301
FXUS65 KBOI 210550
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
1150 PM MDT MON JUL 20 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- HOT TEMPERATURES THIS WEEK, HOTTEST TODAY WITH A HEAT
ADVISORY IN THE SNAKE PLAIN AND HIGH DESERT.
- ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS NEAR THE
IDAHO/NEVADA BORDER TODAY.
- SHOWERS/THUNDERSTORMS INCREASE THROUGH MIDWEEK WITH HEAVY
RAINFALL POSSIBLE ESPECIALLY ON WEDNESDAY.
- AREAS OF SMOKE THROUGH THE WEEK.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED 225 PM MDT MON JUL 20 2026
THE CENTRAL U.S. UPPER-LEVEL RIDGE WILL CONTINUE TO BUILD
NORTHWEST ACROSS THE GREAT BASIN TODAY, CAUSING THE HOTTEST
TEMPERATURES ACROSS THE REGION THROUGH THE SHORT TERM PERIOD.
HIGHS WILL REACH THE UPPER 90S TO 105 DEGREES IN THE LOWER
VALLEYS, AND A HEAT ADVISORY REMAINS IN EFFECT FOR MUCH OF THE
LOWER ELEVATIONS ACROSS THE SNAKE PLAIN AND HIGH DESERT UNTIL 9
PM MDT TONIGHT. SOUTHERLY FLOW ALOFT WILL CONTINUE TO TRANSPORT
MONSOONAL MOISTURE INTO THE REGION, WITH WIDESPREAD PWAT VALUES
ABOVE THE 95TH PERCENTILE (OVER 1.00") TODAY. ISOLATED TO
SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP NEAR THE
IDAHO/NEVADA BORDER THIS AFTERNOON AND EVENING, WITH OUTFLOW
WIND GUSTS TO 40 MPH POSSIBLE. OUTSIDE OF STORMS, BREEZY
CONDITIONS WILL DEVELOP LATE TODAY WITH GUSTS 15-30 MPH, LOCALLY
UP TO 40 MPH IN EASTERN OREGON THIS EVENING. OVERNIGHT, REMNANTS
FROM THESE THUNDERSTORMS ARE EXPECTED TO MOVE NORTH ACROSS SW
IDAHO AS WEAK SHOWERS THAT ARE MOSTLY VIRGA. THERE IS A 10-15%
CHANCE THAT THESE INTENSIFY TO THUNDERSTORMS AS THEY MOVE OVER
THE LOWER SNAKE PLAIN OVERNIGHT AROUND 2 A.M. MDT AND FURTHER
INTO THE BOISE MOUNTAINS.
ON TUESDAY, SHOWER AND THUNDERSTORM POTENTIAL WILL EXPAND
ACROSS HIGHER ELEVATIONS, ESPECIALLY THE WEST-CENTRAL IDAHO
MOUNTAINS AND ID/NV BORDER. PWATS INCREASING FURTHER TUESDAY AS
WELL, WITH WIDESPREAD VALUES NEAR THE 97TH PERCENTILE (NEAR
1.15"). CONTINUED MONSOONAL MOISTURE STREAMING IN WILL ALSO
CREATE LIGHT RAIN / VIRGA SHOWERS OVER SE OREGON, WITH MINIMAL
QPF. TEMPERATURES WILL BE A FEW DEGREES COOLER THAN MONDAY.
BY WEDNESDAY, PRECIPITABLE WATER VALUES WILL RISE TO AROUND
1.25 INCHES, NEAR THE 99TH PERCENTILE. AN EMBEDDED SHORTWAVE
TROUGH WILL INTERACT WITH THIS MOISTURE, INCREASING SHOWER AND
THUNDERSTORM COVERAGE, ESPECIALLY ACROSS EASTERN AREAS WHERE
PRECIPITATION CHANCES WILL REACH 30-70%. THE HIGHER TERRAIN
ACROSS SOUTHEAST OREGON AND FAR SOUTHWEST IDAHO WILL SEE A
20-40% CHANCE OF PRECIPITATION WITH A LESS THAN 20% CHANCE IN
THE LOWER VALLEYS. WITH DEEP MOISTURE IN PLACE AND SLOW
EXPECTED STORM MOTION, THUNDERSTORMS WILL BE CAPABLE OF HEAVY
RAIN AND FLASH FLOODING, ESPECIALLY OVER BURN SCARS AND STEEP
TERRAIN. CURRENT LONG-RANGE FORECAST MODELS HAVE QPF BULLSEYES
OF NEAR 0.5" IN A 3 HOUR PERIOD, WHICH IS QUITE INTENSE. WITH
CONVECTIVE ALLOWING MODELS COMING INTO RANGE TOMORROW, THE
THREAT TIMING AND INTENSITY WILL BECOME CLEARER, HOWEVER THE
CONCERN LEVEL IS ALREADY HIGH. TEMPERATURES WILL BE SIMILAR TO
THAT ON TUESDAY.
WITH SOUTHERLY FLOW ALOFT, SMOKE SHOULD IMPROVE EACH AFTERNOON,
BUT NORTHWEST SURFACE WINDS ARE EXPECTED TO CONTINUALLY
TRANSPORT THE SMOKE BACK INTO SE OREGON AND SW IDAHO.
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED 225 PM MDT MON JUL 20 2026
DRIER THURSDAY AS UPPER FLOW CHANGES FROM SSW TO WSW AND SHIFTS THE
MONSOON FLOW EASTWARD AND OUT OF OUR CWA. THE MAIN UPPER HIGH OVER
THE INTERIOR WESTERN US WILL ALSO EXPAND WESTWARD OUT INTO THE
PACIFIC EFFECTIVELY PREVENTING MORE MONSOON MOISTURE FROM REACHING
OUR AREA. ON MONDAY AN UPPER TROUGH OFF THE NORTHWEST COAST WILL
COME INLAND ACROSS WA AND NORTHERN OR BEGINNING A BREEZY AND COOLER
PERIOD IN OUR CWA.
AVIATION /06Z TUESDAY THROUGH WEDNESDAY/
ISSUED 1146 PM MDT MON JUL 20 2026
GENERALLY VFR. AREAS OF MVFR-IFR VISIBILITY DUE TO WILDFIRE
SMOKE. ISOLATED/SCATTERED SHOWERS WILL SPREAD NORTH THROUGH
MORNING AND AFTERNOON. THUNDERSTORMS RE-DEVELOP NEAR NV-ID
BORDER IN THE AFTERNOON, WITH BRIEF HEAVY RAIN AND OUTFLOWS TO
40 KT. HIGH DENSITY ALTITUDE DURING AFTERNOON HEAT. SURFACE
WINDS: GENERALLY SW-NW 5-15 KT WITH LOCALIZED GUSTS AROUND 25
KT. WINDS ALOFT AT 10KFT MSL: VARIABLE 5-10 KT.
KBOI...GENERALLY VFR. POTENTIAL FOR MVFR VISIBILITY IN THE
EARLY MORNING HOURS DUE TO WILDFIRE SMOKE. A 15% CHANCE OF LIGHT
RAIN AFTER TUE/09Z. HIGH DENSITY ALTITUDE DURING AFTERNOON
HEAT. SURFACE WINDS: VARIABLE AROUND 6 KT THROUGH MORNING, THEN
NW 10-15 KT WITH GUSTS 20-25 KT IN THE AFTERNOON.
BOI WATCHES/WARNINGS/ADVISORIES
ID...AIR QUALITY ALERT UNTIL 3 PM MDT WEDNESDAY FOR IDZ011-012-014-
033.
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.....SH
SHORT TERM...CH
LONG TERM....LC
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