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Area forecast discussion 
National Weather Service Boise Idaho
252 am MST Sat Nov 28 2015

Short through Sunday...a cold stable stagnant
pattern will continue this weekend. A large upper low to our south
will slowly shift east-NE while high pressure aloft builds in from
the west. A very cold air mass has settled into the region. Once
again...temperatures this morning are in the single digits and
teens...with sub-zero readings in much of Harney County and the
Camas Prairie. The stable pattern has also allowed an inversion to
develop and will remain in place for several days. Widespread
stratus/patchy fog encompasses the Treasure valley and upper
Weiser basin. Visibilities will likely improve this
afternoon...but the patchy fog will return this evening and continue
through Sunday morning. There will also be some erosion of the low
stratus this afternoon...but will probably re-develop and expand
throughout the valleys this evening...then improve again Sunday
afternoon. Temperatures will be very cold again tonight...with
record/near record lows expected at a few locations. Winds will be

Long term...Sunday night through Friday...cutoff upper level low
will continue to move east Sunday night with an upper level ridge
over the forecast area Monday through Wednesday. This weather
pattern will keep conditions dry with temperatures remaining below
normal. Models in better agreement with the pattern from
Wednesday through the end of the week but there still are timing
differences on when precipitation will move into the forecast
area. Axis of the ridge will begin to move east as a long wave
trough develops over the eastern Pacific. Models have slowed
down the timing of precipitation so Wednesday looks to be dry but
if timing of precipitation changes could see precipitation move
into the forecast are Wednesday afternoon. As the axis of the
trough moves inland on Friday will see increasing chances of
precipitation over the region Wednesday night through Friday.
Models hinting that this trough could split as it moves over the
area and keep most of the precipitation to the north and south of
the forecast area. With uncertainty on how much this trough will
split will trend probability of precipitation towards climatology and adjust the forecast
as confidence in the models increases. Temperatures will slowly
warm through the end of the week but will be a few degrees below
normal by Friday.


Aviation...widespread LIFR conditions in low stratus and fog in
the Snake River Valley to just west of kjer/ktwf. Conditions may
lift to IFR this afternoon...but expect LIFR conditions to return
shortly after sunset. Kjer/ktwf are VFR at this time but could
see periods of LIFR conditions as the low stratus and fog moves
east. Otherwise generally VFR under mostly clear skies with
patchy morning valley fog. Surface winds variable less than 10
knots. Winds aloft northeasterly 15-25 knots up through 10k feet
mean sea level.


Air stagnation...high pressure will dominate through the middle
of next week...allowing the strong valley inversions to persist.
Mixing heights will remain below 1500 feet above ground level. Winds will be
light. There is a chance the inversion breaks with the arrival of
a cold front late next week.


Boi watches/warnings/advisories...




long term....ja

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