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afdotx

Area forecast discussion
National Weather Service Spokane Washington
251 PM PDT Mon may 29 2017

Synopsis...
high pressure continues over the inland northwest through Tuesday
with another very warm day. There is a small chance of
thunderstorms in the higher elevations, otherwise expect dry
weather. This warm spell will contribute to rises on rivers from
the Cascades into north Idaho. A strong cold front will arrive
Tuesday night with strong gusty winds and a good chance of
showers and thunderstorms. By Wednesday and for the rest of the
week, expect seasonal temperatures, breezy winds and a chance of
showers and thunderstorms in the higher terrain.

&&

Discussion...
tonight through Tuesday...upper level ridge will hold onto the
region one more day. This will bring more of the same...ie warm
and sunny weather to most locations. In fact it should be the
hottest day in the recent stint of weather as 850 mb temps warm
1-2 more degrees over today. That should equate to highs in the
mid 80s and 90s or a couple even a couple degrees warmer than
today. While our confidence is high for that trend over the
eastern half of the forecast area, the warming is less certain
near the Cascades. That is because the ridge will begin its
breakdown which should advect some high level moisture and clouds
over this portion of the forecast area ahead of a strong cold
front. The reduced insolation could result in cooler temperatures
despite the warming at 850 mbs. Speaking of clouds and the cold
front, this could be an interesting situation. Confidence is high
this front will drop temperatures significantly and initially
bring gusty winds. Most model guidance brings the front into the
Cascades during the early evening and across the remainder of the
forecast area overnight. The timing is right to support some winds
of 20-30 mph during the evening across the lower Columbia Basin,
Waterville Plateau, and Wenatchee area, with lesser amounts
overnight across the remainder of the area. Whats less certain is
what to do with precipitation chances.

While much of the precipitation threat will be tied to the arrival
of the front, in the Cascades during the late afternoon, there is
more curiosity for the threat of convection developing ahead of
the upper level trough over southeast Washington and NC Oregon. Most of
the convective allowing models are showing a pretty nice cluster
of thunderstorms developing ahead of the trough in NC Oregon by
mid-afternoon and then pushing it across southeast Washington into NC
Idaho late in the afternoon or early evening. These thunderstorms
(if they form) will benefit from a very unstable air mass which
will develop above the low-level thermal ridge. SBCAPE values
could climb into the 1000-1500 j/kg range while 0-6km shear values
reach 30-35 kts. This could be enough to generate some strong
thunderstorms which would be capable of producing large hail.
Whether or not these can move into southeast Washington or NC Idaho during the
evening before weakening is questionable, but if they do they bear
watching. Otherwise again most of the shower and thunderstorm risk
will be tied to the incoming trough and cold front. These should
mainly impact the Cascades, Okanogan Highlands, and Okanogan
Valley during the evening and then shift into extreme eastern
Washington and north Idaho overnight. The thunderstorm threat will
gradually taper off during the night. Fx

Wednesday through monday: expect a pattern change with bring more
seasonal temperatures, breezy winds in the Columbia Basin and
occasional mountain showers. After the strong cold front push
through the region Tuesday night, an upper level trough will set
up off the Washington coast with a moist southwest flow into the
region accompanied by embedded disturbances. On Wednesday, the
remains of the front linger over the southern Panhandle with a
resurgence of convection in the afternoon and early evening.
Breezy winds will develop with higher gusts in the afternoon while
temperatures feel the effects of the cold air advection and cool
about 20 degrees. The boundary remains stalled Wednesday night
into Thursday with the best chance of precipitation from the Blue
Mountains into the central Idaho Panhandle. The arrival of a
shortwave of Thursday will help enhance convection in most areas
with a chance of thunderstorms possible across northeast
Washington into north Idaho, and kick the boundary east. Another
disturbance arrives on Friday with a repeat of mainly afternoon
and evening convection in the higher terrain. There is a good a
chance for dry weather on Saturday as a shortwave ridge builds
over the region. This will be short lived as another Pacific
trough digs down the West Coast and increases a moist and unstable
southwest flow by Sunday afternoon into Monday. There are some
model discrepancies on the track of this trough so will lean
toward climo pops for Sunday night into Monday. Yet, there may be
signs of warming and drying by middle of next week. /Rfox.

&&

Aviation...
12z tafs: dominating ridge will lead to VFR conditions at all taf
sites through the entire period. Main concern will be the
development of showers and thunderstorms over the mountains of North
Washington and north ID, but far away from the taf sites. Fx

&&

Preliminary point temps/pops...
Spokane 60 89 58 74 53 72 / 0 0 20 20 20 10
Coeur D'Alene 54 87 55 73 51 72 / 0 0 20 30 20 20
Pullman 52 87 55 72 52 70 / 0 0 20 20 50 20
Lewiston 58 94 61 78 56 76 / 0 0 30 20 50 40
Colville 50 90 58 76 52 73 / 0 10 40 30 20 50
Sandpoint 49 85 54 75 49 69 / 10 10 20 30 40 30
Kellogg 49 86 53 76 47 68 / 10 0 10 30 70 50
Moses Lake 56 94 60 80 55 78 / 0 0 40 10 0 10
Wenatchee 62 90 58 79 58 75 / 0 10 30 10 0 20
Omak 52 91 60 79 53 76 / 0 0 30 20 10 20

&&

Otx watches/warnings/advisories...

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