Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 271120

Area Forecast Discussion
National Weather Service Spokane WA
420 AM PDT Wed Jul 27 2016

Another round of scattered thunderstorms is expected this
afternoon across the north. Dry and hot weather is expected
Thursday and Friday. A cold front arrives this weekend, bringing
breezy conditions and cooler weather for the start of next week.


Today through Thursday: Shower and thunderstorm chances continue
across the north through this evening before drier conditions
start in; temperatures will stay above normal.

The Inland NW is still under a dirty ridge. One shortwave will
continue to slip out through north ID early today, keeping an
isolated shower/t-storm threat alive across northeast WA and north
ID. Meanwhile a second shortwave crosses from the Pacific NW
coast to the northern Rockies between late morning and evening.
This will work with increasing surface-based instability to
revitalize showers and thunderstorms around the Cascades and
northern mountains. Some clusters of locally stronger storms are
possible with brief heavy downpours, small hail and locally
abundant lightning. If any pass a burn scar we may have to watch
for some flooding. As remainder of the area, model tend to keep
the precipitation threat at bay. Only a couple models show some
isolated showers and t-storms developing around the Waterville
Plateau and the Spokane/C`dA area. However one of these models is
the ECMWF and it tended to do better with last evening`s
convection. I increased PoPs across the north, including bringing
some into the far northern Columbia Basin, including Spokane and
Kootenai county. The risk wanes after sunset so that by overnight
into Thursday morning the area looks dry. Lastly look for an
increase in Cascade gap winds in the late afternoon/evening.

Thursday afternoon another weak shortwave slides by, but some
milder air surges in aloft and convective instability is more
limited. There may be some isolated shower/t-storms near the far
Cascade crest and near the mountains near the ID Panhandle.
Otherwise expect dry weather with some afternoon cumulus build-ups
around the mountains. /J. Cote`

Thursday night through Friday night: Zonal flow or subtle ridge
pattern will continue through this period with the upper level jet
remaining fixed across the southern half of BC. This will result
in dry weather for most locations with most if not all afternoon
and evening convection expected to remain north of the
International border. Although we cannot entirely rule out a stray
shower or thunderstorm moving into extreme northern Washington or
north Idaho, the odds are too small to place in the forecast
grids. High temperatures on Friday will likely reach the 90s to
lower 100s for most valley locations.

Saturday through Monday: Changes are expected to develop during
this part of the forecast as most model solutions show an upper
level low dropping steadily southward out of Canada. This will
push the upper level jet into the northern Cascades by Saturday
afternoon with it dipping toward the Washington-Oregon border by
late Sunday or Monday. The big change associated with the sagging
jet will be the introduction of much drier dewpoints across most
of the region as a cold front pushes through. Precipitable water
values will drop nearly in half from todays moist readings which
should limit any chance of precipitation. The exception will occur
near the International border where just enough moisture and
instability will remain fixed over the area. Diurnal heating
combined with upslope flow from south-southwest mid-level winds
will lead to isolated convection and possibly a few thunderstorms
between Sunday and Monday. Model potential instability values are
not impressive at least compared to yesterdays readings. However
model soundings show the convection will be just deep enough to
support showers and possible thunderstorms. The bigger story
though will be the potential for enhanced fire conditions behind
the passage of a surface cold front. Looks like the frontal
passage will occur Saturday with plummeting dewpoints expected
which will combine with increasing westerly winds. Right now it
appears relative humidity values will be low enough for fire
weather highlights, however we aren`t sure the winds will be
sufficient. Sunday could see a better chance for enhanced fire
potential as the winds will remain breezy with min relative
humidity levels dropping to near 20 percent over many valley
locations. Temperatures will drop both days with highs in the mid
80s to lower 90s on Saturday and perhaps cooler than normal highs
in the upper 70s to mid 80s on Sunday. By Monday there are
significant model differences as the latest Canadian and previous
ECMWF kept a deeper low fixed over NE Washington and north Idaho,
however the latest ECMWF and GFS depict a shortwave ridge building
ahead of the next upper level low. The slower solution matches up
to the latest GFS ensemble mean and consequently we will keep a
small mention of showers and possible thunderstorms over the far
north and keep cooler yet relatively dry conditions elsewhere.
Highs will remain on the cooler side of normal with highs in the
mid 70s to mid 80s. fx

Monday night through Wednesday: Both the GFS and ECMWF
deterministic models, as well as the GFS ensemble, show another
trough making its way through the region during the far extended
period of the forecast. They differ however in the track and
timing with the GFS bringing the 500 mb cold pool directly over
the Inland Northwest, whereas the EC only grazes our northern
area. Added precipitation chance mainly across our northern
mountains where model agreement was best. With this in mind, the
precipitation, wind, and temperature forecast will be very
dependent on the eventual track of this system. High temperatures
look to remain a few degrees below normal. /Kalin


12Z TAFS: Another weak shortwave moves into the region today,
bringing more isold-sct -shra/-tsra, mainly around the Cascades
and northern mountains. A few may slip across the northern
Columbia Basin in the afternoon to early evening, including in the
vcnty of the GEG-COE. However the risk appears low. Some breezy
conditions will be found near OMK/EAT early and again late this
afternoon/evening near EAT. The shower threat wanes after 03-06Z.
Otherwise expect dry and VFR conditions. /J. Cote`


Spokane        91  65  93  68  94  64 /  20  10   0   0   0   0
Coeur d`Alene  90  60  92  63  93  61 /  20  10  10   0   0   0
Pullman        90  54  92  57  93  57 /   0   0   0   0   0   0
Lewiston       99  68  99  69 100  67 /   0   0   0   0   0   0
Colville       91  58  95  60  95  55 /  20  20  10   0   0   0
Sandpoint      86  54  88  57  89  55 /  20  20  10   0   0   0
Kellogg        88  55  89  57  90  57 /  20  10  10   0   0   0
Moses Lake     97  65  98  66  99  61 /   0   0   0   0   0   0
Wenatchee      96  70  98  70  98  66 /  10   0   0   0   0   0
Omak           95  67  97  68  98  64 /  20  10  10   0   0   0



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