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Area forecast discussion 
National Weather Service Spokane Washington
417 am PST Thursday Feb 11 2016

Synopsis...
a warm front will move across the inland northwest today and
tonight spreading a chance of rain across much of the area with
snow levels at the highest mountain elevation except near the
north Cascades. This front will be followed by the passage of a
cold front on Friday which will bring another chance of
precipitation to much of the area as well as slightly lower snow
levels. Unsettled weather will continue through the weekend into
early next week with valley rain, High Mountain snow and breezy
winds expected. Temperatures will be quite mild on Monday with
many locations seeing highs in the mid 50s to low 60s.



&&

Discussion...
today and tonight...the weather during this period will generally
revolve around a developing warm front. As of 2am, the water vapor
looper was showing a broad swath of moisture oriented from north-northeast-south-southwest
right off the coast. Meanwhile the upper level ridge of high
pressure remains poised over the inland northwest. The ridge is expected
to amplify slightly over the area today and tonight, as height
falls continue develop off the coast. Despite the presence of the
ridge we should see the first chance of precipitation this week,
the question is how soon will it develop and what will most of it
fall as. Looking closely at the latest radar mosaics it appears
the front will come through in two swaths. The first was
responsible for the east-west band of light echoes extending along
the Washington/or border and moving slowly northeastward. This one will
likely weaken as it moves farther northward with weakening
isentropic ascent, especially over the eastern third of Washington
and north Idaho. If anything falls out of this band it will likely
be very light. Over central Washington, the chances for measurable
precipitation are a little better due to slightly deeper moisture
combined with weak upslope flow into the Cascades. We suspect most
of the precipitation will fall as rain, however north of Lake
Chelan current wet-bulb temperatures are below freezing and they
may not climb much this morning. So we expect to see primarily
snow. The second surge of precipitation will bring a much better
chance of measurable precipitation. This wave is likely a
reflection of a compact shortwave located over northern California
moving steadily northward. The hrrr suggests this second band will
track into the Wenatchee and Moses Lake area around midday and
then into NE Washington and north Idaho by late afternoon or early
evening. Snow levels climb steadily with this portion of the warm
front. Wet-bulb zero heights reach 6000 feet or higher across the
entire forecast area save a small portion of the north Cascades
mainly impacting the Methow Valley. It's a tough call as to how
effective the cold air damming will be in this area as the
surrounding air mass is awfully warm. The 850 mb flow maintains a
weak upslope orientation at least through early Friday which is
favorable for keeping snow levels locally down to the valley
floor, however surface temperature per BUFKIT profiles hover near
or slightly above freezing. We put several inches of snow in the
forecast across the upper Methow Valley however that's assuming
any snow which falls is able to accumulate rather than melting as
it falls. Confidence is not high due to the precarious temperature
profiles. Elsewhere we are much more confident about primarily a
rain event. Rainfall totals should range from .15-35 inches across
the northern mountains and extending into the northern Idaho
Panhandle, with lighter amounts across southern Washington and the
central Panhandle. Near the Cascades, precipitation amounts could
range from 0.30-0.70 inches.

For Friday, the ridge finally gives way and a SW-NE oriented upper
level jet pokes into the southern portions of the region by
midday. This will turn the steady warm frontal precipitation to
more of a showery regime with most of the precipitation occurring
near the cold front. The cold front will likely end the
precipitation threat in the Lee of the Cascades during the morning
hours as the upslope flow turns to a downslope westerly regime.
Meanwhile we expect the shower coverage to increase over the
eastern third of Washington and over the Panhandle during the
afternoon as the front destabilizes the atmosphere and enhances
any orographic ascent. Generally speaking the precipitation
amounts from the cold front will be lighter than whats produced
from the warm front.

Temperatures will remain milder both days
over the eastern third of Washington and the Idaho Panhandle with
highs in the 40s to middle 50s. Cooler temperatures will remain a
fixture over central Washington today due to the cold air damming
with highs in the 30s to lower 40s. The cold front should enhance
mixing on Friday bringing an end to the inversions with highs
climbing into the upper 30s to middle 40s. Fx

Friday night through Wednesday...a mild and unsettled weather
pattern is expected this weekend through at least the middle of
next week. Initially a slightly cooler air mass will move in
Friday night and Saturday as an upper trough passes through. Mid
level westerly flow will favor most of these showers for the
Cascade crest and Idaho Panhandle. Snow levels by Saturday
morning lower to 3000-4000 feet with snow showers expected over
the mountain passes. Then an atmospheric river of subtropical
moisture becomes aimed at the area Saturday night into Sunday.
This will bring more rain and snow with snow levels rapidly rising
from 2500-4000 feet initially early Sunday to 6000-7000 feet
Monday as a warm front passes through. The atmospheric river
begins to lift north Sunday night into Monday to near or just
north of the Canadian border by Monday afternoon. Strong mid
level westerly flow throughout this event will favor moderate to
heavy precipitation for the Cascade crest and in the mountains of
the Idaho Panhandle with added orographic lift...with mainly
light amounts over central and eastern Washington as a strong rain
shadow develops. Meanwhile Monday into Tuesday a surface low
tracking into southern British Columbia will result in a strengthening south-
southwest winds which combined with the warmer air mass will lead
to increased snow melt for areas that have snow currently. 850mb
winds increasing to 30-45 kts will likely result in breezy to
windy conditions over the region...especially the upper Columbia
Basin, Spokane area, and Palouse. Jw

&&

Aviation...

12z tafs: upper level ridge remains fixed over the inland northwest during
this period while a warm front will bring an increasing threat of
rain to most of the taf sites. Before the front arrives we are
dealing with yet another round of fog. It's very difficult to tell
how widespread it is since the low clouds are being shielded by high
clouds above. As of 4am, most of the LIFR/IFR fog was around geg and
fafb but low dewpoint depressions suggest it could easily develop at
Coe sff and mwh as well. Confidence is low though so we will
generally mention partial fog and the possibility of rapidly
changing visibilities. By 18z or so the fog threat will decrease for
all sites with VFR conditions generally prevailing at all sites. The
threat of rain will then develop by late afternoon or early evening.
Persistent rain is then expected overnight at all sites except puw
and lws. Cigs will gradually fall and MVFR conditions will likely
develop. Fx

&&

Preliminary point temps/pops...
Spokane 45 38 47 34 45 35 / 10 60 70 50 40 60
Coeur D'Alene 46 37 47 36 45 34 / 10 70 70 70 60 70
Pullman 51 40 52 38 47 36 / 20 30 40 60 40 70
Lewiston 55 44 57 41 54 40 / 10 20 30 50 30 60
Colville 40 34 41 33 43 35 / 10 80 80 50 50 60
Sandpoint 41 35 41 34 42 34 / 10 80 80 90 60 70
Kellogg 42 37 43 35 39 33 / 10 70 60 90 80 90
Moses Lake 46 38 49 34 52 38 / 20 50 40 30 10 40
Wenatchee 39 34 44 33 47 35 / 50 80 50 20 10 50
Omak 38 35 37 30 42 33 / 30 90 70 30 20 40

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...air stagnation advisory until 10 am PST Saturday for east slopes
northern Cascades-Moses Lake area-northeast mountains-
Okanogan Highlands-Okanogan Valley-upper Columbia Basin-
Waterville Plateau-Wenatchee area.

&&

$$

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