Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 080033
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
533 PM PDT TUE JUL 7 2015

.SYNOPSIS....
A weak weather system will bring thunderstorms to northeast
Washington and north Idaho this evening. Drier conditions return
Wednesday with hot temperatures through Thursday. The remainder of
the week will see a slight cooling trend with and increased
chance of showers and wet thunderstorms.

&&

.DISCUSSION...
This evening...made a few updates. Scattered thunderstorms have
developed over Lake Chelan and are drifting south. Some locally
heavy rain is possible with these cells especially as they drift
over the burn scars. Meanwhile bands of showers with embedded
thunderstorms are drifting south across the northern mountains.
Expect occasional lightning and outflow winds.

Rest of tonight through Thursday...A weak cold front is brushing
the northwest corner of the forecast area this afternoon and this
feature will create some potential issues for the fire weather
concerns around the region. First there is the potential for
abundant lightning in and about the cores of any thunderstorms
which develop this afternoon and evening. The currently valid Red
Flag Warning for the northeastern zones and Idaho Panhandle
address this concern.

Satellite and Radar indicate a stubborn line of mid
level convection...thus far with little lightning and little rain
...running from around Inchelium to the Montana border near
Mullan Pass. there is a good chance at least a few thunderstorms
will develop this afternoon and early this evening near or along
this line...with isolated cells popping up to the north of the
line as afternoon heating promotes surface based CAPE values in
the 200 to 600 J/Kg range. The other moderate threat will be gusty
outflow winds moving south from this line during the evening hours
into the Columbia Basin. Most of the fine mesh models do not
suggest this threat...however pattern recognition and the presence
of a dry sub cloud layer suggest this threat does indeed exist
this evening. Nothing severe is expected but outflow gusts in the
30 to 40 mph range are plausible across the highway 2 corridor
from north to south and possibly into the deep basin between 6 pm
and 10 pm this evening. A few largely stationary and short lived
thunderstorms are also possible over the high Cascades.

After this evening`s activity dies down overnight a generally
quiet and clear weather pattern (except for ever present smoky
areas) will return to the area with Wednesday and Thursday
featuring increasingly warm temperatures and decreasing primarily
northeast winds...shifting to terrain driven on Thursday. The
overall pattern will gradually shift to an offshore trough
promoting increasingly moist southerly flow into the
region...possibly triggering the next round of thunderstorms as
early as Thursday afternoon over the Cascades and Camas
Prairie/Blue Mountains...but the main manifestation of this
pattern shift will likely hold off until later in the forecast
period. /Fugazzi

Thursday night through Saturday...An upper level trough of low
pressure will drop south out of the Gulf of Alaska, placing the
region under moist southwest flow aloft. This will bring an
increasing chance of showers and thunderstorms to the Inland
Northwest. For Thursday night, the main threat for showers and
thunderstorms will be across the southeast zones as monsoonal
moisture pushes in from eastern Oregon. Areal coverage of convection
will increase Friday as daytime instability increases and continued
southwest flow taps into a plume of tropical moisture. At this point
it looks like the entire forecast area will be under the threat of
at least isolated showers and thunderstorms with a higher risk for
the rising terrain surrounding the Columbia Basin. Bulk shear will
be weak so organized storms with large hail are not a big concern.
Gusty outflow winds will be possible since the lower layer of the
atmosphere will be dry to start. Rather light winds through 700 mb
will mean that storms will be moving rather slowly and since there
will be ample moisture available, heavy rain will be possible with
thunderstorms. This could cause flash flooding and debris flow over
recent burn scars. Both the GFS and ECMWF show a dry slot moving
into the Cascades Friday night into Saturday, placing the focus on
the extreme eastern WA and the Idaho panhandle.

Increased cloud cover and scattered precipitation will place daytime
temperatures on a slight cooling trend while remaining above
seasonal normals. Overnight lows will remain quite mild. /Kelch

Saturday night through Tuesday: The weather pattern looks to
remain unsettled into early next week. A broad upper level trough
of lower pressure will reside just off the western coastline of
North America. Shortwave disturbances will push across the region
in a moist southwesterly flow pattern. This is expected to result
in a chance for showers and thunderstorms across much of the
region. The timing for each disturbance is still uncertain at this
time, but best chances will be during the peak heating hours of
the afternoon and early evening. Thunderstorms will likely be wet
and will pose a flash flood threat for burn scars. The good news
is that models indicate a stronger steering flow for this period.
This should limit the time any one storm lingers over an area. The
potential for some stronger storms will also be there, but
uncertainty is too high to have much confidence in when and where
stronger storms may develop at this time. A southwesterly flow
pattern typically will favor the ID Panhandle and extreme
southeast portion of WA. Temperatures will also be much cooler
than what has been felt so far this summer. With that said,
temperatures are only going to cool back down into the 80s, which
will be right around seasonal normals. /SVH

&&

.AVIATION...
00Z TAFS: Scattered showers with isolated thunderstorms have
developed across the northern mountain zones, and are drifting
south. Radar trends show a possibility of some convection reaching
the KGEG-KCOE corridor before 03z. High based cumulus over the
KLWS area may produce VCSH. Otherwise most other TAF sites may
escape the convection. Expect VFR and high level clouds this
evening, followe by clearing. Winds will turn out of the
north/northeast as front slow sinks southward. This wind switch
coupled with any thunderstorm outflow may lead to gusty
conditions. Anticipate less wind and cloud cover after 08z and
into Wednesday. /rfox.

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        66  94  67  96  70  93 /  20   0  10  10  10  20
Coeur d`Alene  62  92  61  95  64  92 /  50   0  10  10  10  30
Pullman        56  92  57  94  62  89 /  20   0  10  20  20  30
Lewiston       68  99  69 100  72  96 /  10   0  10  20  20  30
Colville       60  97  60 100  62  97 /  30   0   0  10  10  20
Sandpoint      54  90  54  94  57  91 /  50   0  10  10  10  30
Kellogg        56  90  56  93  62  90 /  50   0  10  10  10  40
Moses Lake     69 100  67 102  71  97 /  10   0   0  10  10  10
Wenatchee      74 101  75 102  75  96 /  20   0   0  10  10  20
Omak           66 100  68 102  68  99 /  20   0   0  10  10  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Red Flag Warning until 9 PM PDT this evening for Northern and
     Central Idaho Panhandle (Zone 101).

WA...Red Flag Warning until 9 PM PDT this evening for East Washington
     Northeast (Zone 686)-East Washington Okanogan Highlands
     (Zone 687).

&&

$$




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