Area Forecast Discussion
Issued by NWS Spokane, WA

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160
FXUS66 KOTX 191235
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
535 AM PDT Thu Oct 19 2017

.SYNOPSIS...
The forecast will remain wet today into Friday as a low pressure
system slowly sags through the region. A cold front will follow on
Friday for showers, gusty winds and cooler temperatures. There
will be a brief break in the precipitation Friday evening, but
that will be short lived as another warm...wet...and windy weather
system arrives on Saturday. Drier conditions are expected for
much of next week.

&&

.DISCUSSION...
Today...Model guidance is in pretty good agreement showing a cold
front moving across the Inland northwest this afternoon and east
into western Montana tonight. This continues the wet southwest
flow over the region through at least this morning. Mid and upper
level moisture from off the Pacific is still well above normal.
The flow along the 300k isentropic surface is mostly parallel to
the surface which would inhibit lift. However, the same south-
southwest flow is good orographically into the Okanogan Highlands,
the Northeast mountains and the north Panhandle mountains. For
this morning the forecast will go with high pops, but back off
some for the rain amounts. The precipitation chances will pick up
this afternoon as the forcing increases with the frontal passage.
This is the period where most areas will see moderate rain.
Southwest winds this morning will be on the increase slightly this
afternoon and tonight ahead of and with the frontal passage with
gusts 15 to 25 mph through the Columbia Basin, the Palouse, and on
some of the ridges.

Tonight...The focus of the precipitation will shift to the
eastern zones late this evening, then into the Panhandle
mountains tonight as the front continues the eastward trek.
Precipitation will become showery but remain moderate along the
front. Snow levels will drop to between 4-6k feet by Friday
morning for high elevation snow. Southerly winds will remain
elevated with gusts increasing to 20-30 mph through the Basin and
the Palouse.


Precipitation through tonight will range from a tenth to around
three tenths for the lower elevations and the southern Idaho
Panhandle. From a half to over an inch will be possible for the
Okanogan Highlands over to the north Panhandle mountains and
similar amounts for the Cascades.

Friday and Friday night...The upper level low will be over the
region on Friday and will kick east on Friday night. Scattered
showers will be possible through the day on Friday as the cold
core moves through the region then decrease Friday night as the
atmosphere stabilizes. Showers will be mainly over the higher
terrain around the Columbia Basin but just about anywhere could
see a showers through the afternoon. The upper level low will
also push the deep moisture plume south of the area so any
precipitation will be much lighter then what we have seen the past
day or two. This will be the windiest period as the surface
gradient increases. Sustained winds of 15 to 25 mph with gusts 25
to 35 mph will be likely, and mainly across the basin, the
Palouse, lower Garfield country along Highway 12 and up north to
the West Plains east to Coeur d`Alene. Tobin

Saturday through Sunday night...A moist atmospheric river
and a strong upper jet aimed at the region will bring rainy and
areas of windy conditions over the weekend...along with mountain
snow on Saturday. The leading edge of the precipitation on
Saturday will arrive as a warm front brings strong isentropic lift
to the region. This will give all areas precipitation in the form
of valley rain and mountain snow. Snow levels start off at
2500-3500 feet Saturday morning...rising to 3500-5000 feet
Saturday afternoon...and then to 5500-8000 feet Saturday evening.
For most passes snow levels rise quickly enough to limit amounts.
The best chances for moderate accumulations will be in the
Cascades especially Washington Pass where heavy snow totals around
a foot are possible. After the front passes Saturday evening the
atmospheric river remains over the region overnight into Sunday
morning...but precipitation will become more confined to the
Cascades and Idaho Panhandle as strong downslope flow kicks in
east of the Cascades. The cold front passes Sunday afternoon with
the Cascades and Idaho Panhandle still favored for more rain.

Models show the potential for 4-7 inches of precipitation near
the Cascade crest in Chelan county with significant slop-over
spilling into Stehekin...Plain...and Leavenworth with 2-3 inches
possible. The rain combined with mountain snow melt will lead to
rises on area rivers and streams but no flooding is expected at
this time. The Stehekin River will be closely monitored. The
Idaho Panhandle may receive 1-1.5 inches of rain in the valleys
with 2 to 3 inches in the mountains falling as mostly rain. Most
areas of Central and Eastern WA should get at least a quarter to a
half inch of rain.

Regarding wind, a strong upper jet of 150 kts noses into southern
BC on Saturday and Saturday night. A low level jet becomes
established over SE Washington into the Central Panhandle
Mountains Saturday night with 850mb winds increasing to 50-60 kts.
Pressure gradients tighten but given the area is in the stable
warm sector soundings don`t show the strongest of winds mixing
down. Still...higher resolution UW-WRF shows potential for 35-45
mph wind gusts over the Upper Columbia Basin...Palouse...Spokane
area...with 45-55 mph wind gusts for the wind prone Pomeroy and
Alpowa Summit areas. These winds will continue into Sunday as the
cold front passes. Wind highlights are possible as the event draws
closer.

Monday through Wednesday: Much quieter weather as an upper ridge
builds in for dry conditions and a warming trend. The past 2 ECMWF
model runs on Wednesday brings in a weak front from the northwest
with the potential for a brief show of rain in the Cascades and
northern mountains. The UKMET, GFS, and Canadian are much stronger
with the ridge so for now will keep forecast dry.  JW

&&

.AVIATION...

12Z TAFS: A cold front will sweep through the forecast area this
afternoon and early evening. Localized stratiform precipitation
is expected early this morning in the warm sector well ahead of
the front and mainly north of a line from about KEAT-KCOE with a
smaller chance for KMWH this morning. Precipitation will increase
in both chance and intensity after about 19-20z as the front moves
through the region. Precipitation may become moderate for short
periods but expect conditons to remain VFR. Winds will be
breezy/gusty and quite variable through the day. For this morning
a low level jet through the Columbia basin will result in areas
of LLWS for KGEG/KSFF/KPUW through about 16z. Winds will increase
once again this afternoon and overnight ahead and with the cold
front passage with gusts 20-25kts. Tobin



&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        55  41  52  36  47  44 /  90  90  40  20  80 100
Coeur d`Alene  55  41  50  36  46  42 /  70 100  60  20  70 100
Pullman        59  41  51  37  49  44 /  20 100  40  30  80 100
Lewiston       66  45  58  41  53  47 /   0  90  40  10  80  90
Colville       55  43  54  35  46  40 / 100  70  40  20  80 100
Sandpoint      51  41  50  34  43  39 / 100 100  80  30  70 100
Kellogg        57  39  45  35  44  38 /  30 100  70  70  60 100
Moses Lake     58  43  59  36  51  47 /  80  40  10  10 100  80
Wenatchee      57  40  55  38  47  42 /  40  20  10  10 100  80
Omak           57  40  57  33  47  40 /  70  40  20  10 100  80

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$



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