Area Forecast Discussion
Issued by NWS Spokane, WA

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651
FXUS66 KOTX 290946
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
246 AM PDT Wed Mar 29 2017

.SYNOPSIS...

A moist frontal system will bring more rain to the Inland
Northwest today. This round of rain will aggravate ongoing field
flooding and heighten the potential for rock slides in areas with
steep terrain. A rare dry day is expected on Friday. The weekend
and early next week will feature average temperatures and scattered
light showers over the mountains.


&&

.DISCUSSION...


...RAIN TODAY AND TONIGHT WILL Aggravate FIELD FLOODING AND ROCK
SLIDE POTENTIAL...

Today and Tonight: The Idaho Panhandle can expect a half inch to
three quarters of an inch of rain by late tonight. Pend Orielle
and Stevens counties will have a good shot at comparable amounts
today and tonight. The West Plains, Spokane area, and the
Washington Palouse will likely get a quarter to half inch. These
areas have been soaked repeatedly this month. More rain will only
aggravate ongoing issues with field flooding in areas with poor
drainage. Small streams will respond once again and steep slopes
will see a heightened risk of rock and mud slides. A Flood Watch
is in effect for counties of the Idaho Panhandle from the Canadian
border to as far south as Lewis and Nez Perce counties. Stevens,
Pend Orielle, and northern Spokane counties are also included in
the Flood Watch along with Asotin county (to capture flooding
along the Grande Ronde River).

A plume of subtropical moisture will spread over the Inland
Northwest this morning. Our most widespread rains from central
Washington through the ID Panhandle will occur early this morning
as a surface low moves over the Olympic Peninsula. Broad
warm/moist advection will produce several hours of steady light to
moderate rain over much of the Inland northwest this morning. By
mid to late morning, mid-level westerly flow should initiate the
rain shadow in the lee of the Cascades. Places like Wenatchee,
Moses Lake, Waterville, and Omak should experience a break in the
persistent rain and may have some peaks of sun this afternoon.
Look for snow levels to be on the rise today with the passage of
the warm front. Early morning snow levels in the 4000-5000ft range
are expected to climb to 6000ft by afternoon and evening. Area
ski resorts should see some accumulation early in the day before a
rain/snow mix comes by afternoon.

Thursday: A cool upper level trough is forecast to buckle over
the Northwest on Thursday as the Polar Jet digs into the Great
Basin. There is general agreement between the GFS, ECMWF, and NAM
that a band of wrap around precipitation (deformation band) will
develop eastern Oregon and southwest Idaho Thursday morning. This
band will be monitored closely. Snow levels will likely be falling
under the heart of this precipitation band and could produce wet
accumulations as low as 3500 feet over the Camas Prairie and Blue
Mountains Thursday morning. Places like Peola, Anatone,
Winchester, and Craigmont could have as much as 2 to 4 inches of
accumulation on grassy surfaces early in the day if this band sets
up just right. For now, our forecast has snow levels as low as
4000 feet Thursday morning with accumulations of 1 to 2 inches,
but these amounts could go up or down depending on the track of
this system and snow levels. /GKoch

Thursday night through Sunday night: This could possibly be the
driest part of the week. By Thursday evening, the upper level
trough digs south and east and pulling out of the region, as a
ridge of high pressure builds in from the west. Northerly low
level winds increase down the Okanogan valley into the western
Basin with drier continental air. Meanwhile sheltered locations
may still hold onto the low boundary layer moisture, as in the
valleys of northeast Washington and north Idaho and leads to the
development of fog and stratus. Dry weather will prevail over the
region for Friday and Friday night with filtered sunshine as high
level clouds increase and temperatures remain near seasonal
normals. On Saturday, the strength of the high pressure ridge is
tested as a weakening cold front blows through the region.
Precipitation chances look limited and affects mainly the
mountains. The medium range models indicate the remains of the
frontal boundary gets stalled over southeast Washington into the
southern Panhandle while a weak upper level shortwave ripples into
the region. This looks to enhance the boundary and increase the
instability with more showers possible not only for the higher
terrain by also near the boundary itself. Breezy westerly winds
are expected to develop from the lee side valleys into the
Columbia Basin Sunday afternoon and evening. Temperatures will
continue to follow seasonal trends, with the mildest days of the
week being Friday into Saturday. /rfox.

Monday through Wednesday: The beginning of next brings another
brief period of shortwave ridging building in by late Monday.
Showers will linger over the eastern zones, especially the Idaho
panhandle during the day on Monday before dry air moves in and
gives us a break from precipitation late Monday into Tuesday.
Models are in quite good agreement on then yet another wet system
moving in by mid week associated with the upper low over the Gulf
of Alaska. Snow levels will be on the increase with even higher
elevations potentially changing over to rain. With yet another
moist frontal system moving through this will warrant keeping an
eye on for potential hydro issues late week. /bwilliams


&&

.AVIATION...
06Z TAFS: Moist westerly flow will lead to rain for the TAF sites
tonight into Wednesday. Downslope flow off the Cascades into
Central Washington as well as off the Blue Mountains into the
Lewiston area should keep prevailing CIGS VFR for these areas while
a moistening boundary layer over Eastern Washington and north
Idaho will lead to lowering CIGS with MVFR conditions becoming
prevalent overnight into Wednesday. Steady rain may begin to
diminish over NE WA/N Idaho Wednesday afternoon but a very moist
boundary layer combined with low level upslope flow will yield an
abundance of stratus...with forecast soundings from the GFS and
NAM indicating a good chance for IFR conditions at KGEG. JW


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        49  37  51  34  54  35 / 100  60  30  10   0   0
Coeur d`Alene  47  38  49  33  53  35 / 100  90  40  10   0   0
Pullman        49  40  49  32  52  36 / 100  90  40  20   0   0
Lewiston       54  43  54  37  56  38 / 100  70  50  10   0   0
Colville       49  36  53  33  53  36 / 100  50  30  10   0   0
Sandpoint      44  38  48  32  50  33 / 100  90  40  10   0   0
Kellogg        46  37  46  31  50  34 / 100 100  50  30  10  10
Moses Lake     56  38  60  33  59  39 /  60  20  10   0   0   0
Wenatchee      54  38  55  35  57  38 /  50  10  10   0   0   0
Omak           51  36  55  31  57  36 /  70  20  10   0   0   0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch from 5 AM PDT early this morning through Friday
     morning for Central Panhandle Mountains-Coeur d`Alene Area-
     Idaho Palouse-Lewis and Southern Nez Perce Counties-
     Lewiston Area-Northern Panhandle.

WA...Flood Watch from 5 AM PDT early this morning through Friday
     morning for Lower Garfield and Asotin Counties-Northeast
     Blue Mountains-Northeast Mountains-Spokane Area.

&&

$$



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