684
FXUS65 KBOI 181149
AFDBOI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
549 AM MDT MON MAY 18 2026
UPDATE
UPDATED AVIATION DISCUSSION.
KEY MESSAGES
- MOUNTAIN SHOWERS ON MONDAY, OTHERWISE DRY, BREEZY AND
SLIGHTLY WARMER.
- DRY WITH TEMPERATURES WARMING BACK ABOVE NORMAL STARTING ON
WEDNESDAY.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED 257 AM MDT MON MAY 18 2026
THE TIGHT SURFACE PRESSURE GRADIENT BEHIND AN EASTWARD EXITING
LOW PRESSURE SYSTEM WILL CONTINUE TO GENERATE BREEZY NORTHWEST
WINDS TODAY ACROSS MUCH OF THE AREA. WIND GUSTS BETWEEN 25 AND
35 MPH CAN BE EXPECTED THIS AFTERNOON, THOUGH THEY WILL NOT BE
QUITE AS STRONG AS WHAT WAS OBSERVED ON SUNDAY. WHILE A STABLE
AIR MASS DOMINATES THE LOWER ELEVATIONS, LINGERING AFTERNOON
INSTABILITY WILL SUPPORT A SLIGHT CHANCE OF LIGHT SHOWERS OVER
THE MOUNTAINS TODAY, WITH MINIMAL ACCUMULATION EXPECTED.
NORTHWEST FLOW ALOFT WILL CARRY INTO TUESDAY AS HIGH PRESSURE
BUILDS OVER THE PACIFIC. A MORE STABLE AND DRY AIR MASS WILL
KEEP CONDITIONS CLEAR ACROSS THE REGION, ALLOWING TEMPERATURES
TO WARM BACK TO NEAR NORMAL VALUES FOR THIS TIME OF YEAR.
BY WEDNESDAY, AN EMBEDDED SHORTWAVE TROUGH WILL MOVE THROUGH THE
INTERMOUNTAIN WEST, TRACKING ACROSS OUR AREA INTO WEDNESDAY
NIGHT. THIS SYSTEM WILL BRING AN INCREASE IN CLOUD COVER ALONG
WITH LIGHT, ISOLATED SHOWERS PRIMARILY FOCUSED ACROSS THE WEST
CENTRAL MOUNTAINS OF IDAHO. THE ARRIVAL OF THIS SHORTWAVE AND
ITS ASSOCIATED CLOUD COVER WILL ALSO WORK TO SLOW DOWN THE
OVERALL WARMING TREND AS WE TRANSITION INTO THE LONG TERM
PERIOD.
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED 257 AM MDT MON MAY 18 2026
A TROUGH OVER MONTANA WILL DIG INTO SOUTHERN IDAHO ON THURSDAY,
BRINGING COOLER TEMPERATURES AND A SLIGHT CHANCE OF HIGH TERRAIN
SHOWERS (10-20% CHANCE). THIS TROUGH WILL QUICKLY MOVE EAST ON
FRIDAY, BRINGING A RETURN TO DRY NORTHWEST FLOW THROUGH SATURDAY
WITH TEMPERATURES 5-10 DEGREES ABOVE NORMAL. A WEAK SHORTWAVE
PASSAGE WILL BRING ANOTHER LOW CHANCE OF SHOWERS OVER HIGH TERRAIN
LATE SATURDAY INTO SUNDAY, BUT FORECAST CONFIDENCE IS VERY LOW. BY
SUNDAY, A RIDGE OF HIGH PRESSURE WILL BUILD INTO THE REGION,
BRINGING WARM AND DRY CONDITIONS AHEAD OF A STRONG UPPER LEVEL LOW
DIVING DOWN OFF THE BRITISH COLUMBIA COAST. MODELS DIVERGE
SUBSTANTIALLY ON THE PATH OF THIS UPPER LEVEL LOW EARLY NEXT WEEK,
WITH SOME MEMBERS (ECMWF) BRINGING THIS LOW DIRECTLY OVER THE REGION
BY MONDAY EVENING. CURRENT FORECAST DOES NOT FAVOR THIS OUTCOME,
WITH A STRONG BIAS TOWARDS THE WARM AND DRY SCENARIO ON MONDAY.
AVIATION /12Z MONDAY THROUGH TUESDAY/
ISSUED 539 AM MDT MON MAY 18 2026
GENERALLY VFR. PATCHY FOG/STRATUS IN SHELTERED MTN VALLEYS THROUGH
MORNING. SCATTERED SHOWERS REDEVELOP MONDAY PM ACROSS E OREGON AND
MTNS OF SW IDAHO. BRIEF MVFR/IFR AND OBSCURATION IN MTN PRECIP.
MONDAY SNOW LEVELS: 5500-6500 FT MSL. SURFACE WINDS: W-N 10-20 KT
WITH AREAS OF GUSTS TO 20-25 KT. WINDS ALOFT AT 10KFT MSL: N-NE 20-
35 KT.
KBOI...VFR. FOOTHILL SHOWERS RETURN MONDAY PM. SURFACE WINDS: NW
10-18 KT WITH GUSTS AROUND 25 KT, DECREASING TO SW-NW 4-8 KT
AFTER TUES/03Z.
BOI WATCHES/WARNINGS/ADVISORIES
ID...FREEZE WARNING UNTIL 8 AM MDT THIS MORNING FOR IDZ016.
OR...NONE.
WWW.WEATHER.GOV/BOISE
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSBOISE
WWW.X.COM/NWSBOISE
AVIATION.....SA
SHORT TERM...JDS
LONG TERM....SA
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