303
FXUS65 KBOI 292046
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
246 PM MDT Mon Apr 29 2024

.SHORT TERM...Tonight through Wednesday night...An unseasonably
cool upper level trough is moving across the Pacific NW today.
This system is bringing a cold front through the area, and has
reached Ontario, OR as of 2pm MDT. This front will continue to
track southeast through the afternoon, and temperatures will
slowly fall behind the front, with rain, snow and graupel
showers mainly north of a line from Burns OR to Boise ID.
Isolated thunderstorms possible too. The front is forecast to
generate windy conditions in the upper Treasure and Magic
Valleys and Camas Prairie through this evening where a wind
advisory remains in effect. The upper level trough will remain
over the area on Tuesday, keeping temperatures around 10 to 15
degrees below normal. The coldest air aloft will reach -30C at
500mb and extend from a line north of Burns to Boise on Tuesday.
Slightly warmer 500mb temperatures near the NV border will
lessen the chance of showers. Scattered showers will redevelop
on Tuesday afternoon with a slight chance of thunderstorms,
where the coldest air aloft is. Another shortwave moves south
into the upper level trough on Wednesday morning, enhancing the
threat of snow showers over the area. 500mb temperatures reach
-33C on Wednesday morning, which is near record cold for this
time of year. Light snow possible down to the valley floors, but
precipitation will be showery in nature, so some places may see
snow, while others will not. Snow showers will linger over the
mountains on Wednesday afternoon, but warmer air aloft and
ridging will bring drier and more stable conditions by Wednesday
evening.

.LONG TERM...Thursday through Monday...Long-term models are
showing poor agreement that gets worse with time. As a result,
most aspects of the forecast have a high degree of uncertainty.
A compact low will move in from the northwest on Thursday,
bringing precipitation through Thursday night with breezy
afternoon winds. Chance of precip is fairly low, 25-35% in
higher terrain and ~10% in lower valleys. Most precipitation
will be rain, but above 5000 ft MSL snow becomes possible since
some colder air lingers from the low earlier in the week.
Instability in central Oregon will support a slight chance of
thunderstorms. The track of this low varies a little model to
model, but most of the disagreement is in the coverage of the
precipitation, hence the mediocre precipitation chances.

A brief calm period persists Friday into Saturday morning thanks
to a ridge of high pressure. At the same time, a deep closed low
from the Gulf of Alaska tracks southeast along the Canadian
west coast. While models are beginning to show more agreement
with each run, they are still not quite there. The GFS continues
to the low making landfall in California, and then putting us
under a deformation zone as it moves east. While the 12z EC now
shows the core of the low moving directly overhead, putting us
under the coldest part of the airmass. This is a fairly big
change from the 06z EC, that showed the low becoming a longwave
trough leading to still unsettled but a notably weaker weather
pattern. The National Blend consensus is area- wide 30-50%
precip chances beginning Saturday afternoon, dropping to 20-40%
Sunday afternoon through the rest of the long-term. Saturday
onwards each afternoon will have a chance of thunderstorms and
breeziness. The spread in maximum temperature forecast is 10-20
degrees each day, with the consensus being normal temps.

&&

.AVIATION...VFR. Widespread rain/snow showers in the north and
isolated to scattered elsewhere. Instances of graupel and
lightning are possible in the north as the chance of
thunderstorms is just below 30%. Mountains obscured. Snow levels
4000-5000 ft MSL, lowering to 2500-3500 ft MSL by Tue/06Z.
Surface winds: W 15-25 kt with gusts to 30 kt this afternoon,
peak gusts of up to 40 kt. Winds aloft at 10kft MSL: W 20-30 kt.


KBOI...VFR with increasing clouds. Slight chance (less than 20
percent) of -SHRA between Mon/18Z and Tue/00Z. Surface winds: NW 12-
15 kt increasing to 15-20 kt with gusts to 23-28 kt this afternoon.
Winds decrease to 8-12 kt around Tue/05z and switch to SE around
Tue/11z.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Wind Advisory until 7 PM MDT this evening IDZ014-016-028.
OR...None.

&&

$$

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SHORT TERM...KA
LONG TERM....JM
AVIATION.....JM