Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 240531
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1031 PM PDT Sat Mar 23 2024

.SYNOPSIS...
A wet and unsettled weather pattern through at least the middle of
next week. As snow levels gradually fall this weekend minor
impacts from winter weather are forecast in the mountains, as well
as north Idaho through Sunday morning. Weaker weather systems will
pass through Monday and Tuesday with more widespread precipitation
Wednesday and Thursday.

&&

.DISCUSSION...

Tonight through Sunday Night: The closed low off the Oregon coast
will drop south into northern California tonight, while a weak
short wave trough drops down from the north. While the trough and
short wave don`t have much lift with it, models continue to show
a low level modified arctic front spilling down into north Idaho
and far NE Washington. There are subtle hints of this beginning
with a 1 PM temperature of 39F at Bonners Ferry, ID with a north
wind, while Spokane Airport was 49F with a southwest wind. Models
continue to show rain changing to snow with forecast timing
around midnight for Bonners Ferry, 1-4 AM Sandpoint and Newport
areas, 5-7 AM Deer Park and Coeur d`Alene areas, and a brief
changeover for the Spokane area above 2000 feet around 8-9 AM.
Models are not showing particularly strong lift, instability, or
upslope flow after the cooler air arrives, with light snow of up
to 1" in the valleys of the Idaho Panhandle and far NE Washington
mainly on grassy surfaces. Higher amounts of 3-5" are forecast
over Lookout Pass and Sherman Pass, but with the snow falling over
a 12 hour period (mainly light intensity) and a lower travel
period have held off on issuing advisories. Other mountain passes
will see light snow as well with up to 2" for Loup Loup and
Stevens Passes. Sunday afternoon as the short wave exits the area
the bulk of lingering showers will be south of I-90 over SE
Washington into the Central Panhandle Mountains. The drier air
continues to move in Sunday night with clearing skies allowing for
colder low temperatures in the mid 20s to mid 30s. Here are the
latest snow probabilities from the 19z NBM:

*Chance of at least 1" of snow: Sandpoint = 60%, Colville = 0%,
 Spokane = 0%, Coeur d`Alene = 20%

*Chance of at least 2" of snow: Sandpoint = 25%, Coeur d`Alene =
 0%

*Chance of at least 4" of snow: Sandpoint = 0%, Lookout Pass =
 70%, Sherman Pass = 20%

*Chance of at least 8" of snow: Lookout Pass = 10%

JW

Monday to Saturday: The Inland NW will remain in an active
pattern, with the next best chance for precipitation coming around
the middle of the week. Temperatures will be near to slightly
below normal at the start of the week, then moderate closer to
normal, approaching slightly above normal toward next weekend.

The work week starts relatively quiet, with the area in a northwest
flow, sitting on the western side of the broader long-wave trough
over the interior United States. Weak impulses slip by the region
in this flow, with PWATs around 90-110% of normal and very weak
conditional instability. This overall set-up will bring shower
chances near the Cascade crest and over eastern third of WA
through the ID Panhandle, while the lee of the Cascades and deeper
basin largely remain dry. The more substantial shortwave disturbance
comes through on Tuesday so that day will have higher PoPs than
Monday, relatively speaking. However the best chance for wetting
rains (>=0.10") will remain near the Cascade crest and over
higher Palouse through central Panhandle both days. Monday morning
temperatures will be cold enough to allow for snow or rain/snow
mix except over the deeper Palouse and L-C Valley, where mainly
rain is possible. But impacts are not likely from that snow. Then
by afternoon and continuing into Tuesday it looks like mainly
mountain snow and lowland rain, save for some localized rain/snow
mix during the overnight/early morning hours in the sheltered
northern valleys. Tuesday night the next organized frontal system
moves toward the region. A shortwave ridge builds in ahead of it,
leading to a brief lull in the broader precipitation chances.

* Mountain snow amounts look relatively light. Models show
  24-hour probabilities of snow amounts of 2 inches or more at
  around 20-30% for most areas Monday and Tuesday, though that
  potential is higher on Tuesday afternoon around the central
  Panhandle mountains. Overall impacts from snow at this time are
  expected to be minor.

By Wednesday the leading warm front pushes up toward the Cascades
in morning, with the occluding cold front coming on its heels
toward midday, before that feature pushes on across eastern WA
and ID through the afternoon and evening and the upper trough come
in overnight into Thursday. The main frontal wave comes with an
increased moisture tap, with PWATs around 140-180% of normal
through Wednesday. Altogether this will bring expanding rain and
mountain snow to the region Wednesday, starting near the Cascades
and western basin in the morning and expanding through the region
toward late morning to afternoon. The PoPs start to wane a bit in
the lee of the Cascades toward evening, but overall the potential
for precipitation elsewhere remains high through Thursday with the
upper trough on the heels of the main front. It is not until
Thursday night into Saturday that the overall potential for
precipitation starts to wane to a greater extent as the broader
system moves out, leaving weaker impulses and drier atmosphere
(with PWATs back to around 80-110% of normal). PoPs do not end,
but the higher potential retreat to the mountain zones by this
time frame. Also by this time frame some snow may mix down toward
the valley floors for the overnight/morning hours. Otherwise it
still looks like mainly lowland rain and mountain snow

* Rain,snow amounts, wind, thunderstorm?: In that Wednesday to
  Thursday time frame we will see some moderate precipitation
  amounts, with most of the area seeing high chance of wetting
  rains (>=0.10"). There is even a modest chance of seeing near a
  third of an inch (0.30") with 24-hour probabilities of that
  amounts around 40-80%. The higher of that range is found around
  the mountain zones. Some light to moderate snow is also possible
  in the mountains, with 24-hour probabilities of >=3 inches
  around 40% and closer to near 70% around the Cascades crest. So
  additional snow is expected around the mountain passes. Those
  probabilities are somewhat comparable to the current system
  (Saturday March 23rd). Also in that Wednesday to Thursday time
  frame breezy conditions are expected, especially over the Basin,
  Spokane Area and Palouse with gusts near 20-30 mph possible.
  Nothing highlight- worthy at this time, but worth a mention. The
  only other thing to monitor for is possible embedded thunderstorms
  Thursday afternoon with some conditional instability, with CAPE
  values around 100-200 J/kg over north and eastern WA and ID.
  Overall at the moment models paint about a 10-15% probability of
  thunderstorms Thursday afternoon in these areas. /Solveig

&&

.AVIATION...
06Z TAFS: An increase in precipitation is expected into Sunday
morning, with snow levels dropping to the valley floors over the
Idaho Panhandle. Widespread IFR and MVFR conditions are forecast
over the eastern third of Washington and North Idaho overnight
into Sunday morning. CIGS will gradually rise over NE Washington
and North Idaho Sunday afternoon as drier air begins to push in
and showers come to an end.


FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high
confidence in Bonners Ferry and Sandpoint changing to snow
overnight, moderate Coeur d`Alene starting near 12z and KGEG
starting near 14-15z. If precipitation changes to all snow,
visibility could lower down to 1-2 miles before precipitation ends
or changes to rain by late Sunday morning.

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

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        34  46  30  49  35  51 /  70  70  10  20  30  50
Coeur d`Alene  33  43  26  44  33  47 /  80  80  10  30  30  60
Pullman        36  44  30  47  35  48 /  60  90  20  60  60  70
Lewiston       41  51  35  52  38  55 /  50  90  20  40  50  60
Colville       37  48  26  49  30  51 /  90  50   0  10  10  40
Sandpoint      32  41  25  43  32  44 /  80  60  10  30  40  80
Kellogg        31  40  28  44  35  43 /  70  90  20  50  50  90
Moses Lake     41  56  35  56  34  59 /  30  30   0  10   0  10
Wenatchee      40  56  36  54  37  56 /  30  20   0  10  10   0
Omak           38  57  35  55  35  58 /  70  20   0  10  10  10

&&

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

$$


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