Twin Falls, Idaho 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

053
FXUS65 KBOI 220327
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
827 PM MST Fri Feb 21 2025

.DISCUSSION...Mid and high clouds will continue to move in from
the west overnight, with light showers spreading across the
higher terrain in the north. This initial weak wave will move
east out of the area Saturday afternoon, only to be followed by
a stronger and quite wet system Saturday night into Sunday.
Latest guidance shows no significant trends, and no update is
needed at this time. See previous discussion (below) for
additional details.

&&

.AVIATION...Mostly VFR. Isolated MVFR/IFR in valley fog and/or
low stratus mainly near KMYL, KONO, and KBKE late tonight.
Surface winds: variable 5 kt or less except NE-SE 5-15 kt near
KJER/KMUO. Winds aloft at 10kft MSL: W 10-20 kt, increasing
about 5 kt Saturday.

KBOI...VFR. Possible MVFR ceilings Sat 12Z-18Z (30% chance).
Surface winds: SE 4-8 kt.

Sunday Outlook...All flight categories expected as widespread
precip continues after moving in Saturday night. Snow levels
generally 6-7000` MSL. Mountains obscured. Surface winds: SE-SW
5-15 kt with gusts 20-30 kt.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Sunday night...A weak upper
wave will track across the region late tonight and Saturday.
Outside of a low chance of showers across e-central Oregon and
w-central Idaho, it most areas remain dry through the day. Any
areas that pick up light snow will see less than a 1/2 inch
through midday Saturday.

A much wetter pattern will unfold late Saturday night into
Sunday as an atmospheric river pushes into the Pac NW. Modeled
precipitable water data show this plume (1-1.5" values) to have
a sub-tropical connection west of the Date Line. While the core
of strongest winds aloft are forecast to remain just north and
west of the region, there will be plenty of moisture transport
in from the coast to generate rain and high elevation snow.
Precipitable water values reach the 98%+ with W-SW winds at
~10kft MSL reaching 30-50 mph. This will favor a period of
continuous moderate to locally heavy precipitation on Sunday,
especially across e-central Oregon, and the w-central ID and
Boise mtns. In these areas snow levels will start between
3500-4500 feet MSL Saturday night, allowing for minor
accumulation of wet snow. The incoming Pacific air mass will
quickly raise snow levels to between 6-8kft across the region on
Sunday, bringing a rain/snow mix or changeover to rain except
across the highest elevations. Total liquid amounts will reach
0.75-1.25" across the mountains with locally higher amounts of
1.5-1.75" translating to a wet 6-12" of snow above 7kft MSL
through Sunday night. At lower elevations, rain totals of
0.1-0.3" are forecast through Sunday night. Valleys and mtn
valleys will see breezy winds while higher mountains, tapping
into the flow aloft, realize the strongest winds with gusts of
30-40 mph. Temperatures will be near normal Saturday and Sunday.

At this point we expect much of the mtn snowpack to be able to
absorb the rain with minimal snowmelt. Some runoff is expected
and with frozen ground this could lead to water ponding in low
lying areas where drainage is limited. There is of some
question on how the lower elevation snowpack will respond but we
do expect rain/melt/higher elevation runoff to impact river
flow. While all rivers are showing forecast rises, the Weiser,
Malheur, Payette and Donner und Blitzen are a few that we`re
keeping an eye on as hydrologic forecasts show a more notable
response in these rivers by Monday. Otherwise expect to see
smaller streams running near bankfull early next week.

LONG TERM...Monday through Friday...The atmospheric river will
weaken on Monday, as zonal upper level low begins to strengthen
over the region. Snow and rain showers will continue over the
mountains through Tuesday, with snow levels rising to around
6500-7500 feet by Monday afternoon. Monday will be the warmest
day of the long term period, with lower elevation highs in the
upper 50s to low 60s (Boise has a 20% chance of exceeding 60F!),
and mountain daytime highs in the mid 30s to mid 40s. Large
precipitation totals from the Sunday-Monday atmospheric river
event will occur, with valleys seeing anywhere from 0.25-0.50
inches of rain and mountains 1.00- 1.25 inches of rain for the
48 hour totals. Snow amounts above 6500- 7500 feet will be low,
with most populated locations/roadways seeing anywhere from 1-3
inches, with high summits seeing up to 12-16 inches.

 A weak low will skirt to north of us on Tuesday, dropping
temperatures by 3-6 degrees and decreasing snow levels to
4500-5500 feet. Lingering snow showers will persist in the West
Central Mountains on Tuesday, but a deep upper level ridge of
high pressure will begin to build across the Western US by late
Tuesday. This will keep our temperatures above normal with dry
conditions through Friday. Excellent model agreement remains
through the long term period in the evolution of the ridge, so
forecast confidence in dry and warm conditions is high.

AVIATION...Widespread MVFR and local IFR conditions in rain and
snow. Mountains obscured. Precipitation diminishing from west to
east overnight. Snow levels 3500-5500 feet MSL, lowering to
3000- 4000 feet MST behind a cold front tonight. Surface winds:
generally E to S 5-15 kt with gusts to 25 kt, shifting to the
W-NW tonight. Winds aloft at 10kft MSL: W-SW 20-35 kt shifting
to the N-NW tonight.

KBOI...VFR with occasional MVFR conditions in rain. Rain may mix
with snow this evening before ending by Thu/06Z. Surface winds:
SE 5-15 kt, gusting to around 20 kt, shifting to the NW less
than 10 kt after Thu/02Z.

&&

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

&&

$$

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DISCUSSION...SP
AVIATION.....SP
SHORT TERM...DG
LONG TERM....SA