Princeton, Oregon Weather Forecast Discussion

453
FXUS65 KBOI 280245
AFDBOI
Area Forecast Discussion
National Weather Service Boise ID
845 PM MDT Sat Sep 27 2025
.DISCUSSION...The upper-level ridge will keep conditions warm
and mostly dry through much of Sunday, with highs approximately
10 degrees above normal across the area. However, increasing
southwesterly flow aloft will begin to draw moisture northward
from a cut-off low centered over southern Nevada and Utah. This
will bring a 10 to 20 percent chance of thunderstorms to the
Idaho-Nevada border late Sunday afternoon and evening.
Monday marks the beginning of a significant weather shift as a
large upper low reaches the Pacific Northwest and slowly moves
inland across the northern Rockies through Thursday. Widespread
rain along with embedded thunderstorms are expected, with the
heaviest precipitation forecast to fall Monday afternoon into
Tuesday. The latest guidance shows about a 50% chance of the
Treasure Valley receiving greater than a quarter of an inch of
total rainfall from Monday night into Tuesday, while rainfall
totals of 0.50 to 1.00 inches are possible in the mountains. The
current forecast handles this well, so no updates are needed at
this time.
&&
.AVIATION...VFR and clear skies overnight. Surface winds: Variable
less than 10kt except E-SE 5-10kt across the Snake River Plain.
Winds aloft at 10kft MSL: S-SW 10-20 kt.
KBOI...VFR with clear skies. Surface winds: E-SE around 5kt.
Sunday Outlook...VFR. Slight chance of showers/thunderstorms in S-
central Idaho Sunday afternoon and evening. Storms capable of
localized outflows up to 30 kt. Increasing mid/high-level clouds
Sunday. Surface winds: SE-SW 5-15 kt. Winds aloft at 10kft MSL: S-SW
15-25 kt.
&&
.PREV DISCUSSION...
SHORT TERM...Tonight through Monday night...Latest models
continue warm, dry weather through Sunday, except for a 10-20
percent chance of thunderstorms Sunday afternoon and evening
near the south-central ID/NV border due to a weak upper low
in NV. The strong Pacific cold front and supporting deep upper
trough in the Gulf of Alaska are now forecast to reach our CWA
a few hours later than previous forecast, with eastern Oregon
getting its first sprinkles before sunrise Monday, western
Idaho getting its first rain Monday morning, and central Idaho
Monday afternoon. The delay will also allow south-central Idaho
to stay warmer and drier than before through the morning hours.
Rainfall will maximize Monday night in Idaho while decreasing
in eastern Oregon. Rain amounts look less than before, with
Monday having generally less than 0.25 inch, and Monday night
around .50 inch in the Idaho mountains and 0.25 inch in the
Idaho valleys and eastern Oregon, with more to follow on
Tuesday. Instability supports a chance of thunderstorms Monday
afternoon and evening, more in Idaho than in Oregon. Winds will
stay light through Sunday, except SW gusts will increase to 30
mph in southern Harney County Sunday afternoon. Winds will
become west or northwest 10-20 mph behind the cold front Monday,
with strongest gusts (near 40 mph) in southern Harney County
Monday afternoon and evening.
LONG TERM...Tuesday through Saturday...A strong upper low over
the Western coast of British Columbia will continue to steer
shortwave troughs across the Northwest region Tuesday through
Saturday. Widespread precipitation and significant cooling are
expected throughout the area from Tuesday to Friday. Peak valley
temperatures are expected to trend down into the lower 70s
Tuesday and into the upper 60s Wednesday to the end of the week.
Tuesday afternoon will see favorable chances for thunderstorms,
mainly for Southwest Idaho. The expected cooling trend and
increasing cloud covers will mostly hinder convective potentials
through the rest of the week except Thursday, as an embedded
shortwave trough may develop thunderstorms over the central
mountains. The highest elevations may see a rain-snow mix
throughout the extended period. Long-term guidances generally
favor the upper low steering into the area as a longwave trough
Friday through Saturday. Saturday will mostly see precipitation
concentrated along higher elevations.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
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DISCUSSION...JDS
AVIATION.....TL
SHORT TERM...LC
LONG TERM....JY

NWS BOI Office Area Forecast Discussion