501 
FXUS65 KBOI 302127
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
227 PM MST Thu Nov 30 2023

.SHORT TERM...Tonight through Saturday night...A shortwave
trough will move across the region tonight, spreading generally
1 to 2 inches of snow to all elevations. A Winter Weather 
Advisory remains in effect from 5 PM MST /4 PM PST / to either 5
PM MST Friday or 5 AM MST Saturday, depending on the exact area, 
unchanged since early this morning. All roads will be snow-
covered by Friday morning, and slippery conditions should be 
expected. A series of additional wetter and progressively warmer
storms will follow, and these will bring heavy snow to the 
mountains through the weekend. Totals over 3 feet are likely at 
elevations above around 6000 ft. Additional snows in lower 
elevations will occur Friday through sometime Saturday, with 1 
to 4 inches possible, depending on exact location. Snow will 
change to rain Saturday, earliest in southeast Oregon, then 
spreading into southwest Idaho in the afternoon. Winds will 
increase Saturday, resulting in periods of blowing snow. As snow
changes to rain at lower elevations, the blowing snow will be 
confined to higher and higher elevations as Saturday gives way 
to Saturday night.

As mentioned yesterday, there is significant uncertainty about
the exact timing of the changeover from snow to rain in the
Boise area. Around 1.5 inches are expected overnight Friday and
through about noon Saturday. After that is when the uncertainty
kicks in. It is likely that another 1/2 inch to inch will fall
before it changes to rain around 3 PM MST. However, it could
change to rain sooner (30% chance), and eliminate the afternoon
snowfall total. There is a very small chance it could continue 
as snow through the afternoon and into the evening, but that is 
the least likely solution (5% chance) at this time.

For the remainder of the area, breezy conditions Friday
afternoon and evening will increase further Saturday. This will
lead to blowing snow through Saturday night, but the elevations
affected will continue to become more limited in time. A brief 
period of blowing snow resulting in limited visibilities 
(dangerous on roadways, obviously) will likely occur Saturday 
late morning through early afternoon in many areas near and 
south of the Snake River in southwest Idaho, and over much of 
southeastern Oregon in the morning. At this time, it is thought 
that the duration of low visibilities at any one point will be 
short enough that a winter weather advisory is not warranted, 
but this could change as additional model runs are received. 

Temperatures will naturally vary with the rising snow levels.
Readings tonight through Saturday morning will be below normal
in all areas, and typical diurnal ranges will be limited by
cloud cover and precipitation. Saturday afternoon and night,
temperatures will rise to near normal over much of the southern
portion of the CWA.

.LONG TERM...Sunday through Thursday...Precipitation will continue 
into Monday as an atmospheric river continues to transport moisture 
into the area. Expect rain coverage to increase as the AR pulls on 
warmer air and raises snow levels to 6000-7000 ft MSL by Sunday 
afternoon. At this point, any remaining snow accumulation will be 
limited to the mountains, but a few flurries may still be possible 
in mountain valleys. Up to an inch of rain is expected after snow 
ends in lower valleys. Winds will pick up Sunday, creating hazardous 
conditions in SW Idaho along the NV border. Sustained winds up to 30 
kt and gusts to 50 kt are possible. The winds alone are significant, 
but continued precipitation, especially snowfall, may reduce 
visibilities. Moisture flow will be mostly north of us by Monday 
afternoon. The total snow accumulations by the end of the 
precipitation will be a few inches in lower valleys, 8-12" in 
mountain valleys, and much more along ridges and summits. 

Beginning Tuesday a broad ridge will build in the region, holding 
temps steady about 10 degree above normal and clearing skies. The 
development of an inversion creating stagnant air is only of minor 
concern, and is unlikely to last long. During the ridge, moisture 
will continue to be transported north of us, with a 30% it tracks 
more south and produces precipitation in our area. Probabilities of 
precipitation will rise into Thursday as the next Pacific trough 
moves inland.

&&

.AVIATION...MVFR/IFR in SE Oregon, VFR becoming MVFR/IFR 
in SW Idaho by 01/08z. Snow in SE OR is spreading eastward, with 
some snow already in the Snake Valley. A N-S band of snow at KBNO, 
will reach KBOI by 01/06z, and KTWF by 01/10z. Expect a four hour 
break before more snow arrives Friday afternoon. Mountain 
obscuration in low ceilings and precipitation. Surface winds: SW 5-
15 kt and SE 5-10 kt in the Snake Valley, gusts W 15-25 kt after 
01/04z. Winds aloft at 10k feet MSL: W 15-25 kt.

Weekend Outlook...Widespread precipitation through the weekend with 
MVFR/IFR/LIFR conditions in most areas through Sunday. Snow will 
shift to valley rain by Saturday afternoon/evening, with snow levels 
expected to be around 4000-5000 feet MSL by Saturday evening, then 
5000-6000 feet MSL by Sunday morning. Mountains obscured. Surface 
winds will be SW 10-20 kt in general. However, 25-35 kt surface 
winds and gusts in excess of 40 kt expected 03/00z through 04/00z in 
SW ID.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory from 5 PM this afternoon to 5 AM MST 
     Saturday IDZ011-013-014-033.
     Winter Storm Watch from late Friday night through Sunday 
     afternoon IDZ011-013.
     Winter Weather Advisory from 5 PM this afternoon to 5 PM MST 
     Friday IDZ012-029.
OR...Winter Weather Advisory from 4 PM this afternoon to 4 AM PST 
     Saturday ORZ062.
     Winter Weather Advisory from 5 PM this afternoon to 5 PM MST 
     Friday ORZ064.

&&

$$

www.weather.gov/Boise
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SHORT TERM...SP
LONG TERM....JM
AVIATION.....JM