438
FXUS65 KBOI 221649
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1049 AM MDT TUE SEP 22 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- WARM TEMPERATURES THROUGH THURSDAY, WITH VALUES 10 TO 15
DEGREES ABOVE NORMAL THURSDAY.
- CHANCE OF SHOWERS AND THUNDERSTORMS TUESDAY, MOSTLY ACROSS
HIGHER TERRAIN OF SOUTHWEST IDAHO.
- COOLER TEMPERATURES HEADING INTO THIS WEEKEND WITH A CHANCE
OF PRECIPITATION ACROSS SE OREGON AND PORTIONS OF SW IDAHO
FRIDAY.
SHORT TERM /THROUGH THURSDAY NIGHT/
ISSUED 246 AM MDT TUE SEP 22 2026
A CUT-OFF LOW OVER CALIFORNIA MOVES TOWARDS MONTANA TODAY,
COOLING AND MOISTENING MID-LEVELS. THE DESTABILIZATION OF MID-
LEVELS SUPPORTS THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS
THIS AFTERNOON. ON THE EAST SIDE OF THE LOW, IN IDAHO, HIGHER
ATMOSPHERIC MOISTURE WILL PRODUCE MORE WIDESPREAD CLOUD COVER
INHIBITING INSTABILITY. SO WHILE PRECIPITATION IS LIKELY IN
S-CENTRAL IDAHO, THE SNAKE PLAIN, AND CENTRAL IDAHO MOUNTAINS:
IT WILL LIKELY BE A SHALLOWER STORM MODE. SHALLOW DEVELOPMENT
SUPPORTS WIDESPREAD RAIN SHOWERS WITH WEAK EMBEDDED
THUNDERSTORMS IN THIS AREA.
MOISTURE WRAPPING AROUND THE CENTER
OF THE LOW WILL MOVE INTO A LESS UNSTABLE ENVIRONMENT IN
SOUTHEAST OREGON, BUT MORE SPARSE CLOUD COVER WILL STILL
SUPPORT CONVECTIVE INITIATION. A MORE DISCRETE STORM MODE IS
EXPECTED HERE, BUT THE LIMITED INSTABILITY WILL KEEP
THUNDERSTORMS WEAK. IN ALL AREAS, THE PRIMARY HAZARD WITH THIS
SYSTEM WILL BE GUSTY OUTFLOW WINDS NEAR PRECIPITATION. OUTFLOW
WINDS UP TO 45 MPH ARE POSSIBLE, ALONGSIDE LIGHTNING, SMALL
HAIL, AND BRIEF MODERATE- HEAVY RAINFALL. PRECIPITATION WILL
DISSIPATE AROUND SUNSET AS SURFACE HEATING ENDS AND THE LOW
MOVES EAST.
THE CUT-OFF LOW TRANSITIONS TO A LONG WAVE TROUGH AS IT REJOINS
THE JET STREAM POSITIONED NORTH OF OUR AREA. IN TURN, THIS
BRINGS THE JET SLIGHTLY FURTHER SOUTH, PUTTING US IN THE
BOUNDARY ZONE OF BUILDING HEIGHTS TO OUR SOUTH AND WARM
SOUTHWESTERLY FLOW DIRECTLY OVERHEAD AND TO THE NORTH. THE
SOUTHWESTERLY FLOW STRENGTHENS AND BECOMES MORE SOUTHERLY
THROUGH THURSDAY AS A STRONG LONGWAVE TROUGH DEVELOPS OVER THE
WEST COAST. THUS, TEMPERATURES WILL WARM SLIGHTLY TUESDAY INTO
WEDNESDAY, AND SHARPLY WEDNESDAY INTO THURSDAY MAKING THURSDAY
THE HOTTEST DAY IN THE 7-DAY FORECAST. TEMPERATURES RISE TO
10-15 DEGREES ABOVE NORMAL ON THURSDAY, WITH MANY LOWER VALLEYS
FORECAST TO SEE MAXIMUM TEMPERATURES IN THE LOW-MID 90S. THIS
FORECAST HAS TRENDED UPWARDS THE PAST FEW DAYS AS HIGH-
RESOLUTION MODELS BEGIN TO CAPTURE WINDS ON THURSDAY. AHEAD OF
THAT BUILDING COASTAL TROUGH, WINDS IN THE SNAKE PLAIN RISE TO
15 TO 25 MPH WITH WIND GUSTS UP TO 35 MPH. WITH WINDS COMING OUT
OF THE SOUTHEAST, OR DOWNSLOPE IN THE SNAKE PLAIN, WE COULD SEE
THE TEMPERATURE FORECAST CONTINUE TO TREND UPWARDS ON THURSDAY
DESPITE INCREASING CLOUDS AHEAD OF THE TROUGH. ELEVATED FIRE
WEATHER CONDITIONS DEVELOP DUE TO THE COMBINATION OF STRONG
WINDS AND HOT TEMPERATURES THAT AFTERNOON.
LONG TERM /FRIDAY THROUGH TUESDAY/
ISSUED 246 AM MDT TUE SEP 22 2026
SHARPLY COOLING TEMPERATURES, GUSTY WINDS, AND PRECIPITATION TO
THE WEST AND NORTH ARE ALL SLATED FOR LATER THIS WEEK AND
WEEKEND AS A STRONG COASTAL TROUGH AND ASSOCIATED COLD FRONT
MIGRATE INLAND. THE COLD FRONTAL PASSAGE ITSELF WILL OCCUR EARLY
FRIDAY AFTERNOON IN THE LATEST SYNOPTIC MODEL RUNS, WITH GOOD
AGREEMENT EVEN AMONGST FORECAST SYSTEMS AND PHYSICAL/AI CORES.
PRE- FRONTAL WINDS GUST 25 TO 35 MPH ACROSS THE AREA THAT
MORNING, WINDS SLIGHTLY WEAKEN AROUND SUNRISE, AND THEN GROW
EVEN STRONGER IN PEAK AFTERNOON HEATING AND IN THE POST-FRONTAL
ENVIRONMENT WITH GUSTS UP TO 30 TO 45 MP. WINDS REMAIN STRONG
30 TO 40 MPH THROUGH FRIDAY NIGHT IN THE SNAKE PLAIN. FOR MOST
OF THE AREA, THE STRONG FRONTAL WINDS ARE THE PRIMARY FORECAST
CONCERN. SHOWERS ALONG AND BEHIND THE FRONT WILL BE LIMITED TO
SOUTH- CENTRAL OREGON, NORTHEASTERN OREGON, AND NORTH-CENTRAL
IDAHO. SOUTHWESTERN IDAHO REMAINS DRIER DUE TO THE TROUGH
SWINGING NORTHWARD WHILE IT MOVES INLAND. IN AREAS EXPECTED TO
SEE SHOWERS, WEAK EMBEDDED THUNDERSTORMS ARE POSSIBLE TOO.
NOTABLE RAINFALL AMOUNTS ARE LIMITED TO HIGHER TERRAIN NEAR THE
BLUE MOUNTAINS IN OREGON AND THE WEST-CENTRAL MOUNTAINS IN
IDAHO, AROUND 0.1 INCHES THROUGH THE FRONTAL PASSAGE. FORECAST
AMOUNTS COULD RISE IF THE TROUGHS TRACK MOVES FURTHER SOUTH, OR
IF INSTABILITY INCREASES AND SHOWERS GROW STRONGER. TEMPERATURES
COOL ABOUT 5-10 DEGREES AS THE FRONT MOVES THROUGH ON FRIDAY,
AND ABOUT 10-15 DEGREES SATURDAY BEHIND THE FRONT.
COOLER TEMPERATURES STICK AROUND THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK AS A TRAILING TROUGH AMPLIFIES OFF THE COAST.
MAXIMUM TEMPERATURES SATURDAY THROUGH TUESDAY WILL BE AROUND
ROOM TEMPERATURE IN LOWER ELEVATIONS AND IN THE LOW 60S TO HIGH
50S IN HIGHER TERRAIN TOWNS. SOME MILD NORTHWESTERLY GUSTINESS
IS EXPECTED TO PERSIST THROUGH THE WEEKEND EACH AFTERNOON. THE
TRAILING TROUGH ARRIVES SUNDAY EVENING, LOOKING MUCH WEAKER THAN
THE TROUGH FRIDAY. PRECIPITATION IS POSSIBLE SUNDAY THROUGH
MONDAY IN NE OREGON AND N-CENTRAL IDAHO AGAIN, WITH 20 TO 30 MPH
GUSTS POSSIBLE IN THE SNAKE PLAIN AT THE SAME TIME. MODELS
DIVERGE BEYOND TUESDAY.
AVIATION /18Z TUESDAY THROUGH WEDNESDAY/
ISSUED 1049 AM MDT TUE SEP 22 2026
VFR WITH HIGH CLOUDS. ISOLATED SHOWERS/THUNDERSTORMS THIS
AFTERNOON. MAINLY NEAR KTWF/KJER, OVER THE CENTRAL ID MTNS, AND
SE OREGON HIGHLANDS. STORMS CAPABLE OF OUTFLOWS TO 25-35 KT,
LIGHTNING, AND MODERATE RAIN. SURFACE WINDS: BECOMING NW 5-15 KT
THIS AFTERNOON, THEN GENERALLY VARIABLE UNDER 10 KT OVERNIGHT.
WINDS ALOFT AT 10KFT MSL: VARIABLE 5-10 KT.
KBOI...VFR WITH FEW/SCT HIGH CLOUDS. SURFACE WINDS: BECOMING NW
5-10 KT THIS AFTERNOON. THEN S-SE 3-8 KT OVERNIGHT.
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.....NF
SHORT TERM...JM
LONG TERM....JM
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