818
FXUS65 KBOI 221554
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
954 AM MDT Wed May 22 2024

.DISCUSSION...
An area of showers has shifted into south-central Idaho this
morning, with partial clearing occurring in its wake across
southwest Idaho and eastern Oregon. The presence of steep mid-
level lapse rates and drier air aloft will allow for sufficient
destabilization for scattered thunderstorm development later
this morning and afternoon across southwest Idaho. Latest HREF
guidance maximizes precipitation chances (70-90% chance) north
and east of Boise (including the Boise Mountains) after 10 AM
MDT. Forecast soundings suggest gusty winds of 40-50 mph, and
perhaps some small hail, will accompany the strongest storms.
Given the amount of flow aloft and the speed of individual
storms, the threat for widespread activity will end by mid-
afternoon for most of southwest Idaho, and shift into the Magic
Valley for this evening. Isolated showers/thunderstorms will
likely persist, however. Temperatures will also be quite cool
both today and tomorrow, and will struggle to get much above 60
degrees in even the warmest locations. Much quieter weather is
on tap for tomorrow, with breezy winds being the primary impact.


&&

.AVIATION...Numerous rain and snow showers. Isolated to scattered
thunderstorms through 23/03Z. Periods of MVFR/IFR in precip.
Mountains obscured. Snow levels around 6000-7000 ft MSL will lower
to 4500-5000 ft MSL this afternoon. Surface winds: variable 5-15 kt
this morning, then generally W-NW 10-25 kt with gusts 25-35 kt late
this morning through this evening with cold front. Winds aloft at
10k ft MSL: W-NW 20-35 kt.

KBOI...A 60% chance of showers and a 30% chance of thunderstorms 17Z-
22z. Less than 30% chance of showers 22Z-03Z. Winds: variable or
southeast 5-10 kt through 16Z, then W to NW 10-20 kt with gusts up
to 25-30 kt after 18Z with cold front, decreasing around sunset.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Friday night...Widespread
precipitation will continue this morning as a closed low
approaches east Oregon and southwest Idaho from the north-
northwest. Snow levels are currently around 6500-7000 ft MSL,
but will quickly lower to around 4500-5000 ft MSL as the cold
front arrives late this morning/afternoon. Conditions will
become unstable and promote convective shower activity and
isolated/scattered thunderstorms, mainly for far eastern Oregon
and over southwest Idaho. Meanwhile, a swath of drier air will
start to move into southeastern Oregon late this afternoon/eve,
shunting much of the shower activity toward the east and south
for the remainder of the day. The exception will be the wrap-
around showers from the closed low continuing over east-central
Oregon and central Idaho through early Thursday.

Latest model runs move this low eastward out of the area more
quickly on Thursday, but a slight chance (20%) of showers will
linger over central Idaho mountains through Thursday afternoon.
Overall, precipitation totals will be highest over southwest
Idaho where around 0.2 to 0.5 inches of rainfall is forecast for
the valleys, and up to 0.75 to 1.25 inches of liquid equivalent
over the higher terrain. Light snow accumulations may be
possible down to 4500-5000 ft MSL today and tonight, while
several inches of late season snow can be expected generally
above 7000 ft MSL. In addition to the precipitation, west and
northwest winds will ramp up late this morning/afternoon across
the area, especially over south-central Oregon. As a result, a
Wind Advisory has been issued for southern Harney County due to
wind gusts up to 45-50 mph possible in the afternoon and early
evening. Temperatures will be much colder today compared to
Tuesday, roughly 10-15 degrees below normal.

Drier, northwesterly flow aloft will replace the low on
Thursday, with temperatures rebounding by a few degrees.
Further warming anticipated Friday ahead of a weak shortwave
trough forecast to arrive late Friday. This shortwave will come
ahead of the next low pressure system, and introduce a chance
of (20-35%) of showers for east-central Oregon and west-central
Idaho by Friday evening. Snow levels late Friday will begin
around 7000-7500 ft MSL.

LONG TERM...Saturday through Wednesday...Cloudy and unsettled
conditions will continue to spread throughout most of the region
as the leading edge of a North Pacific low pressure system
packed full of inclement weather treats quickly slides across.
Lower probabilities (10-30%) for showers are anticipated across
most of the valleys and other regional low lying areas while
higher values (40-80%) dominate the Boise, West Central and
Owyhee Mountains. As the associated cold pool of moist air
temporarily blankets primarily the northern zones, snow levels
will lower enough to bring snowfall possibilities back into the
picture - mostly in areas with elevations 5000ft and above
during the low`s brief stay. This same cooling condition will
also destabilize the local atmosphere enough (as reflected in
borderline CAPE, LI`s accompanied by orographic lift and surface
heating converging during that time) to encourage a slight
chance for afternoon through evening thunderstorms across Baker
county, Oregon and the Mountains of Southeastern Idaho on
Saturday. Breezy winds will also be a weather factor across the
major valleys and Owyhee and Steens Mountain areas and
especially near showers and thunderstorms. By Sunday afternoon,
conditions will dramatically improve to sunny and warmer as the
low exits and drier, warmer ridging builds in. This warming
trend will continue throughout the remainder of the period with
highs increasing and ranging from mid 70`s thru mid 80`s.
However, these improving conditions will be short lived as
starting Tuesday conditions will slowly deteriorate as pockets
of moisture and instability begin trickling into northern
Oregon increasing the chances once again for precipitation.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...Wind Advisory until 8 PM PDT this evening ORZ061.

&&

$$

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DISCUSSION...JR
AVIATION.....SP
SHORT TERM...SH
LONG TERM....WH