Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 251155
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
455 AM PDT MON MAY 25 2015

.SYNOPSIS...
A slow moving low pressure system will bring scattered afternoon
and evening thunderstorms to the Inland Northwest today through
Wednesday. Locally heavy downpours, frequent lightning, and small
hail will be possible the next several days. Low pressure will
gradually depart by Thursday bringing a decrease in precipitation
chances. Next weekend looks like it will be quite warm with
afternoon temperatures well into the 80s.

&&

.DISCUSSION...
Memorial Day through Tuesday night: Satellite imagery early this
morning shows a tightly wrapped upper level low centered over
southern BC. Showers with isolated thunderstorms will continue to
form on the eastern portion of the upper level low through the
morning hours. This will include areas primarily northeast of a
line from Republic to Pullman. The upper level low will slowly
track over the northern portion of the WA Cascades and over the
Waterville Plateau through this afternoon. Water vapor satellite
imagery shows a dry slot extending across the northwest portion of
the forecast area through 2:00 AM this morning. This drier air
will also progress eastward through the day. This will result in a
decreasing chance for convective showers and thunderstorms from
west to east across portions of extreme eastern WA. However,
colder temperatures aloft associated with the upper level low will
result in steepening mid level lapse rates from the East Slopes of
the Northern Cascades to the Northeast Mtns and into the western
portion of the basin. This will result in showers increasing
through the late morning and afternoon hours across these areas.
Thunderstorms are also expected to occur as the atmosphere
destabilizes in the afternoon. These thunderstorms will be slow
moving and contain very heavy rainfall. Greatest coverage of
showers and thunderstorms is expected over the northern mountains
and mainly north of Lake Chelan in the Cascades over to the
Northeast Mtns. Heavy rainfall will be a concern for the recent
burn scars. Greatest concern this afternoon will be for the
potential of flash flooding and/or debris flows over and near the
Carlton Complex and Devils Elbow burn scars. Recent burn scars
south of Lake Chelan will also see the possibility for heavy
rainfall today, but chances are not quite as high.

The center of the upper level low will shift more into the basin
on Tuesday. This will result in another day of increased
convective activity through the late morning and afternoon hours.
All areas will see at least a chance for some isolated
thunderstorms. Chances will be a bit higher for thunderstorms
further south across the east slopes of the norther Cascades. This
will result in a better chance for heavy rainfall over the Chiwaukum,
Mills Canyon and Colokum Tarps burn scars, as well as, the Carlton
Complex and Devils Elbow burn scars. P-wats will be a bit higher
on Tuesday and is expected to be greater risk for flash flooding
and/or debris flows at or near these burn scars compared to today.

Temperatures will be noticeably cooler today compared to the past
few days. High temperatures are expected to be in the mid and
upper 60s and 70s across the region. Expect similar temperatures
on Tuesday. /SVH

Wednesday and Thursday: Our slow moving upper low is expected to
drift into northeast Oregon and the southern Idaho Panhandle on
Wednesday. Our highest concentration of showers and thunderstorms
should be in the vicinity of the 500mb cold pool including the
Blue Mountains, Camas Prairie, and Clearwater Mountains. The NAM,
GFS, ECWMF and SREF produce a secondary convective signal over the
northern Washington Cascades. So Wednesday has the potential to be
another day of closely monitoring the Cascade Burn Scars. By
Thursday, our pesky low should be over southern Idaho and northern
Utah leaving the Inland Northwest under the influence of weak
residual cyclonic 500mb flow...namely over the Idaho Panhandle.
With less upper support, afternoon/evening thunderstorms should be
more terrain based. The lowlands of the Columbia Basin, Palouse,
and West Plains will probably be free of showers while the
mountains have a shot at scattered diurnally driven showers and
thunderstorms.

Friday through Sunday: The Pacific Northwest will be between a
weak upper ridge building over the Great Basin and an elongated,
strung-out trough over southwestern Canada Friday through Sunday.
The evening run of the medium range models are not as warm for the
upcoming weekend, but still suggest well above average
temperatures. It is doubtful that any given day between Friday and
Sunday will be completely free of showers, but it is tough to
figure what areas stand the best shot of convection given the
subtle differences in the strength of the ridge to the south and
the trough to the north. Even though the ECMWF and GFS have backed
off on their 20C and warmer 850mb temperatures for next weekend,
places like Lewiston, Moses Lake, Wenatchee, and Omak could have a
shot at hitting 90 degrees Friday, Saturday or Sunday for the
first time this year. /GKoch

&&

.AVIATION...
12Z TAFS: A mid level cold front will slowly push across extreme
eastern WA and into the ID Panhandle this morning into the early
afternoon. This will combine with some instability at mid levels
to generate showers and thunderstorms across the Spokane-Coeur
d`Alene corridor through the morning hours. A moist boundary layer
is also expected to result in some low stratus early this morning
with MVFR cigs possible. A short break is expected late in the
morning, but low levels will destabilize quickly in the afternoon
for the possibility of surface based showers and thunderstorms across
much of the northern portions of eastern WA over into the ID
Panhandle. This will include the KGEG, KSFF and KCOE TAF sites.
KEAT and KMWH may see isolated thunderstorms push in off of the
Cascades and the Waterville Plateau late this afternoon, but
confidence is low. Isolated to scattered showers will persist over
much of the region through 12Z Tuesday.


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        70  51  70  52  76  54 /  40  40  70  40  30  20
Coeur d`Alene  67  49  69  50  75  51 /  60  40  70  40  40  30
Pullman        68  45  68  47  72  49 /  20  10  40  30  40  20
Lewiston       77  53  74  55  78  56 /  20  10  30  20  30  20
Colville       70  50  73  50  82  51 /  80  70  70  40  30  30
Sandpoint      64  47  69  49  74  50 /  70  50  70  50  40  30
Kellogg        67  45  68  47  73  49 /  80  50  70  50  50  40
Moses Lake     78  53  78  53  83  55 /  20  20  20  20  10  10
Wenatchee      77  57  76  59  83  60 /  30  20  50  30  20  20
Omak           76  50  76  51  82  52 /  70  70  70  40  20  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.
&&

$$


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