILL FALL
ROUGHLY 5 TO 10 DEGREES BELOW SEASONAL AVERAGES, HOLDING VALLEY
HIGHS IN THE MID TO UPPER 70S THROUGH THE UPCOMING WEEKEND AND
INTO MONDAY. AFTERNOON WIND GUSTS WILL REMAIN ELEVATED DAILY,
FAVORING TYPICAL WIND-PRONE CORRIDORS INCLUDING SOUTHEAST OREGON
AND TERRAIN SOUTH OF THE SNAKE RIVER PLAIN. THE WIDE VARIATIONS
IN PRECIPITATION AMONG THE ENSEMBLE CLUSTERS IS DUE TO THE
POTENTIAL ENTRAINMENT OF TROPICAL MOISTURE FROM THE HURRICANE
FORECAST TO FORM OFF THE COAST OF BAJA CALIFORNIA OVER THE NEXT
48 HOURS. WHILE THE CONFIDENCE IN PRECIPITATION AMOUNTS IS LOW,
HIGH CONFIDENCE EXISTS FOR A PROLONGED COOL, WINDY, AND
PERIODICALLY UNSETTLED PATTERN THROUGH MONDAY.
AVIATION /12Z MONDAY THROUGH TUESDAY/
ISSUED 603 AM MDT MON AUG 31 2026
VFR. SHOWERS AND THUNDERSTORMS DEVELOPING SOUTH/EAST OF KTWF LATE
THIS AFTERNOON/EVENING. STORMS CAPABLE OF OUTFLOWS TO 25-35 KT.
SURFACE WINDS: LIGHT AND VARIABLE. WINDS ALOFT AT 10KFT MSL: W
5-15 KT.
KBOI...VFR. SURFACE WINDS: SOUTHEAST 5-10 KTS SWITCHING TO THE
WEST-NORTHWEST AROUND 00Z TUESDAY.
BOI WATCHES/WARNINGS/ADVISORIES
ID...NONE.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
AVIATION.....JDS
SHORT TERM...JDS
LONG TERM....JDS
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