181
FXUS66 KOTX 181023
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
323 AM PDT Sat May 18 2024

.SYNOPSIS...
Cooler and unsettled weather will continue through the weekend.
This morning will be quite chilly, with the potential for frost
in the sheltered valleys of north Idaho, northeast and north
central Washington. A wetter low pressure system is expected on
Wednesday and will keep temperatures below normal.

&&

.DISCUSSION...

Today: After a healthy dose of wind Thursday and Friday, residents
of the Inland Northwest can expect more typical May weather today.
Deep low pressure over Montana and the Dakotas will migrate east
today. It will still be locally breezy this afternoon and evening,
but not out of the ordinary. Folks in Wenatchee and other
locations prone to breezy winds through the Cascade gaps will
experience "normal" late day west winds of 20 to 30 mph.
Elsewhere, west winds of 10 to 20 mph will be common across the
Columbia Basin, eastern Washington and north Idaho. Westerly
pressure gradients will tighten this afternoon as an upper level
disturbance moves inland. This disturbance will also enhance
afternoon instability showers. The most significant concentrations
of showers and embedded thunderstorms will occur across our
counties near the Canadian border. Republic, Colville, Metaline,
and Bonners Ferry have a 50 to 70 percent chance of measurable
precipitation this afternoon and early this afternoon and evening.
Further south, chances for measurable precipitation this
afternoon and early this evening decrease to 20 to 30 percent for
Spokane and Coeur d`Alene with about a 15 percent chance of
lightning around the metro in the evening.

Tonight: The mid-level circulation associated with our incoming
disturbance is progged to move through the center of Washington
this evening toward the southern Idaho Panhandle by early Sunday
morning. Model ensembles generate enough lift and cooling aloft to
sustain clusters of showers through the night across north Idaho
and the eastern third of Washington. At this time, it looks like
there will be enough shower activity and cloud debris to interrupt
radiational cooling. It will still be a chilly night, but cold
pockets like Deer Park, Colville, and sheltered valleys of north
Idaho should remain in the mid to upper 30s.

Sunday: It will be a cool and showery day in north Idaho and
northeast Washington. Clusters of showers and thunderstorms will
develop under a chilly upper level trough and the mountainous
terrain will enhance shower chances. The National Blend of Models
(NBM) gives Colville, Deer Park, Sandpoint, and Kellogg a 60 to 80
percent chance of showers. Despite high chances for showers,
probabilities for 24 hour amounts exceeding a quarter inch are
relatively low for north Idaho and northeast Washington...only 10
to 20 percent per the NBM. While localized amounts to a half inch
may occur under a slow moving thunderstorm, the cool air mass and
low precipitable water values don`t support heavy rain. And with
snow levels in the 4000-5000ft range motorists headed over Lookout
Pass or Sherman Pass could see snow or a rain/snow mix Sunday.

Monday: For outdoor activities, Monday looks like the best day
region-wide for mild temperatures and dry weather. With the
exception of a 30 percent chance of showers over the mountainous
terrain of north Idaho, the remainder of the Inland Northwest
should be dry as a shortwave ridge builds across western and
central Washington. Afternoon temperatures will range from the
mid 60s in Sandpoint and Kellogg to the mid 70s in Omak, Moses
Lake, and Wenatchee. And with winds of 5 to 15 mph region-wide,
Monday looks like a great day to be outdoors before rain chances
increase again Tuesday and Wednesday. /GKoch

Tuesday to Friday: Models are converging to show a good potential
for wet weather as we head into the middle of next week for much,
but not all, of the area and precipitation chances continue into
the at least the end of next week. Tuesday into Wednesday a strong
system drops south along the BC coastline and into the region.
The leading warm front noses in from the west-northwest Tuesday
afternoon and Tuesday night. The parent low drops into the region
Wednesday, though there are still some disagreements on how
quickly and this will have implications on the precise timing of
the higher precipitation potential. Precipitation chances start
into Cascades and northern mountains Tuesday, then start to expand
and increase Tuesday night into Wednesday morning as deeper
moisture wraps into the incoming low. Regional PWATs increase to
120-150% of normal. EFI table show some higher than normal
precipitation anomalies around the eastern third of WA and ID.
Between Tuesday night and Wednesday night show the probabilities
for wetting rains (>=0.10") around 70-95% (the higher end of that
range near the eastern mountains. These probabilities cover all
but the deeper basin and lee-side zones, where probabilities for
wetting rain is around 30-50%. For the >=0.25" of rain ensembles
show about a 40-75% chance. For >=0.50" of rain, ensembles show
about 20-50% around the Cascade crest and the NE WA and ID
Panhandle mountain zones.

Hydrology-wise, river forecasts show some rises starting around
the middle of next week, though at this time nothing is forecast
to push to flood levels on any mainstem rivers. We will keep an
eye on any smaller streams/creeks and watch for any debris
flow/mudslide and ponding of water potential. Confidence in
details will increase as we get closer.

Additionally, Wednesday afternoon and evening will bring at least
a slight chance of embedded t-storms. The instability parameters
are not too impressive, with about 100 J/kg of CAPE over the the
north and eastern CWA, but given the dynamic low having a slight
chance in the forecast is prudent until models start to settle on
a more solid solution. There will be some breeziness both Tuesday
and Wednesday, particularly over central WA, with gusts in the
15-25 mph range. If the track or timing of the low changes it
could impact the strength of those winds (up or down) so stay
tuned.

Lastly, I did hold temperatures down toward the lower 25-50%
percentile of solutions, as the rain may make it hard for some
areas to get to 60. The forecast may need to be lowered further
than what I have. Milder readings are forecast where rain amounts
will be less, with more 60s and perhaps some low 70s in the lee
of the Cascades and deeper basin.

Going into Thursday and Friday of next week, model agreement is a
bit mushier, with the placement of the various low pressure
centers and embedded shortwave highly varied between model to
model. Either way, these features will be in the region and keep
rain chances alive. About 35-40% of the model place the primary
trough axis near the coast, while 60-65% place it to the east-
southeast of WA. So there is some slight favor toward that latter
longer-wave set-up. Some lingering steadier and locally higher
precipitation amounts are possible then over eastern parts of the
CWA, particularly the central Panhandle, Thursday. The
Spokane/Cd`A area and/or the Palouse could be painted with some
higher precipitation amounts too as some solutions wrap some
steadier moisture back into these areas too, but confidence is
only medium. Right now. The afternoon hours will continue to come
with slight t-storms chances around the mountains mostly and some
marginally breezy conditions. Right now both of these features
look like more of a nuisance than a big impact. Temperature will
remain below normal Thursday, then may start to trend closer to
normal by Friday. /Solveig

&&

.AVIATION...
06Z TAFS: Gusty gap winds of 20-30kt will gradually ease overnight
as the mountain wave cloud across eastern WA thins. Isolated
showers will decrease overnight across the northern mountains.
Otherwise anticipate VFR conditions late tonight into Saturday.
Gusty westerly winds return after 18z across most of the TAF
sites. Mid level clouds expand across extreme eastern WA into
north ID with spotty showers after 22Z into the evening. /rfox.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: High chance for
VFR conditions late tonight into Saturday and low chance of MVFR
with showers Saturday afternoon and evening. /rfox.


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

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        62  40  60  39  69  44 /  20  40  50  20   0   0
Coeur d`Alene  60  39  56  39  66  42 /  30  40  60  20  10   0
Pullman        59  36  57  38  63  42 /  10  30  30  10  10   0
Lewiston       69  43  64  45  71  48 /   0  20  20  10  10   0
Colville       61  33  63  34  71  38 /  70  70  70  20  10  10
Sandpoint      58  36  54  38  64  41 /  70  60  80  20  30  10
Kellogg        56  40  52  41  61  43 /  40  50  70  20  40  10
Moses Lake     67  39  69  42  76  46 /  10  10  10   0   0   0
Wenatchee      63  42  67  44  73  50 /  10  10  10   0   0   0
Omak           66  39  68  41  76  47 /  40  30  20  10   0   0

&&

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

$$