Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 082344

Area Forecast Discussion
National Weather Service Spokane WA
444 PM PDT THU OCT 8 2015

Cloudy skies remain as weak high pressure builds into the area.
The weather becomes more active over the weekend, with periods of
rain and breezy to windy conditions. The threat of showers largely
retreats to the mountains early next week.



Tonight through Friday night...Ridge of weak high pressure cluttered
with moisture some lingering moisture from yesterdays rainfall
along with middle and high level moisture streaming up through the
west side of the ridge and over Eastern Washington and Northern
Idaho is likely to keep a good portion of the evening rather
cloudy. Some weak ridge amplification takes place to displace
enough of the moisture streaming through it up to the north so
that only minor pops for light rain remain near the the north and
west. There is a possibility that low clouds and fog may again
form as boundary level moisture remains high and the low level
flow switches slightly to push it back to the east as dew points
remain quite high. Overnight low temperatures for the next night
or two in fact should remain on the warm side of normal given this
pattern inhibiting effective radiational cooling at night. Friday
into Friday night the ridge axis gets pushed into Northwest
Montana and this allows disturbances running along the west side
of the ridge tied into the moisture draped along it to have a
better possibility of producing some rainfall as they move across
the ridge, but this is mostly for locations north of I-90 on
Friday. Friday night this rain potential expands further east and
south but may only extend a few miles south of I-90. /Pelatti


Saturday through Sunday: A dynamic upper level shortwave trough of
lower pressure will swing across the region Saturday night. The
cold front associated with this system will produce gusty winds
across the region. Winds will increase through the afternoon on
Saturday, but expected to become quite gusty Saturday
evening/night with cold front passage. Winds at 850 mbs will be
right around 40 kts; however, the 12Z GFS solution is on the
stronger end of the model guidance with 850 mb winds closer to 50
kts across the Palouse and into the NE Blue Mtns. The GFS also has
a tighter pressure gradient across the region compared to the NAM,
ECMWF and Canadian. I did not put in winds as strong as the GFS
would suggest, so there is the potential for even stronger winds
if this model ends up verifying. Sustained wind speeds of up to 25 mph
with gusts up to 45 mph are expected with frontal passage.
Stronger wind gusts will be possible in the mountains to around 60
mph. Any light weight items will be at risk of being blown around,
high profile vehicles may have some difficulties and localized
power outages from broken tree branches on power lines will be
possible with the winds.

There will also be a juicy P-wat plume (around 0.80 inches) ahead
of the front. This will result in an increasing chance for precip
late Saturday afternoon with best chances for the evening hours.
Strong westerly flow will limit precip accumulations in the lee of
the Cascades and out into the western basin. Highest precip
accumulations will likely be over the Cascade crest and in the ID
Panhandle. The front will sweep across quickly, but is expected to
result in a brief period of more moderate rainfall rates right
along the front itself. Storm total rainfall is expected to range
between a tenth to a quarter of an inch from extreme eastern WA
into the ID Panhandle. The higher terrain in the ID Panhandle will
likely see a bit more between a quarter of an inch to a half an
inch due to favorable upslope flow. Snow levels will fall quickly
behind the front as well across the East Slopes of the Northern
Cascades to around 5,000 feet. This is expected to result in a
couple of inches of snow accumulation above this elevations
primarily near the crest.

Sunday night and Monday night: There will be a break in the
weather Sunday night. Models then indicate the potential for a
much weaker system pushing across the region Monday into Monday
night. There is more model discrepancy with this weather system
than the weekend. This has resulted in lower confidence in the
details, but at least a chance of some rain and generally breezy
conditions can be expected. Typical Autumn temperatures are
expected through the weekend into early next week. /SVH

Tuesday through Thursday: This period is expected to be warm and
dry. A ridge pattern is going to dominate the region for the
extent of the period. The models are in good agreement with this
scenario. This will keep the region precip free. Temperatures are
the main impact for the region. The highs are expected to be near
5 to 10 degrees above the season normals for this time of year.
High temperatures are expected to be in the upper 60s to low 70s.
Lows are expected to be in the range of mid 30s to low 40s. /JDC


00z TAFS: Mid and high clouds are expected to decrease tonight
which combined with a moist low level air mass will result in
areas of fog and stratus to develop. However increasing south-
southeast boundary layer winds on the palouse extending up into
Spokane and Coeur D`Alene leads to lower confidence of these TAF
sites being impacted. Meanwhile the S-SE flow will keep abundant
lower level moisture trapped along the East Slopes of the Cascades
and northern valleys where stratus is expected to be more
extensive...including KEAT. Soundings also indicate a brief fog
threat at KMWH but for now left conditions VFR at KMWH and will
re-evaluate with 06z TAF issuance here.  JW


Spokane        53  72  53  71  50  62 /   0  10  20  20  70  20
Coeur d`Alene  52  74  51  72  49  61 /  10  10  20  20  70  30
Pullman        54  77  50  75  49  61 /   0  10  10  10  70  40
Lewiston       55  77  54  80  54  68 /   0  10  10  10  70  30
Colville       48  72  48  68  46  63 /  10  10  20  50  80  10
Sandpoint      49  72  48  69  47  60 /  10  10  30  30  80  40
Kellogg        51  72  49  71  47  57 /  10  10  20  20  80  60
Moses Lake     53  78  53  74  51  68 /   0  10  20  20  20   0
Wenatchee      53  75  55  72  48  67 /  10  10  30  20  20   0
Omak           52  73  51  67  43  64 /  20  20  20  30  20   0



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