841
FXUS65 KBOI 192116
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
216 PM MST Sun Jan 19 2025

.SHORT TERM...Tonight through Tuesday night...An upper level
ridge will build off the coast of the Pacific Northwest through
the next few days. Simultaneously, a deep longwave trough will
dig into the southwestern US. This will keep us squarely in
cold, northerly flow, with Arctic air plunging into the region
through Tuesday. Temperatures will be about 8-10 degrees below
normal through Tuesday morning, with increasing temperatures
through next week thanks to the high pressure moving in and the
trough exiting the Great Plains. This northerly flow will also
allow for light northwest winds to kick up this afternoon, which
will make cool temperatures feel even colder. Some light
southeast winds will begin on Monday afternoon, mainly in the
Snake River Valley. This will help delay the onset of the
inversion and stagnant air conditions until later this week.

A weak convergence zone will set up over the Magic Valley this
evening, with light snow possible mainly over Twin Falls-Jerome.
Accumulations will be minimal thanks to dry surface air and
weakening dynamics overnight. Some light upslope snow showers
are possible with the cold front moving through the West Central
Mountains as well, although confidence is low (<20% chance).


.LONG TERM...Wednesday through Sunday...The ridge of high
pressure will weaken slightly as it continues to try to push
inland through Thursday. This will bring a slight warming trend
to the region, with continued dry conditions and a low potential
for air stagnation on Thursday and Friday morning. The lowest
mixing heights with the greatest potential for air stagnation
and lingering cold pools are in sheltered valleys near Weiser,
ID and Burns, OR.

Models then agree on a shortwave trough bringing snow to
primarily high elevations (30-40% chance) by Friday evening.
There is a low chance of snow in valleys (10-20%), but
accumulations would be minimal if present at all. This trough
will move out of the region by Saturday afternoon, plunging us
back into cold northerly flow with temperatures near to slightly
below normal. Model agreement is high in the long term, with
only minor differences in the extent and timing of Friday`s
shortwave passage.

&&

.AVIATION...Generally VFR. Isolated snow showers creating brief
MVFR and mountain obscuration for central ID mtns mainly east
of KMYL. Potential for snow showers to reach KTWF/KJER around
20/04Z. Surface winds: variable less than 10 kt, then NW-N 5-10
kt this afternoon. Winds aloft at 10kft MSL: NW-N 15-25 kt.

KBOI...VFR. Surface winds: variable or SE up to 10 kt, becoming NW 6-
12 kt after 19/18Z.

&&

.AIR STAGNATION...The ridge of high pressure will continue to
build along the West Coast, but higher diurnally driven winds
will prevent extensive stagnant conditions through Tuesday.
Sheltered valleys will see mixing heights around 1,000-1,500
feet on Wednesday and Thursday, which could allow for some
significant cold pools and fog to form. However, confidence is
low on the extent of the inversion and strength of the stable
surface layer. The system on Friday should scour out the
inversion and related stagnant conditions.

&&

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

&&

$$

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SHORT TERM...SA
LONG TERM....SA
AVIATION.....SA
AIR STAGNATION...SA