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FXUS66 KOTX 231141

Area Forecast Discussion
National Weather Service Spokane WA
440 AM PDT WED JUL 23 2014

A strong storm system will move through the region today, bringing
the potential for thunderstorms and heavy rain. Cool and windy
weather is expected for Thursday. Temperatures will rebound by the
weekend and be accompanied by dry conditions. Hot weather will
return to the area on Sunday and early next week.


Today and tonight: A strong storm system comes into the region,
with a good chance of showers and thunderstorms. Low pressure is
centered off the Washington coast this morning and is forecast to
reach NE WA/SE BC by Thursday morning. Ahead of it is a moist
southwest flow, with PWATs around 1 inch (or about 180% of normal)
and surface dew points in the 50s to low 60s. This morning showers
and thunderstorms, associated with a mid-level disturbance and
slug of mid-level instability that came in from Oregon, will
continue to lift northward and out into BC and MT. This will leave
some lull in the bigger precipitation threat from around 15-20Z
for a good chunk of the region. However other showers are expected
to continue near the Cascades with the offshore low approaching
and the next shortwave pivoting around it.

Then this afternoon and evening the next round of showers and
thunderstorms develops. As temperatures warm into the 70s and
80s the convective instability blossoms: SBCAPE values from 18
and 00Z rise to between 200 and 1000 J/kg. The best of it centered
along and north and east of a line from Mazama to Othello. In that
region models paint the core of it across the northeast mountains
south into the Palouse and across the north and central Panhandle.
So going into the afternoon a theta-e ridge slips in from the
south, while the cold front and supporting upper low push into
the Cascades and east toward the Idaho Panhandle by this evening.
These latter several features would be enough to bring a good
threat of showers and thunderstorms. But the coupling of one jet
streak tracking up from the Great Basin into central Idaho and
second jet streak rounding the upper low, with a fair amount of
diffluence over eastern Washington and north Idaho, makes me even
more confident there is enough lift out there to bring showers
and thunderstorms.

Models still paint some of the higher precipitation amounts along
the cold front and upper low over the Cascades, supporting the
potential for flooding. Hence the flash flood watch remains in
place, especially with concerns in the burn scar areas from this
and the past few summers. The threat of strong to locally severe
thunderstorms also remains over much of eastern WA and north ID
too given the forces of lift, moisture and instability coming
together. With 0-6km bulk shear between 30 to 50kts, storms will
have the potential to be more organized. Looking at forecast
soundings, the CAPE appears to be relatively thin and tall, with
a relatively dry sub-cloud layer. This lends thinking that the
main threat from storms will be hail and gusty winds.

Going into the late evening and overnight the cold front is
pushed east of the region, with the upper low near the WA/BC
border. Some elevated instability lingers across the Canadian
border, petering out southwest toward the Waterville Plateau. Some
weak instability lingers near the Clearwaters too. Thus the
primary shower chances will continue near the Cascade crest,
northern mountains and across Idaho, especially through the early
overnight. The remainder of the area should see things drying out,
with some clearing from the southwest.

The other issue will be winds. Outside of those generated with
thunderstorms, synoptic winds are expected to pick up from the
west-southwest this afternoon and tonight along and behind the
front. By mid to later afternoon winds in the 10 to 20 mph range
will be possible, especially over the east Chelan county, across
the Basin into the Spokane/C`dA area, Palouse and L-C Valley.
Gusts near 30 mph or so will also be possible. Speeds abate some
overnight, but still remain relatively breezy for the time of day.
/J. Cote`

Thursday through Sunday...Model guidance indicates the cold pool
aloft associated with the anomalous upper low will be centered
over the northern reaches of the forecast area as Thursday dawns.
This should promote continued showers...but given the time of day
before appreciable surface based instability can be generated
these lingering showers will be primarily left over rain showers
from the previous evening`s convective activity with only a few
isolated thunderstorms centered mainly over the mountainous
terrain north of the Columbia Basin. Thursday overall will be a
day of general improvement as the offending upper low begins to
move out of the region to the northeast during the afternoon. The
cooler maritime air mass in the wake of the upper low will
manifest itself as much cooler than normal temperatures on
Thursday with generally breezy conditions with gusts to near 30
mph over the exposed terrain of the basin and Cascade gaps.

Friday through Sunday will feature a drying and warming trend as a
mid-summer 4 corners upper level ridge builds into the region. A
general warming trend to back above normal will become noticeable
starting Friday and continuing through the weekend with lighter
winds and a dry and stable air mass precluding any precipitation.

Monday through Wednesday: A ridging pattern is expected to be over
the region for this period. This will lead to a dry and warming
trend in the temperatures. The models are in good agreement for
this period with the exception of the GFS showing a shortwave on
Monday morning. The lack of moisture kept the chance of showers
out the forecast. Temperatures are expected to be in the 90s for
the region during this period. /JDC


12Z TAFS: Low pressure off the coast this Wednesday morning will
move inland over the next 24 hours. Isolated showers will be
possible around the TAF sites this morning, but a better threat
of showers and thunderstorms develops this afternoon, first around
EAT near 18-21Z and elsewhere starting between 20-23Z, before the
threat begins to wane after 00Z-06Z from west to east. Some of the
thunderstorms may be strong and isolated severe thunderstorms are
not out of the question. Predominantly VFR conditions are forecast.
Yet heavier storms may produce brief MVFR/IFR cigs/vis, with the
potential for heavy downpours, gusty winds and hail. Aside from
possible winds with thunderstorms, general winds will increase
for this afternoon and evening with sustained speeds between
10-20kts and gusts up to 30kts, before decreasing after 03-06Z.
/J. Cote`


Spokane        83  52  71  51  77  55 /  50  80  20  10   0   0
Coeur d`Alene  84  53  67  52  76  51 /  50  80  40  10   0   0
Pullman        84  49  69  46  76  44 /  40  70  10   0   0   0
Lewiston       90  58  78  57  84  56 /  40  60  10   0   0   0
Colville       81  51  71  51  80  50 /  60  80  50  10   0   0
Sandpoint      85  51  66  49  73  49 /  50  80  50  10   0   0
Kellogg        85  52  65  50  73  51 /  40  80  40  10   0   0
Moses Lake     83  56  75  57  84  57 /  50  40  10   0   0   0
Wenatchee      75  58  73  59  83  61 /  70  40  20   0   0   0
Omak           77  55  74  53  84  54 /  80  60  20  10   0   0


WA...Flash Flood Watch from 8 AM PDT this morning through this
     evening for East Slopes Northern Cascades-Okanogan Valley-
     Wenatchee Area.



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