FXUS66 KOTX 242318

Area Forecast Discussion
National Weather Service Spokane WA
418 PM PDT Thu May 24 2018

More showers and thunderstorms are expected through Saturday,
mainly over the Idaho Panhandle and extreme eastern Washington.
Drier and seasonably warm conditions are expected for the
remainder of the Memorial Day weekend. More showery weather is
expected next week accompanied by cooler more seasonal


Tonight and Friday...Satellite reveals an offshore upper level
trough approaching the west coast this afternoon...splitting into
a closed low and northern branch trough structure as it does.
Ahead of this trough and over the western US a weak short wave
ridge is popping up over the inland northwest...removing any
synoptic lift from the equation to interact with a continued
unstable and moist air mass over the region. Thus...Showers and a
few thunderstorms are still apparent over the mountains
surrounding the basin this afternoon and evening triggered by
orographic ascent...but the widespread and rambunctious activity
noted throughout the region yesterday and last night will not
repeat today. The existing showers and storms will likely die
shortly after sunset this evening for a quiet and benign overnight
period and into Friday morning.

Friday will probably resemble today as far as showers and isolated
thunderstorm activity...highly mountain oriented with the basin
dry and mostly sunny. As the ridge axis moves off to the east a
few degrees of cooling will be likely for Friday's high
temperatures...but there will still be no appreciable change to
the overall air mass characteristics on Friday.

Friday night and Saturday...During this period the offshore
splitting trough will move inland with the closed low portion
settling into the Great Basin but with the northern branch trough
transiting the forecast area. This will bring a change in the
weather...mainly with a cold front and provide lift and focus for
a more coherent round of showers and isolated thunderstorms
mainly over the eastern third of Washington and especially the
Idaho Panhandle overnight Friday and into Saturday morning. This
front will also promote breezy conditions near the Cascade gaps
and down the Okanogan Valley. The post frontal air mass will be
noticeably cooler with saturday's high temperature retracting back
toward but maybe not quite normal readings. In fact depending on
precipitation prevalence cloud cover over the Idaho panhandle
temperatures may be below normal on Saturday...down into the the
mid to upper 60s. Showers and afternoon isolated thunderstorms
will be found over the Idaho panhandle Saturday with the rest of
the forecast area in a more stable air mass under sunny and dry

Sunday looks like a splendid day for outdoor activities as the
Great basin closed low tracks eastward and the northern branch
storm track retreats into Canada allowing an upper level ridge to
build into the region. A warming trend will begin again on Sunday
with temperatures recovering into the upper 70s and lower 80s in
the basin and most valleys. /Fugazzi

Monday through Thursday: High pressure strengthens over the Northwest
Monday to close out the holiday weekend with dry and warm
conditions. In fact, Monday could prove to be the warmest day of
the next seven days with most communities warming into the mid to
upper 80s. The only caveat to Monday will be a sliver of moisture
and instability brushing southern Lewis and southeastern Shoshone
County keeping a small risk for showers and t-storms from the
Camas Prairie to southern Shoshone County. Tuesday through
Thursday, a cooler trough of low pressure swings into the region
from the Gulf of Alaska. There are still some differences between
the medium range models regarding the exact timing of the trof
axis and cold front being ushered through but these differences
appear to be shrinking with each run and moving toward a Tuesday
timing. A band of showers will accompany the showers with the best
chance for light showers will be over the Idaho Panhandle and
mountains of NE while little to no measurable precipitation falls
in the lee of the Cascades and Columbia Basin. Winds will be
breezy with the front and each day but speeds look to remain in
check and only increase on the order of 10-20 mph with afternoon
gusts around 20-30 mph. Temperatures will peak on Monday then cool
each day returning to the 70s by midweek. /sb


00Z TAFS: Under a moist and unstable boundary layer and light
southwest flow aloft, afternoon convection has bloomed over the
northern mountains and Blue mountains with isolated thunderstorms
which should taper off between 02z-03z. May see VCSH near KLWS,
but the remaining TAF sites should be dry. Expect mostly clear and
VFR skies overnight with light winds. Cirrus will increase after
18z Friday. Isolated afternoon convection is possible mainly in
the mountains, but should be less than seen today. /rfox.


Spokane 57 79 55 71 50 77 / 0 10 20 20 10 10
Coeur d'Alene 56 80 54 70 48 77 / 10 10 30 20 10 10
Pullman 55 76 52 65 46 71 / 10 10 50 40 10 10
Lewiston 59 82 57 70 51 77 / 30 20 60 50 10 10
Colville 55 82 53 79 48 84 / 20 10 10 10 10 0
Sandpoint 53 80 52 72 46 78 / 20 20 30 20 10 10
Kellogg 54 78 51 66 46 74 / 20 20 50 40 10 10
Moses Lake 56 82 53 79 49 82 / 0 10 10 0 10 0
Wenatchee 56 79 53 77 51 83 / 0 10 10 0 10 0
Omak 56 82 53 80 50 83 / 10 10 10 0 10 0




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