FXUS65 KBOI 230228
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
828 PM MDT Tue Oct 22 2024

.DISCUSSION...No forecast changes for now although fog is being
considered in the valleys Thursday morning. Current east-west
cloud band across our CWA and southwestward into the Pacific
looks threatening but it has no pcpn in our area. However,
models develop a cold front in the north Pacific overnight
45-50N/ 130-135W and bring it rapidly inland through our CWA
Wednesday afternoon and evening. Latest hi-res models show near
certainty of .05 to .10 inch of rain in the valleys and .10 to
.35 inch in the mountains as the front moves through. The pcpn
should all be east of our CWA by 3 AM MDT Thursday. Snow level
will be above 6000 feet MSL during pcpn, then fall to 4500-5000
feet after it ends, so only the higher mountains can expect any
snow. We see that after several days of mild, dry weather, GFS
and ECM models develop an upper trough over the PacNW early
next week, possibly cold and moist enough for wet snow down to
valley floors Tuesday.

&&

.AVIATION...VFR. High clouds tonight. Cold frontal passage will
bring areas of MVFR/IFR conditions Wednesday afternoon and
evening. Surface winds: variable less than 10 kt. Winds aloft
at 10kft MSL: generally SW 20-30 kt.

KBOI...VFR with high clouds. Cold frontal passage expected
Wednesday evening between 24/00z-24/03z will bring MVFR
conditions in rain, along with wind gusts up to 30 kts.
Variable winds 5 kt or less overnight.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Thursday night...High-level
clouds will persist into the evening as the region remains under
the influence of a moist upper-level jet. This should have
little effect on temperatures, with lows expected to dip into
the upper 30s by Wednesday morning.

The main focus is on a strong upper-level trough and cold front
expected to pass through Wednesday afternoon and evening. While
the low-pressure system, currently located near 132 W and 48 N,
appears unimpressive on satellite imagery, model guidance
consistently shows it intensifying offshore tonight before
moving quickly inland Wednesday.

A few light rain showers are forecast across our northern zones
Wednesday morning, but most precipitation will accompany the
frontal passage in the afternoon and evening. The front is
expected to reach Baker City and Burns by around 1 PM PDT, the
Boise Metro area by 8 PM MDT, and the Western Magic Valley by
approximately 11 PM MDT. During this time, expect brief wind
gusts of up to 45 MPH, along with moderate rain. The heaviest
rainfall, around 0.35 inches, is likely in the higher terrain
near the Nevada border and the West Central Mountains. Ensemble
models suggest a 60% chance of 0.10 inches of rain for the
Treasure Valley. Snow levels will remain high for most of the
event, dropping to mountain valley floors after the frontal
passage. Elevations above 6,000 feet could see light snow
accumulations of up to 1 inch, while mountain valleys around
5,000 feet might experience precipitation ending as snow, though
without accumulation.

Temperatures will stay above normal across southwest Idaho on
Wednesday until the front moves through in the evening. By
Thursday morning, lows could approach freezing as cold air
settles in behind the front.

LONG TERM...Friday through Tuesday...Temperatures will rise
5-10 degrees each day Friday and Saturday as an upper level
ridge amplifies over the area and southwest flow aloft
strengthens. Saturday looks to be the warmest day, with lower
valley highs reaching the upper 60s to around 70 degrees, or
around 10 degrees above normal. Winds will become breezy across
portions of southeast Oregon and the higher terrain of southwest
Idaho Saturday afternoon. On Sunday, an upper level trough and
cold front will begin to move into the Pacific Northwest with a
chance of rain and high elevation snow increasing through the
day. The trough axis is expected to move across our area Monday
and Tuesday with rain and snow chances peaking Sunday night and
Monday at 40-80% and decreasing slightly on Tuesday.
Temperatures will begin to cool on Sunday, but cooler air within
the core of the trough will push in Monday and Tuesday with
high temperatures cooling to around 5-10 degrees below normal.
Snow levels will fall to 4500-5500 feet on Monday and 3000-4500
feet on Tuesday. Winds will become gusty as the trough moves
across the area.

&&

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

&&

$$

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DISCUSSION...LC
AVIATION.....SP
SHORT TERM...JDS/LC
LONG TERM....ST