Area Forecast Discussion
Issued by NWS Spokane, WA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
000
FXUS66 KOTX 260525 CCA
AFDOTX

Area Forecast Discussion...CORRECTED
National Weather Service Spokane WA
1025 PM PDT Mon Mar 25 2024

.SYNOPSIS...
Near seasonal temperatures are forecast on Tuesday with a mix of
rain and snow showers. A wetter storm system arrives Wednesday
and Thursday delivering widespread precipitation before warmer and
drier weather returns next weekend.

&&

.DISCUSSION...
Tonight through Tuesday Night: A cool upper trough will remain
over the region into Tuesday with the upper jet south of the
region. In addition very weak disturbances embedded within the
trough will produce showers, with the highest focus during peak
heating (afternoon and early evening), as well as the Cascade
crest, Idaho Panhandle, and eastern third of Washington. Yet weak
forcing will promote some overnight/morning showers as well with
snow levels as low as 2500 feet. One such weak wave will track
across the Cascades overnight/Tuesday AM producing 2-4" of snow
over Stevens Pass for winter driving conditions. Light
accumulations of an inch are also forecast for Lookout Pass. A
short wave ridge Tuesday Night will bring a brief period of quiet
weather before the next system arrives Wednesday. JW

Wednesday and Thursday: An organized frontal wave moves into the
region between Wednesday and Thursday. Temperatures are forecast
to be slightly below normal Wednesday, then closer to normal
Thursday. A warm front pushes up to the Cascades Wednesday
morning. Then an occluding cold front comes on its heels toward
midday, pushing across eastern WA and ID through the afternoon and
evening. Then overnight into Thursday an unstable upper trough
shifts onshore. The primary frontal wave comes with an increased
moisture tap, with PWATs around 0.45 to 0.65 inches (or 130-170%
of normal) before drier air starts in Thursday. Look for expanding
rain and mainly mountain snow Wednesday, starting near the
Cascades in the morning and expanding through the region for the
afternoon and evening. Some snow or a rain/snow mix is possible
Wednesday morning around the Cascade valleys through north-central
WA and maybe even the West Plains of Spokane if precipitation
starts early enough. Some snow may also mix in some of the
sheltered northern valleys overnight into Thursday morning.
Overall PoPs peak Wednesday evening, but will be starting to wane
in the lee of the Cascades especially heading into later evening
to the overnight. The potential for precipitation elsewhere
remains high through Thursday with the upper trough on the heels
of the main front. However some decrease in precipitation possible
early Thursday morning before expanding again Thursday afternoon.
The only other thing that may develop will be patchy fog over the
typical valleys over NE WA and north ID.

* Rain amounts: The 24-hour probability of >=0.10 inches of rain
  (i.e. a wetting rain) is around 80-100% over a good portion of
  the our CWA, with 60-70% around the deeper Columbia Basin and
  near the Okanogan County/BC border. The 24-hour probability of
  >=0.25 inch of rain is around 60-90% over the Cascade crest,
  northeast WA and the ID Panhandle and only about 20-50% around
  the deeper Columbia Basin and lee of the Cascades. So this looks
  like a wet system. Hydrographs show some rises on rivers with
  this system, but nothing is projected to reach action level,
  much less flood stage. However there could be some ponding of
  water in poor drainage areas and typical urban areas and some
  minor rock/mudslides may be found. Confidence in any of that is
  low.

* Snow amounts: snow accumulation in the mountains have trended
  slightly lower. The snow that has the potential for impacts will
  be around the Cascade crest and over the north-central WA
  passes. The official forecast for Stevens Pass right now has
  about 2-4 inches of snow through Wednesday night and about 1-2
  inches Thursday. Similar amounts are in the forecast around
  Sherman Pass. Meanwhile the Idaho Passes have about 1-3 inches
  total for the whole 48 hour period. Some individual 48-hour
  snowfall probabilities, between 4 AM Wednesday to 4 AM Friday,
  are found below:

                     >=1"   >=2"   >=4"   >=6"
      Stevens Pass    95%    90%    70%    42%
      Blewett Pass    45%    24%     4%     1%
      Sherman Pass    79%    67%    28%     8%
      Loup Loup Pass  45%    24%    12%     1%
      Lookout Pass    81%    58%    20%     4%

* Winds and thunderstorm threat: breezy conditions are still
  expected, especially over the Basin, Spokane Area and Palouse
  with gusts near 20-30 mph possible. Thursday now looks like the
  breezier day, with better mixing and instability compared to
  Wednesday. Nothing highlight-worthy at this time, but worth
  knowing about. Embedded thunderstorms will also be possible
  Thursday afternoon and evening with some conditional
  instability, with CAPE values around 100-300 J/kg over north and
  eastern WA and ID. Overall models paint about a 10-20%
  probability of thunderstorms Thursday afternoon, which is
  slightly higher than a few days ago. Thunderstorms that might
  develop could produce gusty winds, isolated lightning and small
  hail or graupel.

Thursday night to Monday the overall potential for precipitation
starts to wane, comparatively speaking. The center of the parent
long-wave trough sags toward California, leaving somewhat weaker
waves that pass through the region through Saturday. This will
keep shower chances alive across the region, particularly in the
afternoon and evening hours and around the mountains and southeast
WA. We will have to keep a little bit of an eye on the Saturday
shortwave as some guidance shows a slightly strong shortwave that
draws a bit more moisture into southeast WA/lower ID. But the
confidence right now leans toward a lighter shower potential. By
Sunday and Monday a ridge starts to build in. Limited shower
chances linger over southeast WA and the higher mountains Sunday,
then the potential just lingers near the immediate Cascade crest
and central Panhandle mountains. Otherwise it looks drier. Some
patchy fog is still possible Friday morning in the sheltered
northern valleys. There is also some springtime breeziness in the
unsheltered areas over in the afternoon, with gusts near 15 mph.
Temperatures are projected to push above normal, with afternoon
high temperatures in the 50s to lower 60s Friday rising to upper
50s and 60s toward Monday. The higher values are projected to be
in the typical areas over the deeper Columbia Basin and L-C
Valley. A few spots could even push 70 in the deep basin by
Monday. /Solveig

&&

.AVIATION...
06Z TAFS: The boundary layer will moisten overnight likely
creating a layer of 1500-2500ft ceilings for Spokane, Coeur
d`Alene, Sandpoint, Deer Park, and Colville between 11-14z. During
this timeframe, clusters of showers are generated by the HREF and
other models across southeast Washington and the southern Idaho
Panhandle including Pullman and Lewiston with 2000-3000ft ceilings
into 17-19z. Afternoon destabilization will generate additional
convective showers across the eastern third of Washington and
north Idaho between 21-00z which are handled in the TAF sites with
PROB30 groups.

FORECAST CONFIDENCE AND/OR ALTERNATE SCENARIOS: There is high
confidence in stratus expanding once again overnight into Tuesday
morning per pattern recognition and HREF probabilities of 60-90%
of MVFR conditions. /GKoch

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

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  53  32  50  38  52 /  20  30   0  50 100  70
Coeur d`Alene  32  48  31  48  36  49 /  30  60  10  40  90  90
Pullman        35  48  31  49  37  50 /  50  70  10  40 100  80
Lewiston       40  55  35  56  41  57 /  60  60   0  30  90  60
Colville       30  51  29  48  35  50 /  10  50  10  50 100  80
Sandpoint      32  45  31  46  37  46 /  40  70  20  40 100 100
Kellogg        35  43  33  47  39  45 /  50  80  30  30  90  90
Moses Lake     35  59  34  51  36  57 /   0  10   0  70  50  10
Wenatchee      38  56  36  45  36  52 /  10   0   0  80  40  20
Omak           37  58  35  48  37  55 /   0  10   0  60  70  40

&&

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

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.