Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 242342
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
442 PM PDT Wed May 24 2017

.SYNOPSIS...
Cooler than average temperatures are expected again on Thursday
with scattered showers and a few thunderstorms. Strong high
pressure will build over the region this weekend bringing dry
weather and warm temperatures for Memorial Day. Look for afternoon
temperatures in the 80s by Sunday and Monday. Our warm weekend
will likely cause rises on rivers in central and north central
Washington next week.

&&

.DISCUSSION...

Tonight: Our gusty west winds will decrease quickly this evening
as or west to east surface pressure gradient relaxes. Through
about 7 PM, we will have the potential for gusts in the 35 to 40
mph range through the Cascade gaps including areas around
Wenatchee, Chelan, Waterville, and Vantage. One of the shortwave
features contributing to the decrease in the pressure gradient is
a 500mb trough pivoting into northeast Washington out of southern
B.C. Regional radar imagery at 2 PM shows weak reflectivity in the
vicinity of Bonners Ferry, Priest Lake, and Kettle Falls. Web
cameras show some weak rain shafts under the increasing cloud
deck, but so far we have seen no rain reported from any weather
stations. Pavement at Laurier, Priest Lake, Bonners Ferry appears
to be dry. Strong low level dry advection behind last night`s cold
front will make it difficult for any significant rain to make it
to the ground. Many areas have a surface dewpoint in the 20s this
afternoon...quite dry. Needless to say, our precipitation chances
this evening and through the night is pretty slim as our 500mb
trough moves southward through our region.

Thursday: Our chances for rain showers will increase on Thursday.
An upper level trough and deep cyclonic flow will create an
environment favorable for afternoon and early evening showers. Our
surface dewpoints will be on the rise as our dry downslope winds
are replaced by lighter winds originating from Canada. The GFS and
NAM forecast the best surface based instability over the mountains
of northeast and north central Washington and the high terrain of
north Idaho. Scattered showers will likely develop over these
areas and drift southward into the Upper Basin, Spokane area, and
possibly the Palouse. A few of the strongest cells will be capable
of brief heavy rain, small hail, and a handful of lightning
strikes.

Friday: High pressure will begin building along the coast on
Friday. A few showers may pop up over the Panhandle mountains
Fri, but the rest of the Northwest will begin a warming and drying
trend that will carry through the Memorial Day Weekend. /GKoch

Saturday through Monday night...An upper ridge will build over the
region through the Memorial Day Weekend bringing a warming trend
under clear to mostly clear skies for most locations. High
temperatures for Sunday and Memorial Day will warm into the 80s
with the warmest locations such as Moses Lake, Wenatchee, and
Lewiston reaching near 90. The GFS and ECMWF show the ridge axis
setting up over Eastern Washington with weak impulses riding up
along the back side of the ridge up the Washington Cascades, then
east along the Canadian border, and then south along the front
side of the ridge into western Montana. This combined with steep
lapse rates and CAPE values of 500-800 J/KG could touch off a few
isolated storms over the mountains. However with the warm
temperatures aloft and some convective inhibition in
place...confidence is low of storms firing with the better chances
expected north of the Canadian border and east of the area in
Montana.

The warm temperatures will result in another round of snow melt
with river rises next week. Current forecast has the Okanogan and
Stehekin Rivers at the highest risk for flooding...and the Methow
rising back up to near flood stage. Will also have to keep a close
eye on the Kettle, Entiat...and Similkameen Rivers. JW

Tuesday and Wednesday: No major changes to the weather pattern to
start Tuesday, but beginning late Tuesday model solutions diverge
in how the persistent upper ridge will break down, if at all. The
Canadian is the most bullish bringing in a deep trough late
Tuesday into Wednesday, while the GFS shows a much weaker wave.
The EC, though, wants to hang onto the ridge through mid week. The
EC has been moving toward this continued ridge pattern over the
past few days while others are pretty noisy run-to-run. Without
something to increase confidence, will keep us in the warm/dry
pattern. Under the more moist SW flow a few mountain showers or
thunderstorms will be possible. Temperatures remain above normal
through the period, in the 80s and low 90s. /bw

&&

.AVIATION...
00Z TAFs: Gusty west or northwest winds will persist through
02-04z time frame for the airports across the region. Localized
gusts to 40 mph will be possible at the Wenatchee and Chelan
airports courtesy of Cascade gap wind effects. Further east,
Spokane, Coeur d`Alene, Pullman, and Lewiston can expect gusts in
the 25-30 mph range through about 02z. Radar is showing some
showers moving down in the northerly flow. With very dry
conditions at the surface, think virga or some very light
sprinkles at best is possible for the KGEG-KSFF-KCOE this evening.
Clouds will persist through the night with widely scattered
showers possible Thur aftn...mainly across the northern mountains
of WA and ID. Skies will start to clear late in the afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        44  66  47  74  51  78 /  10  20  10  10   0   0
Coeur d`Alene  44  65  44  73  47  77 /  10  30  20  10  10   0
Pullman        44  64  44  70  48  75 /  10  20  10  10   0   0
Lewiston       49  69  49  77  53  82 /  10  20  10  10  10   0
Colville       45  68  44  77  48  80 /  10  30  20   0   0   0
Sandpoint      39  64  41  70  44  75 /  20  30  30  10  10   0
Kellogg        41  63  40  71  43  75 /  20  30  20  20  10   0
Moses Lake     48  74  47  83  52  85 /   0  10  10   0   0   0
Wenatchee      48  73  50  82  55  84 /  10  20  10   0   0   0
Omak           48  74  50  81  53  84 /   0  30  20   0   0   0

&&

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

$$


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