Nampa, Idaho 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

331
FXUS65 KBOI 130816
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
216 AM MDT Tue May 13 2025

.SHORT TERM...Today through Thursday night...As an upper low
pressure system moves overhead, showers and thunderstorms will
develop over SE Oregon and Idaho this afternoon. Thunderstorms
have the best chance of formation over terrain, but a stray
storm could drift into the lower elevations. There may be some
limiting factors for proper convection: PWs below 50th
percentile, and moist adiabatic lapse rates in the effective
layer will limit CAPE. Outflow gusts are possible outside of
stronger showers and storms, but DCAPE values generally less
than 400 J/kg and HRRR forecast wind gusts suggest peak outflows
may reach 40 mph. Still strong, but much less than what has been
possible the previous few days. Snow levels are around 6kft MSL
during precipitation, so minor accumulation (up to 3") is
possible across higher terrain. Snow accumulation is most likely
in the Boise Mountains Tuesday afternoon. The low exits eastward
on Wednesday, with decreasing precipitation chances but still
enough for isolated showers and storms Wednesday afternoon. With
the low overhead/exiting, general gusts of 25 to 35 mph are
expected across open terrain Tuesday/Wednesday afternoons. A
very weak and brief ridge moves in behind the low for Thursday.
While it was previously forecast to warm us up close to normal
for this time of year, it has weakened enough that temperatures
stay about 5 degrees below normal.


.LONG TERM...Friday through Tuesday...A weak upper level trough will
move through early Friday, leading to a chance of showers mainly in
the higher terrain on the Idaho side. Any rainfall will be fairly
light for this time of year. There is a slight chance of
thunderstorms in extreme SE Owyhee and southern Twin Falls counties.
Saturday, a stronger trough will move onshore, with significant
disagreement on the location of a closed upper low that is expected
to form Saturday afternoon. Some models have the closed low along
the CA-OR border, while others have it as far north as Seattle. The
location will have important implications for moisture transport and
convective potential. At this time, ensemble mean seems like the way
to go, so stuck with NBM guidance on precipitation and thunder
potential. The chance of rain reaches its highest level of the long
term period Saturday afternoon into the evening (60-80%), with
thunderstorms favored over the southern portion of the area in the
afternoon and in the southeast Saturday evening. This low should
push a cold front through Saturday night into Sunday morning, and
after highs just a few degrees below normal Friday and Saturday,
Sunday should see highs 5-10 degrees below normal. The chance of
rain decreases from west to east Saturday night and Sunday, with a
slight chance to chance remaining only on the Idaho side Sunday
afternoon. Thunderstorm chances move to the east Sunday, generally
from just east of McCall to Boise to central Owyhee County.

The trough axis will move off to the east Sunday night into Monday
morning, and enough moisture and cold air aloft will remain to
warrant 20-40% chance of showers over the higher terrain generally
east of McCall Monday, with even lower chances farther east Tuesday.
Thunderstorm potential should be limited to our far southeast
Monday, and gone altogether Tuesday. Temps are forecast to warm back
up to near normal by Tuesday. Winds will increase in Oregon
Saturday, then become even stronger as the trough axis moves
overhead and to our east Sunday. Gusts 30-35 mph are expected to be
common across lower elevations Sunday into Sunday evening. Gusty
winds will continue Monday and Tuesday, but are not expected to be
as strong as Sunday.

&&

.AVIATION...Mainly VFR. Scattered showers will move southward today,
mainly across the higher terrain. Isolated thunderstorms this
afternoon and evening have the potential to create localized
MVFR/IFR conditions and mountain obscuration. Snow levels will be 6-
7kft MSL today. Surface winds: W-NW 10-20 kt with local gusts to 30
kt, decreasing to 5-15 kt tonight, except remaining strong from KMUO
south and east through KTWF/KJER and surrounding area. Winds aloft
at 10kft MSL: N to NW 10-25 kt.

KBOI...VFR. A 40-60% chance of showers late Tuesday morning and
afternoon with potential (10% chance) for MVFR ceilings. Winds NW
around 15kt with gusts to 25 kt this afternoon, decreasing to around
10 kt by 06Z.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.

&&

$$

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SHORT TERM...JM
LONG TERM....SP
AVIATION.....SP