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Area forecast discussion 
National Weather Service Spokane Washington
434 PM PDT Monday Oct 20 2014

Synopsis...

A cold front is very slowly approaching the inland northwest which
will bring an end to the above average temperatures. Not all areas
will see rain with the passage of this first front but a series of
very moist systems will continue to impact the region through the
week...bringing widespread rain and lowering snow levels to the
higher peaks. The active pattern will continue through the weekend
with the potential for heavy rain continuing as moisture
associated with former typhoons makes its way toward the Pacific
northwest early next week.

Discussion...
tonight through Wednesday night...
overview and model discussion: an upper level ridge of high
pressure is positioned over the central US ... between two
long wave trofs. The feature we are concerned with is a massive
trof over the northeastern Pacific with multiple shortwaves
embedded in the ancticyclonic circulation. The parent low is
located well northeast of the inland northwest...near the Alaska
Peninsula. Closer to home is the first of many shortwaves that
will bring an end to the early Fall weather and replace it with
more normal late Fall weather. The frontal boundary
associated with this first trof is located near the Washington/or coast
and will slowly move inland tonight thanks to a potent vort Max
rounding the base of the trof. Showers are evident along and west
of the Cascades with high clouds having a hard time progressing
east...giving eastern Washington and northern Idaho one last
mostly sunny and near 70 degree day.

Models have had a hard time capturing the very slow forward
progress of this frontal boundary. The poor initialization is
leading to a difference in model solutions in the very short
term...mainly regarding the precipitation potential overnight in
the southeastern portion of our area. The NAM is the outlier which
is bringing a narrow band of heavy precipitation late this evening
over Adams and Lincoln counties...with a maximum of .50 inch of
water...while the sref, GFS, and European model (ecmwf) are all indicating precip
amounts closer to from a trace to .10. Quite the difference for
the first 12 hours of a forecast!

Will have to watch how the radar trends this evening but at this
time we are discounting the NAM and leaning heavily toward the
sref, GFS, and European model (ecmwf) solution. The more common solution focuses
the lift and subsequent heavier precipitation amounts mainly in
pendleton's forecast area...but it will clip Asotin, Nez Perce,
and Lewis counties. No widespread flooding is expected but
certainly localized standing water could lead to some minor issues
if these counties do see the .50 plus that is possible overnight.

Beyond tonight and continuing into Wednesday, the models are in
better agreement with the large scale features adding to our
confidence.

Weather highlights through Wednesday night: the only other
potential impact of note is lowering snow levels over the
Bitterroot Mountain range with expected precipitation overnight.
Snow levels will stay above our highest passes in the region so no
travel impacts are expected. While we don't expect to see snow
sticking to the ground, it's hard to rule out seeing snow
accumulating on the highest peaks and maybe snow briefly mixing
with rain at our highest Road passes. Again, no impacts are
expected at this point.

The remainder of this period will consist of a brief drying period
before the next much more vigorous system arrives (we'll call it
storm 2). The arrival of storm 2 is preliminarily scheduled for
late Tuesday night along the Cascade crest...spreading to the
Idaho Panhandle by Wednesday afternoon. The initial surge of
heaviest precipitation will remain over Chelan, Okanogan, Douglas,
and Ferry counties. The impressive fetch of subtropical moisture
being tapped by this low pressure system will raise precipitable
waters values across the region 150-200% of normal. Localized
flooding will be more of a concern with storm 2...especially
considering the recent burn scars. 36-48 hour local rainfall
totals with storm 2 could exceed 2 near the Cascade crest with
1 likely over much of the northern third of Washington and the
Idaho Panhandle.
Ab

Thursday through Monday...cool and unsettled weather will dominate
the large scale weather pattern as a Pacific trough sends a series
of weather impulses our way. The region will be in moist southwest
flow aloft or Thursday and Friday. A strong jet stream will propel
a fetch of deep moisture of tropical origins toward the pacnw
coast. While most of the forecast area will see a decent amount of
precipitation from an extended period of moist and unstable
southwest flow on Thursday and Friday along with some high
elevation snow for the Cascades, the inland northwest will see the
full benefit of this moisture with a strong warm front pushing
north into the region Friday night into Saturday. The strong warm
air advection associated with this warm front will keep
temperatures rather mild overnight Friday. In fact, some of the
southern valley locations like Wenatchee and George may only cool
a few degrees from friday's Max temps. A cold front will sweep
through the region Saturday, followed by the passage of the upper
trough Saturday night. We may see a brief break in the wet weather
on Sunday into Monday before the next Pacific storm approaches
with another round of valley rain and mountain snow. /Kelch

&&

Aviation...
06z tafs: slow moving cold front spreading, thickening, and
lowering clouds from west to east right now near Moses Lake and
points west. This will continue overnight and the front will exit
north Idaho tomorrow afternoon/evening. Some moderate to heavy
rain may occur along a very thin and elongated area within the
frontal band per some of the short term models which may cause
MVFR ceilings and visibilities at times. As to be expected after
rainfall there is the possibility of fog and low cloud formation
afterwards. /Pelatti

&&

Preliminary point temps/pops...
Spokane 47 57 43 54 47 57 / 50 30 10 90 90 80
Coeur D'Alene 46 55 40 54 45 56 / 50 50 20 90 90 80
Pullman 45 56 41 59 47 56 / 70 60 10 70 60 70
Lewiston 49 61 43 64 50 60 / 70 70 10 30 20 70
Colville 46 57 42 52 46 57 / 40 30 20 100 100 80
Sandpoint 45 54 40 52 44 55 / 40 50 30 100 100 90
Kellogg 43 51 38 53 44 52 / 60 90 30 60 80 80
Moses Lake 46 64 45 58 49 62 / 30 10 20 90 60 50
Wenatchee 45 62 45 55 46 60 / 40 10 60 80 80 50
Omak 43 60 44 53 45 58 / 50 10 60 100 80 60

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&

$$

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