Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 292148
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
248 PM PDT SAT AUG 29 2015

.SYNOPSIS...
Look for the wind to decrease early this evening as our fast
moving cold front moves out of the Inland Northwest. A vigorous
upper level disturbance will bring the Inland Northwest some much
needed rain on Sunday. Area wildfires will have a good chance of a
tenth to a quarter inch of rain. A cool and moist weather pattern
is expected much of next week.

&&

.DISCUSSION...
Tonight: The cold front has now pushed north of the region into
BC. The strongest gusts have likely passed now that the strong
cold air advection with the front has subsided. Much of the winds
for the rest of this afternoon into the early evening will be
gradient driven. Models show the strongest winds occurring across
the western basin, on the Waterville Plateau and up the Okanogan
Valley. This is where the tightest portion of the gradient will
be. There may also be some wind tunneling effect as the winds flow
up the Okanogan Valley as well that will provide some additional
enhancement. Expect these areas to see sustained wind speeds of
25 to 35 mph with gusts up to 50 mph possible through about 5:00
PM this afternoon before beginning to subside in the evening. The
basin and Waterville Plateau will also see a significant blowing
dust threat with visibility down to one-quarter mile at times. We
will leave the Dust Storm Warning out for these areas. We did go
ahead and cancelled the Dust Storm Warning for the Spokane Area
and WA Palouse and replaced it with a Wind Advisory for the rest
of this afternoon and evening. Wind speeds will be a bit weaker
here more in the range of 25 to 30 mph sustained wind speeds with
gusts generally only up to 45 mph for the remainder of the
afternoon and early evening. The current line of showers over
extreme eastern WA will push into the ID Panhandle by the early
evening and then move out of the region late this evening. Another
round of showers will move into the Cascades this evening with
rain spreading into eastern WA overnight into Sunday. /SVH

Sunday: The heart of the upper level trough will pass over
eastern Washington and north Idaho on Sunday. The 500mb cold pool
is expected to be in the -20C to -22C range and resembles a
vigorous autumn storm system. The GFS, NAM and ECMWF wring out a
good deal of moisture along the 700-500mb cold front. This system
should bring the most widespread rains we have seen in weeks.
There is good agreement between the models that widespread rain
amounts of a tenth to a quarter of an inch will fall from north
central Washington through northeast Washington into the Idaho
Panhandle. Forecast soundings suggest a small possibility of
lightning embedded in the rain showers Sunday, but thunderstorms
should not be the kind that produce flash flooding. We may see
some highly localized rock slides and small debris flows in the
burn areas, but life-threatening flash flooding looks highly
unlikely with this fall-type storm system. Sunday will be breezy
in the afternoon with gusts of 20 to 30 mph, but morning rainfall
and much cooler/humid conditions will diminish our chance for
blowing dust.

Monday and Tuesday: The upper level trough will reload along the
coast of British Columbia Monday and Tuesday. It looks like the
Inland Northwest will remain under a cool, but mainly dry west to
southwest flow. Showers look to be mainly confined to the Cascade
Crest and the mountains along the Canadian border. The strong on-
shore flow in the mid-levels will produce a tight surface pressure
gradient which will result in breezy winds across the Palouse,
West Plains, and Columbia Basin. /GKoch

Tuesday night through Saturday...Cooler and continued unsettled
weather will be persisted through the rest of the week. The models
have been advertising an upper level trough that will swing over
the region. The confidence of the trough`s timing and speed was
marginal but the confidence seems to have increased with the 12z
models. The GFS and ECMWF agree on a slower timing showing the
cold core rotating across southern B.C. This pattern seems to be
more late fall like instead of early September. Anticipate showery
conditions primarily near the Canadian border being closer to the
low center and being enhanced during the afternoon and evening
hours. Did add a slight chance of thunderstorms embedded in the
showers associated with the cold air aloft and the best
instability. This will be best chance for the active convection
will be over north central Washington on Wednesday, then shifting
across northeast Washington and north Idaho on Thursday and
Friday. Occasional breeziness will develop in the afternoon and
evening especially across the Columbia Basin. Will continue to
include patchy smoke across the region, mainly near the wild fires
and following the downstream wind patterns. There is some thought
that the winds and precipitation may help disperse the smoke as
the weather pattern remains active. Expect temperatures running
below normal for early September, with daytime highs in the 70s.
/rfox.

&&

.AVIATION...
18Z TAFS: The combination of smoke and blowing dust will
contribute to visibility problems that are difficult to forecast.
Look for frequent amendments through the early evening. Strong
west or southwest wind gusts are expected to max by early
afternoon right behind the cold front. The poorest blowing dust
visibility will likely occur at Moses Lake, Spokane, and possibly
Pullman due to dryland wheat fields upwind of these airports.
Visibility restrictions due to smoke in Lewiston should improve
through the day as wind disperses smoke. /GKoch

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        53  66  51  70  53  72 /  20  80  10  20  10  10
Coeur d`Alene  52  63  49  70  51  72 /  20  80  10  20  10  10
Pullman        52  65  49  73  51  73 /  20  60  10  10   0  10
Lewiston       58  72  54  81  57  81 /  20  70  10  10  10  10
Colville       51  68  50  71  50  72 /  30  90  10  30  20  30
Sandpoint      50  61  48  67  49  70 /  20  90  20  30  10  20
Kellogg        49  60  46  70  48  73 /  30  90  20  20  10  10
Moses Lake     55  75  54  77  55  77 /  40  80  10  10  10  20
Wenatchee      56  74  54  75  55  75 /  70  40  10  10  10  20
Omak           52  74  51  74  51  74 /  70  50  10  20  20  30

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Red Flag Warning until 7 PM PDT this evening for Northern and
     Central Idaho Panhandle (Zone 101).

     Wind Advisory until 8 PM PDT this evening for Central Panhandle
     Mountains-Coeur d`Alene Area-Idaho Palouse-Lewis and
     Southern Nez Perce Counties-Lewiston Area-Northern
     Panhandle.

WA...Red Flag Warning until 7 PM PDT this evening for East Washington
     Central Cascade Valleys (Zone 677)-East Washington
     Northeast (Zone 686)-East Washington Northern Columbia
     Basin (Zone 673)-East Washington Okanogan Highlands (Zone
     687)-East Washington Okanogan/Methow Valleys (Zone 684)-
     East Washington Palouse and Spokane Area (Zone 674).

     Wind Advisory until 8 PM PDT this evening for East Slopes
     Northern Cascades-Lower Garfield and Asotin Counties-
     Northeast Blue Mountains-Northeast Mountains-Okanogan
     Highlands-Okanogan Valley-Spokane Area-Washington Palouse-
     Wenatchee Area.

     DUST Storm Warning until 5 PM PDT this afternoon for Moses Lake
     Area-Upper Columbia Basin-Waterville Plateau.

&&

$$


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