Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 261229
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
529 AM PDT Wed Apr 26 2017

.SYNOPSIS...
Expect cool, breezy, and showery weather for the rest of this
week. Showers will be most numerous today with isolated
thunderstorms possible over the northern mountains. Mountain
passes could see a few inches of snow overnight Wednesday into
Thursday morning. A ridge of high pressure moves in Saturday
delivering a brief dry period before more unsettled weather moves
in Sunday and into early next week.

&&

.DISCUSSION...
Today through Thursday: An occluded front is pushing across the
region at 200 AM this morning. Light rain and high mountain snow
above 5000 feet is expected with this feature through this morning
and mainly over the Panhandle by 700 AM. There is another wave
behind this front that is currently just beginning to move into
western OR. Latest model runs continue to have the moisture
associated with this second wave further south than previously
thought. It is looking more and more like the bulk of the precip
will remain over OR and into southern ID. We will mainly just get
hit by the northern fringe on Wednesday from the Northeast Blue
Mtns to the Camas Prairie. However, this doesn`t mean that the
rest of the region will be dry today. There is a good possibility
for mid level clouds to break up across the northern portions of
the region to allow just enough surface heating to destabilize the
atmosphere for the afternoon. The bulk of the shower activity, at
least a the start of the afternoon, will be over the Okanogan
Highlands to the Northern Panhandle. There will be weak surface
based CAPE, but I do think we will see enough charge separation
for isolated thunderstorms with the showers over the northern mtns.
This convection may then migrate further south across the
Spokane-Coeur d`Alene corridor by the late afternoon or early
evening hours. Winds will be breezy today as well with strongest
winds funneling out of the Wenatchee River Valley, Moses Lake Area
and over into the Palouse. Expect wind gusts in the 30-40 mph
range across these areas.

Snow levels will drop overnight down to around 3000 feet. The
cooler air will bring a chance for accumulating snow over Stevens
Pass and Lookout Pass. Higher resolution models indicate a Puget
Sound Convergence Zone (PSCZ) setting up over the northern
Cascades and could line up over Stevens Pass. This feature
typically will bring a narrow swath of intense precip. It`s
possible that the precip turns over to snow at Stevens Pass by
late afternoon with heavy accumulations for the evening.
Confidence is low, however, since it is difficult to know where
this convergence zone will set up. The snow showers are expected
to be lighter over Lookout Pass, but may result in 1-3 inches of
snow by Thursday morning.

The atmosphere will remain conditionally unstable for Thursday. We
don`t look to be as unstable as today with dew point temperatures
a bit cooler. Best chances for showers will be over the eastern
half of the forecast area with grauple possible under stronger
showers. /SVH

Thursday night and Friday...The upper level steering flow will
transition from northwest Thursday night to northerly by Friday
as an Upper level low shifts to the east and high pressure begins
to push inland on Friday. Model guidance is similar and has been
consistent showing several weak waves dropping through the region
on the backside of the exiting trough. The waves when combined
with weak instability and orographic lift will result in a good
set up for showers through sunset Friday evening. The only thing
lacking is a decent moisture source. There will still be a chance
to see localized moderate to heavy showers late in the day across
northeast Washington and the Idaho Panhandle. Guidance shows a
bulls eye of between a quarter to a half inch over the north
Panhandle. Otherwise precipitation amounts will be between a tenth
and a quarter of an inch. Because we will be on the cool side of
the jet snow levels will range from 3500-4500 and 2-13 inches of
new snow will be possible for the central mountains. With more
sunshine and slightly warmer 850 temperatures afternoon highs will
be 3-4 degrees warmer then on Thursday.

Friday night through Saturday...The ridge will nose into the region
Friday night for a day of mostly dry weather. Temperatures will
be on the rise. With highs in the mid 50s to mid 60s. By late in
the day Saturday clouds will be on the increase as another upper
level low moves through B.C. and bends down the low. Some low end
chance pops were kept in the forecast for the northeast Washington
mountains and the north Panhandle mountains, with any
accumulations being light.

Saturday night through Sunday night...The chances for
precipitation will increase Saturday night through Sunday as the
aforementioned low drags a warm front through the region. Models
start to show some differences on timing and chose to lean towards
the slower and drier EC/Canadian as compared to the wetter GFS. A
fairly strong, for the season, warm front will track across the
region and with available moisture increasing to about 200 percent
of normal will result in another round of widespread showers for
most areas outside of the Columbia basin. Precipitation amounts
for most places that see rain will be under a tenth of an inch,
however along the Cascade crest and the Panhandle mountains a few
locations may see up to a half inch. Snow levels will be around
5500 feet so only the highest peaks will see measurable snow. Yet
another quick hitting short wave disturbance will be possible
early Monday morning to keep showers in the forecast. But all is
not lost it does look like there will be a warming trend by mid
week. Tobin

Monday through Wednesday: Monday the models diverge on the the
evolution of the ridge that begins to build in during the first
half of the week. The GFS drops a disturbance through on Monday
keeping better rain chances in the forecast, while the EC and
Canadian begins to build in the ridge with only scattered showers.
For now, will keep some rain chances around, mostly outside of the
basin on Monday. The best chance will be for the panhandle
mountains. Beyond Monday models are in quite good agreement that
an upper ridge will build in for the middle of the week. This will
bring dry conditions and warmer temperatures, closer to average by
Wednesday. If models continue their trend, this ridge could bring
us the warmest temperatures of the year late in the week. /bw

&&

.AVIATION...
12Z TAFS: A frontal band will spread light to moderate rain
through the early morning east of a line from KOMK to KALW. The
added rainfall will keep the boundary layer moist with MVFR/IFR
conditions persisting at KGEG, KSFF, KCOE and KPUW through much of
this morning. A stronger disturbance will push east of the
Cascade Mtns this afternoon. The bulk of the moisture with this
wave will remain across Oregon, but the northern fringe will
impact KPUW and KLWS after 19Z into the early evening. MVFR cigs
will be possible through the afternoon at KPUW. The atmosphere
will destabilize across the northern mtns this afternoon with
numerous showers and isolated thunderstorms possible with
convection impacting the Spokane/Coeur d`Alene corridor by the
late afternoon hours. In addition, winds will be breezy this
afternoon, especially at KEAT with gusts up to around 35 kts by
the late afternoon hours. /SVH

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        54  36  51  36  54  37 /  60  40  40  20  30  20
Coeur d`Alene  52  35  49  35  52  34 / 100  40  70  40  30  20
Pullman        52  37  50  36  52  36 /  90  50  40  20  30  10
Lewiston       57  41  55  39  57  39 /  70  30  30  20  20  10
Colville       52  37  52  37  57  36 /  90  70  40  10  30  10
Sandpoint      50  36  47  36  50  34 / 100  90  80  50  40  50
Kellogg        47  35  43  34  46  33 / 100  70  70  60  40  20
Moses Lake     62  40  61  38  62  37 /  10   0  10   0  10   0
Wenatchee      59  39  58  39  60  38 /   0   0   0   0  10   0
Omak           61  38  59  38  62  37 /  30   0  10  10  20  10

&&

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

$$


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