Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 282330

Area Forecast Discussion
National Weather Service Spokane WA
430 PM PDT SAT MAY 28 2016

The Memorial Day weekend will be cool and locally breezy.
Scattered showers are expected to impact the Idaho Panhandle and
northeast Washington at times over the holiday weekend. Sunday`s
system will also produce wind gusts of 20 to 30 mph during the
afternoon and evening along the East Slopes of the Cascades into
the Columbia Basin. Warmer weather will develop by Wednesday and
carry into next weekend.


Tonight and Sunday: A broad upper level trough over southern
British Columbia will be the weather feature of note tonight
through Sunday. A shortwave is expected to round the base of the
B.C. trough on Sunday enhancing convective showers and tightening
the westerly surface pressure gradient.

The best chances for showers and embedded thunderstorms will be
in the mountainous areas along the Canadian border Sunday
afternoon. The increasing westerly flow should activate the
Cascade rain shadow leaving much of central Washington in the lee
of the Cascades high and dry. Marginal surface based CAPE of 100
to 300 J/Kg combined with 0-3km bulk shear values of 15 to 20kts
suggest garden variety thunderstorms capable of brief heavy rain,
pea hail, and wind gusts to 35 mph. Cells should move from the west
or southwest around 30 mph limiting the threat of flash flooding.

Sunday will be breezy in the afternoon and evening. The Columbia
Basin, Palouse, and West Plains will experience sustained west or
southwest winds around 15 mph with gusts of 20 to 25 mph. Cascade
gap winds will likely peak late in the afternoon and early in the
evening in places like Wenatchee, Chelan, and Vantage with gusts
in the 30mph or more. As wind decrease overnight, the sheltered
valleys of northeast Washington and far north Idaho will be quite
chilly Sunday night. Places like Deer Park, Newport, Priest Lake,
and Republic will likely dip into the mid to upper 30s by Monday
morning. /GKoch

Monday through Thursday night: There will be a few showers
lingering over the north Idaho Panhandle Monday but this activity
will clear out by late afternoon and high pressure will strengthen
delivering a warming trend through the week. Models are not as
toasty as runs were indicating yesterday but the pattern still
favors afternoon highs warming back into the 80s to lower 90s
nearly 8 to 15 degrees above normal. The GFS/GEM are still
preferred over the ECMWF which is now better aligned with the GFS
but also shown moderate wavering over the last 24 hours. These
solutions suggest surging 850mb temperatures from near 11C on
Monday to 21C supporting mid 80s to lower 90s.

One item of note that  models are starting to pick up on is an
influx in mid-level moisture Thursday. This moisture first
arrives near the Cascades in the morning then spreads into
southeastern WA and N Idaho in the afternoon. Tracing this
moisture upstream in the models indicates origins near California
but not necessarily from the Pacific or Gulf. This appears to
manifest from convection processes and get drawn northward as
southerly flow increases ahead of an approaching trough. Whether
this moisture equates to passing clouds or manifest into showers
and t-storms is still highly uncertain but worth keeping an eye on
Thursday given the potential for very warm temperatures, deep
instability, and perhaps a passing disturbance across the northern
mountains. /sb

Friday through Saturday night: Ridge remains in place across the
region at the start of the period with continued above normal
temperatures and dry conditions. Models differ in minor shortwave
features as well as the evolution of the breakdown of the upper
ridge, which currently looks to hold off until at least after this
extended forecast. The main forecast challenge during this period
will be forecast high temperatures as models have been rather
inconsistent on just how warm we will get. Only minor changes were
made to the forecast to trend temperatures down slightly Friday,
especially over the east slopes of the Cascades as the GFS
advertised a band of mid to high level clouds associated with a
midlevel front. Further changes to the temperature forecast in the
far extended may be needed as model agreement improves. Either
way, above normal temperatures appear likely which could lead to
some rises on areas streams that still have sufficient snow pack
left. /Kalin


00Z TAFS: The next system swings into the region over the next
24 hours. Tonight the leading shower threat will be found over
the northern mountains and far northern Columbia Basin. TAF sites
will main see middle to high clouds, though a few showers may be
found in the vcnty of EAT early this evening and some stray
sprinkles cannot be ruled out near GEG to COE around 05-09Z.
Sunday the main trough swings in, with a threat of showers around
the eastern TAF sites in the afternoon. There will also be a
threat of thunderstorms, but the risk will mainly be north and
east of the TAF sites. Lingering gusty winds this evening near the
Cascades/western Columbia basin will abate after 01-04Z. Winds
increase again Sunday especially after midday. Gusts near
20-30kts are possible, strongest late near the EAT. /J. Cote`


Spokane        46  68  44  69  45  75 /  10  20  10  10  10   0
Coeur d`Alene  45  68  44  69  43  73 /  10  20  10  20  10   0
Pullman        45  68  43  67  42  72 /   0  10   0  10   0   0
Lewiston       51  75  50  75  49  81 /   0  10   0  10   0   0
Colville       45  69  43  72  42  80 /  10  30  20  20  10   0
Sandpoint      43  65  43  67  39  73 /  10  40  20  20  20   0
Kellogg        42  65  43  64  39  71 /  10  20  20  20  20   0
Moses Lake     49  75  46  76  45  82 /  10  10   0   0   0   0
Wenatchee      51  73  49  75  54  81 /  10  10   0   0   0   0
Omak           48  72  45  76  49  81 /  20  20   0   0   0   0



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