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FXUS65 KBOI 021643 AFDBOI

Area Forecast Discussion National Weather Service Boise ID 943 AM MST Sat Dec 2 2023

DISCUSSION
Forecast remains on track with no updates needed this morning. Temperatures have risen into the low to mid 30s in most valley locations along the I-84 corridor including Baker City, Boise and Twin Falls and areas of light rain will continue along that route today. Snow is expected to turn to rain along the highway 95 route through the Weiser River valley later this morning and the Winter Weather Advisory will be allowed to expire there. Meanwhile, a Winter Storm Warning will remain in effect along the highway 55 route north of Boise into Cascade, Donnelly and McCall where periods of low visibility in heavy snow and blowing snow will continue. Windy conditions will develop this afternoon across much of southeastern Oregon and in the highlands of southwestern Idaho. Gusty winds are also likely in the Magic Valley of Idaho this afternoon.


AVIATION
MVFR/IFR and local LIFR due to widespread rain and snow/low ceilings. Areas of mist and fog KONO-KEUL through 02/17z then improving. Mountains obscured. Areas of LLWS in excess of 30 kt south of a line from KBNO-KEUL-KTWF 02/22z-03/02z.

Surface winds: SW-SE 10-20 kt, except W-SW 20-30 kt with gusts 35-50 kt in E Oregon and S of Snake River. Winds aloft at 10k feet MSL: W- NW 40-70 kt.

Sunday Outlook...MVFR to LIFR conditions due to widespread precipitation, with low elevation rain and snow over higher elevations. Mountains obscured. Patchy fog is possible between snow showers. Snow levels rise to 5000-6500 ft Sunday. Areas of LLWS in excess of 30 kt. Surface Winds: generally SW-SE 5-15 kt, except SW 20-30 kt with gusts 35-50 kt for E Oregon and S of Snake River.
Winds aloft at 10k feet MSL: W to NW 40-60 kt.



PREV DISCUSSION
SHORT TERM
Today through Monday night
Clouds spread rapidly eastward into our CWA during the night as the next short wave trough from the Gulf of Alaska reached the northwest coast. This trough will bring widespread heavy precipitation to our CWA today along with considerable wind, with snow level slowly rising above the valley floors. A Winter Storm Warning is in effect in Idaho north of the Snake Basin Snake today through Sunday, both for today's storm and a second one Sunday.
Hi-res models change snow to rain in the Snake Basin today and then back to snow from the northeast tonight. Other models stay with rain in the Snake Basin tonight which looks more likely as even the dew points are forecast to rise above freezing. A Wind Advisory also remains in effect for southern parts of our CWA today, i.e., southern Harney and Malheur Counties in Oregon, and south of the Snake River in Idaho. Winds will cause blowing and drifting snow in central and northern areas, but the stronger winds in the south will blow where snow becomes wet or changes to rain. The second storm, on Sunday, will bring another surge of moderate to heavy precipitation, but snow levels will rise to 6000 feet in Idaho and 7000 feet in Oregon, resulting in rain where most of the population lives. Further warming will occur Sunday night and Monday as precipitation tapers from south to north.

LONG TERM
Tuesday through Saturday
An upper level ridge will build over the Northern Rockies on Tuesday as a deep upper level trough remains over the Gulf of Alaska. This will place our area in mild southwest flow, bringing temperatures 10-15 degrees above normal. An atmospheric river will be aimed at the Pacific Northwest coast on Tuesday between the ridge and trough, but most of the precipitation will remain to our northwest, with light precipitation possible across our northern areas. A shortwave trough will move through our area on Wednesday and bring a 40-80% chance of precipitation to all areas, with the best chance in the central ID mountains. Generally light precipitation amounts are expected, except in the mountains where southwest flow aloft will enhance totals. Snow levels will remain high with this system, generally around 6000-7500 feet.
Precipitation chances will continue into Thursday as broad troughing continues over our area. Temperatures will cool several degrees on Thursday with snow levels lowering to 4500-5500 feet as a deeper trough approaches from the west.
This trough will move through on Friday with another round of precipitation and snow levels eventually lowering to valley floors. However, precipitation is expected to taper off as temperatures become cold enough for snow in the lower elevations. An upper level ridge building into the Pacific Northwest on Saturday will bring drier conditions with northerly flow aloft cooling temperatures to near normal.

BOI WATCHES/WARNINGS/ADVISORIES
ID...Winter Storm Warning until 5 PM MST Sunday IDZ011-013-028.
Wind Advisory until 11 PM MST this evening IDZ015-016-029-030.
Winter Weather Advisory until 11 AM MST this morning IDZ033.
OR...Wind Advisory until 11 PM MST /10 PM PST/ this evening ORZ061-063.

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