155
FXUS65 KBOI 030207
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
807 PM MDT Thu May 2 2024

.DISCUSSION...Isolated to scattered showers will persist for
much of the area through late evening, then a short-wave ridge
of high pressure is expected to move overhead for much of
Friday. This will lead to a warming/drying trend for Friday,
with temperatures rising 10-15 degrees from high temps today.
The next weather-maker, a deep low pressure system, is expected
to usher in gusty SE winds for much of Saturday, along with
increasing precipitation chances Saturday afternoon into mid day
Sunday. Current guidance indicates a 60-70% chance of at least
0.5 inches of precipitation with the weekend system, and a
30-40% chance of an inch or more. Those with outdoor plans this
weekend should follow the situation closely.


&&

.AVIATION...FR, except MVFR in scattered showers and/or low clouds
mainly impacting SW Idaho. Areas of mountain obscuration. Showers
decreasing overnight. Snow levels 4500-5500 ft MSL. Surface winds:
variable or NW 5-15 kt, then S to SE 5-15 kt Fri afternoon.
Winds aloft at 10kft MSL: NW to NE 15-25 kt, veering to S after
Fri/15Z.

KBOI...Isolated rain showers at/near terminal could bring brief MVFR
ceilings. Best chance for rain after Fri/04Z, ending by Fri/09Z. VFR
and clearing Friday. Light NW or variable winds, becoming SE 5-15 kt
around Fri/21Z.

Weekend Outlook...Widespread precipitation moves into SE Oregon mid-
morning Saturday, then into SW Idaho Saturday afternoon. A 20%
chance of thunderstorms Saturday afternoon in SW Idaho. Scattered to
numerous showers continue Sunday. Snow levels 6000-7000 ft MSL,
lowering to 4000-5000 ft Sunday. Mountains obscured. Surface winds:
SE 15-25 kt with gusts 25-35 kt Saturday afternoon, W 5-15 kt
with gusts to 25 kt Sunday.


&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Saturday night...A dynamic
weather pattern is unfolding over the next few days,
characterized by a shortwave passage today followed by the
arrival of a robust cold core low pressure system over the
weekend. This setup indicates a high potential for significant
rainfall during the upcoming weekend.

The shortwave is currently tracking east-southeast, expected to
reach southeast Oregon later today and southwest Idaho tonight.
Convective activity, including showers and thunderstorms, has
already commenced across southeast Oregon, with further
development anticipated south of the Treasure Valley through
this evening. While eastern portions of the Upper Treasure
Valley and Western Magic Valley may experience some activity
later today, the majority of the Treasure Valley should remain
dry until late tonight. Showers and thunderstorms could bring
brief heavy rain, along with graupel below 4000 feet. Higher
elevations may see a transition to graupel or snow with minimal
accumulation.

As the shortwave moves out of the region tonight, wrap-around
showers from the east will persist across the West Central and
Boise Mountains, extending into much of the Western Snake River
Plain into early Friday. Friday itself is expected to be warm
and dry as a weak ridge builds over the area, with temperatures
reaching the mid to upper 60s in the lower valleys.

The subsequent weather system, characterized by a deep closed
low, will sweep across the forecast area late Saturday. A
substantial precipitation band will form along the cold front
preceding the low, spreading from southeast Oregon early
Saturday to southwest Idaho by late afternoon. Recent model runs
suggest increased precipitation amounts, with a 60-80%
probability of 0.25" or more of liquid across much of the area,
and a 10-20% chance of exceeding 1.00. Snow levels are expected
to remain elevated above 6500 feet, limiting snowfall to the
highest mountain peaks.

Winds will intensify on Saturday, initially from the east as
the low draws in air, then shifting to the northwest behind the
cold front Saturday night. Sustained winds of 20-30 mph, with
gusts of 30-40 mph, are anticipated ahead of the front along the
I-84 corridor from Twin Falls to Baker City, as well as over
higher open terrain in southeast Oregon. Additionally, there is
a potential for thunderstorms ahead of the cold front across
south-central Idaho on Saturday afternoon, with forecasted
surface temperatures in the low 70s and favorable atmospheric
conditions supporting a few stronger thunderstorms.


LONG TERM...Sunday through Thursday...Unsettled weather from a
deep low continues to dominate the earlier parts of the long-
term forecast. Sunday`s max temp drops 10-20 degrees below
normal under the very cold airmass, though the min temps are
`only` 5 degrees below normal. A 60-80% chance of precipitation
exists throughout the area late Sunday, dropping to 20-40% in
lower valleys and 50-70% for higher elevations early Monday
through later Tuesday. There is a brief peak in activity Monday
evening as an embedded upper shortwave is carried through in the
northwest flow aloft. Late Sunday through Tuesday, lower
elevation liquid precip totals will be 0.05-0.20 inches. Higher
elevation liquid totals of 0.3-0.5 inches will likely fall as
1-6 inches varying greatly with elevation as snow levels are
forecast to be 4000-5000 ft MSL. There is a very small chance
(<5%) that parts of the Snake Plain see an early morning flurry,
but accumulation is not expected even if it does happen.

Conditions become more stable early Wednesday as the upper
gradient weakens and most of the energy heads east. A few
models are resolving a very positively-tilted weak trough
moving through Wednesday evening, but some models show close to
nothing, thus there exists only a 10-20% chance of
precipitation. Thursday and potentially onwards models generally
agree on a very mundane pattern as a closed high develops to
our northwest and upper gradients weaken significantly.

&&

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

&&

$$

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DISCUSSION...MC
AVIATION.....SH
SHORT TERM...JDS
LONG TERM....JM