Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Spokane Washington
450 am PDT Wednesday Aug 5 2015
cooler temperatures, continued breezy conditions, along with a
chance of showers and a few thunderstorms over the northern
mountains are expected through Thursday in the wake of a cold
front. Another threat of showers and thunderstorms arrives this
weekend, as yet another low pressure system is expected to move
into the region.
today through thursday: a cold upper level low pressure system
will nudge further south across British Columbia today. Satellite imagery shows
moisture about to move into northwest Washington. This moisture will push
into the Cascades up across the northern mountains through this
afternoon. This will also result in an increasing chance for
showers across these areas. Best chances will be along the Cascade
crest. Chances will become much less along the Lee side of the
Cascades where westerly flow will result in downsloping and drier
Cooler and more moist air will funnel through the Cascade gaps.
This will act to strengthen the cross Cascade pressure gradient
with winds becoming increasingly more gusty through the day. These
winds will also funnel out across the interior basin. Winds will
be strongest along the Lee slopes of the Cascades. The Wenatchee
area and Waterville Plateau could see gusts as strong as 30-35
mph. Wind gusts closer to 25 mph are expected across the basin.
Although we will see moisture increasing across the Cascades
today, it is not expected advect much across the basin. This will
result in yet another day of breezy winds with dry conditions, and
will be a potential problem for rapid spread of any new or ongoing
The upper level low will eject more quickly east of the region on
Thursday. A lingering upper level cold pool aloft will keep the
northeast mtns and northern Panhandle weakly unstable, but,
overall, a decreasing trend in showers and cloud cover can be
expected. Both Wednesday and Thursday will be relatively cool
compared to the hot conditions that have been experienced for much
of the Summer season. Expect temperatures near to or slightly
below normal with highs ranging from the mid 70s to mid 80s. /Svh
Thursday night through Wednesday...through this period of the
forecast we will see the exit of one upper level low for a brief
warming and drying trend...followed by another closed low that
will affect the weather through the weekend and well into next
week. Model guidance is similar through Tuesday...before showing
some differences Tuesday and Wednesday.
Thursday night through early Saturday...high pressure will track
through the region ahead of the next upper low approaching the
eastern Pacific. This will result in a 24-36 hour period of a
warming and drying trend. Temperatures will rebound quickly with
highs right around normal. Winds will be light and terrain driven.
Saturday afternoon through Monday...an upper level low will move
out of the Gulf of Alaska and take up position off the Washington
coast...then linger in that area through the weekend. Several
waves will eject off the parent low and track through the region.
Moisture associated with these weak waves will be focused across
the north Cascades and along the northern mountains near the
Canadian border. None of these waves look particularly robust or
carry much in the way of deep moisture. But showers with embedded
thunderstorms will be possible through the weekend. Each of these
waves will also increase southwesterly winds for breezy conditions
A secondary wave was progged to move through Oregon and clip the
southeast zones through the weekend. That wave now looks to to
take a more southerly Route. As such the chance for showers and
embedded thunderstorms were pushed back to Sunday and Monday as
the main low begins to move inland.
Tuesday and Wednesday...enough differences begin to show up in
the model guidance for only low confidence in this portion of the
forecast. The upper level low is expected to split with the
northern track opening into a wave and tracking northeast with
various solutions. The southern wave is expected to close off and
linger somewhere between about 130w off the cal coast and in the
vicinity of Lake Tahoe. The solution will be somewhere in between.
The forecast has some lingering, mainly mountains showers with
temperatures remaining near normal. Tobin
12z tafs: an axis of mid level instability extending from
northeast or into the southern Idaho Panhandle will result in
isolated to scattered thunderstorms through this morning. There is
high confidence that this convection will remain south and east of
the klws taf site. A deep upper level low pressure system will set
up over southern British Columbia this afternoon into tonight. This will result
in increasing showers over the Cascades and northern mountains.
This may lead to mountain obscurations late this afternoon into
the nighttime hours, especially across the northern Cascades.
Winds will also be gusty this afternoon/evening with gusts to
between 25-35 mph possible. /Svh
Preliminary point temps/pops...
Spokane 81 58 77 56 84 60 / 0 10 10 0 0 10
Coeur D'Alene 80 56 78 53 85 56 / 0 10 10 0 0 10
Pullman 80 53 76 49 84 54 / 0 0 0 0 0 10
Lewiston 88 62 85 59 91 65 / 0 0 10 0 0 10
Colville 81 55 80 53 87 55 / 10 30 20 0 10 10
Sandpoint 80 51 75 46 82 49 / 0 30 30 10 10 10
Kellogg 78 53 75 51 84 53 / 0 10 10 0 10 10
Moses Lake 86 57 83 55 88 59 / 0 0 0 0 0 10
Wenatchee 83 64 85 63 90 67 / 0 10 10 0 0 10
Omak 83 56 85 55 89 59 / 10 20 10 10 0 10
Washington...red flag warning until 9 PM PDT this evening for East Washington
central Cascade valleys (zone 677)-East Washington northern
Columbia Basin (zone 673)-East Washington Palouse and
Spokane area (zone 674).