848
FXUS66 KOTX 152228
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
328 PM PDT Thu Aug 15 2024

.SYNOPSIS...
Showers and thunderstorms will continue through this evening and
overnight across eastern Washington and north Idaho. Thunderstorms
Thursday will bring the potential for gusty outflow winds.
Thunderstorms will return on Friday across the northern mountains
with concerns for flash flooding over burn scars. More showers
and thunderstorms are possible late Saturday afternoon and night
for central WA. Temperatures will be warmer on Saturday with dry
and breezy northeast winds across the Columbia Basin, West Plains,
and southeast Washington.

&&

.DISCUSSION...
Tonight and Friday: An upper level trough in eastern Oregon will
move northward into eastern Washington and north Idaho late this
afternoon and evening. Weak impulses rotating around the main trough
has allowed for thunderstorm development over the central Panhandle
mountains this afternoon. As the main trough over eastern Oregon
moves north into the region, there will be another round of showers
and thunderstorms to move into the central Panhandle and southeast
Washington later this evening and move into the CdA/Spokane area
overnight. The biggest concern with convection will be lightning
and gusty outflow winds. Models are showing DCAPE (downdraft CAPE)
between 800-900 J/kg for the Camas Prairie, into southeast
Washington, and across much of the Central Panhandle Mountains.
Wind gusts up to 40 mph will be possible with stronger convective
cells. Convection then looks to transition into more of a
stratiform precipitation with isolated lightning overnight as
instability decreases across the Northern Panhandle into the
Northeast Mountains and Okanogan Highlands.

On Friday, models indicate 500-1000 J/kg of surface based CAPE from
the east slopes of the northern Cascades and across the northern
mountains for Friday afternoon and evening. Model soundings are
showing moist and unstable profiles with very slow storm motions.
Forcing does not look to be overly strong with convection being
focused over the mountains where orographic influences aid in
development. Thunderstorms that development will be slow moving with
concerns for flash flooding and debris flows in and around the burn
scars in the North Cascades. The best potential for showers do look
to be for areas north Lake Chelan in Chelan County and Okanogan
County.

Saturday: A deep upper level low will move toward the Pacific
Northwest coast late Friday night and early Saturday morning. This
will pump up the upper level ridge across eastern Washington and
north Idaho with temperatures warming into the upper 80s and 90s
across much of the region.  Models are showing a surface low to move
northward across eastern Washington and north Idaho Saturday
evening. This will bring showers and thunderstorms across the
western and central Washington Saturday evening into Sunday. With
the placement of the surface low, thinking far eastern Washington
and north Idaho will miss out on precipitation chances. Breezy
northeast winds will set up across eastern Washington and north
Idaho with this low with an 70 to 100 percent chance for sustained
winds above 15 mph across the Waterville Plateau through the
Columbia Basin and into the West Plains and the Snake River area.
RHs in the upper teens to low 20s on Saturday will elevate fire
concerns across these areas. As this low moves northward, these
areas will see a distinct wind shift to the southwest overnight
Saturday into Sunday. /vmt

Sunday through Thursday: The majority of the extended forecast will
see low pressure to our west along the coast and a ridge just to the
east of the Inland Northwest. Chances for showers/thunderstorms will
linger into Sunday across the Cascades and northern mountains.
Forecast then looks to turn drier for Monday through early
Wednesday. Chances for storms return Wednesday afternoon through
Thursday, though confidence in the pattern is far from set in stone.
Daytime temps near daily normals through much of the extended,
though Monday looks the warmest with temps around 5 degrees above
average. Best chances for gusty winds will be near any thunderstorms
that develop through the period, though locally breezy winds are
anticipated Sunday across central Washington. /KD


&&

.AVIATION...
00Z TAFS: An upper level shortwave will bring showers and
thunderstorms across eastern Washington and north Idaho through
the evening and overnight. Some of these thunderstorms may become
strong with gusty outflow winds up to 40 kts impacting airports
in extreme eastern Washington namely KLWS- KPUW. Thunderstorms
will also be capable of heavy rain that brings a brief period of
MVFR conditions after 01Z. Moderate rain with lowering ceilings is
expected across the northern Idaho Panhandle into northeast
Washington overnight into Friday morning. Isolated embedded
thunderstorms will be possible overnight as well.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High confidence
for VFR conditions today across the majority of the TAF period.
The exception will be for locations under heavy showers where
brief MVFR conditions are possible. Moderate to high confidence
for thunderstorms at KLWS and KPUW this evening and moderate
confidence for thunderstorms across KGEG-KSFF-KCOE.

-----------------------

Confidence descriptors:
Low - Less than a 30 percent chance
Moderate - 30 to 70
percent chance
High - Greater than a 70 percent chance

For additional probabilistic information for NWS Spokane airports,
please refer to the Aviation Dashboard on our webpage:
https:/www.weather.gov/otx/avndashboard

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        59  80  56  90  59  83 /  50  40   0   0  30   0
Coeur d`Alene  57  78  54  87  57  82 /  60  70  10   0  20   0
Pullman        52  78  52  90  53  81 /  60  20   0  10  10   0
Lewiston       62  86  62  97  64  90 /  60  10   0   0  10   0
Colville       50  79  44  87  48  83 /  30  60  20   0  30  10
Sandpoint      55  73  51  84  55  81 /  60  80  10   0  20  10
Kellogg        58  74  57  88  59  81 /  90  70  10   0  20   0
Moses Lake     56  83  55  93  57  83 /  20  10   0  20  50   0
Wenatchee      62  83  62  90  63  81 /  10  10   0  20  60  10
Omak           62  87  59  93  62  88 /  20  50  10  10  50  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...Flash Flood Watch from Friday morning through Friday evening for
     Central Chelan County-Okanogan Highlands-Okanogan Valley-
     Upper Columbia Basin-Wenatchee Area-Western Chelan County-
     Western Okanogan County.

&&

$$