Area forecast discussion
National Weather Service Spokane Washington
450 PM PDT Sat may 25 2013
Synopsis...
Memorial Day weekend is expected to be a little cooler than
average, and a series of weak upper level disturbances will bring
the potential for scattered showers through Monday. The moist,
showery weather pattern is expected to linger into late next week.
&&
Discussion...
tonight and Sunday...after lingering showers die off this evening
mainly near the Cascades and northern mountains, attention will
then shift to a wave rotating around a closed low near the North
Washington coast. This wave will swing into western Oregon/southwest
Washington overnight tonight...then move slowly into the
Washington Cascades and southeast Washington during the day
Sunday. Models are in good agreement with this scenario. As it
does so the closed low will open up into a weak negative tilt
trough. Increased diffluent southerly flow will increase the
chances for showers especially in the Cascades, as well as
southeast Washington, Lewiston area, Palouse, and central
Panhandle mountains where instability will be greatest. Uncapped
cape values of 200-500 j/kg could also spark a few thunderstorms
from the Blue Mountains in southeast Washington towards the
central Panhandle mountains in Idaho. Elsewhere less instability
and only weak lift will support a 20-30 percent chance of rain
showers. A weak thermal ridge lifts up into western Montana
clipping the north Idaho Panhandle Sunday afternoon which will
result in 6-10 degrees of warming compared to Saturday high temps.
Jw
Sunday night through Tuesday...the upper low that has brought
several days of cool and unsettled weather to the region will
finally eject east into Montana Sunday night and Monday...but not
before dragging one last short wave through the southern fringes
of the low. This will result in continued showers across my east
and southeast zones Sunday evening. But don't expect much of a
break in the weather. Enough moisture and instability will linger
through Monday for a chance of showers mainly tied to the higher
terrain outside of the Columbia Basin. No big changes in
temperatures are expected with highs remaining on the cool side of
normal.
The next weather system will move quickly into the region as an
occluded front late Monday and Tuesday. Moisture associated with the
warm front will stream into the region from the southwest. Not
much lift with the warm front but the large amount of moisture
that comes with it makes it prudent to keep the mention of
precipitation in the forecast for Monday afternoon and early
evening. The models are similar that the focus of the
precipitation will be with the cold front as it moves through the
region. The front looks to cross the Cascades from the west after
06z then slowly move east through the forecast area Tuesday
morning...before getting hung up across the eastern third of the
forecast area Tuesday afternoon. With the exception of the lower
east slopes and perhaps the deep basin just about all areas will
have a chance to pick up measurable precipitation...with the
northern and eastern mountains very likely to see a wetting rain.
The models are showing a negatively tilted trough just nosing into
southwest Washington Tuesday afternoon. It appears the best
instability will remain west of the Cascades for now and will hold
off on adding thunderstorms for now. /Tobin
Tuesday night through Saturday...cool and unsettled weather
associated with a negatively tilted trough will prevail for much of
the work week. The focus for precipitation will be eastern half of
the forecast area, and the northeast zones in particular, where a
boundary will stall. Draped from northwest to southeast, this
boundary will be a forcing mechanism along with favorable upslope
flow to bring a good chance of showers to the rising terrain north
and east of the Columbia Basin. As we get into next weekend, this
boundary will weaken as the upper low drifts off to the southeast.
This will allow drier and warmer conditions to push in from the west
and spread across the inland northwest for Friday into Saturday.
Beyond next weekend...medium range models are hinting that an upper
level ridge may build over the eastern Pacific for the beginning of
next week, bringing warmer and drier weather for the first week of
June. /Kelch
&&
Aviation...
00z tafs: cumulus cloud cover and northern mtn showers will decrease
in coverage this evening. A shortwave trough of lower pressure just
off the northwest Oregon coastline will push inland tonight. This
will spread some mid and high level cloud cover across the region.
Showers are expected to develop out ahead of this wave with showers
pushing northward out of Oregon late Sunday morning. All terminals
will see a chance for some showers through the day on Sunday, but
the best chances will be across the southern half of the region from
keat to kpuw and klws. /Svh
&&
Preliminary point temps/pops...
Spokane 44 67 47 66 47 62 / 10 30 20 30 30 50
Coeur D'Alene 40 68 46 65 44 61 / 10 30 40 40 20 60
Pullman 40 64 45 66 45 60 / 10 50 40 20 30 50
Lewiston 46 69 50 73 51 67 / 10 50 40 20 30 50
Colville 39 73 46 70 45 68 / 20 20 20 50 20 50
Sandpoint 36 67 44 64 42 62 / 10 20 40 50 20 50
Kellogg 40 65 46 62 46 58 / 10 40 50 50 30 60
Moses Lake 44 68 49 72 50 70 / 10 30 20 10 30 30
Wenatchee 49 66 50 69 52 68 / 10 40 10 10 20 40
Omak 39 69 46 71 46 68 / 20 20 10 20 30 50
&&
Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&
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