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Area forecast discussion 
National Weather Service Spokane Washington
254 PM PDT Wednesday may 27 2015

Synopsis...
scattered showers and thunderstorms will decrease after sunset but
return on Thursday and Friday although more focused on mountainous
areas. A warming trend into the mid 80s by Saturday and Sunday
will Grace the region with a small chance of mainly mountain showers
and thunderstorms. The large next storm system will bring a better
chance of showers and thunderstorms and cooler temperatures on
Monday and Tuesday.

&&

Discussion...

This evening and tonight: showers and thunderstorms will continue
through sunset across a majority of southeastern Washington and the lower
Idaho Panhandle as an area of low pressure slowly departs to the
south. Activity north of a line from Mullan to La Crosse will be
more isolated in nature and contend with increasing large scale
subsidence. We are seeing isolated cells busting through the cin
layer near Loup Loup and another just north of Lake Wenatchee so
depsite the lack of activity right now, a small threat will remain
in place through dark but the overall threat for heavy rain on the
burn scars is low. There are two satellite waves that will enhance
or produce small clusters of storms. One is diving south into
Adams County and will be out of our area soon. The second is just
entering far northeastern Washington and could bring last gasp of showers
and storms across the NE mtns and into the Upper Basin through the
evening.

The main threats with any storms will be brief heavy downpours...small
hail...and lightning strikes. Storms near the blue mtns and Camas
Prairie will be nearly stationary and more favoraved to produce
rainfall amounts that could lead to localized flood problems. On
the contrary, the lack of wind shear in this environment will also
mean less organization within the storm structure and quicker
collapse of initial updrafts.

Areas of fog possible again by morning, especially near rivers and
areas that receive appreciable rainfall this afternoon.
Temperatures will be near to slightly warmer compared to this
morning. /Sb

Thursday through Saturday night...this period will be
characterized by a warming trend with plenty of sunshine over most
locations...but marred by the potential for afternoon and evening
showers and thunderstorms mainly over the high terrain surrounding
the basin. Overall...the upper level low currently circulating
over the region will move off to the east on Thursday and cease
to be a factor in convective initiation...however a second upper
low descending down the Canadian Pacific coast and ejecting inland
over British Columbia will prevent a strong ridge from moving over
the region. Instead this low will promote a more southwesterly low
aloft through Thursday and Friday...allowing a strong warm up to
well above normal temperatures...mainly in the 80s with a few low
90 readings in the deep basin by Saturday.

Adequate moisture to fuel thunderstorms will continue to prevail
over the region and assuming dew points remain elevated to near
current levels with expected high temperatures in general most
locations will achieve anywhere from a few hundreds to near 1000
joules/kg each afternoon. However...on Thursday dynamic support
will be absent so thunderstorms will be confined to the mountain
zones. On Friday the GFS and NAM models both sense a weak wave
crossing the region in the southwesterly flow aloft generating
some moderate DPVA and jet divergence as well as weak cooling
aloft. This will likely allow another round of afternoon and
evening storms and the presence of this weak energy aloft may
allow storm initiation over the rising terrain of the eastern
basin and the Waterville Plateau...in addition to the mountain
zones.

By Saturday drier air finally invades the region effectively
suppressing any further thunderstorm threat except for a small
lingering chance over the Idaho Panhandle. The surface thermal
trough will remain over the basin and the drier air will heat more
efficiently resulting in the highest temperatures of the week for
a splendidly benign beginning for weekend outdoor activities.
/Fugazzi

Sunday through Wednesday...an active weather pattern will prevail
across the inland northwest during this time period as an upper
level trough takes aim at the region. Timing differences between
the GFS and European model (ecmwf) are starting to be resolved with the 12z run
today. The GFS has shown better run-to-run consistency up to this
point and now the latest run of the ec is trending closer to the
GFS timing. With confidence increasing, I have increased pops and
thunderstorm coverage for Monday/Monday night time period. The
upper trough will track toward the pacnw coast Sunday, placing the
forecast area under warm and moist southwest flow. This will keep
temperatures above normal Sunday with some shower and thunderstorm
coverage possible across the southeast zones. As the trough swings
inland Sunday night into Monday it will take on a negative tilt.
This pattern is a favorable one for showers and thunderstorms
across the forecast area. A decent amount of shear and surface-
based cape values of 500 to 1000 j/kg Monday afternoon means that
some thunderstorms could become organized. A tap into a sub
tropical moisture fetch supports heavy rain as a threat as well.
Tuesday the upper low drifts over the inland northwest with the
threat of scattered showers and thunderstorms continuing in an
unstable atmosphere. By Wednesday the low starts to exit to the
east and thunderstorm coverage will be more focused on the eastern
zones. Daytime temperatures will be on a cooling trend as the
region comes under the influence of the upper low with associated
clouds and precipitation. Expect widespread 80s on Sunday to be
replaced by 70s for the first half of the work week. /Kelch

&&

Aviation...
18z tafs: isolated to scattered showers will be possible across
much of the region with the highest probabilities near kgeg,
ksff, kcoe, kpuw, and klws taf sites. The stronger cells will
bring the potential for heavy rainfall...small hail...and
occasional lightning strikes as well as brief MVFR conditions.
The moist atmosphere has produced very little in the way of wind
gusts with T-storms over the last few days. Most convection will
dissipate near sunset with a small chance for elevated showers to
drop south vcnty keat/kmwh after 03z assoc with a weak front. /Sb




&&

Preliminary point temps/pops...
Spokane 52 79 57 82 59 85 / 20 10 10 20 10 10
Coeur D'Alene 49 78 54 82 56 83 / 30 20 20 30 20 20
Pullman 46 75 52 82 56 83 / 30 20 20 20 20 20
Lewiston 52 83 58 88 63 90 / 40 10 10 20 20 20
Colville 53 82 54 83 54 86 / 30 20 20 30 20 20
Sandpoint 50 78 51 81 52 80 / 30 20 20 30 20 20
Kellogg 47 76 49 81 53 81 / 40 40 40 30 30 20
Moses Lake 53 86 58 90 59 92 / 10 10 10 10 10 10
Wenatchee 59 86 64 89 63 90 / 10 10 10 10 10 10
Omak 51 86 56 87 54 90 / 20 10 10 20 20 10

&&

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

$$

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