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Area Forecast Discussion (AFD)

Issued by Spokane, WA (OTX)

                            
000
FXUS66 KOTX 212145
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
245 PM PDT Thu Mar 21 2019

.SYNOPSIS...
Friday will be a few degrees cooler as clouds increase ahead of a
weak cold front. The chance for showers will increase Friday night
as the front moves across the region. The weekend will feature
temperatures near average with rain and mountain snow showers over
the Idaho Panhandle and portions of eastern Washington. Typical
cool and showery weather is expected much of next week with high
temperatures mainly in the 50s.


&&

.DISCUSSION...

Tonight: Tonight will be another chilly one with light winds and 
mainly clear skies. Bands of high clouds will wrap around low 
pressure over the Great Basin, but the high level moisture 
shouldn't hinder radiational cooling much. Most lowland 
communities across the Inland Northwest will experience overnight 
temperatures in the 30s. 

Friday: A slow moving trough will reach the WA/OR coast Friday 
afternoon spreading increasing mid and high clouds across 
Washington and north Idaho on Friday. Most of our region should be
2 to 5 degrees cooler on Friday than today. Showers associated 
with the incoming trough will mainly be limited to western 
Washington and the high terrain of the Cascades.

Friday night and Saturday: A weak cold frontal passage will occur
Fri night as the upper level trough shears and stretches apart.
The strongest moisture advection and upper level support will dig
into California and Nevada Fri night into Saturday. The models
have been pretty consistent very little measurable precipitation
across the Columbia Basin and north central Washington Fri night.
The help of orographic forcing should yield some rain and snow
showers over the Idaho Panhandle on Saturday. With snow levels
expected to be around 4500 feet, skiers may witness periods of
light snow.

Saturday night and Sunday: Up through Saturday night,
precipitation amounts look to be showery and light. We will be
watching Saturday night and Sunday for the potential of some more
significant amounts as a shortwave pivots northeast out of
northern Nevada. The potential for wet snow accumulations (above
4000 ft) and the potential for rain onto fields soaked by melting
snow are reasons to monitor this wave. Model agreement isn't good
with the track and timing of this wave. The GFS lifts the wave 
far enough north Saturday night to produce a quarter to half inch 
of liquid equivalent across the southern Idaho Panhandle and clips
the Camas Prairie with enough moisture for accumulating snow 
above 4000 feet. The NAM is slower with the majority of the 
precipitation arriving during the day Sunday. The ECMWF drags the 
trough far enough south yielding much lighter and spottier 
precipitation. The NWS blend of models seems to favor the track
further south similar to the ECMWF which is reflected in our
forecast. /GKoch

Monday to Thursday: The Inland Northwest will be in a more 
active pattern, with periodic opportunities for precipitation. 
Looking at the big picture a broad trough sets up off the coast 
and sends occasional shortwaves inland. There are timing 
disagreements regarding these individual features, which basically
means there are modest chances for precipitation but we are still
pinning down when chances will be highest. One wave exits early 
Monday and a second comes through sometime between Monday night 
and Tuesday. So Monday looks mostly dry, save for limited shower 
chances in the north early and then in the Cascades and far 
western Basin later in the day. Then Monday evening into Tuesday 
broader chances expand across the region, with some suggestion 
that the threat will lift toward the mountains into Tuesday 
afternoon. This is accompanied by some breezy conditions. 
Additional impulses will bring additional shower chances going 
into Wednesday and Thursday. 

As for precipitation-type: overall it looks like valley rain and 
mountain snow, with snow levels averaging 3-4kft. However 
nighttime temperatures will be near freezing in spots, enough to 
allow for some mix down to valley floors. As for precipitation 
amounts: some moderate amounts are possible closer to the Cascades
and far western Columbia basin and northern mountains with the 
Monday/Tuesday front. Where this falls as snow will largely be in 
the mountains, but we will have to monitor the Cascades passes and
places like Sherman Pass for travel impacts. Overall afternoon 
temperatures are expected to be near seasonal norms, while 
overnight lows are expected to be near to slightly below normal. 
/Cote'



&&

.HYDROLOGY...

A Flood Watch has been issued for areas in and around Moscow 
Idaho. Paradise Creek rose sharply last evening in response to
lowland snow melt. It crested a foot shy of Flood Stage (9.2 
feet) before dropping this morning. Another rise will occur this
afternoon and evening as our diurnal melting cycle begins. The
Paradise Creek basin still has ripe snow. If a similar amount of
water (roughly 110 cubic feet per second) reaches the river gauge
tonight, the river will be close to Flood Stage. Tomorrow
afternoon looks 3 to 5 degrees cooler. The basin will also be
gradually losing snow the next few days. By the weekend, cooler
temps and less runoff should lead to lower flows into Paradise
Creek.

For the remainder of the Palouse, West Plains, and Upper Columbia
Basin, snow cover will become increasingly patchy the next few
days. As the snow disappears, we expect some more minor field
flooding. Snow is ripening in the lowlands of Bonner and Boundary
counties, so small streams are expected to experience rises the
next few days. At this time, the precipitation moving into the
region for the weekend looks to be showery with light basin
average amounts. This is generally good news, along with the
arrival of cooler daytime temperatures over the weekend into 
early next week. /GKoch

&&

.AVIATION...
18Z TAFS: Bands of high clouds are expected to spread into the
Inland Northwest as high level moisture wraps around low pressure
in the Great Basin. NAM MOS guidance forecasts the development of
widespread low stratus overnight into Friday morning. The NAM has
struggled to handle low level moisture fields this week. Low level
humidity has been too high, so the NAM MOS has been disregarded. 
/GKoch



&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        34  57  38  54  35  53 /   0   0  10  20  20  20 
Coeur d'Alene  33  55  38  51  34  50 /   0  10  20  20  30  30 
Pullman        34  55  38  47  33  47 /   0   0  20  20  20  20 
Lewiston       38  59  43  53  37  54 /   0   0  30  30  20  20 
Colville       27  58  37  54  33  54 /   0  10  20  30  20  30 
Sandpoint      31  53  36  50  34  48 /   0  10  20  30  30  40 
Kellogg        37  56  37  51  34  50 /   0  10  20  30  30  50 
Moses Lake     35  63  39  59  34  58 /   0   0  10   0  10   0 
Wenatchee      38  58  41  54  36  54 /   0   0  30   0  10  10 
Omak           34  62  39  56  36  54 /   0   0  30  10  20  20 

&&

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

&&

$$