715
FXUS65 KBOI 212339
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
539 PM MDT TUE JUL 21 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS TODAY, MAINLY
OVER THE HIGHER TERRAIN OF THE ID/NV BORDER AND WEST-CENTRAL
ID MOUNTAINS.
- SHOWER/THUNDERSTORM COVERAGE AND CHANCES INCREASE WEDNESDAY
WITH HEAVY RAINFALL POSSIBLE, ESPECIALLY OVER THE CENTRAL
IDAHO MOUNTAINS.
- HOT TEMPERATURES AND AREAS OF SMOKE THROUGH THE WEEK.
SHORT TERM /THROUGH THURSDAY NIGHT/
ISSUED 211 PM MDT TUE JUL 21 2026
LIGHT RAIN / VIRGA SHOWERS HAVE BEEN ONGOING THROUGH THE
MORNING INTO EARLY AFTERNOON, WITH SOME AREAS PICKING UP A
COUPLE HUNDRETHS. SOUTHERLY FLOW ALOFT WILL BE MAINTAINED TODAY
AS THE UPPER-LEVEL RIDGE REMAINS IN THE SOUTH-CENTRAL CONUS AND
A LOW PRESSURE SYSTEM MOVES NORTH ALONG THE PACIFIC NW COAST.
MONSOONAL MOISTURE WILL CONTINUE TO INCREASE OVER THE ENTIRE
AREA TODAY, AND EVEN MORE ON WEDNESDAY. PRECIPITABLE WATER WILL
CLIMB WELL OVER 1 INCH, RISING ABOVE THE 95TH PERCENTILE TODAY
AND CLOSER TO THE 99TH PERCENTILE ON WEDNESDAY, INDICATING A
VERY MOIST AIRMASS. INSTABILITY THIS AFTERNOON AND EVENING WILL
BE LIMITED AND FOCUSED OVER THE HIGHER TERRAIN, WHERE THERE IS A
20-40% CHANCE OF SHOWERS AND THUNDERSTORMS DEVELOPING.
THUNDERSTORMS MAY PRODUCE BRIEF HEAVY RAIN AND GUSTS 40-50 MPH.
SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE TONIGHT NEAR
THE NEVADA BORDER AS AN IMPULSE LIFTS NORTH. THE INCREASING
MOISTURE AND CLOUD COVER WILL BRING A FEW DEGREES OF COOLING
TODAY IN MOST AREAS COMPARED TO YESTERDAY, BUT IT WILL STILL BE
HOT. SIMILAR TO YESTERDAY, SMOKE SHOULD DECREASE IN THE
AFTERNOON AS DAYTIME HEATING MIXES OUT SMOKE NEAR THE SURFACE.
OUTSIDE OF STORMS, WINDS WILL BE LOCALLY BREEZY WITH GUSTS 15-25
MPH. NORTHWEST SURFACE WINDS WILL TRANSPORT SMOKE FROM
WILDFIRES IN OREGON BACK ACROSS THE AREA TONIGHT.
SOUTHERLY FLOW ALOFT WILL CONTINUE WEDNESDAY, WITH A SHORTWAVE
TROUGH EXPECTED TO AID CONVECTION IN THE AFTERNOON AND EVENING
ACROSS THE CENTRAL IDAHO MOUNTAINS, WHERE THE CHANCE OF SHOWERS
AND THUNDERSTORMS WILL RISE TO 40-90%. DEEP MOISTURE AND
EXPECTED SLOW STORM MOTION WILL RESULT IN THE POTENTIAL FOR
HEAVY RAIN AND FLASH FLOODING, ESPECIALLY OVER BURN SCARS AND
STEEP TERRAIN, INCLUDING THE WAPITI BURN AREA. QPF TOTALS NEAR
THE WAPITI HAVE BULLSEYES OF NEAR 0.5" IN 3 HOURS, AND NEAR
0.2" IN 1 HOUR. A FLASH FLOOD WATCH HAS BEEN ISSUED FOR THE
WAPITI BURN AREA FROM 12 PM MDT TO 9 PM MDT WEDNESDAY TO MATCH
THE CONFIDENCE FOR THIS THREAT. MODELS ALSO INDICATE THE
POTENTIAL FOR GUSTY OUTFLOW WINDS AS COLD POOLS FROM
THUNDERSTORMS DESCEND OVER THE MOUNTAINS, WITH WIND GUSTS FROM
40-50 MPH POSSIBLE. ELSEWHERE, A 20-40% CHANCE OF SHOWERS AND
THUNDERSTORMS WILL DEVELOP ACROSS THE HIGHER TERRAIN WITH A LESS
THAN 20% CHANCE IN THE LOWER ELEVATIONS. INCREASED
CLOUDS/SHOWERS WILL COOL MOST AREAS SLIGHTLY.
THE UPPER-LEVEL LOW MOVING UP THE PACIFIC NW COAST TUESDAY AND
WEDNESDAY WILL BEGIN TO MAKES ITS WAY ONSHORE THURSDAY, SHIFTING THE
FLOW ALOFT TO SOUTHWESTERLY. THIS WILL BEGIN TO PUSH MONSOONAL
MOISTURE TO THE EAST, BUT THERE WILL STILL BE ENOUGH MOISTURE
AND INSTABILITY FOR A 10-20% CHANCE OF SHOWERS AND
THUNDERSTORMS. DECREASING MOISTURE WILL ALLOW TEMPERATURES TO
RISE WITH LOWER VALLEY HIGHS ONCE AGAIN NEAR 100 DEGREES. BREEZY
CONDITIONS WILL DEVELOP ACROSS SOUTHEAST OREGON IN RESPONSE TO
THE SOUTHWEST FLOW. SMOKE MAY CONTINUE TO IMPACT THE AREA
WEDNESDAY AND THURSDAY WITH IMPROVEMENT EACH AFTERNOON.
LONG TERM /FRIDAY THROUGH TUESDAY/
ISSUED 211 PM MDT TUE JUL 21 2026
FRIDAY LOOKS VERY HOT AS THE UPPER HIGH OVER THE GREAT BASIN
BUILDS TO MAXIMUM AMPLITUDE WHILE AN UPPER TROUGH STAYS OFF THE
NORTHWEST COAST. HIGH TEMPS WILL REACH 102 TO 106 DEGREES IN THE
TREASURE VALLEY AND SOUTHERN MALHEUR COUNTY, WITH 90S IN THE
MOUNTAINS AS HIGH AS 5000 FEET. BY THEN MOST OF THE MONSOON
MOISTURE WILL BE EAST OF OUR CWA BUT EASTERN OWYHEE COUNTY AND
TWIN FALLS COUNTY WILL STILL BE IN IT WITH A SLIGHT CHANCE OF
THUNDERSTORMS. ON SATURDAY, UPPER WINDS WILL BECOME MORE WESTERLY
AS PART OF THE OFFSHORE TROUGH COMES INLAND. THIS MEANS SLIGHTLY
COOLER TEMPS ALTHOUGH STILL HOT, BUT ALSO DRIER. HOT, DRY WEATHER
WILL CONTINUE THROUGH TUESDAY.
AVIATION /00Z WEDNESDAY THROUGH THURSDAY/
ISSUED 529 PM MDT TUE JUL 21 2026
GENERALLY VFR, WITH AREAS OF MVFR/IFR DUE TO WILDFIRE SMOKE.
VISIBILITY WILL BE AT A MINIMUM OVERNIGHT, WITH IMPROVEMENT
DURING THE PEAK OF DAYTIME HEATING. SHOWERS AND THUNDERSTORMS
WILL BE POSSIBLE THIS EVENING AND OVERNIGHT NEAR THE NEVADA
BORDER, WITH MORE WIDESPREAD ACTIVITY WEDNESDAY AFTERNOON. HIGH
DENSITY ALTITUDE DUE TO CONTINUED HOT TEMPERATURES.
THUNDERSTORMS WEDNESDAY AFTERNOON COULD BRING TORRENTIAL RAIN,
WIND GUSTS TO 40 KT AND TERRAIN OBSCURATION. THE MOST LIKELY
IMPACTED AREA WILL BE IN CENTRAL IDAHO. SURFACE WINDS: W-NW
AROUND 10 KT, BECOMING VARIABLE LESS THAN 10 KT OVERNIGHT. WINDS
ALOFT AT 10KFT MSL: WSW AROUND 10 KT.
KBOI...VFR WITH MID/HIGH CLOUDS, THEN VISIBILITY REDUCTIONS DUE
TO WILDFIRE SMOKE OVERNIGHT INTO EARLY WEDNESDAY. HIGH DENSITY
ALTITUDE WEDNESDAY AFTERNOON. SHOWERS WILL TRY TO MAKE IT TO
THE TERMINAL WEDNESDAY AFTERNOON, AND THERE IS POTENTIAL FOR
GUSTY OUTFLOW WINDS WEDNESDAY EVENING. SURFACE WINDS: W-NW UP TO
15 KT WITH HIGHER GUSTS THIS EVENING, BECOMING VARIABLE LESS
THAN 10 KT OVERNIGHT. SWINGING BACK TO THE WNW WEDNESDAY
AFTERNOON.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR QUALITY ALERT UNTIL 3 PM MDT WEDNESDAY FOR IDZ011-012-014-
033.
FLASH FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY
EVENING FOR IDZ013.
OR...AIR QUALITY ALERT UNTIL 1 PM MDT /NOON PDT/ WEDNESDAY FOR
ORZ061>064.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
AVIATION.....MC
SHORT TERM...CH
LONG TERM....LC
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