Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 302050

Area Forecast Discussion
National Weather Service Boise ID
150 PM MST Mon Jan 30 2023

.SHORT TERM...Tonight through Wednesday night...Cold temperatures
will continue tonight and tomorrow, with gradual warming for most
areas after that. Northwest upper level flow will have just enough
moisture to bring isolated showers to the northern mountains
tonight through Tuesday night, but amounts will be minimal. An
inversion will develop this week, and an Air Stagnation Advisory
has been issued for much of the area. More on that in the Air
Stagnation section below. As the inversion strengthens, cold air
will pool in valleys, especially the lower Treasure Valley east
into Ada County as far as populated areas are concerns. Diurnal
ranges will become limited by late Tue into Wednesday night. This
will maintain more of the cold temperatures there compared to
areas other than valleys, which will see a nice warmup in the
coming days. Finally, low clouds are expected to cover the Camas
Prairie tonight, potentially limiting the typical night-time drop
in temperatures. Confidence is only moderate for this occurrence,
so went ahead and brought the min temperature forecast down to -17
for tonight. If clouds do cover the area most of the night, the
low will be closer to -10.

.LONG TERM...Thursday through Monday...Thursday will be partly
cloudy and dry under an upper level high pressure ridge. Friday and
Friday night, a weak upper level trough will bring light snow to the
mountains. It is still uncertain whether this system will create
enough mixing to dislodge cold air trapped in the valleys. Sunday
and Sunday night, a deeper trough will bring more widespread
precipitation, with snow changing to rain in the lower valleys
Sunday afternoon as warmer air moves inland. Models are trending
slightly cooler on Monday as the upper level flow shifts into the
north behind the trough. The latest ensemble blends are showing a 5-
10 degree range of possible temperatures each day. The current
forecast has temperatures 5-10 degrees below normal on Thursday,
then near normal for the rest of the period.


.AVIATION...Stratus patches locally obscuring higher terrain.
Otherwise VFR with mostly clear skies through this evening. After
31/06z high and mid level clouds increasing from the north as a warm
front aloft crosses the area. Surface winds: variable 10 kt or less.
Winds aloft at 10k feet MSL: N-NW 20-35 kt.


.AIR STAGNATION...An upper level ridge will approach the area from
the west and then pass over Wed night into Thu. This pattern is
one that often leads to inversions, which in turn result in air
stagnation. An Air Stagnation Advisory has been issued through
Friday. Air quality may degrade as the week progresses. One area
that was included in the advisory but may see limited stagnation
is in and around Mountain Home. This is because winds will
increase above 10 mph both Tue and Wed afternoons, providing some
mixing. Winds are expected to decrease Thu and Fri, hence the
area`s inclusion in the advisory.


ID...Air Stagnation Advisory until 1 PM MST Friday
OR...Air Stagnation Advisory until 1 PM MST Friday ORZ061>064.



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