654
FXUS65 KBOI 011548
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
948 AM MDT Wed May 1 2024

.DISCUSSION...
A weak shortwave observed on satellite this morning is drifting
southeast over the forecast area. Currently, it`s generating
light snow showers across the West Central and Boise Mountains
due to increased instability and forcing. This pattern will
persist into the afternoon and evening as the shortwave moves
out of the region into northern Utah.

Snow levels are hovering around 3500 feet throughout the day,
resulting in predominantly snowy conditions in most mountainous
areas. Lower mountain valleys might experience a mix of rain and
snow in the afternoon. Snow accumulation will be minimal, with
most places expecting around 0.1 to 0.3 in total.

High-resolution models had difficulty predicting showers in the
Western Snake Plain last night. Although the latest runs
indicate no showers in the valley today, confidence is low due
to their unreliable performance yesterday and early this
morning. Should showers manage to reach the valley, they are
likely to bring light rain.

In the Western Magic Valley, wind gusts of up to 40 MPH are
possible in the afternoon. However, models consistently predict
winds below advisory criteria. Minor adjustments have been made
to wind and POP forecasts to align better with the latest
guidance and radar trends today. An updated forecast will be
released shortly.

&&

.AVIATION...Mainly VFR. Scattered to numerous rain/snow showers and
isolated thunderstorms, mainly north of a KBKE-KBOI-KSUN line. Snow
showers obscuring mountains and producing brief MVFR/IFR conditions.
Snow levels 3500-4500 ft MSL. Showers ending this evening, with
additional rain and snow moving into SE Oregon overnight. Surface
winds: W-NW 5-15 kt, with gusts to 30 kt through Thurs/03z near
KTWF/KJER/KGNG, becoming variable less than 10 kt overnight. Winds
aloft at 10kft MSL: W-NW 15-25 kt.

KBOI...VFR with scattered to broken clouds 4000-9000 ft AGL, lowest
this morning. Isolated showers will pass north of the terminal
today. Snow levels around 4000 ft. Surface winds generally NW 5-15
kt with gusts to around 20 kt through 03Z, becoming SE 5-10 kt
overnight.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Friday night...A well defined mid-
level circulation over e-central Oregon is tracking
southeastward along the I-84 corridor. This feature and
accompanying cold air aloft will be the focus of shower
development today as it tracks through w-central Idaho. Daytime
instability and dynamics will support vigorous showers and a
slight chance (15%) of thunderstorms across e-central and the
w-central ID mtns. While showers will be concentrated over
higher terrain, some spillover is possible in the Snake Plain,
especially areas near the foothills. Snow levels will be
3500-4500 feet so heavier showers/thundersnow could reduce
visibility. Today will have the feel of an early spring day as
highs top out around 10 degrees below normal and gusty northwest
winds bring a wind chill. Gusts up to 25 mph are possible for
most, with stronger gusts to 35 mph expected across s-central
Idaho. There is little rest before the next trough arrives
Wednesday night into Thursday with another round of
precipitation. This system will track through SE Oregon
bringing widespread rain/snow showers to the mountains (50-80%)
with lower probability for measurable rain in the Snake Plain
(20-30%). Snow levels will start between 3500-4500 feet Thursday
morning, rising to 4500-6000 feet in the afternoon. By Thursday
night the wave is exiting into eastern Idaho allowing for drier
conditions to develop. A short wave ridge transits the
Intermountain NW Friday bringing dry and seasonable conditions.
Friday night will see clouds and precipitation chances increase
across SE Oregon as a deep closed low approaches the Pac NW
coast. Today is the coolest day with temperatures around 10
degrees below normal. Thursday is slightly warmer, before
reaching normal on Friday.

LONG TERM...Saturday through Wednesday...An upper level low will
deepen off the PacNW coast on Saturday, bringing warm southwest
flow to the region ahead of cooler and unsettled conditions
through much of the long term period. Model agreement remains
quite high during the early part of the weekend, with the
deterministic storm tracks aligning more with the ECMWF AI 00Z
run, pushing the low center further into our region. Therefore,
confidence is increasing in a potentially impactful winter
weather event for the region, especially over higher terrain.

Temperatures will be highest on Saturday, with the best chance for
precipitation (60-70% chance) in southeast Oregon on Saturday
ahead of the colder and wetter air mass that will move in to
the region on Sunday. This low will have record low 500 mb
heights, so record cold temperatures are likely along with low
elevation snow Sunday morning. Snow levels will be around
5000-6000 feet on Saturday, dropping to 4000-5000 feet by Sunday
during the day. However, there is a potential for snow levels
to drop to valley floors overnight on Sunday, it will just
depend on how models continue to resolve this record cold system
as we get closer to the weekend. This system also looks quite
moist, with precipitable water values near the 90th percentile.
Heavy mountain snow accumulations are likely, with the potential
for snow accumulations in the valleys as well. Current models
show high confidence (60-70% chance) of more than 8 inches of
snow above 7000 feet from Saturday to Monday. Model blends show
about a 20-30% chance of at least a tenth of an inch of snowfall
in the Treasure Valley by Sunday morning. Daytime highs will
warm quite a bit due to the higher sun angle this time of year,
so any snowfall below 5000 feet will likely melt later in the
day.

The low will then dig and deepen into the Great Plains by
Monday, but cold and moist northwest flow will continue keeping
snow levels around 5000-6000 feet through the early part of
next week, with widespread precipitation likely each day through
Wednesday. There is some disagreement towards the end of the
period, with the potential for a ridge to build in by Wednesday
night, but cluster and ensembles show quite a bit of range,
leading to low forecast confidence by the end of the long term
period.

&&

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

&&

$$

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DISCUSSION...JDS
AVIATION.....ST
SHORT TERM...DG
LONG TERM....SA