Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 241210
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
510 AM PDT Wed May 24 2017

.SYNOPSIS...
A cold front exits to the east and upper trough settles in today.
Blustery conditions will persist, with afternoon temperatures a
solid twenty degrees cooler than yesterday. A few showers are
possible today too, but largely around the mountains. Scattered
showers and thunderstorms will be possible on Thursday. Sunny,
warmer weather returns for the Memorial Day Weekend, with high
temperatures warming back into the 80s.


&&

.DISCUSSION...
Today and tonight: The weather will be cooler and breezy to
windy, with limited shower chances. This morning a cold front is
shifting east and an upper trough is taking hold, with some
embedded shortwaves. The onshore flow near the Cascades and the
passing cold front in the east will allow some risk for showers in
these areas. Some of the might even fall as snow near the Cascade
crest, though accumulations should be light if any. The shortwave
that pivots in later this morning and afternoon will bring in
some scattered to broken middle to high clouds. Some cumulus
build-ups are expected around the mountains, where there will also
be a threat of showers. A few showers could slip off the northern
mountains toward the northern Spokane/C`dA area, but threat is
low. As for the risk of thunderstorms, the risk is limited. No
models are showing significant convective instability. While there
may be some embedded thunderstorms, especially toward the ID/MT
border, the risk is a bit too small to include in the forecast.
This evening, with the sunset, the threat of showers is largely
expected to wane. A few may linger around the Central Panhandle
through later evening. Another embedded shortwave drops toward
the Cascades late which may bring a few showers toward western
Okanogan county overnight. Otherwise expect partly to mostly
cloudy skies.

Temperatures will be noticeably lower today than yesterday, as
the modest to strong CAA behind the front drops 850mb temperatures
from the mid to upper teens to mid to upper single digits. This
translates to afternoon highs about 15-20 degrees lower than
yesterday or, stated differently, about 5-10 degrees below normal.
Tonight the clouds should, however, help to insulate the region
so that lows will be near to just a degree or two within range of
normal.

Winds will periodically remain in the breezy to windy category
through the day. Models generally show some decline in speeds
through the early part of this morning, before they pick up again
between mid to late morning to afternoon. Values will hover near
advisory level in some spots, particularly near the East Slopes
of the Cascades into the Waterville Plateau. Models then show a
clearer signal of declining speeds after about 02-04Z (7-9 pm).
For now will let the current advisory expire but conditions will
be monitored should another be necessary later on. However the
front has passed and I`m not sure the secondary shortwave and
gradient will be strong enough to warrant additional advisories
for that second increase in speeds. /J. Cote`

Thursday through Friday evening...The period begins with good
model agreement depicting northerly flow aloft under the western
flank of a departing upper low over Saskatchewan...but with a spur
wave dropping out of Canada in this northerly flow and passing
through the forecast area during the day Thursday. This wave
brings with it a shot of cooler air aloft which will destabilize
the atmosphere during the afternoon and early evening hours
bringing a scattered showers and a moderate chance of thunderstorms
to much of the region. These storms will be garden variety hit-
and-miss rain producers with possibly small hail...and while
concentrated over the mountains north and east of the
basin...the general instability will mean just about everywhere
will possess at least a small chance of a shower or storm during
the prime heating period. This activity will die out during the
overnight hours but return again on Friday to the Idaho Panhandle
while the remainder of the forecast area dries out as a strong
upper level ridge arrives onshore and stabilizes the air mass.

Friday night through Tuesday...From Friday night onward through
the holiday weekend good model agreement continues depicting a
strong ridge aloft over the region with a placid surface pressure
gradient...heralding a pleasant and warm Memorial day weekend.
Moisture and afternoon instability will remain adequate for a
small chance of thunderstorms each afternoon and evening over the
mountains arcing the basin but this threat will be small owing to
no triggering mechanism beyond orography. Temperatures will rise
well above normal this weekend with highs in the 80s becoming
common Sunday and Monday. There are some indications that the
upper ridge may begin to break down on Tuesday...a more moist
southwesterly flow begins to impact the region although no
coherent thunderstorm triggering short waves are defined as of
yet in any models. At this time the best bet is a sight cool
down...still above average...and a slightly better chance of
mountain thunderstorms. /Fugazzi

&&

.AVIATION...
12Z TAFs: An upper trough will settle in with cooler and continue
breezy to locally windy conditions. The speeds are expected to
have a relative lull early this morning, before they pick up again
later this morning and afternoon, then start to wane after about
02-04Z tonight. Peak gusts in the 25 to 40 kt range are possible,
especially in the 18/19Z to 02Z time frame. Skies will be mostly
clear early today, then middle to high clouds are expected to
come in, but conditions should primarily remain VFR. A threat of
showers develops about the mountains this afternoon. A few may
drop south toward the GEG/SFF/COE area late this afternoon through
early evening, but the risk of one coming even into the vcnty of
a TAF sites is low. /J. Cote`

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        62  46  67  47  71  51 /  10  20  20  10  10  10
Coeur d`Alene  62  44  66  44  70  47 /  20  20  30  30  10  10
Pullman        61  44  64  43  69  47 /   0  10  20  20  10  10
Lewiston       68  48  70  48  75  52 /   0  10  20  20  10  10
Colville       63  45  68  46  74  48 /  20  20  40  20   0  10
Sandpoint      61  40  64  41  69  42 /  20  20  30  50  10  10
Kellogg        58  41  63  41  68  43 /  20  20  30  40  40  10
Moses Lake     71  48  74  49  79  52 /   0  10  10  10   0   0
Wenatchee      68  49  74  51  79  55 /   0  10  20  10   0   0
Omak           70  49  74  49  79  53 /   0  10  20  10   0   0

&&

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

&&

$$


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