000
FXUS66 KOTX 212352
AFDOTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
452 PM PDT Tue May 21 2013

.SYNOPSIS...
A strong cold front will sweep through the region this afternoon
into this evening with showers...a chance of thunderstorms and
breezy winds. Cool and showery weather will continue through much
of the week, but with some improvement for the holiday weekend.

&&

.DISCUSSION...
Tonight and Wednesday: A Big weather change is expected. A strong
cold front has moved through eastern Washington and will exit
north Idaho this evening. A band of strong thunderstorms will
march across northeast Washington and north Idaho by early this
evening with small hail and gusty winds. Meanwhile, a deformation
band of steady rain will slowly move across the Columbia Basin
into the Idaho panhandle through the night as a deep upper level
low creeps from the Washington coast inland. Wet and cool
conditions will prevail into Wednesday as the upper level low
wobbles east of the Cascades during the day. Then a secondary band
of showers develop associated with the low center, which looks
like it tracks across the Columbia basin Wednesday morning and
toward the northeast Washington mountains and Idaho panhandle by
late afternoon and early evening. Snow levels will plummet
overnight, especially across from the Cascades, to the Blue
mountains, Palouse and into Central Idaho panhandle by Wednesday
morning, with snow down to around 3k ft. The second deformation
band will lift toward the Canadian border by afternoon while snow
levels only creep up to 4k ft by afternoon. What little daytime
heating expected along with the cold air aloft will raise
instability slightly and lead to a small chance of thunderstorms
in the Cascades and Blue mountains by Wednesday afternoon.
Temperatures will be significantly cooler of 10 to 15 degrees from
today. /rfox.

Wednesday Night and Thursday: The Inland Northwest should
experience a bit of a drying trend Wednesday night into Thursday.
The large deformation band associated with a bent back frontal
occlusion is expected to migrate toward the Canadian Rockies
Wednesday night and remain well north and east of the region
through Thursday. Models have been in decent agreement the last
several runs that there should be a relative lull in precipitation
over the northern Panhandle and southeast British Columbia on
Thursday. This is good news for the swollen Kootenai and Moyie
Rivers. On Thursday, our attention will turn toward the center of
the 500mb low over western Washington and it`s upper level cold
pool. Moisture and instability profiles suggest that the best
chances for showers on Thursday will be over the Cascades and
possibly the Okanogan Highlands. The NAM and GFS both prog upwards
of 200 J/KG of surface based CAPE over the Cascades Thursday
afternoon. This won`t be a particularly moisture-rich environment
and 700-500mb flow suggests storm motion around 20 mph. However,
we will monitor any convection over the Cascades closely this year
over the burn scar areas near Wenatchee and Chelan. These scars
will have a heightened potential for mud slides.

Friday and Friday Night: The 12z models suggest that the focus for
showers will shift from the Cascades on Thursday toward northeast
Oregon and southeast Washington on Friday. The GFS and ECMWF are
in good agreement that the 500mb cold pool will drift into
northern Oregon by Friday afternoon. The highest chances for
showers looks to be in the Lewiston, Pomeroy, Winchester, Pullman
and St. Maries zones. Thunderstorms may need to be added to the
forecast (SE Washington and central/southern ID Panhandle) for
Friday afternoon if the models continue to advertise this track
and timing of the 500mb cold pool. /GKoch

Saturday through Tuesday...The Inland Northwest will continue to see
unsettled conditions through the holiday weekend. The upper low and
associated synoptic forcing will weaken so precipitation should be
more scattered in nature. Orographic ascent will become a more
significant forcing mechanism so there will be a better chance of
showers for the rising terrain north and east of the basin. With
less cloud cover and precip expected, temperatures will trend closer
to seasonal normals. /Kelch


&&

.AVIATION...
00Z TAFS: Several bands of rain are expected over eastern Washington
and northern Idaho tonight into Wednesday. The threat of
thunderstorms will dwindle quickly this evening as strong low level
cooling invades the region behind a cold front. The 18Z NAM was used
a guidance for the TAFs. It appears that a light band of rain in the
Pullman and Spokane area between 00z-03z will decay and be followed
by another more organized band of light to moderate rain after 08z.
Ceilings in the cool and wet air mass will probably fall below 2000
feet at many of the airports in the region on Wednesday morning.
Afternoon showers are expected tomorrow under the upper level cold
pool with the highest concentration over the Cascades with the
favorable southeast upslope flow. /GKoch


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        41  51  37  61  44  61 /  80  80  20  30  10  40
Coeur d`Alene  42  48  36  61  41  60 /  80  90  30  30  20  50
Pullman        40  51  35  61  40  58 /  80  70  20  20  20  60
Lewiston       45  59  41  67  46  65 /  70  70  20  30  20  50
Colville       46  56  37  66  41  68 /  90  90  60  30  20  40
Sandpoint      45  50  37  60  40  62 /  90 100  70  40  20  40
Kellogg        42  44  35  57  42  57 /  90  90  70  30  40  60
Moses Lake     45  62  40  67  45  67 /  60  40  20  30  20  30
Wenatchee      44  57  40  65  45  65 /  60  40  30  40  20  30
Omak           44  59  36  66  41  68 /  70  80  50  40  20  30

&&

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

$$