151
FXUS66 KOTX 210958
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
258 AM PDT Tue May 21 2024

.SYNOPSIS...
A wet low pressure system is expected to move in the latter half
of today into Wednesday, and linger into Thursday. Another
weather system will move in on Friday and Saturday bringing more
unsettled weather into the Memorial Day weekend. Monday will be
the warmest day of the holiday weekend.

&&

.DISCUSSION...
Today through Wednesday: A low will be dropping into the Pacific
Northwest from BC. It will bring widespread precip for the next
couple of days. The Low will push a warm front through the Inland
Northwest today with a cold front following on Wednesday.

For Tuesday, precip will start in the Cascades around midday and
shift East through the rest of the day. It will bring widespread
rain as the snow levels are still remaining above 6000 ft. Amounts
range from a few hundreths for the Okanogan Valley and valleys along
the Cascades to near 0.4" for the Idaho Panhandle. Highs for the day
will hindered by the increasing clouds. Most areas will reach into
the 60s with some into the upper 50s. Overnight lows will be in the
40s.

The cold front will pass early Wednesday. It will drop snow levels
to around 4000 feet. It will bring another round of rain to the
lower elevations and mountain snow. Depending on the timing, light
snow could impact travel over the passes. Ensembles are showing the
potential for a 2 to 3 inches of snow falling in these areas. But
surface temperatures remain above freezing and snow mixing with rain
will affect any accumulations. Rain will be heaviest across Northern
Washington and Idaho Panhandle. An additional 0.3" is expected. The
precip for the rest of the region ranges from a few hundreths to
near 0.2". Dynamics along the cold front could spawn an isolated
thunderstorm as moves through the Inland Northwest. Highs for day
will be in the 50s to low 60s. Overnight lows will be in the upper
30s and 40s.

Thursday: The Inland Northwest will be between systems Thursday
as the trough exits into Wyoming and the next trough begins to
approach the northern BC coast. Showers will remain in the
forecast for northern WA, extreme eastern WA and the ID Panhandle
with a 20-30% chance of thunderstorms in the afternoon across the
northern counties. Temperatures will rebound from Wednesday`s
cool temps, but we will still remain several degrees below
average. Central WA will be 3 to 5 degrees below average with
highs in the low 70s. Eastern WA and the ID Panhandle will be 5 to
10 degrees below average with highs in the upper 50s to low 60s.

Friday and Saturday: The trough moves toward the region Friday.
The timing seems to have slowed down a bit. We will still see an
increase in showers throughout the day, which continues through
the night. The low moves into Washington early Saturday for you
guessed it, more rain for the region. Friday and Saturday will be
the two wetter days of the Memorial Holiday weekend. Temperatures
will continue to be below average. 850mb temps cool enough for
some snow possible in the mountains, and a 20-25% chance of an
inch of snow at Lookout and Sherman Passes. Both days will see
afternoon thunderstorms develop, but right now only have about 20%
chance in the forecast.

Sunday and Monday: Sunday the trough exits the region with a
20-30% chance of rain showers across NE WA and the ID Panhandle
under the northwest flow aloft. Sunday morning lows will be our
coolest of the week given the exiting trough and thinning clouds.
Some of the northern valleys could once again see frost. Our
daytime temperatures will start to rebound into the 60s Sunday
and even further on Monday - into the 70s, which will be at or a
couple degrees above average, as 55% of the model ensembles
suggest a south to southwest flow from a more amplified ridge
either directly over us or just to our east. Monday looks to be
the driest day of the Memorial Weekend.

Tuesday: Ensembles agree on the ridge somewhere across the west
or intermountain west. Placement is still uncertain. 30% of
ensembles have the ridge axis further east into eastern MT with a
trough approaching the Pac NW coast. This would result in cooler
temps and a chance of precip. For now, forecast is dry except
along the crest and temperatures are above average, which is
supported by 70% of the ensembles. /Nisbet

&&

.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

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        64  45  56  42  63  45 /  20  90  90  30  30  20
Coeur d`Alene  62  46  53  41  60  44 /  10 100  90  50  50  30
Pullman        62  43  52  40  57  40 /  10  90  90  50  30  10
Lewiston       70  51  60  45  64  45 /  10  90  90  50  30   0
Colville       65  41  55  37  65  40 /  30 100 100  50  60  50
Sandpoint      61  44  52  40  58  45 /  20  90 100  70  60  50
Kellogg        60  46  49  43  57  43 /  10  90 100  80  60  30
Moses Lake     69  45  61  44  71  44 /  40  60  60  10   0   0
Wenatchee      65  46  58  46  71  48 /  50  50  50  10   0   0
Omak           67  45  59  43  71  46 /  60  60  80  20  20  10

&&

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

$$