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Area forecast discussion 
National Weather Service Spokane Washington
530 am PDT Fri Oct 21 2016

the atmospheric river which delivered moderate to heavy rains to
much of the inland northwest will remain over southeast Washington
and the southern Idaho Panhandle today and tonight. This will
bring a renewed threat of rain later this morning and into
tonight. Moderate rainfall amounts will be possible again in these
areas, especially tonight. Meanwhile another trough of low
pressure will move into the Cascades this evening and through the
north Idaho Panhandle overnight. This will bring a threat of light
rain showers to these areas. Drier weather is expected for most
locations on Saturday into early Sunday but the next weather system
is expected to move push a threat of rain into the Cascades late
in the day and across the remainder of the area late Monday or
Tuesday. Wet and unsettled weather will then continue through most
of the week.


today through Saturday night...the atmospheric river which
brought widespread moderate to heavy rains to much of the inland
northwest has since moved into extreme southeast Washington and
the southern Panhandle as of early this morning per the latest
blended precipitable water product. Whereas moisture values in
this plume were around an inch yesterday, they have since fallen
to around 0.60-0.70 inches. This drying trend combined with little
if any deep ascent along the feature has led to a rapid decrease
in precipitation in that area. If the plume were going to sag
south of the region today, the forecast would be a relatively easy
one. However that's not whats expected as the plume is forecast to
move slowly northward later today as the next upper level trough
moves into western Washington. This will result in an increasing
precipitation trend after mid-morning and then really picking up
during the afternoon and evening. Much of this increase can be
attributed to the 850-700 mb winds shifting from their current west-southwest
orientation to more of a south-southwest one. This will result in much strong
isentropic ascent and a growing area of precipitation over southeast
Washington and the southern half of the Idaho Panhandle. We are
fairly certain that this will occur as all models solutions are
showing this increasing precipitation trend and as of 2am...the
ramifications of this shift was resulting in a precipitation
uptick near the central Oregon Cascades. Extrapolation of this
feature places the increased precipitation threat into the southeast part
of our forecast area before mid-morning. What's questionable
though is how far north will the shield of precipitation drift.
Some models have it as far north as a Sandpoint-Spokane-riztville
line while others keep it south of a Kellogg-Pullman-Walla Walla
line. In cases like this it pays to defer to to an ensemble mean
position which suggests the best chances will hedge toward the
southern solutions, however confidence is low and it could easily
rain farther north. Initially the precipitation will be light with
most totals coming in at less than 0.20 inches for the day but
there will be convective enhancement within this band with model
lifted index values nearing 0 during the afternoon. This could
lead to locally heavier amounts but it should not be widespread.
The scenario becomes more complex overnight as the aforementioned
shortwave trough moves into the Cascades this evening. The
approach of this trough will introduce another round of
precipitation near the Cascades while it will enhance the ascent
along moisture plume to the southeast. Looks like precipitation
totals could range from 0.25 to 0.50 inches from the Blue
Mountains to the Camas Prairie and extending into southern
Shoshone County overnight. The Cascade feature itself will not be
impressive from a rainfall standpoint as much of what falls will
initially occur near the crest and could have a rough time
spreading into the Lee valleys and western Columbia Basin as the
850-700 mb flow will primarily be out of the west and there should
be a well-defined rain shadow. The threat of precipitation along
this trough will redevelop over NE Washington and the north Idaho
Panhandle late tonight and into early Saturday morning. Once this
trough moves east of the Idaho Panhandle by midday the threat of
precipitation across the inland northwest will dwindle rapidly.

Aside from the varying precipitation threats today, another tough
problem will be the stratus and fog which has become entrenched
across the Columbia Basin, northern Washington and Idaho valleys
and the Spokane area. It's very difficult to ascertain how
widespread these cloud are since they are being obscured by a
thick blanket of higher clouds, however late last evening the fog
product was showing these clouds were fairly widespread. That
being said it's quite conceivable that sunshine could be limited
today across these areas that don't see much threat of rain today
due to limited mixing potential in the lower atmosphere. Fx

Sunday through thursday: showery and mild weather will continue
through the weekend and into next week as an upper level low
persists in the eastern Pacific and gradually sinks further south
along the West Coast. Shortwaves in the moist southwest flow have
the potential to bring showers to the region, but at this time
precipitation seems fairly light. A frontal band associated with the
offshore low will move across western Washington on Sunday and
remains stalled up to the Cascades by Sunday night. Models seem to
have a difficult time on slow moving systems, and this is not
exception. There is some indications that the frontal band will
nudge further east of Cascades although prefrontal showers are
possible by Monday afternoon across northeast Washington into north
Idaho. Monday also looks to be the mildest day of the week. It seems
that the GFS/European model (ecmwf) push the frontal boundary across the inland northwest
Monday night into Tuesday with up to a 0.25" of rainfall possible
and locally gusty southwest winds. By Tuesday night and beyond, the
weather pattern gets a bit messy. The upper level Pacific trough
slips southward and a weak Flat Ridge builds over the Pacific
northwest. Yet another moisture plume becomes evident in the
southwest and increases the chances of precipitation across Oregon
into Washington. The timing and track of this moisture is difficult
to find consistency among the models, so opted broad brush the area
with a chance of rain and High Mountain snow for Tuesday night
through mid week. Expect rainfall amounts to continue to ratchet up
during the week. Aside from Monday, temperatures will be near
seasonal normals across the region.


12z tafs: early this morning the main feature on satellite was a
swath of moisture and some isolated showers hovering over the lws
and puw area associated with yesterdays atmospheric river. This
feature is expected to drift very slowly northward today and will
gradually spread the threat of precipitation up toward geg-sff-Coe
although it may not get that far north. The showers could bring
periodic MVFR cigs to puw but lws will likely remain in the VFR
category. The threat of precipitation will likely continue into the
evening for this area. For geg/sff/Coe/mwh the forecast is much
tougher due to a deck of low stratus and fog. We have no idea how
widespread it is since it is being covered by high clouds, however
suffice it to say conditions could vary rapidly from IFR at times to
brief VFR breaks. Not confident this low cloud cover will break
before early afternoon at geg/sff/Coe as the low level mixing
potential is low. The best chances for improving conditions will
come with the threat of showers later today. Some models are eager
to bring showers into this area, however based on satellite, we have
a feeling it could remain just to the south. When and if the low
clouds break later today and into the evening, there is a good
chance it could reform later tonight as we get influenced by
increasing SW low level winds combined with a saturated boundary
layer. Of all sites, the eat one is the easiest as it should see no
fog and prevalent VFR conditions. Fx


Preliminary point temps/pops...
Spokane 53 42 53 41 56 44 / 10 20 20 10 10 20
Coeur D'Alene 54 43 52 42 56 42 / 20 20 20 10 20 20
Pullman 55 43 54 43 59 45 / 30 30 10 10 10 20
Lewiston 60 46 60 46 62 47 / 30 60 10 10 10 20
Colville 52 39 52 38 55 41 / 0 20 10 10 20 20
Sandpoint 51 40 49 37 54 40 / 10 20 30 10 20 20
Kellogg 52 41 48 40 55 41 / 50 50 40 10 10 20
Moses Lake 56 40 58 42 58 43 / 0 0 0 10 10 10
Wenatchee 56 41 57 42 55 42 / 0 10 0 10 20 20
Omak 54 37 56 40 54 41 / 0 10 0 10 20 30


Otx watches/warnings/advisories...


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