170
NZUS99 KBOI 281207
TXTSFD
IDAHO STATE FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
507 AM MST SUN DEC 28 2025
HIGH PRESSURE WILL FIRMLY ESTABLISH ITSELF OVER IDAHO ON MONDAY AND REMAIN THE
DOMINANT WEATHER FEATURE THROUGH AT LEAST THURSDAY. THIS PERIOD WILL BE
CHARACTERIZED BY DRY CONDITIONS AND LIGHT WINDS ACROSS THE STATE. UNDER THIS
STABLE PATTERN, STRONG TEMPERATURE INVERSIONS ARE EXPECTED TO DEVELOP IN THE
VALLEYS, TRAPPING COLD AIR NEAR THE SURFACE WHILE TEMPERATURES MODERATE IN THE
HIGH COUNTRY. THESE INVERSIONS WILL LIKELY LEAD TO THE FORMATION OF WIDESPREAD
VALLEY FOG AND LOW STRATUS CLOUDS, PARTICULARLY DURING THE OVERNIGHT AND
MORNING HOURS. AIR STAGNATION IS ALSO A CONCERN, WITH POTENTIAL FOR DEGRADED
AIR QUALITY IN VALLEY LOCATIONS DUE TO POOR MIXING. BY LATE THURSDAY AND INTO
FRIDAY, THE RIDGE OF HIGH PRESSURE WILL SHIFT EASTWARD AS A PACIFIC STORM
SYSTEM APPROACHES THE REGION. THIS TRANSITION WILL BRING A RETURN OF UNSETTLED
WEATHER TO IDAHO FOR THE WEEKEND. PRECIPITATION CHANCES WILL INCREASE FROM WEST
TO EAST BEGINNING FRIDAY AND CONTINUING THROUGH SUNDAY, WITH SNOW EXPECTED IN
THE MOUNTAINS AND A MIX OF RAIN AND SNOW IN THE LOWER VALLEYS. BREEZY WINDS
ACCOMPANYING THIS SYSTEM WILL HELP SCOUR OUT THE COLD, STAGNANT AIR FROM THE
VALLEYS.
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