Area forecast discussion
National Weather Service Spokane Washington
238 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 European model (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 Idaho 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...
18z tafs: a cold front will sweep through the taf sites today
lowering cigs, showers, a wind switch with gusty winds. The front
will push from keat to kmwh through 21z, and then March to the kgeg
vcnty, kpuw and klws toward 00z. Anticipate light high based showers
ahead of the front with the potential for thunderstorms. The best
chance for thunderstorms will be north and east of kgeg this
afternoon. Behind the front, expect cigs to continue to lower
overnight with steady light rain. Snow levels will drop to 4-5k ft
overnight. Cigs will be nearing MVFR by 12z. The rain will taper off
to shower by Wednesday morning. /Rfox.
&&
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...
Idaho...none.
Washington...none.
&&
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