Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 030927
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
227 AM PDT THU SEP 3 2015

.SYNOPSIS...
A cool and showery weather pattern is expected for the remainder
of the work week as a cold storm system moves by the area.
Widespread rain is expected in the Panhandle and extreme eastern
Washington on Saturday. Drier and warmer weather is expected by
early next week.

&&

.DISCUSSION...
Today through Friday: The threat of showers and a few thunderstorms
will continue around the rim of the Columbia Basin, especially
near the mountains, as a broad trough settles into the Pacific
Northwest. The low at the center of the trough migrates south from
Vancouver Island to western Oregon in the next 36 hours. Impulses
pivoting around to its east side will work with regional
instability and moisture to bring those shower chances, even as
the cold front continue to edge away from the southeast CWA.

First this morning the best chance of showers will linger near
the aforementioned cold front, from the Blues to southeast
Shoshone county, and closer to the parent trough near the Cascade
crest and northern mountains with one of those embedded mid-level
shortwaves passing. I cannot rule out some isolated embedded
thunderstorms too, with a ribbon of elevated instability
represented by high level total totals between 30 to 37 C.
Additionally some isolated sprinkles or a brief shower cannot be
ruled out across the eastern Columbia Basin, including the
Spokane/C`dA Area and Palouse, with the passing shortwave. But the
threat should be mainly early in the morning (before 8 or 9 AM).
Going into the afternoon the shower threat across the southeast is
expected to wane some as the front edges away, but not end
entirely as another shortwave rounds the trough. The expanding
afternoon instability and one of those impulses rounding the
trough will lead to increasing shower and isolated thunderstorm
chances around the Cascades and Waterville Plateau into the
northern mountains again. The threat will wane again through the
evening with the loss of daytime heating. Then going into Friday
the low migrating south and another impulse rounding it will help
stall the front just southeast of the CWA and eventually buckle it
back west. Renewed afternoon instability will again mean renewed
shower and thunderstorm chances across the Cascades and northern
mountains. Chances will also expand back into southeast WA through
the Panhandle. However the overall highest threat will be near the
Cascade crest, the Blue Mountains and southeast Shoshone county.

Through this time frame snow levels will generally be above pass
level, ranging from near 5500-6000 feet in the Cascades to near
6500-7500 feet toward the Central Panhandle. Yet this may be low
enough to bring some light accumulation to the higher peaks.

Winds will also be occasionally breezy. As that low migrates
south Thursday night into Friday the north-to-south pressure
gradient increases. This points to the potential for some breezy
and gusty conditions. The winds are expected to first increase
down the Okanogan Valley into the western Columbia Basin as air
channels through this region. The gradient and winds then begins
to increase down the Purcell Trench, from Bonners Ferry to
Sandpoint out through the Coeur d`Alene area in the afternoon.
Right now it looks too marginal for any critical fire conditions
but it will be monitored.

Temperatures will remain below normal under the trough. The main
potential impact could be during the night hours when temperatures
drop into the 30s and 40s for some. Some locations may even drop
to or below freezing, especially in the sheltered northeast
valleys. The areal coverage may not be enough to warrant a freeze
warning but this too will be monitored. Some patchy frost was
added to the forecast as well for tonight/Friday morning. /J. Cote`

Saturday through Wednesday...The long holiday weekend looks to be
a mixed bag for outdoor activities. Models are now in good
agreement in forming a band of wrap around precipitation over the
eastern half of the forecast area...forming Saturday night and
maxing out with widespread light rain east of a line from about
Republic to Ritzville during the day Saturday...then gradually
tapering off from west to east Saturday night until by Sunday only
residual showers will remain in the Idaho Panhandle. The Cascades
and deep basin should remain dry but variably smoky with continued
breezy winds from the north becoming more westerly on Saturday
during this period. Temperatures will remain below normal and many
locations under the precipitation shield may have trouble breaking
60 degrees on Saturday.

After this closed low system ejects to the east on Sunday forecast
model consensus breaks down somewhat. The GFS wants to bring a
fairly strong short wave trough through the region implying a
reasonably good chance of continued showers over much of the area
Monday...while the ECMWF also displays a short wave but less
strong and more limited to the Canadian border region implying
only mountain showers. In fact through the rest of the extended
forecast both models indicate a general progressive pattern with
embedded weak disturbances transiting the northern tier zones from
time to time. Only way out on Wednesday is there agreement of the
beginnings of a sustained ridge pattern.

Thus the extended period looks unsettled and continued at least
slightly below average temperature-wise. No big storm systems are
expected but the parade of weak systems brushing the region leave
a chance of showers mainly over the north and the Panhandle
mountains through Tuesday. /Fugazzi


&&

.AVIATION...
06Z TAFs: The surface boundary has moved a little south this
evening and is now draped over extreme southeast WA and the
central panhandle mountains of Idaho with some clearing north and
west of the front. Expect the front to finally exit the forecast
area by early Thursday morning with clearing skies in most areas.
Expect winds of 10 kts or less. The presence of the upper level
low, spinning over southeast BC will keep some shower activity
over the Cascade crest and possibly across the northern tier but
precipitation is not expected at any TAF site. /EK




&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        66  38  69  46  62  46 /  10   0  10  20  60  40
Coeur d`Alene  65  38  68  45  60  46 /  10   0  10  30  70  40
Pullman        66  35  69  40  59  43 /  10   0  10  50  60  50
Lewiston       71  45  74  50  66  52 /  20  10  10  40  60  50
Colville       68  35  71  42  66  43 /  20  10  10  10  30  30
Sandpoint      65  34  67  44  61  42 /  20  10  10  30  60  40
Kellogg        63  37  67  43  57  46 /  20  10  30  50  70  50
Moses Lake     71  43  71  47  73  47 /  10   0   0  10  20  10
Wenatchee      69  48  72  52  74  57 /  10  20  10  10  10  10
Omak           68  42  70  45  74  47 /  20  30  10  10  10  10

&&

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

$$



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