Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 070029
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
528 PM PDT MON JUL 6 2015

.SYNOPSIS....
After a warm and dry conditions, another weather system drops in
from Canada Tuesday, with a threat of showers and thunderstorms
across, largely across the north. Drier conditions return around
mid-week, before additional shower and thunderstorm chances
return toward Friday into next weekend.

&&

.DISCUSSION...

Tonight through Tuesday night....The weather during this period
will revolve around a shortwave trough currently dropping
southeast through southern British Columbia. This feature is
expected to drop toward NE corner of Washington and the northern
tip of the Idaho Panhandle overnight. As it does we expect to see
increasing amounts of mid level moisture and instability track
into that area. Model soundings in the vicinity of this feature
suggest we will see some of this instability and moisture develop
into showers late tonight and persist into Tuesday morning. The
soundings also suggest a very small chance for a few lightning
strikes due to elevated instability near the Canadian border
toward morning but the threat isn`t great enough to place in the
forecasts at this time. A much better threat of showers and
thunderstorms will arrive during the afternoon and evening hours
as a more robust upper level shortwave tracks south across the
Canadian border. This shortwave will lower temperatures in the
upper atmosphere while warming and moistening the lower
atmosphere, a prime recipe for thunderstorms provided sufficient
lifting. And it looks like this shortwave will provide the
necessary lift. So the pieces are in place for a decent
thunderstorm event. Most of them will likely occur over NE
Washington and north Idaho based on the best potential instability
combined with the best upper level forcing from the positioning of
the jet stream. However the threat will likely extend west toward
the Cascades as well. Looks like most of the thunderstorms will
initiate by early afternoon near the Canadian border and spread
south through the evening. Based on wind profiles and instability
parameters we don`t expect to see any strong thunderstorms however
based on elevated cloud bases and rather dry conditions below
there will be a chance of some moderate thunderstorm outflow
winds. Also based on the dry sub-cloud layer we don`t expect to
see widespread heavy rains, however most of the storms will
produce some rainfall. The other threat will be for new fire
starts based on the extremely dry fuels. The question is how much
lightning will we see. Based on the instability parameters it
looks like most will occur over extreme NE Washington and the
northern Idaho Panhandle. The fire weather watch still seems like
a good call, however in an effort to coordinate with neighboring
offices will leave the watch going rather than upgrading to a red
flag warning.

The threat of thunder should ware rapidly overnight as the
shortwave begins to shear and stretch as it moves toward the
Washington/Oregon border. fx.

Wednesday through Monday: After a relative lull, the active
pattern continues with the return of the threat of showers and
thunderstorms. Temperatures will remain above normal much of the
period, but look for a relative cool-down toward the weekend. And
beyond next Monday models suggest perhaps a return to more
seasonal temperatures.

First on Wednesday a front stalls over the southern ID Panhandle
and northeast OR. Behind it is drier air and broader subsidence.
So for the most part the region will be dry. Yet there will be a
small risk of showers or t-storms along that boundary during the
afternoon near the Blues, Camas Prairie and far southeast Shoshone
county. There is the off-chance for shower showers near the
Cascades of Chelan county in the northeast flow, but confidence is
rather low and there is not real mention of it other than here.

Secondly on Thursday low pressure off the CA coast moves toward
the western Great Basin. So the flow over our area turns east-
southeast, the stalled front edges north and some weak mid-level
disturbances lift in. And some moisture starts to expand north. So
look for a better threat of showers and thunderstorms over the
southeast CWA and near the Cascades. Clouds will begin to increase
elsewhere.

Thirdly from Friday through Monday the pattern changes. The
former CA low stretches toward the High Plains and a trough
deepening in the Pacific approaches the coast. The flow turns
southwest and a better fetch of moisture rides in, with PWATs
rising to an inch or so. Systems passing in this pattern will have
increased instability and the aforementioned moisture to bring the
increasing threat of showers and thunderstorms across the region.
Models are not in the best agreement regarding the timing the
individual shortwaves that will bring in these precipitation
chances. At this time models suggest a boundary passing Friday or
Friday night and then a shortwave riding in on a modest jet streak
Sunday appear to be the catalyst.

In general look for the best threat of showers and thunderstorms
each day around the mountain zones, especially in the afternoon
and evening hours. As for the valley and basin zones loose
agreement suggests Friday/Friday night and Sunday may be the
periods with a better threat of showers and thunderstorms with the
passage of the aforementioned features. As said, there is some
disagreement on timing so stay tuned as things come into better
focus. Regardless of timing, given the amount of moisture and the
potential instability models depict at this point I`d be hard-
pressed to say that there will be no chance in the valley/basin
areas.

With the increasing moisture during this time it is expected the
showers and thunderstorms will be wetter. So while there will
still be some concern for wildfire ignitions from any lightning,
the overall threat appears smaller compared to the current
pattern. Another issue we will monitor is the potential for
localized flooding, especially around any burn scars from last
years or even this years newer wildfires. This will be due to the
potential for wetter and potentially slower-moving or training
storms. /J. Cote`

&&

.AVIATION...
00Z TAFS: VFR conditions will continue through the forecast
period. Mid and high level moisture will stream in from the north.
A weak disturbance will brush the Canadian border overnight and
dig south over north Idaho on Tuesday. This will help increase
cloud cover and bring a threat of convection to the north and east
of the KGEG-KCOE corridor. Winds will be light and diurnally
driven overnight and into Tuesday morning. Expect a push of
north-northeast winds by Tuesday afternoon. rfox.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        66  91  65  93  66  96 /   0  20  20  10  10  10
Coeur d`Alene  60  89  61  91  61  95 /  10  50  20  10  10  10
Pullman        57  90  57  91  57  94 /   0  10  10  10  10  10
Lewiston       66  98  68  99  69 100 /   0  10  10  10  10  10
Colville       63  91  60  97  61 100 /  10  50  30  10   0  10
Sandpoint      55  84  55  90  54  94 /  20  50  40  10  10  10
Kellogg        58  87  56  90  57  93 /   0  40  30  10  10  20
Moses Lake     65 100  69 100  67 102 /   0   0  10  10   0  10
Wenatchee      69  99  72 101  73 102 /   0  10  10  10   0  10
Omak           65  98  65 100  67 102 /  10  10  10  10   0  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...FIRE Weather Watch from Tuesday afternoon through Tuesday
     evening for Northern and Central Idaho Panhandle (Zone 101).

WA...FIRE Weather Watch from Tuesday afternoon through Tuesday
     evening for East Washington North Cascades (Zone 685)-East
     Washington Northeast (Zone 686)-East Washington Okanogan
     Highlands (Zone 687).

&&

$$



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