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Area forecast discussion
National Weather Service Spokane Washington
231 PM PDT Wed Mar 22 2017

Synopsis...showers and a few isolated thunderstorms will be
possible today. A few isolated mountain showers will be possible
for Thursday, otherwise it will be dry. Then another storm system
will bring widespread rain and mountain snow Friday. Flooding
issues will persist through much of the week in the absence of a
prolonged period of dry weather. The weather will remain unruly
through the first part of next week as a couple more storm systems
are expected to track through the region.



&&

Discussion...
tonight through Friday night...radar and satellite imagery show a
blossoming cu field and associated convective showers over far
eastern Washington and the central Idaho Panhandle this afternoon.
Brief downpours, small hail, potentially gusty winds and perhaps
isolated lightning strikes would be the main threats. Short range
guidance indicate this activity could continue into the early to
mid evening hours before decreasing overnight as the cold front
clears the area. Once the showers clear out tonight, most areas
will see a brief break from the precipitation for Thursday as a
Flat Ridge of high pressure builds in.

By Thursday evening/night, our next upper level low and associated
occluded frontal boundary approaches the coast. This will bring
widespread precipitation to the region Thursday night through
Friday, before the focus shifts to far eastern Washington and the
Idaho Panhandle by Friday night for continued showery conditions.
Precipitable water values will rebound to the 90th percentile with this system
with 24 hour rainfall totals generally in the 0.25 to 0.5 inch
range, and slightly lower amounts in the immediate Lee of the
Cascades. Pockets of over 0.5 inch are indicated by most models,
but as to where these areas will end up are still uncertain. Snow
levels will start low enough Friday morning to allow for some wet
snow to mix in across the northern valleys before rising above
4000 feet by the afternoon. Temperatures will generally fall a
degree or two below their seasonal normals for this period. /Kalin

Saturday through Wednesday...for this time of the year the models
are in pretty good agreement through Sunday night, then begin to
diverge in solutions. Those differences are not uncommon during
the transition from winter to Summer. A weakening/splitting upper
level low will scoot through the region Friday night and Saturday
with mainly mountain showers for Saturday and Saturday night. The
next is expected Sunday night and lingers into Tuesday. This where
model solutions begin to diverge, and this portion of the
forecast leans in favor of the gefs/European model (ecmwf) means. In between these
systems a ridge of high pressure will track through the region for
a break in the wet and unruly weather.

Saturday and Saturday night...as mentioned above a splitting upper
level low will track through the region. A warm front on Friday
will get pushed east and allow a weak cold front to move from west
to east across the forecast area between 06z and 18z Saturday.
The atmosphere will destabilize enough to support wide spread
showers. Orographic lift will put the focus of the heaviest
showers near the Cascades crest and the Idaho Panhandle. However
with 500mb temps -25c to -30c and lapse rates 6-8c/km most places
outside of the deep basin will have a chance to see showers. We
lose the deep moisture tap from earlier in the week, but with
pwats around 150 percent of normal some of the showers will be
moderate to heavy. Showers will come to a quick end around sunset
as we lose the heating of the day and high pressure quickly builds
into the region from the west. This is not a strong front at all,
but winds should increase out of the southwest from 10-20 mph
with local gusts 25 to 30 mph. Some of the higher elevations could
see 2-4 inches of snow. Otherwise expect a tenth to two tenths of
rain for most places outside of the deep basin

Sunday...should be a quiet day as the ridge moves through the
region. Some showers will be possible for the Cascades and the
Panhandle mountains but these should be isolated.

Sunday night through Tuesday...the process starts all over again
as a warm front moves into the region Sunday night and Monday for
a period of stratiform precipitation, followed quickly by a cold
front Monday morning. The upper level low will remain over the
area through Tuesday, so we expect widespread showers for the
mountains and afternoon showers for the remainder of the area.
This storm system is also expected to tap into much deeper Pacific
moisture and will result in a better chance for moderate to heavy
showers. Tobin




&&

Aviation...
18z tafs: stratus and localized dense fog is hanging in many of
the taf sites late this morning as warm front moves slowly
through the area. The atmosphere will destabilize this afternoon
to support showers from the Columbia Basin north and east into the
Idaho Panhandle 21-04z. Isold -tsra will be possible vcnty
kpuw/klws...north to the kgeg/kcoe corridor. Confidence in -shra
is much better than -tsra and this should allow cigs/vsby to
increase to VFR/MVFR through 04-06z. Then expect the low stratus
to redevelop 6-15z for the kgeg-kcoe corridor and kmwh/keat. Tobin

$$

Hydrology...
the main Stem rivers have crested but flooding will
persist on the Spokane River...Lake Coeur D'Alene and the St. Joe
river through the middle of next week. As far as the areal flood
warnings...these have been extended until noon Saturday for
Ferry...Stevens...Pend Oreille...boundary...Bonner...Shoshone...and
north and far west portions of Spokane counties. There remains
several reports of small stream flooding...field flooding...lake
flooding...and/or water over roads in these counties. Also
additional mudslides in steep terrain are possible especially
under the heavier showers today...and again on Friday as the next
wet system arrives due to saturated soils. Flood waters are
receding in the community of Sprague so the Flood Warning here
will be cancelled this afternoon. Jw

&&

Preliminary point temps/pops...
Spokane 33 48 36 47 37 51 / 40 0 30 100 60 50
Coeur D'Alene 33 46 33 45 36 49 / 50 0 20 100 80 70
Pullman 35 49 37 48 37 50 / 30 0 30 100 70 60
Lewiston 37 55 40 54 40 56 / 40 0 30 90 70 60
Colville 33 48 34 46 35 50 / 30 0 30 80 50 50
Sandpoint 33 45 30 43 34 46 / 60 0 20 90 80 60
Kellogg 33 44 32 44 34 45 / 60 10 10 90 90 70
Moses Lake 32 56 40 54 37 59 / 10 0 40 70 30 10
Wenatchee 33 51 36 50 36 54 / 10 0 60 60 30 10
Omak 32 51 36 49 36 54 / 10 0 50 70 30 20

&&

Otx watches/warnings/advisories...
Idaho...none.

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