Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 200535
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1035 PM PDT Thu Apr 19 2018

.SYNOPSIS...
Dry, mild conditions are expected to continue through Friday. A
quick moving cold front will bring scattered showers Friday night
and windy conditions on Saturday. The new work week is expected
to start dry and mild and probably remain dry with a warming trend
through the week.


&&

.DISCUSSION...
Tonight through Friday...The forecast area will exist under a dry
upper level ridge tonight and Friday...sandwiched between an upper
level low to the south over the Great basin and the next
approaching Gulf of Alaska trough. Satellite indicates this next
trough amplifying as it approaches the coast and will serve to
slow down and direct the clearly apparent deep moisture feed in a
more south to north trajectory. This will give the forecast area
one more day of dry and mild conditions...with some increase in
high clouds during the day tomorrow.

Friday night and Saturday...This time frame will witness the
transit of the next weather system through the area. Models are
in good agreement and consistent in pivoting this short wave
quickly through the region. Friday night and early Saturday
morning will bring the best chance of precipitation as the
moisture feed pushes into the area with the short wave aloft and a
moderately strong cold front at the surface providing adequate
lift for scattered showers over the basin and probably more
numerous valley rain and mountain snow showers in the mountains
north and east of the basin as well as over the high Cascades.
This does not look like a significant precipitation event due to
the quick hitting nature of the front and short residence time of
the moisture feed before passing off tho the east. A few
hundredths of an inch of rain over the eastern basin zones and up
to a tenth of an inch or so in the mountain zones...falling as 1
to 3 inches of snow above 4000 feet.

The more salient issue for Saturday looks to be the wind potential
behind the front as the short wave passage promotes surface
cyclogenesis east of the Canadian Rockies during the day. The
gradient forming over the forecast area and the gust potential
from mixing in the post frontal air mass looks like it will
support 15 to 25 mph sustained southwest winds with gusts in the
30 to 35 mph range. Not enough to achieve any wind highlight
criteria...but solidly breezy to windy and capable of producing
some patchy blowing dust to reduce visibilities from time to time
near freshly worked fields in the basin along the I-90 corridor.
The air mass will quickly dry out as the winds increase saturday
morning and any further precipitation will be limited to the
Idaho panhandle mountains by afternoon.

Saturday night through Thursday...A weak follow on wave will drop
through the area Saturday night and Sunday but the models suggest
any forcing will be focused to the south of the region and
pulling dry air into the area from Canada for a dry day Sunday
with temperatures just beginning to recover back toward normal
after a cool Saturday. Monday and Tuesday models all advertise an
upper level rideg building over the area with a distinct warm up
to above average temperatures...in the 60s over most basin and
valley locations...and dry and probably sunny conditions. Model
agreement deteriorates after Tuesday...but where loose agreement
exists is the depiction of a broad split flow over the western US
with the forecast area under a zonal flow regime north of another
Great Basin or California coastal upper low. The forecast remains
dry under this flow...and continued mild through the end of the
extended forecast...although one model...the GFS...for the second
day now depicts a fairly impressive fetch of Pacific moisture
impinging on the northwest coast late Wednesday for the potential
of at least high clouds and possibly some mountain showers by
Thursday. Forecast confidence is pretty high for the next 5
days...but begins to deteriorate by next Wednesday or Thursday.
/Fugazzi

&&

.AVIATION...
06Z TAFS: Weak high pressure begins to flatten as next shortwave
approaches NW Coast. Moisture begins to spill inland in the form
of mid to high clouds through 00z but overall, VFR conditions to
prevail with high confidence. Cold front and band of light showers
moves into Central WA 03-06z. Cigs around Moses Lake and
Wenatchee lower near 10K ft AGL but precipitation chances appear
minimal. /sb

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        40  62  43  54  34  57 /   0  10  40  10   0   0
Coeur d`Alene  37  61  41  53  33  56 /   0   0  40  30   0   0
Pullman        36  60  43  53  34  55 /   0   0  20  10   0   0
Lewiston       42  65  47  60  39  61 /   0   0  10  10   0   0
Colville       35  63  43  57  33  59 /   0   0  30  20   0   0
Sandpoint      34  58  40  50  32  54 /   0   0  40  60   0   0
Kellogg        36  58  39  50  32  55 /   0   0  30  50   0   0
Moses Lake     39  65  45  60  36  62 /   0   0  20   0   0   0
Wenatchee      43  64  43  58  37  60 /   0  10  20  10   0   0
Omak           39  63  45  61  36  61 /   0   0  20  10   0   0

&&

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

&&

$$



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