Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 281538

Area Forecast Discussion
National Weather Service Boise ID
938 AM MDT Fri Oct 28 2016

.DISCUSSION...Light to moderate rainfall continues in Owyhee
County and areas east and south along a stalled front. Moisture
is being advected in from the southwest by an upper level
shortwave that`s currently moving onshore in central California,
so this rainfall is expected to continue through the day today.
This shortwave is still expected to move NE across our area later
this evening. The forecast looks on track with the areal coverage
of POPS and QPF amounts, so no update will be needed this morning.


.AVIATION...VFR, except widespread MVFR/IFR conditions in
rain south and east of a KREO-KMUO-KSUN line (including KTWF, KJER)
through 19Z. Patchy MVFR fog will continue in the northern mountain
valleys (including KMYL) through 18Z. Scattered-numerous MVFR
showers south and east of a KBNO-KONO-KMYL line after 19Z, with
local IFR conditions possible in heavier showers. Surface winds:
Variable 10 knots or less. Winds aloft at 10K feet MSL: Southwest up
to 20 knots.


SHORT TERM...At 3 AM MDT the main swath of precipitation
extended across southern Malheur County through Owyhee
County, the Magic Valley, and Camas Prairie.  The back
edge was roughly Rome, OR, Mountain Home, Challis, or a
little farther east than forecast.  Models have it surging
northward 50 to 100 miles in western and central Idaho
this afternoon and evening, then shifting east as a short
wave trough comes through from Nevada.  A second band of
rain has developed since midnight MDT from central Malheur
County to the west central Idaho Mountains.  This band is
associated with an eastward-moving cold front.  Instability
will slowly increase during the day ahead of the front and
we have a slight chance of thunderstorms in Twin Falls
County this evening when the cold front gets there.  After
about 12 to 18 hours without pcpn, the next Pacific short
wave trough will bring showers to eastern Oregon Saturday
morning, and western-most Idaho Saturday afternoon.  High
temps will be 3 to 5 degrees cooler today then little change
Saturday.  No significant winds today or tonight, but
southeast winds will be 15 to 25 mph in the Treasure Valley

LONG TERM...Saturday night through Thursday...Upper level trough
off the west coast Saturday night will shift east with the axis of
the trough along the west coast by Sunday night. As this upper
level trough continues to shift east it will weaken and will be over
northern Idaho by Monday morning. This trough will bring showers to
the forecast area Saturday night through Sunday night, then decrease
over the region Monday as the upper level trough continues to move
east. Monday night and Tuesday models begin to diverge on the
weather pattern. Models hinting at another weaker upper level trough
to move into the Pacific Northwest Monday night and Tuesday but
differ on timing and placement of precipitation with this system.
With uncertainty in the models will keep the trend of slight chance
pops and will make changes to the forecast when confidence in the
models increases. Tuesday night through Thursday models are in
better agreement with the weather pattern with a ridge building over
the region as another upper level long wave trough develops off the
west coast. Even though models seem to agree on the upper level
pattern, there are some discrepancies as to how much moisture will
move through the flow and where precipitation will be. Models
indicate that any precipitation in the southwesterly flow will
remain to the west of the forecast area, but if the ECMWF is correct
a weak short wave trough will break through the ridge and bring
at least a slight chance of precipitation to the region Wednesday
night into Thursday morning. Will not make any changes in the
forecast for the Tuesday night through Thursday time period due to
the uncertainty with the models.





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