163
FXUS66 KOTX 210509
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1009 PM PDT Mon May 20 2024

.SYNOPSIS...
There will be a short break between weather systems into early
Tuesday. Then a wet low pressure system is expected to move in the
latter half of Tuesday into Wednesday, and linger into Thursday.
Another weather system will move in on Friday bringing more
unsettled weather into the Memorial Day weekend.

&&

.DISCUSSION...
Evening update: Shower activity is winding down with the loss of
daytime heating. As of 745 PM a few showers lingered mainly over
the Idaho Panhandle and made a few minor tweaks to the forecast
based on radar trends. Also adjusted low temperatures for tonight,
based on some of the newer guidance. Most of the changes were
tweaks of a couple degrees, except for Colville where a more
significant drop was made since last night got quite chilly (in
the upper 20s) and there will be another opportunity for a quick
drop in temperatures this evening as skies clear. JW

&&

.AVIATION...
06Z TAFS: Showers are winding down with loss of daytime heating.
Patchy valley fog is expected over the mountain valleys of NE
Washington and North Idaho between 09-15z and is not likely for
the Spokane and Coeur d`Alene areas with RH 20-30% lower compared
to 24 hours ago. A low pressure system will spread across Eastern
Washington late Tuesday afternoon and evening bringing lowering
CIGS to MVFR over most of Eastern Washington and North Idaho.
Downslope off the Cascades should keep conditions VFR for most of
the Central WA airports through 06z Wed including Omak, Wenatchee,
Chelan, Winthrop, and Moses Lake.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high
confidence in CIGS lowering to MVFR between 02-06z Wednesday over
Eastern Washington and North Idaho as rain spreads in. HREF shows
at least a 70% chance of CIGS lowering to MVFR for
KGEG/KSFF/KCOE/KPUW. For Wenatchee there is a 80-90% chance of
conditions remaining VFR through the TAF period.

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

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

&&

.PREV DISCUSSION... /issued 449 PM PDT Mon May 20 2024/

Tonight: Convective showers this afternoon are much more subdued
compared to this time yesterday. The low pressure trough axis has
swung through into western Montana leaving the Inland Northwest on
the back edge with cumulus build ups from differential heating
combating subsidence aloft with higher heights moving in. There is
still a 20% chance for a lightning strike or two with stronger
updrafts, thunderstorm potential overall will be less compared to
what we saw yesterday evening. Skies will then quickly clear out
overnight. There will be the potential for a redevelopment of fog
in the mountain valleys of northeast Washington and in the Idaho
Panhandle tonight as the surface radiates out. Fog coverage is
expected to be less and more so confined in the mountain valleys
instead of extending out into the Spokane Area like it did earlier
this morning.

Tuesday into Tuesday night: Tomorrow will start out dry, but a
warm front will quickly move into the region ahead of a robust low
pressure system that drops south across BC. The warm front will a
shot of increased precipitable waters from around 0.45 inches to
around 0.75 inches. The combination of good dynamics with the
front drawing in ample moisture off of the Pacific Ocean will
bring an increasing chance for rain through the afternoon and into
the overnight hours. Light rain is expected to begin in the
Cascades by noon, and then push east of the Cascades into the
basin and Okanogan Highlands/Valley by mid afternoon. The
thickening clouds and rainfall will subdue our warming through the
day with high temperatures generally in the 60s.

Precipitation will become enhanced in the evening as it continues
its march into the Idaho Panhandle by the late evening hours.
Steady precipitation into Tuesday night will result in soaking
rains in the lowlands across much of the region. The exception
will be in the lee of the Cascades where downsloping will result
in less accumulations with places like Wenatchee, Quincy, and
Ephrata struggling to receive at least a tenth of an inch of
precipitation. Snow levels will be lowering late in the night into
Wednesday morning as the cold front quickly catches up the warm
front. /SVH

Wednesday through Sunday: Widespread rain is expected throughout the
day Wednesday as the low continues to trek eastward. The forecast
continues to be on track with the rain totals. Over the
mountains, totals will be upwards of 0.5 inches to over an inch,
with a quarter to half an inch in the lower elevations. The
Columbia Basin will miss out on much of the rain with less than
0.05 inches expected. Snow will be limited to the highest terrain,
with one to two inches forecasted at Washington Pass, and Stevens
Pass will remain mainly as rain, with the possibility of a few
snowflakes mixed in. This rain, along with additional snowmelt
from the mountains will lead to a slight rise in creeks and
rivers, but should remain below action stage. During the day on
Wednesday, an isolated lightning strike is possible but don`t
expect to see any. Wednesday`s temperatures will be the coolest of
the week, with high temperatures in the 50s as the system passes
through. In areas that receive limited rain could see breezy winds
with gusts up to 25 mph mainly in the Columbia Basin and
Waterville Plateau.

For Thursday through the weekend, scattered showers will continue,
especially in northeast WA and ID Panhandle. Another low arrives
late Friday into Saturday, with additional rain to the area.
Temperatures will conintue to stay slightly below normal for this
time of year. Ensembles are hinting that by Monday, a ridge will
begin to build, warming temperatures. /KM

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        41  63  45  55  41  62 /   0  30  80  90  30  30
Coeur d`Alene  39  62  45  54  41  60 /  10  10  90  90  40  30
Pullman        40  61  44  52  39  57 /  10  10  90  90  50  30
Lewiston       46  70  50  60  46  65 /  20  10  90  90  50  30
Colville       32  63  40  55  36  64 /   0  40  80  90  40  50
Sandpoint      36  61  45  52  41  60 /  10  20  90 100  60  50
Kellogg        40  60  46  50  43  57 /  20  10  90 100  70  50
Moses Lake     46  67  45  62  44  72 /   0  40  50  60  20   0
Wenatchee      49  64  47  60  46  70 /   0  40  30  40  10   0
Omak           42  65  45  62  44  72 /   0  40  50  70  20  10

&&

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

$$