Flood in Washington, March 14 to 19, 2017

Area Forecast Discussion
National Weather Service Spokane WA
1108 PM PDT Tue Mar 14 2017

.SYNOPSIS...
Rain and mild weather will bring flooding over the Idaho
Panhandle and portions of eastern Washington this week. Several
rounds of rain are expected through Wednesday night. Cooler and
drier conditions Thursday into Friday will allow some of our
rivers to temporarily recede. However, more rain Friday night and
Saturday will raise concerns for flooding through the weekend.

&&

.DISCUSSION... /issued 257 PM PDT Tue Mar 14 2017/

Tonight through Wednesday night: The wet weather persists as a
fetch of Pacific moisture continues to stream over into the
region. Currently a shortwave aloft has brushed from the northern
Cascades into BC and brought a frontal boundary through north
central WA. This boundary still persists from north Idaho into the
central Basin with light showers in the low lands and persistent
rain with high mountain snow over the Idaho panhandle. Overnight,
the boundary is expected to transition into a warm front and lift
northward. Winds will be light and rain increases across the
Columbia Basin and into northeast Washington. This round of rain
will persist through Wednesday before a cold front swings through
north central WA Wednesday evening and finally exits southeast WA
by late Wednesday night. Behind this front, anticipate locally
breezy winds. For this 36 hour period, anticipate additional
rainfall amounts of 0.5" to 0.75" for extreme eastern Washington
and 0.75" to 1.25" for north Idaho. Higher amounts are possible in
the mountains. This added rainfall will prolong the flooding
concerns through Wednesday night and current flood highlights will
remain in effect. /rfox.

Thursday: Breezy west winds and the opportunity to see some
sunshine will be on tap for Thursday. More importantly, the Inland
Northwest will experience a mainly dry day with the exception of
some widely scattered showers over the Panhandle mountains and the
Cascade Crest. Our rivers and streams will also benefit from
cooler overnight temperatures Wednesday night and especially
Thursday night. Many locations Thursday night will fall below
freezing for several hours slowing our rate of melting snow.

Friday: It looks like the Inland Northwest may be able to have one
more dry day on Friday before our next round of warm frontal
precipitation arrives late in the afternoon or evening. Of the
morning model runs, the GFS is the fastest to develop rain east of
the Cascades Friday. At this time, we are carrying a 20-30 percent
chance of light rain Friday afternoon for north Idaho and central
and eastern Washington. If the ECMWF, Canadian, and NAM models
verify, precipitation won't begin until early evening. Snow levels
may begin as low as 2000-3000 feet Friday afternoon/evening along
the Canadian border. Strong southerly flow accompanying the warm
front Friday night will push snow levels quickly into the
5000-7000 ft range. The arrival of more rain, mild winds, and
rising snow levels will raise concerns for more runoff into the
weekend. /GKoch

Saturday through Tuesday...Rain will continue on Saturday along
with mild and breezy conditions ahead of a cold front. Snow levels
will be high...ranging from 5-6k feet along the East Slopes of the
Cascades to 7-8k feet over SE Washington into the Idaho
Panhandle. Strong south-southwest flow with 850mb winds of 40-50
kts will focus the heaviest rain over the mountains of NE
Washington and the north Idaho Panhandle. A combination of rain
and snow melt will lead to additional rises on area rivers and
streams with more flooding possible. A strong cold front passes
Saturday evening with windy conditions likely for the Columbia
Basin...Spokane area...and in the mountains. Drier air behind the
front will result in a quick end to precipitation...with little in
the way of post-frontal showers expected. Sunday and Monday will
bring much quieter weather as the next upper trough approaching
the west coast digs south off the California coast allowing a weak
ridge to move over the area. Cooler air moving in behind the cold
front from Saturday evening will allow temperatures to cool
towards normal values for both Sunday and Monday. On Tuesday the
upper trough off the California coast may begin to advect in
increased moisture from the southwest. Unlike recent systems it
looks like only light precipitation amounts as the brunt of the
forcing passes south of the region for the middle of next week. JW

&&

.AVIATION...
06Z TAFS: -ra will continue across the region through the night.
Though there will likely be breaks across the TAF locations. A
drier period is expected aft about 15Z, but will be short lived as
a cold front moves across the region starting aft 22Z for KEAT and
will bring several hrs of more rain. This front will push through
Spokane area ard 02Z. South to southwest winds 15-20 mph with some
gusts as high as 30 mph will increase aft 18Z for the Spokane area
TAFS and KMWH...and will decrease aft the front passes. Most cigs
and vsby should remain VFR, but cannot rule out some IFR fog for
KLWS and KPUW overnight and KMWH...KEAT aft 12Z.

&&

.HYDROLOGY...

Mild temperatures, high snow levels, and a couple more rounds of
rain tonight through Wednesday night will have many rivers and
streams in north Idaho and eastern Washington on the rise. A drier
and somewhat cooler pattern Thursday through Friday afternoon will
help slow runoff for a 24 to 48 hour period. Unfortunately, the
arrival of a vigorous warm front Friday night will push snow
levels high once again and produce another round of moderate
rainfall. The weekend precipitation is the reason for a secondary
bump in many of our hydrographs. A transition to cooler conditions
early to middle of next week should allow our creeks and smaller
rivers to recede as well as improvement in our field flooding.
Our larger rivers like the St Joe and Spokane will be slower to
rise and fall as it takes several days for water to work through
Lake Coeur d'Alene. /GKoch

&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        46  54  37  48  29  49 /  90  90  90  10  10  20
Coeur d'Alene  44  52  36  48  29  48 / 100 100  90  20  10  10
Pullman        49  56  39  49  31  55 /  80  90 100  10   0  10
Lewiston       49  62  42  57  35  60 /  60  70  90  10   0  10
Colville       43  51  36  51  29  47 /  90  90  80  20  10  20
Sandpoint      38  50  37  46  28  45 / 100 100 100  40  20  10
Kellogg        44  51  37  45  29  49 / 100 100 100  40  10  10
Moses Lake     45  59  36  56  29  51 /  60  60  40  10   0  30
Wenatchee      42  54  36  53  32  45 /  60  60  50  10  10  30
Omak           39  52  34  52  28  46 /  80  70  60  10  10  20

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch through late Wednesday night for Central Panhandle
     Mountains-Idaho Palouse-Lewis and Southern Nez Perce
     Counties-Lewiston Area.

WA...Flood Watch through late Wednesday night for Lower Garfield and
     Asotin Counties-Northeast Blue Mountains-Northeast
     Mountains-Okanogan Highlands-Washington Palouse.

&&

Hazardous Weather Outlook
National Weather Service Spokane WA
226 PM PDT Tue Mar 14 2017

IDZ001>004-026-027-WAZ031>033-036>038-152130-
NORTHERN PANHANDLE-COEUR D'ALENE AREA-IDAHO PALOUSE-
CENTRAL PANHANDLE MOUNTAINS-LEWISTON AREA-
LEWIS AND SOUTHERN NEZ PERCE COUNTIES-NORTHEAST BLUE MOUNTAINS-
LOWER GARFIELD AND ASOTIN COUNTIES-WASHINGTON PALOUSE-
SPOKANE AREA-NORTHEAST MOUNTAINS-OKANOGAN HIGHLANDS-
226 PM PDT Tue Mar 14 2017

This Hazardous Weather Outlook is for portions of North Idaho...
North Central Idaho...North Central Washington...Northeast
Washington and Southeast Washington.

.DAY ONE...THIS AFTERNOON AND TONIGHT

Occasional light to moderate rain will continue into tonight.
Mild temperatures will lead to increased snow melt. Flooding
issues on small streams and urban areas will continue.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

Warmer temperatures and rain on Wednesday will encourage spring
snow melt and additional flooding. Large main stem rivers will
remain high through the week although small streams will likely
fall Thursday and Friday due to a break in rain and cooler
temperatures. Another round of mild and wet weather over the
weekend combined with more snow melt will lead to another rise on
rivers and streams which may result in additional flooding into
early next week.

WAZ034-035-041>044-152130-
MOSES LAKE AREA-UPPER COLUMBIA BASIN-WENATCHEE AREA-
EAST SLOPES NORTHERN CASCADES-OKANOGAN VALLEY-WATERVILLE PLATEAU-
226 PM PDT Tue Mar 14 2017

This Hazardous Weather Outlook is for portions of Central
Washington...East Central Washington and North Central
Washington.

.DAY ONE...THIS AFTERNOON AND TONIGHT

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

No hazardous weather is expected at this time.