Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 271244
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
443 AM PST THU NOV 27 2014

.SYNOPSIS...
Mild and breezy weather is expected Thanksgiving with areas of
fog in the morning. Snow levels should rise above the mountain
passes. Motorists with plans to travel over the mountain passes
should experience good conditions today through Friday afternoon.
The arrival of a very cold and windy arctic front Friday Night
into Saturday will bring winter driving conditions to the mountain
passes and much cooler weather for the weekend.

&&

.DISCUSSION...

Today through Fri: The biggest changes to the fcst were to
decrease the amnt of pcpn for all non-mountain zones, increase the
winds, and warm temperatures a bit. Though by far the most
eventful part of the fcst will be Fri Nt through the weekend as
we deal with a significant cold front passage that will produce
snow for all elevations, gusty cold north winds and temps as low
as the single digits, we have some relatively mild, but windy
weather to deal with first. Currently behind a cool frontal
passage late yesterday, we`re still anticipating sfc winds to
increase slowly and help to mix out any dense fog now in the Upper
Columbia Basin. We`ve extended the dense fog advsy a few more
hours and will be watched carefully. The good news is that temps
are above freezing, so very slick roads shouldn`t be a big problem
on this important Thanksgiving day travel morning. Today and
Friday all of Ern Wa and N Id will be in a mild pre-arctic cold
front air mass, with well- above normal temps. However, this same
pattern typically favors very gusty winds. This time it`s no
different. Most model guidance shows persistent 850mb winds
(roughly 5k ft above the sfc) from the southwest at 35-45kt.
Expect these winds to begin to increase this morning. Temps will
be mild, even low temps for areas that manage to remain coupled
with these winds aloft (non- valley sites). bz

Friday night through Sunday...The wet but mild weather pattern
will come to an end as an arctic front slides south across the
region bringing much colder and drier air with it. A strong
surface low will slide south across eastern WA and north ID Friday
night, bringing a good chance of precipitation to the eastern half
of the forecast area along with strong gusty southwest winds. Snow
levels will start out around 5k ft Friday evening then come
crashing down overnight. The bulk of the precip will fall as rain
in the valleys. By the time the cold air moves in, the low will be
over central Idaho with showers limited to the southeast zones.
The Camas Prairie may see some low end advisory snowfall but even
this amount is uncertain.

On Saturday the exiting low and building high pressure over
southern BC will set up a strong surface pressure gradient that
will channel northerly winds down the Okanogan Valley and Purcell
Trench and into the basin. This pattern shows the potential for
wind highlights and will continue to be monitored. Saturday
morning temperatures will likely be the high for the day as the
frigid air continues to march south across the area. The rest of
the weekend will continue the cold and dry trend with lows in the
single digits across the northern zones. Valley highs in the 20s
will be common.

Sunday night through Wednesday...The cold temperatures will start
to moderate as northerly winds are replaced by more westerly flow.
Model solutions diverge when it comes to moisture over the region.
The GFS wants to bring the surface boundary back north as a warm
front but the new run of the ECMWF brings a shortwave trough
across the northeast zones. No big changes made to the extended
forecast at this point other than to trend PoPs toward climo for
the end of the forecast period. /Kelch

&&

.AVIATION...
12Z TAFS: We`ve made significant changes to the wind fcst for the
Spokane/ C`Da and Pullman TAFs... increasing the winds speeds
significantly especially for KGEG. 12z OTX raob and VWP showed
40-50kts 1500-2500ft of the sfc contributing significantly to the
rapid mixing at KGEG and simultaneous gusts to 25 kts. These winds
should peak this morning, but only decrease slightly during the
day. For sites that have not mixed, LLWS has been added for the
next few hours. As far as the IFR/LIFR ceilings and/or vsby at
KMWH and KEAT... these are expected to become VFR by mid morning.

NOTE: The VIS sensor at EAT is out of service so amendments to
VIS are not scheduled. bz

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        55  41  50  27  27  12 /  30  20  70  60  10   0
Coeur d`Alene  54  41  49  29  29  12 /  40  40  80  90  20  10
Pullman        55  43  53  32  32  16 /  30  30  90  90  50  10
Lewiston       57  46  56  38  38  23 /  20  20  60  70  60  20
Colville       51  40  47  22  22   7 /  50  40  70  60  10   0
Sandpoint      48  38  45  26  26   8 /  70  70  80  90  20  10
Kellogg        48  39  45  30  30  12 /  80  70  90 100  50  10
Moses Lake     56  41  56  27  27  12 /  10  20  30  30  10   0
Wenatchee      51  41  51  29  29  13 /  10  30  20  20  10   0
Omak           47  37  46  16  16   3 /  20  20  30  20  10   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Dense Fog Advisory until 7 AM PST this morning for Moses Lake
     Area-Upper Columbia Basin-Waterville Plateau.

&&

$$



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