Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 160421

Area Forecast Discussion
National Weather Service Boise ID
921 PM MST Mon Jan 15 2018

.DISCUSSION...Updated forecast to add dense fog wording to Weiser
Basin and the central mountains for the rest of tonight, otherwise
forecast is on track. The 00Z models show little change in
handling a weakening short wave trough that will move through the
region in the next 24 hours. Higher precipitation amounts will
fall across southeast Oregon zones early Tuesday, with lighter
amounts across southwest Idaho zones (may not see measurable
precipitation reach the Western Magic Valley). Higher terrain of
northern Harney and Malheur counties, and Baker county could see
snow, though any accumulation will be less than an inch.


.AVIATION...VFR, except for patchy LIFR valley fog in the KMYL and
Long Valley areas and the lower Treasure Valley west of KBOI. Upper
level trough passage Tuesday will bring widespread MVFR/IFR
conditions to Southeast Oregon and the West Central and Boise
Mountains. Snow levels will range from around 3500 ft MSL in Baker
County Oregon and the west central Idaho mountains to 6500 ft MSL
along the Nevada border. Surface winds variable 10kt or less, except
east 10-20 kts from KMUO to KJER and KTWF. Winds aloft at 10k ft MSL
south 5-15kt increasing to 15-30kt after 00z Tuesday.


SHORT TERM...Tonight through Wednesday...The upper ridge than
resulted in the dry mild weather the last few days will shift east
tonight. The ridge will be followed by a short wave trough and
accompanying weak front on Tuesday. Widespread precipitation will
overspread southeast Oregon Tuesday morning. Rain may briefly mix
with freezing rain or snow before changing to all rain in north-
central Harney County (including Burns) and north-central Malhuer
County early Tuesday morning. Temperatures will be cold enough for
snow in Baker County (including Baker City) for up to an inch of
snowfall Tuesday morning. The trough will weaken when it arrives
in southwest Idaho late Tuesday morning through Tuesday afternoon.
Snow accumulations of up to an inch are expected in the higher
elevations across the north. The weakening trough will move to our
east by Tuesday evening and will be followed by a building upper
ridge through Wednesday. Above normal temperatures will continue,
albeit slightly cooler on Tuesday followed by a warmup on
Wednesday. Winds will be light, even with the frontal passage on
Tuesday, except for gusty east winds from Mountain Home to Jerome.

LONG TERM...Wednesday night through Saturday...The warm upper
level high pressure ridge responsible for the unseasonably mild
weather will move east of our area Wednesday night, allowing a
pattern change to more winterlike weather as the jet stream shifts
south of our area. Based on current model timing, the cold front
on the leading edge of a cold upper level low pressure trough will
reach southeast Oregon and southwest Idaho Thursday afternoon.
Valley rain and mountain snow above 6000 feet will become
widespread as the front approaches. Southerly flow ahead of the
front will provide one more day with above normal temperatures.
Following the front, temperatures will drop to near normal for
Friday through Saturday. As the upper level trough moves over the
Intermountain Region on Friday, it will generate scattered snow
showers at lower elevations and more numerous snow showers over
the mountains. Only isolated to scattered snow showers are
expected Friday night and Saturday as the trough exits and weak
high pressure moves over our area.

Saturday night through Monday...An active pattern controls the
weather over the extended three day period as a series of trough-
ridge couplets speed through the area starting off with a dirty
ridge. Widespread moisture is anticipated in the forms of mixed
rain and snow in the lowers valleys with snow elsewhere with
little likelihood of breaks. Predominant breezy Westerly winds are
expected with strong gusty southwest winds busting through around
the mid-point of the period affecting mostly the westerly half of
the CWA...Treasure Valley shadowing setup likely as a result
which could lessen precipitation amounts in those locations. Winds
directions in the Treasure Valley will go from Southeasterly
gradually changing to westerly. Overall temperatures will hover a
few degrees above normal.





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