Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 052237
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
237 PM PST FRI FEB 5 2016

.SYNOPSIS...
Another frontal system will arrive tonight bringing rain to the
lowlands and snow to the mountains. It will become windy after
midnight tonight with gusts up to 45 mph over southeast
Washington, the Palouse, and West Plains. Dry weather and light
winds will develop on Sunday and continue through mid week as a
strong high pressure system sets up over the region. More active
weather is expected by the end of the work week.

&&

.DISCUSSION...
...WINDY CONDITIONS TONIGHT INTO SATURDAY MORNING...

Tonight and Saturday: A dynamic shortwave trough of lower pressure
will race across the region tonight. Satellite imagery shows the
cold front just off the coast of WA at around 2:00 PM this
afternoon. The water vapor channel indicates good darkening
immediately behind the front. This is a good signal that once the
precip shuts off, we will see low clouds mixing out and stronger
winds aloft mixing down. Precip will mainly be confined right
along the cold front for most areas. This will result in a short
duration precip event of between 2-4 hours. The exceptions will be
the east slopes of the northern Cascades and the ID Panhandle.

The slop over precip across the Cascade crest has the potential
to extend a bit further into the east slopes more than usual as
high resolution models (i.e. HRRR) indicate a moderately strong
Puget Sound Convergent Zone (PSCZ) setting up. Snow fall amounts
in the east slopes of the northern Cascades will likely be fairly
light with the front this evening, but snowfall rates may be quite
heavy underneath the PSCZ through the overnight hours. The HRRR
model shows this convergent zone first extending over the Methow
Valley late in the evening through about 2:00 AM and then
concentrating further south between Plain and Lake Chelan late
tonight into Saturday morning. It is not uncommon to see snowfall
rates of 1-2 inches per hour underneath the PSCZ due to the
convective nature of the snowfall. Because of this, we have made a
minor adjustment to the Winter Weather Advisory to include Plain
and locations along Lake Chelan such as Lucerne.

Snowfall amounts are not expected to be as heavy across the ID
Panhandle, but some ongoing snow showers are expected to continue
through Saturday morning. Some showers may be on the heavier side
behind the cold front as lapse rates steepen a bit. The main
impact will be going over Lookout Pass where around 2-4 inches of
snow will be possible.

The other impact with this storm system will be for some windy
conditions. The GFS model indicates the strongest potential for
winds. It shows winds up at 850 mbs of up around 50 kts, but other
model guidance are closer to 40-45 kts. There will be decent cold
air advection with the passage of the cold front with a degree of
confidence that these stronger winds aloft will be able to mix
down to the surface despite a nighttime passage. Strongest wind
gusts are expected to take place across the Spokane Area, on the
Palouse, and in the Northeast Blue Mtns (including around Pomeroy
and over Alpowa Summit). Strongest gust will likely occur with
cold front passage late tonight into early Saturday morning in the
range of 40-45 mph. Winds will then be generally breezy for the
rest of the day on Saturday. Gust potential will be borderline
advisory criteria, but confidence is low and duration will likely
be fairly short if achieved. /SVH

Saturday night through Friday...Model agreement is good and
consistent for multiple runs now in depicting a strong upper level
ridge over the region from Sunday through Wednesday. Confidence
is high for a run of dry weather after lingering snow showers from
Saturday`s system die out over the Idaho Panhandle. The areal
extent of at least morning fog and low clouds...potentially
deteriorating air quality and temperatures will be the main
forecast problems during this strong ridge inversion scenario.

The region may be broken out into three distinct areas of varying
weather. Firstly...over the Palouse and points south as far west
as Ritzville or so a persistent easterly gradient will likely keep
fog and low clouds to a minimum and allow temperatures to elevate
int the solid 40s and even into the 50s by mid week.

The easterly gradient will serve to pool an increasingly moist and
stagnant boundary layer in the deep basin and Cascades
Valleys...banked against the mountains. It is here where the best
chance of significant fog and stratus and the lowest chance of
daytime sun will be found. Also the coolest temperatures and
weakest diurnal swings.

Over the northern Columbia basin and many of the valleys of
northeast Washington and north Idaho a regime of overnight and
morning fog and low clouds with at least partial sunshine in the
afternoons and evenings look plausible...with the protected
valleys north of the basin slowest to scrub each day.

On or about Thursday models are coming into loose agreement on
breaking down or at least substantially weakening the upper ridge
with both the GFS and EC depicting a short wave passage either
Wednesday night or Thursday...followed by a more active close to
the work week with follow on waves. At this time none of these
disturbances looks particularly strong or organized...but well
worth increasing precipitation chances for valley rain and
mountain snow for late in the week. /Fugazzi

&&

.AVIATION...
18Z TAFS: A weak disturbance overtopping the ridge of high
pressure over the aviation area will keep light snow and rain
along the edges of the area yet away from the TAF sites so no
mention made as far as precipitation in them for today. Some pesky
fog and low clouds are on the decrease in the Columbia Basin at
KMWH and further west to KEAT as well but as the southwest winds
increase ahead of the next weather system to pass through tonight
this fog and low cloud should decrease/erode. Next weather system
brings in mostly rain for lowland aviation sites with snow for the
mountains. Before the winds with the frontal passage mix down
there is likely to be a few hours of low level wind shear between
06Z-10Z Saturday...then after the winds mix down to allow for
gusty primarily southwest winds for the rest of the night and into
Saturday Morning...with gusts up to 40 mph at Spokane and Pullman
still. /Pelatti

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        33  40  28  40  30  43 /  70  10   0  10   0   0
Coeur d`Alene  32  40  26  39  30  44 / 100  20  10  10   0   0
Pullman        36  42  30  44  33  48 /  60  10  10  10   0   0
Lewiston       40  50  32  50  35  54 /  20  10  10  10   0   0
Colville       32  39  27  36  29  41 /  80  10   0  10   0   0
Sandpoint      33  39  27  36  29  41 / 100  30  10  10   0   0
Kellogg        32  36  26  37  30  43 / 100  60  10  10   0   0
Moses Lake     32  46  29  43  31  45 /  40   0   0  10   0   0
Wenatchee      31  42  29  38  30  40 /  40  10   0  10   0   0
Omak           30  40  26  34  29  38 /  60   0   0  10   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Winter Weather Advisory from 6 PM this evening to 8 AM PST
     Saturday for East Slopes Northern Cascades.

&&

$$


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