Area Forecast Discussion
Issued by NWS Spokane, WA

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000
FXUS66 KOTX 101103
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
303 AM PST WED FEB 10 2016

.SYNOPSIS...
Strong high pressure will persist into Wednesday, with dry and
mild conditions. A more progressive and unsettled pattern will
return late this week, bringing a chance of light rain Thursday in
the Cascades, then throughout the region Friday into the weekend.


&&

.DISCUSSION...
Today and tonight...The unusually strong ridge which has
blanketed the Inland Northwest for the past several days will
finally begin to weaken as minor upper level disturbances track
through the region. Looking at the latest satellite loops, the
first disturbance is currently tracking through the eastern third
of Washington right now, with another one moving into western
Washington. Based on GOES BUFR sounding and radar data, both are
rather minor features. The easternmost feature only contains high
clouds, while the western one is producing a few sprinkles near
the coast. This second feature is expected to move into the
Cascades later today and could produce some very light
precipitation mainly near the crest. Otherwise the main impact of
these systems will be an increased cloud trend compared to the
last couple days as well as slightly cooler temperatures.
Nonetheless, readings will still remain warmer than normal for
this time of year with highs generally in the mid 40s to mid 50s
for most valley locations. The exception once again will occur
over the far NW part of the forecast area, namely the Methow
Valley and Okanogan Valley and Highlands due to a very stubborn
cold pool near the ground. Looks like this could stick around
until we get a more robust front through the area, which won`t
likely be today. The other problem for today will be the potential
for fog. We suspect the coverage should be greater than we have
seen for the past couple days as the wind fields are generally
lighter with higher humidity levels. Hard to tell where most of it
will form, however the HRRR suggests most of it will occur over
the western Columbia Basin. This is not supported at this time by
the fog product but will bear watching. Meanwhile for the first
time this week, visibility restrictions were developing over parts
of the Spokane/CdA area and suspect the trend will be for
increasing fog. For tonight, the second front will receive a
little boost in strength as a shortwave trough currently around
127w moves inland. We don`t think this will produce much weather
other than a chance of light precipitation again near the
Cascades. The increased cloud cover should minimize the fog
potential overnight.

For Thursday and Thursday night...the ridge looks like it could
rebound again as pressure falls develop around 140w. The
interesting thing from this development is it takes the residual
moisture from tonight`s front and pivots it from a north-south
orientation to more of an east-west orientation as a warm front
pushes northward. The isentropic ascent from this front begins to
steepen and precipitation chances will increase steadily from
Thursday afternoon into Thursday night. Light to moderate
precipitation is expected to develop with a few locations near the
Cascades nearing up to half an inch. The remainder of the area
will see amounts generally ranging from .10-.25 inches. While most
of this will fall as rain with snow rising to 5500 feet near the
Canadian Border and to 7000 feet or higher south of I-90, there
is the possibility of a messy mix across the upper Methow Valley.
Model BUFR soundings are showing a temperature right around
freezing near the ground and extending up to nearly 5000 feet
through much of the event. Strangely the NAM BUFR is showing an
initial precip type of rain by midday Thursday followed by snow.
Given the warm air advection associated with the warm front and
little potential for wet bulb cooling, this seems unlikely.
However this will need to be watched especially if the
precipitation begins earlier and falls into an initially cooler
air mass. fx

Friday through Tuesday...An active weather pattern is expected
during the extended period. A cold front will track across the
Inland NW Friday into Friday night followed by cool and showery
weather on Saturday as the upper trough axis swings through. Snow
levels early on Friday start off at 6000-7000 feet before lowering
to 3000-4000 feet Saturday morning behind the cold front. Behind
the cold front mid level westerly flow will favor showers most
prevalent near the Cascade crest and Idaho Panhandle with snow
showers expected over the passes. Given the time of year (mid-
February) and its associated higher sun angle compared to late
December road temperatures may be too warm for significant travel
impacts over the passes but this will continue to be monitored.
Another warm front will pass through Sunday into Monday bringing
another round of precipitation with rising snow levels. Monday
has the potential to be very mild with the Inland NW in the warm
sector with breezy south- southwest winds as pressure gradients
tighten. The details differ after Monday with the timing of a cold
front with the ECMWF showing Monday night and GFS Tuesday night.
Given these uncertainties no changes were made to the Tuesday
forecast which favors the slower solution. This front may bring
in breezy to windy conditions once it passes. JW


&&

.AVIATION...
06Z TAFS: Fog and stratus was observed for most of the mountain
valleys this morning and along the Spokane/Columbia
rivers...closer to water sources. The inversion will remain strong
again tonight and fog/stratus will likely form in those areas
again tonight. However the strong ridge of high pressure that has
been over the region will shift east and bend slightly overnight.
This will allow upper level clouds to move into the region
overnight as well...and this may mitigate somewhat the strong
radiational cooling. In addition the surface flow will gradually
come around to southerly through the evening and this should pile
up the moisture for the northern valleys. With the exception of
the eastern basin and the Palouse at least some fog and stratus
will be possible for the TAF sites. So KLWS/KPUW can expect VFR
conditions through 00z. At the other TAF sites current VFR
conditions will likely drop down to MVFR cigs/vsby between 12-18z
then bounce back to VFR with a thickening but high cloud deck.
Tobin



&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        46  34  46  38  48  36 /   0   0  30  40  60  70
Coeur d`Alene  46  34  46  37  47  37 /   0   0  20  50  60  80
Pullman        51  39  51  40  52  38 /   0   0  10  20  50  60
Lewiston       55  40  56  42  57  42 /   0   0   0  10  40  50
Colville       42  32  41  35  42  36 /   0  10  50  70  60  70
Sandpoint      42  33  43  35  44  34 /   0  10  30  70  60  90
Kellogg        43  35  44  38  44  36 /   0   0  20  50  50  90
Moses Lake     47  34  47  38  48  37 /   0   0  30  30  50  40
Wenatchee      42  33  40  35  45  35 /   0   0  50  70  50  30
Omak           36  31  37  34  38  34 /   0   0  50  70  50  40

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Air Stagnation Advisory until 10 AM PST Saturday for East Slopes
     Northern Cascades-Moses Lake Area-Northeast Mountains-
     Okanogan Highlands-Okanogan Valley-Upper Columbia Basin-
     Waterville Plateau-Wenatchee Area.

&&

$$


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