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Area forecast discussion 
National Weather Service Spokane Washington
440 am PDT Sat Oct 25 2014

Synopsis...

A series of systems will pass through the region during the period.
The first system today is expected to bring the threat of isolated
thunderstorms and high winds to the region. Remnants of Hurricane Ana
on Tuesday will deliver widespread rainfall to the inland
northwest. Another rain producing system is possible by next
weekend.

&&

Discussion...
today and tonight...
taking a look at the big picture across the country, the one
feature that really stands out is the deep upper level trof
approaching the West Coast. This vigorous system will usher in
quite a bit of high impact weather over the next 36 hours.

Overview:
at 12z, a 986 mb low is moving rapidly northeast toward the
Washington and Oregon coast...and will make landfall this
afternoon at about 993 mb between Astoria and Aberdeen. The warm
front that lifted north into British Columbia overnight will be
replaced by a cold front ahead of the center of low pressure.
Before the front pushes inland, much of the inland northwest will
see at least a partial clearing. The clearing skies coupled with
the warm temperatures should further destabilize the
atmosphere...resulting in the possibility of isolated
thunderstorms.

Thunderstorms?
But first, a line of showers will develop along the cold
front...ushering clouds quickly back across the inland northwest
early this afternoon. The cold air aloft will further destabilize
the atmosphere leading to numerous showers by the evening hours
with the aforementioned isolated rumble of thunder. While we
painted much of eastern Washington and the entire Idaho Panhandle
with isolated thunderstorms, the best chance will be late this
evening over extreme southeastern Washington and the central
Panhandle. The models have not been too aggressive with the
chances of thunder but after bumping up afternoon high temperatures
due to the anticipated clearing in the warm sector, the NAM and
sref especially are showing enough instability to warrant the
isolated chance. Either way, widespread showers will impact the
region late afternoon through the evening hours with localized
heavy downpours possible.

Wind:
the biggest impact from this storm system will be the wind. As
the main line of Showers Pass through the region late in the
evening, the pressure gradient will tighten considerably. Common
with this storm path, a Lee-side low will develop east of the
Canadian rockies over Alberta. The low that moves inland this
afternoon will eventually merge with the Lee-side low. High
pressure building southwest of the region coupled with the 994 mb
low to our northeast will squeeze the pressure gradient and result
in strong winds. A Wind Advisory that was issued earlier will be
updated momentarily to include Spokane Metro with gusts to 50 mph
not out of the question. The peak of the event will be
overnight...midnight through sunrise. In a way we are fortunate
that the timing is not during Max heating. The overnight hours
will work against the strongest winds mixing down to the surface.
Despite the fortunate timing, we are still anticipating
several impacts from this storm.

Impacts:
the main impacts from this storm will be the possibility of light
weight objects being picked up and thrown by the gusty winds. This
includes branches that will likely fall on power lines and result
in local power outages. Caution is also advised on the roadways
with dangerous Crosswinds affecting high profile vehicles. Lastly
and not nearly as important...but this storm will bring an end to
much of the very Scenic fall foliage.
/Ab

Sunday through monday: winds will be on the decrease during Sunday
as the deep low pressure system moves east of our area. These
situations are often tricky. The pressure gradient is decreasing
which should allow winds to decrease, but the daytime heating
allows more momentum mixing from aloft. Winds will be breezy to
windy through much of the day. Showers will mainly be confined to
the Panhandle and northeast mountains, but there's actually enough
afternoon instability to allow showers to develop over the eastern
basin. These showers should die off Sunday evening.

As the upper trough swings through the area, the flow on the
backside of the trough turns to northwesterly, allowing cooler air
to filter into the inland northwest. This will result in the
coolest day of the autumn so far. A few locations may not reach
50f on Monday. The Panhandle and extreme eastern Washington will probably
start the day with a stratus layer that will slowly burn off by
midday. Rj

Monday night through wednesday: a southwest flow pattern will
carry the remnants of Hurricane Ana through the Pacific northwest
during this period. The eastern side of the Cascades will begin to
receive precip beginning Monday night. The moisture will continue
to progress west to east through the inland northwest on Tuesday
morning. With snow levels expected to be around four to five
thousand feet, the higher elevations could receive a light dusting
of snow with rain for the valleys. This system is expected to
bring more than half an inch of precip to the Cascades. The
Waterville Plateau could see a couple tenths of an inch. The
extreme eastern Washington and Idaho Panhandle could get around a
quarter of an inch of rain. Winds with this system will remain
fairly light as gusts could reach around 18 miles per hour. High temperatures
will range from the mid 40s to 50s for most habitated locations.

Thursday through saturday: the models disagree with this period.
The European model (ecmwf) is keeping a strong ridge over the region than the GFS
for this period. The GFS will begin to bring another round of
precip into the region on Thursday afternoon while the European model (ecmwf) keeps
it west of the Cascades until late Saturday. The pops were
dropped to a slight chance for most of the Columbia Basin.
Temperatures for this period will still be several degrees above
normal with highs near 60 and lows near 40. /Jdc

Aviation...
06z tafs: a warm front lifting into eastern Washington and north Idaho will
bring areas of mainly light rain. The band of light rain has
lifted north of all taf sites. Low level moisture and light winds
behind the warm front will promote low stratus and patchy fog for
keat and kmwh through at least 18z Saturday. Confidence is low
that MVFR cigs may develop at klws but light downsloping winds
may keep VFR conditions there. Shower threat develops again
through the afternoon Saturday. This will be accompanied by
increased winds with gusts increasing to 25 to 30 kts after 03z
Sunday.



12z tafs: the warm front lifted north with light rain in most
areas. Now that we are in the warm sector, expected a bit more fog
but the high clouds and breezy conditions are preventing any
widespread fog from developing. The exception is keat where a IFR
ceilings persist. This morning we expect conditions to improve
briefly before winds in most taf locations turn southeast and
eventually southwest. The approaching cold front will bring
widespread rain showers with the very slight chance of
thunderstorms to the eastern sites...not enough of a threat to
include in the taf. Ceilings and visibilities will remain marginal
to VFR in rain as winds continue to turn southwesterly and very
gusty by late evening. Updates to tafs at 12z were limited to
adjusting for improved morning ceilings and adding stronger winds
in the last 6 hours.

&&

Preliminary point temps/pops...
Spokane 64 44 52 36 50 38 / 20 70 30 10 10 20
Coeur D'Alene 65 43 52 36 48 34 / 20 70 40 30 20 20
Pullman 69 43 52 37 51 36 / 20 60 30 20 10 10
Lewiston 71 48 58 41 56 40 / 0 60 20 20 10 10
Colville 62 44 53 32 51 35 / 30 80 50 20 10 20
Sandpoint 62 43 49 34 46 33 / 10 80 70 30 20 20
Kellogg 62 42 45 36 43 31 / 10 90 50 50 30 20
Moses Lake 64 46 59 35 55 40 / 20 50 10 10 0 30
Wenatchee 62 43 58 40 56 43 / 30 50 20 10 0 50
Omak 59 41 54 34 52 39 / 60 60 30 10 0 40

&&

Otx watches/warnings/advisories...
Idaho...none.
Washington...Wind Advisory from 8 PM this evening to 3 PM PDT Sunday for
lower Garfield and Asotin counties-Spokane area-upper
Columbia Basin-Washington Palouse.

&&

$$

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