Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 222143

Area Forecast Discussion
National Weather Service Spokane WA
243 PM PDT Sat Oct 22 2016

Overall drier weather is into Sunday except for areas near the
Cascades where next weather system is expected to bring a little
rain late tonight and early Sunday. Increasing chances of wet and
unsettled weather with rain and high mountain snow will begin
again Monday. A wet and mild low pressure system will arrive on
Wednesday with moderate to locally heavy rainfall possible across
the east slopes of the northern Cascades.


Tonight and Sunday...
A widespread lower cloud deck will continue to hang around this evening
with light boundary layer winds not able to sufficiently scour resident
moisture over the region. Isolated showers will be possible near the
Canadian border near Ione and Porthill but end by sunset. A weather
pattern shift will put a dent in the low cloud cover this evening
and overnight but shift and form clouds in other places.

Easterly surface winds will increase tonight ahead of a Pacific trough
becoming parked off the west coast. This will down slope off the
Bitteroot mountains and sufficiently dry parts of the ID Panhandle
and eastern Washington to prevent fog formation tonight. However,
the northeast WA valleys where the drying winds won`t quite reach
may see some patchy valley fog tonight. While the low clouds get
mixed out in many areas higher clouds will fill in the sky tonight
ahead of the cold front approaching the west coast. This front
will increase chances of precipitation over the Cascades with only
light precipitation expected going into Sunday morning. Even a few
sprinkles could fall as far east as Wenatchee, Omak and the
Okanogan Highlands Sunday morning. The front stalls and weakens on
the west side of the Cascades with minimal additional showers
possible on the Cascade Crest Sunday afternoon. The remaining
areas east toward the Idaho Panhandle will be mainly dry with
broken to overcast cloud cover Sunday with temperatures warmer by
2 to 5 degrees. TC

Sunday night through Tuesday: Low pressure off of Vancouver Island
and the WA coast will send across an occluded front Monday night
into Tuesday morning. There will be increasing mid to high level
clouds on Monday with sprinkles possible at times; however, much
of the precipitation is expected to arrive with the front itself.
Although most areas will see the possibility for a light amount of
measurable precipitation Monday night, best chances will be
reserved over the northern mountains where orographics will result
in some additional enhancement. The mountains from the Cascades
over the Northern Panhandle will see up to around a quarter of an
inch of precipitation. Much of the basin will see up to around a
tenth of an inch of precipitaiton with the Central Panhandle Mtns
receiving up to two tenths of an inch or so.


Tuesday night through Thursday: The storm system that arrives on
Wednesday will be much wetter, at least for the northern and
western portion of the forecast area. The shortwave disturbance
will pack more dynamics and tap into a sub-tropical moisture plume
with an inch plus P-wat plume. The surface low will track offshore
with easterly flow across the region. The combination of strong
isentropic ascent and good upslope flow will focus precipitation
across the Cascade Mtns. Temperatures will remain mild with snow
levels climbing above 7,000 feet.

* Rainfall Amounts: The Cascade Mtns will see between an inch and
  an inch and a half. Rainfall amounts will decrease further east,
  but still expecting a wet day for the Wenatchee Area and
  Okanogan Valley. These areas will see between a half an inch and
  three-quarters of an inch of rainfall. Downsloping winds off of
  the higher terrain in the Panhandle will limit rainfall amounts
  to under a quarter of an inch this far east.

* Impacts: Much of the region has already seen a very wet October
  to date. We will have had a pretty good break since our last
  good soaker, so it is difficult to say what another inch plus of
  rain will do across the Cascades. Since soils are on the wetter
  side, we will see an increased risk for minor mud flows and
  debris slides. Highest risk areas will be in and around recent
  burn scars. Low lying areas may see some minor flooding as well,
  especially if any culverts become plugged up with debris. /SVH

Friday through Sunday:
This period is expected to be continue the wet October for the
Inland Northwest. The models are showing a widespread precip event
as a Low positioned off the CA coast pushes moisture into the
region. Models do not have good agreement on the timing of this
push. The window fro precip will be around the Friday afternoon to
evening. With this being a southern push, this event is expected
to be mainly rain with a very limited amount of snow for the
extreme elevations of the Cascades. A brief break is from the
rain is expected for Saturday afternoon before the models begin to
bring in another wave of moisture for Sunday afternoon to evening.
Again the timing of this wave is not in good agreement.
Temperatures will be in the range of upper 40s to 50s for highs
and upper 30s to mid 40s for lows. /JDC


18Z TAFS:  KGEG, KSFF and KCOE taf sites will be impacted by an MVFR
low cloud deck until late this afternoon around 23Z as moisture is
slow to mix out in the more moist low levels of the air mass. KMWH
also will have a lower IFR deck of cloud in the area until around
19Z as fog lifts in abundant sun. The northeast mountains and
Idaho Panhandle will have significant low cloud cover over the region
until around 02Z Sunday (early Saturday evening). After the fog
is gone, the odds of it reforming tonight are much smaller than
they have been over the past few nights. This is due to a
transition to drier E-NE winds in the lower atmosphere. While the
NE winds should deter fog, it could deepen moisture at EAT late
tonight while an upper level disturbance approaches the Cascades.
This will result in an increasing chance of precipitation near the
Cascade. Not confident this will impact EAT, but at a minimum
there should be lowered cigs with a small chance of MVFR
conditions. tc


Spokane        39  54  45  58  45  53 /   0  10  10  20  90  30
Coeur d`Alene  40  56  44  58  45  52 /   0  10  10  20  80  40
Pullman        42  58  46  62  46  54 /   0  10  10  10  80  40
Lewiston       45  61  48  65  49  59 /   0  10  10  10  40  30
Colville       36  54  41  56  43  52 /   0  10  10  20  90  30
Sandpoint      35  52  40  55  42  48 /  10  10  10  20  80  40
Kellogg        39  56  42  57  44  49 /   0  10  10  20  80  80
Moses Lake     41  58  43  58  42  58 /   0  10  10  20  60  10
Wenatchee      44  55  43  55  43  57 /  10  10  10  40  80  10
Omak           41  55  42  55  43  55 /  10  20  10  40  90  20



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