Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 221239

Area Forecast Discussion
National Weather Service Spokane WA
517 AM PDT Sat Oct 22 2016

Drier weather will develop today across most of the Inland
Northwest after a weak upper level disturbance tracks through the
Idaho Panhandle this morning. The drier weather is expected to
persist through the weekend for most locations, but the next
weather system is expected to  push a threat of rain into the
Cascades late tonight and Sunday. Meanwhile dry weather will
likely persist over most of the area until late Monday or
Tuesday. Wet and unsettled weather will then continue through most
of the week.



Today through Sunday...2 distinct systems will impact the
Inland NW today. The first is the remnants of the atmospheric
river which moved into the area 2 days ago. According to the
blended precipitable water tool it was still entrenched over
extreme SE Washington and extended into the central Idaho
Panhandle. Decent isentropic ascent was continuing to produce
light to moderate precipitation along this boundary, but it won`t
likely do that for much longer. The reason is a more progressive
trough axis was plowing rapidly eastward through the eastern third
of Washington and will soon move into Idaho. This feature also was
producing some precipitation along a line from Davenport to
Colville, but it was relatively light and fast moving.
Extrapolation of this trough places it into western Montana before
mid-morning. We should see a drier weather picture develop once
this trough moves through the forecast area with little threat of
precipitation for the remainder of the day. The difficult part of
the forecast will then deal with what will happen to the stratus
entrenched over much of the region. Will it burn off or persist
through most of the day? Unlike yesterday at this time there is
quite a bit more stratus than fog and that trend should likely
continue with a gradual drying trend expected in the boundary
layer with a little bit stronger winds.

By late this afternoon and tonight the relatively dry weather will
continue as the low-level winds turn more east to northeast with
the next low pressure area approaching the coast. According to the
NAM model this will take most of the low-level moisture and pile
it toward the Cascades. The dewpoints are also expected to fall
quite a bit given this offshore flow. This suggests fog (if any
forms) will be much less prevalent that what we`ve been seeing
lately. The exception could be over the protected valleys of
northeast and north-central Washington. While most locations will
be dry, the one exception will develop near the Cascades as the
low level moisture piling will coincide with deepening mid-level
moisture associated with the offshore low. This will result in an
increasing threat of light precipitation, mainly west of a
Wenatchee to Omak line. This threat will continue through Sunday.
Any precipitation which forms should be much lighter than what we
have seen lately as there are no signs of an atmospheric river
intrusion. fx

Sunday night through Wednesday night....A prolonged interval of
general warm southerly flow marks most, if not all of this time
interval. Numerous weather systems with fairly well maintained
moisture taps extending toward the south/southwest move through the
forecast area and allow the general trend of forecast temperatures
to remain generally on the warm side of normal with any snow still
confined to the higher mountains. Per the most recent GFS run the
most significant weather features of note to pass include an
occluded front sweeping through Monday night with a slow exit
Tuesday followed by a warm front Wednesday morning which is followed
by another occluded front that moves in and stalls out over the
forecast area Wednesday and on through Wednesday night. /Pelatti

Thursday through Saturday...Multiple features of interest at
the start of this period with a closed low in the Gulf of Alaska
and then either an open wave or closed low along the California
coast shown by the GFS/GFS ensemble and ECMWF respectively.
Models diverge even further after that with how they handle
pieces of energy being spun around the main Gulf of Alaska low
and a new low digging off the CA/OR coast. In any event, it looks
like the rainy pattern will continue with some breaks in the
precip thrown in, although it`s too early to get into the
specifics of when that may occur. Thus at least slight chances of
rain were included throughout the entire extended forecast. With
no major influx of cold air evident, temperatures will likely not
deviate much from what we have been seeing with 50s being fairly
common for highs. /Kalin


12Z TAFS: Once again most of the forecast sites will be influenced
by a broad blanket of low clouds covering much of NE WA and N ID.
Winds have picked up quite a bit over extreme E WA behind a passing
upper level disturbance. While this should greatly lower the threat
for dense fog and LIFR conditions, the SW direction will still
likely lead to MVFR cigs and even some IFR conditions (mainly at GEG
and PUW). Confidence is good that conditions will improve to VFR by
midday. The most difficult forecast this morning is for MWH. Dense
fog and LIFR conditions reformed over the past hour and it appears
to be expanding per satellite. The HRRR model depicts this fog and
its been consistently suggesting it will be gone by 18-20z as the
inversion is shallow. 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. fx


Spokane        52  39  54  45  58  45 /  10   0  10  10  20  60
Coeur d`Alene  52  40  56  44  58  45 /  20   0  10  20  20  60
Pullman        54  43  57  46  62  46 /   0   0  10  10  10  60
Lewiston       59  45  61  48  65  49 /   0   0  10  10  10  40
Colville       53  36  54  41  56  44 /  20   0  10  30  30  80
Sandpoint      50  36  52  40  55  42 /  40   0  10  20  20  60
Kellogg        49  39  56  42  57  42 /  30   0  10  10  20  50
Moses Lake     57  41  59  43  58  43 /   0   0  10  20  20  60
Wenatchee      57  43  55  43  55  42 /   0  10  10  20  40  70
Omak           55  40  55  42  55  44 /   0  10  10  30  40  80



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