Area Forecast Discussion
Issued by NWS Spokane, WA

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742
FXUS66 KOTX 241138
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
338 AM PST Fri Nov 24 2017

.SYNOPSIS...
Showers will linger in the mountains today and tonight, otherwise
there will be a brief break in the weather. More wet and unsettled
weather will move back into the region on Saturday into Sunday
with another weather disturbance moving in early next week.


&&

.DISCUSSION...
Today through early Saturday...Westerly flow will be over the
Pacific Northwest today as the low pulls away from the area.
Model guidance is reflecting the satellite with some drier air
moving through this flow. There will still be a chance for
mountain rain and snow showers for the Cascades and Panhandle
mountains in orographic flow. The flow begins to buckle tonight
and Saturday as another weather system sets up in the eastern
Pacific. For tonight and Saturday morning the moisture will get
pushed north into southern Canada and that will result in the
chance of showers moving up into the northern mountains tonight
and Saturday. Snow levels across the north will drop to around
3000 feet today and below 2000 feet tonight and early Saturday.
Precipitation amounts will be a tenth or two and will result in
1-3 inches of snow for the mountains, and possibly as much as 4-6
inches near the crest of the Cascades. Temperatures will cool down
10-12 degrees with the cold air advection, but this is still 5-7
degrees above normal.

Saturday and Saturday night...The flow will back to the southwest
as an upper level low slides south in the eastern Pacific. The
southwesterly flow will once again tap into deeper subtropical
moisture, maybe not as deep as the past weather system, but pretty
close. Incoming moisture increases to well over 200 percent. Lift
will be provided by isentropic upglide and this combination will
open the door for another period of warm stratiform precipitation.
Precipitation will likely start across the southern Washington
Cascades by late Saturday afternoon, but quickly moves northeast
across the forecast area Saturday evening. Snow levels will
increase rapidly with the warm air advection. Snow levels will
increase to to around 8000 feet across the southern zones and
between 5000-6000 feet across the north by Sunday morning.
Precipitation will be as valley rain and high mountain snow. The
Cascades will be able to accumulate 3-5 inches of wet high snow
early Saturday evening, before the snow turns over to rain. Tobin

Sunday and Sunday night: Cold front looks to swing across the
region during the day. There are some timing differences amongst
the models with the 00Z GFS and NAM noticeably faster than the
00Z Canadian and ECMWF solutions. The forecast will favor the
ECMWF solution, which is in good with the Canadian model on
timing with the front pushing across the basin in the afternoon
and then into the Panhandle by the early evening. This frontal
passage has some similarities to the front that just went through
on Thanksgiving, but there are also a few key differences. Low to
mid level lapse rates will not be nearly as steep as yesterday. So
we are not looking at repeat for predominantly convective
precipitation and no thunderstorms expected. Precipitation that
forms ahead of the front will be stratiform in nature with little
to no precip in the rain shadow the Cascade Mountains.
Precipitation amounts will pick up across the eastern two-thirds
of the forecast area. The mountains stand to receive between a
quarter to a half an inch of precipitation with around a quarter
of an inch possible in the eastern basin into the Spokane/Coeur
d`Alene areas down to the Palouse and L-C Valley. We are looking
at all rain except for snow over the Cascade crest as snow levels
drop behind the cold front. Winds will increase behind the front.
Since precip will be stratiform, we won`t see winds really pick up
until frontal passage. Strongest winds are expected across
exposed areas of the basin and into the Spokane Area late Sunday
afternoon into Sunday evening. Winds at 850 mbs will decrease
quickly once the front blows through. With these factors in mind,
I expect winds to be weaker with this front than what we observed
with the front on Thanksgiving. Expect wind gusts up to around 30
mph.

Monday through Thursday: Temperatures will cool back to average
for late November next week. Another shortwave trough of lower
pressure will swing across Tuesday night into Wednesday. This
wave will be transient and swing through fairly quickly.
Precipitation amounts will be much less compared to the recent
storm systems we have been getting. Those weather systems have
been tapping into a good source of moisture from the tropical
Pacific. The disturbance for next week will not have that same
kind of moisture tap. Snow levels will be lower though. It does
not look like they will be low enough for much snow in the
valleys, but elevations down to around 3,000 feet will see the
possibility for some snow. There will be another 24 to 48 hour
period of dry weather at the end of the work week before
precipitation chances increase for next week with models
indicating a deep upper level trough digging in over the region.
/SVH


&&

.AVIATION...
12Z TAFS: Westerly flow will be over the region today and tonight
with isolated to scattered showers possible near the Cascade
crest and along the ID/MT border. A wave cloud has developed down
stream of the Cascades this morning and will result in a
high level scattered-broken deck this AM. For the TAF site this
period will bring a break in the weather. Some patchy fog will be
possible for the basin and up near the KGEG/KSFF/KCOE corridor at
times, but not enough to be put in the forecast for now. Expect
VFR conditions through 12z Saturday. Tobin


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        45  32  45  39  52  33 /  10  10  10  70  60  80
Coeur d`Alene  44  32  45  37  52  33 /  10  10  10  70  70  80
Pullman        46  32  47  41  55  35 /  10   0  10  50  40  80
Lewiston       52  33  51  41  57  38 /  10   0  10  30  20  70
Colville       44  33  42  35  47  31 /  10  10  10  70  80  80
Sandpoint      42  32  42  35  48  33 /  10  20  10  70  60  80
Kellogg        41  30  44  36  50  33 /  20  10  10  70  60  80
Moses Lake     50  31  45  36  51  31 /  10  10  20  50  60  40
Wenatchee      48  31  41  35  46  32 /  10  10  30  70  60  30
Omak           46  32  42  35  46  31 /  10  10  20  70  80  30

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$



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