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Office: BOI

FXUS65 KBOI 161636
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
936 AM MST Sat Dec 16 2017

.DISCUSSION...Last night's cold front brought 1-2 inches of snow
to se Oregon, and 1 inch or less to western Idaho.  The front, and
cooling aloft, partially cleared the inversion.  West/northwest
surface winds 15-30 mph later today should finish the job.  Tonight
will be mostly clear and quite cold, with lighter winds and fresh
snow on the ground.  Patchy dense fog will form in the valleys
overnight and Sunday morning.  Warming aloft Sunday through Tuesday
will form a new inversion near the surface, but a storm from the
Gulf of Alaska Wednesday will clear it out.  Current forecast is
on track.

&&

.AVIATION...Generally VFR with areas of dense fog / low stratus near
KONO, KEUL, and across the Magic Valley. Conditions are expected to
improve throughout the day. MVFR/IFR conditions expected to return
around 17/00Z. Surface winds: 5-15 kts, increasing to 15-25 kts with
gusts to 30 kts along the Snake River Plain, 16/17Z-17/00Z. Winds
aloft at 10 KFT MSL: NNW 20-30 kts, decreasing to 10-20 kts before
17/06Z.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Sunday...Snowfall continues to move
through the western Magic Valley this morning as the trough
continues to sweep through the area. Most snowfall is expected to
taper off by the late morning hours. North-northwesterly flow,
associated with a ridge off the Pacific coast, will then return
to the area and is expected to last into Sunday. This system will
return inversion conditions late tonight and through Sunday, with
the potential for some low stratus and patchy fog. Patchy dense
fog will be possible on Sunday morning, but pinpointing this
development remains a challenge. For now, patchy fog wording will
remain. Temperatures will be able to warm today, with values much
closer to seasonal normals. However, temperatures will again cool
on Sunday due to the influence of the inversion. Weak amounts of
moisture in the flow may produce a few showers across Baker
County, OR and into the West Central Mountains of Idaho on Sunday
afternoon. Coverage will not be significant, with any snowfall
having minimal impacts.

LONG TERM...Sunday night through Friday...Sunday night through
Tuesday moist relatively warm westerly flow aloft will provide
scattered snow and rain showers for Baker County Oregon and the
central Idaho mountains, with snow levels around 4000 feet.
Tuesday night and Wednesday a strong cold front, followed by a
deep upper level trough from the gulf of Alaska, will bring
widespread precipitation, with snow levels lowering from around
4000 feet Tuesday night to the valley floors by Wednesday evening.
The trough will move south of our area Wednesday night, replaced
by northerly flow aloft over the Intermountain Region starting
Thursday. Temperatures are not expected to be unusually cold, with
readings in the valleys Thursday and Friday close to what they
were during the inversion of the past week, but with considerably
less cloud cover.

&&

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

&&

$$

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DISCUSSION...LC
AVIATION.....AB
PREV SHORT TERM...KB
PREV LONG TERM....JT



Office: PIH FXUS65 KPIH 161701 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 1001 AM MST Sat Dec 16 2017 .UPDATE...Satellite observations and the 12Z model runs suggest the 700 mb level winds are trying to close off a circulation roughly over the Eastern Magic Valley. This may be a very short lived feature, but it may be enough to enhance snow fall over Interstate 86 between Pocatello and Cold Water and the I-84/86 interchange. Updated forecasts for potential of an additional 1 to 2 inches of snow in tha area through 5 pm, and issued a Winter Weather Advisory for the South Central Highlands until 8 pm. Wind gusts to 47 mph near Yale were also a concern and bumped the winds higher as a result. They are not very widespread though. RS && .PREV DISCUSSION... /issued 251 AM MST Sat Dec 16 2017/ SHORT TERM...Through Monday night. Strong, consolidated trough of Low Pressure is approaching the Oregon/Idaho border as of this writing. As a result, Snowfall has quickly blossomed along and East of a Camas to INL to Burley line, with some embedded convective elements resulting in some brief Moderate bursts of Snow. With cold initial pavement temperatures, any untreated surfaces have quickly turned Snow-covered this morning. As we head thorugh the rest of the Morning, the northern portion of the trough begins to lose its punch as the dynamics shift southward over California. Thus, we should see a brief reduction in Snowfall rates around Sunrise. A convergence band is still expected to develop from near Mackay southeast to Idaho Fall shortly after Sunrise, and will then work southwestward down the Snake Plain through the morning. Combined with gradually backing mid-level winds to the west and northwest through the morning, expect Snowfall rates to become re-energized across the Interstate Corridor from Pocatello to Idaho falls between 6-9 AM. Snow then expected to gradually taper off from north to south, ending around Noon for Pocatello. Expect Snow Showers to linger between Pocatello and Burley south to the Utah line until late afternoon. Across the Wyoming border region, Snow will follow a similar trend of tapering off from North to South, with lingering Snow Showers hanging on across the Bear Lake region until after Sunset. Snow Showers should end for the far Southeast Corner around Midnight. In terms of Snowfall amounts, still expect 1-3" across the Interstate Corridor from Pocatello to Idaho Falls and west to Coldwater, with similar amounts east to the Wyoming border. Amounts will gradually taper down as one heads West across the Arco Desert. Locally higher amounts possible in favored upslope enhanced higher terrain areas south and east of the Interstate corridor. Another concern is the briefly breezy conditions expected this morning across the Eastern Magic Valley. The Interstate 84 corridor from Burley to Sweetzer Summit will see wind gusts to 40 mph this morning, particularly around Idahome and Yale, which will cause local drifting Snow. The story Sunday will be the return of low clouds and Fog across the Snake Plain in the wake of the departing system. A weak High Pressure Ridge will gradually build across the region on Monday in response to a strengthening low in the Gulf of Alaska. Moisture spilling over the top of the ridge will allow for light Snow Shower development across the Sawtooths and Island Park areas southward to around Palisades. Southerly downslope flow expected to develop from Burley to Pocatello, which should allow any lingering Fog/Low clouds to diminish. Downsloping should allow temperatures to climb above Freezing for these areas and points South. AD/Valle LONG TERM...Tuesday through Saturday. Main focus is on a fast moving but potent cold front that arrives Wednesday. This will bring widespread snow to the region. Right now, amounts look relatively light with 1 to 3 inches possible with higher amounts in the high country. But, these numbers will probably change over the next few days as we get more and more data into the models. Afterwards, we will have some residual snow showers Wednesday night into Thursday. But, definitely looks colder, possibly coldest air of the season so far with many locations in the single digits for lows Friday morning. Valle AVIATION...Expect snow across much of the region today. This will produce lower ceilings and visibilities today, although probably higher than we've seen the past several days with the fog and stratus. Snow should end tonight, but may see fog and low stratus redevelop across parts of the region...joy. Valle AIR QUALITY...Poor air quality continues for Franklin county because of temperature inversions. A cold front arrives today which will bring snow to the region and may actually improve the air quality. Valle && .PIH WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 PM MST this afternoon for IDZ019>021. Winter Weather Advisory until 8 PM MST this evening for IDZ022- 023-025. && $$