Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 202227
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
227 PM PST Mon Nov 20 2017

.SYNOPSIS...
Expect wet and mild weather as a series of storm systems brings
several rounds of precipitation this week. Snow levels will be
quite high Tuesday, Wednesday, and Thursday allowing motorists to
travel over mountain passes on wet pavement. Snow levels will
begin to lower just as travelers are heading home Friday into the
weekend.


&&

.DISCUSSION...

Tonight through Tuesday night: A strong shortwave is punching into
the region at this hour and will become sheared apart upon
reaching Western Montana. The main impacts from this wave will be
to bring a drying trend from west to east along with a brief
period of gusty winds. Wind gusts in the 30-40 mph range will be
common across Southeastern WA particularly between Ritzville and
Pullman and points south between 1PM and 4PM then quickly shut off
this evening. The remainder of the Columbia Basin including the
Spokane Area should also blow but thinking gusts will be more in
the 20 to 25 mph range. We are seeing substantial clearing over
the Cascades and working into the Western Basin while showers
continue to fall across the Idaho Panhandle and far SE WA. This
activity will diminish this evening and end overnight. Meanwhile,
wintry travel conditions will continue for the next few hours
across Lookout Pass. As the snow ends, expect cool temperatures to
keep a threat for slick conditions on any mountain passes where
not treated.

The next low pressure system is already reloading off the WA Coast
and following this evening`s shortwave passage, will bring the
plume of subtropical moisture back into the region ahead of a
strong warm front. This will be a strong southerly push of warmer
air and steady climb of snow levels above all valley floors and
eventually all mountain passes. The tricky part of this forecast
will be precipitation type within the East Slopes of the WA
Cascades. Precipitation will expand into these areas between 4AM
and 10AM Tuesday morning. Satellite and CAMS indicate a great deal
of clearing over Central WA right now. In addition, light snow
fell across the Methow Valley today. This combination will lead to
good radiational cooling and the onset of precipitation expected
when valley temperatures are right at or below freezing. Many of
the hi-res models and post-processed data from ensembles suggest a
period of of freezing rain or sleet while the warmer air punches
northward and before switching to all rain. This is a not an ideal
pattern for significant ice accumulations but will be monitored
closely, paying particular attention to temperatures tonight. It
is not out of the question, that low clouds form and keep
conditions warmer than expected so lots of variables will come
into play. Low clouds look to be more of an issue for the valleys
of NE WA and N ID and we see little to no sign of mixed wintry
precipitation types.

QPF amounts for the Tuesday and Tuesday night period will be
around an inch or more in the mountains of Idaho and Cascade
Crest. Most other areas will be around half to three quarters of
an inch, locally lower in the deep Basin and Highway 97 corridor.
Mid and high mountain snow should be able to absorb any rain that
falls in the higher elevations once the switch occurs. The one
area of concern for the lowlands will once again be Paradise Creek
flowing through Moscow. Moscow Mtn picked up an inch or two or
snow and currently holds around 2.50" of water in the snowpack.
This has not ripened yet but may start to with some warmer winds
expected this evening and again Tuesday and additional rainfall.
The rise contributed mainly from rainfall today fell just shy of
bankfull so the next rise on Tuesday may begin to have minor
impacts. /sb

Wednesday through Monday: Very active period of weather continues.
Strong, warm southwesterly flow pattern continues to bring rain
and high snow levels to the area on Wednesday. This is all ahead
of a deep low that drops down out of Alaska into the Gulf of
Alaska. A similar system will move through the Aleutians on
Thursday, acting as a kicker. The old low will eject out of the
Gulf and move across southern Canada. This will bring about a
short-lived break in the weather, sometime around Friday or
Saturday. This will also allow temperatures to cool, with lowering
snow levels.

But the second low will bring yet another round of warm
precipitation for the weekend. This should help the holiday
travelers with high snow levels on Sunday.  When this second low
moves onshore, it will drop snow levels considerably for Monday
and Tuesday.

For Thanksgiving, we`re likely looking at the warmest Turkey Day
ever in Spokane. See below for more details. This is a tricky
call. Temperatures aloft will actually peak Wednesday night or
Thursday morning. But there should also be quite a bit of wind on
Thanksgiving, and that mechanical mixing will help temperatures at
the surface warm up. Also, it will be mostly cloudy with rain,
mainly north of Spokane. So the best chances for record warmth
will likely be south of I-90. Suffice to say, it will be a balmy
Thanksgiving for the Inland NW, with temperatures about 20 degrees
above normal.  RJ


&&

.AVIATION...
18Z TAFs: A strong shortwave is tracking into the region. Steady
pcpn developing ahead of the system will lead to low cigs and
periods of light to moderate rain at the terminals. Cold front
crosses through 19-21z bringing a transition to showers and
increase in winds. This should lead to improving cigs/vis.
Midlevels clear this evening but confidence is low how this will
impact the saturated boundary layer, especially across NE WA and
N ID. If stratus clears, fog will be possible as winds decr this
evening and switch back to the E/SE. If the stratus holds firm,
this will be the main restrictions before the next moist laden
warm front arrives after 16z. Wenatchee and Moses Lake will stand
a better shot for clearing, some fog, but quicker onset of top-
down saturation with the onset of pcpn. /sb

&&

.CLIMATE...
The normal high for Spokane on Thursday is 38F.  The record high
is 60F, set in 1933. But this wasn`t Thanksgiving Day that year.
So the record warmest Thanksgiving is 55F, set on 3 different
days:

27 Nov 2014
26 Nov 1998
29 Nov 1883

The current forecast for Spokane Airport is 57F. The forecast for
downtown Felts Field is 59F.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        34  46  41  53  45  57 /  10 100 100  70  50  60
Coeur d`Alene  33  45  40  53  44  56 /  50 100 100  70  50  70
Pullman        37  49  44  56  47  59 /  10  90 100  70  30  70
Lewiston       39  53  46  59  48  62 /  10  80  80  70  20  50
Colville       32  41  36  47  40  53 /  30 100 100  60  40  70
Sandpoint      31  41  37  47  41  52 /  90 100 100  70  70  90
Kellogg        32  42  39  49  43  51 /  80 100 100  80  40  90
Moses Lake     33  44  38  52  42  60 /   0 100  80  60  40  30
Wenatchee      33  40  36  48  40  55 /  10 100  40  60  30  50
Omak           33  42  36  47  42  54 /  10 100  70  50  40  70

&&

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

&&

$$


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