Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Spokane Washington
524 PM PDT Wednesday Apr 23 2014

Synopsis...
occasional precipitation chances, breezy conditions and relatively
cool temperatures dominate the weather pattern. The next organized
storm system will bring steady light rain late tonight and into
Thursday, followed by a threat of more scattered showers, and
perhaps some thunder, Thursday afternoon. Showers will remain a
threat into the weekend, before a relative lull comes for the
start of the new work week.

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Discussion...
tonight through Thursday...the forecast area is in the grip of a
showery regime this afternoon as an exiting upper level wave
provides enough lift to work with some surface based instability
generating scattered showers...some with small hail. It is not out
of the question that a brief thunderstorm or two may pop up during
the early evening pre-sunset hours over the Palouse and Idaho
Panhandle. After sunset most of this activity should die
down...especially across the northern tier zones...however the
next organized and strong Pacific storm is already moving onshore
with regional radar suggesting an incipient warm frontal
precipitation shield forming along the Oregon/Washington border.

Models are in good agreement with the evolution of this system. A
warm front will form and consolidate west to east over the
forecast area tonight leading to an onset of light stratiform rain
at all locations...probably the west and south zones this evening
and through the remainder of the area later tonight. By Thursday
morning all of the forecast area will be subject to rain. The
trailing occluded front will likely cross the Cascades and bring
some drying to the deep basin zones after 9 am or so as some
downslope effect kicks in...with a tapering to showers in the
eastern basin late in the morning. This will not be the end of it
though...cooling aloft from the approach of the trough driving
the occluded front combined with potential sunbreaks over much of
the region after the morning rain shield moves out will conspire
to produce scattered to numerous convective showers and a decent
potential for isolated thunderstorms east of a line from Omak to
Lewiston during the afternoon hours. Only the deep basin/Cascades
Lee zones will be effectively done with any significant
precipitation by afternoon. Breezy conditions will once again
develop over the exposed terrain of the basin with wind gusts near
30 mph in the well mixed Post frontal air mass. Temperatures on
Thursday will be heavily influenced by mixing over the basin and
heavily influenced by continuing precipitation over the
orographically influenced northeast mountains and Idaho
Panhandle...suggesting near or slightly above normal in the deep
basin to below normal in the northeast and Panhandle zones.
/Fugazzi

Thursday night through Saturday...an upper level trough centered
just off the Washington/or coast Thursday night will slowly move across
the inland northwest Friday and Saturday. A stronger disturbance
embedded within this trough will drop well south of the area into
California...but some of this moisture will get picked up in the
southerly flow ahead of the trough into the Blue Mountains,
Camas Prairie, and Idaho Panhandle clipping far eastern
Washington. This will keep the highest coverage of showers in
these areas with low level upslope flow into the high terrain
further favoring high pops. Elsewhere isolated to scattered
shower coverage is expected mainly over the mountains due to
terrain forcing. Overall shower coverage will be greatest during
afternoon/early evening hours when the atmosphere is moderately
unstable. Jw

Saturday night through Wednesday...cluttered and progressive zonal
flow that amplifies ever so slightly on Monday continues to keep
eastern Washington and northern Idaho generally cooler and
potentially wetter than normal along with persistent intervals of
breezy/gusty winds at least through Monday night. There has been
some model consistency in bringing in and amplifying a ridge of
high pressure for Tuesday and Wednesday with the more favored
European model (ecmwf) solution not only amplifying the ridge more but holding it
in place longer through that next workweek which would suggest a
nice warming and drying trend. /Pelatti



&&

Aviation...
00z tafs: the region will transition from an unstable showery
regime to a stable rainfall overnight. Diurnally driven showers
under a pool of lingering instability east of a line frm kmlp to
kcqv will wane with sunset. Meanwhile...a moist warm front will
approach from the south-southwest bringing lower cigs and steady rain to all
terminals aft 04z. A cold front passage btwn 13-18z will end the
steady rain and promote incr winds. A brief drying trend will be
followed by a destabilizing atmosphere and widely scattered -shra
through late aftn. Isolated thunderstorms are strong possibility
but coverage at this time does not warrant a prevailing line in
the 00z tafs. Thunderstorms in the vicinity could be included with the 06z issuance. /Sb



&&

Preliminary point temps/pops...
Spokane 40 58 38 54 37 56 / 80 100 40 40 30 20
Coeur D'Alene 39 53 37 53 36 55 / 70 100 70 50 50 40
Pullman 42 55 39 50 36 53 / 70 100 50 50 50 30
Lewiston 46 62 44 55 42 59 / 50 100 60 70 50 30
Colville 37 59 35 61 38 61 / 70 100 60 40 20 30
Sandpoint 38 51 36 54 38 54 / 70 100 80 50 50 50
Kellogg 37 50 36 52 36 50 / 70 100 70 70 60 60
Moses Lake 44 64 40 61 39 63 / 80 70 10 10 10 10
Wenatchee 45 63 43 61 41 62 / 70 60 10 10 10 10
Omak 39 62 36 62 34 62 / 80 100 10 20 10 10

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...none.
&&

$$