Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 212342

Area Forecast Discussion
National Weather Service Spokane WA
442 PM PDT Wed Mar 21 2018

A change in the weather is expected as a deep upper level low
digs offshore tonight. This will pool moisture into the region
from the south resulting in an increasing chance of precipitation
beginning this evening and continuing at times through Thursday.
Most of this precipitation will fall as rain however snow will be
possible over the higher mountains. A cold front late Thursday
will bring gusty winds and deliver significantly cooler conditions
from Friday through the weekend with the threat of rain and snow
showers each day.


Tonight and Thursday: The warm front will continue to move north
across the Inland northwest this afternoon and evening. It will
provide some light rain across the region. The last several runs
of the HRRR has shown heavier periods of rain moving up the
Okanogan Valley, and across the Palouse early this evening. That
is a result of the precip that is currently occurring down in
Portland and along the WA/OR border. The upper level trough moving
out of the Gulf of Alaska will push south through the night and
pick up the moisture that is streaming into California. Our
heavier stratiform precipitation will move into the Cascades
between 10pm and midnight and then spread east through the night
across eastern WA and north ID. The models have been consistent
for days of the heaviest precipitation occurring overnight into
early Thur morning across the eastern Cascades. There is a period
in the morning when precipitation intensity will decrease, and
then models show heavy precip again in the afternoon as the cold
front begins to push over the Cascades. The heaviest precip in the
afternoon will be across the eastern Cascades and stretch across
the northern tier of WA.

Liquid Precipitation Amounts: Precip amounts will vary. The
highest accumulations will be in the northern Cascades north of
Lake Chelan where they could see an inch to an inch and a half in
the mountains. They valleys will see over three quarters of an
inch. The Columbia Basin will see the least precip with a few
hundredths up to a quarter of an inch possible. Most of the Basin
will see about a tenth of an inch. All other locations will see
0.30 to 0.50 in the valleys with 0.50 to 0.75 in the mountains.
The Okanogan Highlands higher terrain could see up to an inch.

Snow Levels: Snow levels tonight will be above 5k ft. It isn`t
until Thursday afternoon that snow levels will start to fall as
the cold front pushes over the Cascades. The heaviest
precipitation will occur while snow levels are high. By late Thur
afternoon snow levels in the Cascades will drop down to about 3k

Snow Amounts: In the Cascades above 5k ft will see the heaviest
snow amounts. 7 to 14 inches is possible with amounts 20-22 inches
possible as you approach the Canadian border. In the 3-5k ft
range they could see a dusting up to 3 or 4 inches, locally up to
5 along the Canadian border. No snow is expected down to the
valley floors in the Methow, Lake Chelan, Leavenworth areas. North
Id Panhandle will also see some snow accumulation in the
mountains...about 1-3 inches, which would fall either early Thur
morning, or Thur evening.

Winds: Winds will increase ahead of the cold front Thursday
morning across the Palouse and into the Columbia Basin. In the
afternoon the winds will push into the Spokane area. Southeast
winds 10 to 15 mph in the morning becoming southwest 15 to 25 with
gusts up to 30 mph. As the front goes through after 3pm, there
could be local gusts up to 40 mph.

Thunder: Both the GFS and NAM are showing some instability in the
afternoon across the Columbia Basin (north and east of Moses Lake)
and moving north and east through the afternoon ahead of the cold
front. Have added a slight chance of thunder to these locations.

Thursday night through Sunday...A vigorous cold front will move
from west to east Thursday night and drag an upper level low into
the region. The upper level low will dominate the weather through
the weekend. The result will be cool and unstable conditions
which will support isolated to scattered rain and snow showers
across the region from Thursday afternoon through Sunday. One
thing in our favor is that model guidance is very similar in
showing very dry air moving into the region behind the front. This
would mean localized brief moderate rain and snow showers, but
overall not widespread moderate to heavy precipitation.

Snow levels will drop down to near valley floors Friday then
rebound slightly Friday and Saturday to 2000-3000 feet. Some of
the higher terrain in the mountains could see some decent
accumulations through Friday. The passes will see measurable snow
with Sherman Pass and Lookout Pass getting 4-8 inches Friday and
Saturday. This will likely come in the form of brief heavy snow
showers. The northern valleys down towards the Spokane-Coeur
D`Alene metro and south to Pullman-Moscow could see localized
heavy snow/graupel showers that could result in a quick quarter to
half inch of snow. Both of these will have the potential to make
driving conditions quite dicey in a short period of time.

Temperatures will drop 7-10 degrees on Friday behind the front and
another 3-5 degrees Saturday dropping temperatures in the mid to
upper 40s, before rebounding a little Sunday. Gusty winds will
continue through early Friday with gusts through the Basin,
Pa;louse and ridges 30-40 mph.

Monday through Wednesday...High pressure will build into the
region Sunday night with a flat ridge over the region that will
slowly strengthen through the week. This will bring a drying trend
with temperatures warming back to normal through the week with
spring like conditions. Tobin


00Z TAFs: A storm system will move into the region tonight and
linger over the region for several days. Several waves of
moisture will move from south to north through the night. Timing
these waves out past a few hours will be tough, but expect that
cigs will lower and rain chances will increase with each
successful wave. Precipitaiton will be stratiform and moderate at
times. A cold front will move across the Cascades after 18z
Thursday, move quickly through the area and be along the ID/MT
border by 00-03z. This period...18-00z will be when the area will
receive the heaviest rain and also gusty winds to 25 kts. VFR
conditions can be expected through 18z, followed by VFR/MVFR
conditons 18-00z. Tobin


Spokane        43  52  31  46  30  41 /  50  90  80  30  50  60
Coeur d`Alene  41  51  30  44  29  39 /  50  90  90  40  50  60
Pullman        45  52  32  45  31  42 /  50  90  80  40  60  60
Lewiston       47  59  36  53  36  48 /  30  70  60  30  40  50
Colville       41  53  31  47  28  45 /  70 100 100  50  50  60
Sandpoint      38  47  31  43  29  39 /  70  90 100  40  50  70
Kellogg        38  49  29  42  28  38 /  60  80 100  50  50  70
Moses Lake     43  56  31  53  29  51 /  50  60  10  20  30  30
Wenatchee      39  49  31  48  29  50 /  90  80   0  40  20  20
Omak           42  51  31  48  28  48 /  90 100  20  60  30  40


ID...Flood Watch from 8 PM PDT this evening through Thursday evening
     for Northern Panhandle.

WA...Flood Watch from 8 PM PDT this evening through Thursday evening
     for East Slopes Northern Cascades-Northeast Mountains-
     Okanogan Highlands-Okanogan Valley-Wenatchee Area.


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