Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Spokane Washington
444 am PDT Wednesday Oct 1 2014

Synopsis...
another system skims by the region late today into tonight, with
some clouds and breezy conditions and continued cooler than
average temperatures. High pressure will gradually build in
through the weekend and linger into the middle of next week. This
will result in generally dry weather, with temperatures warming to
above average.

&&

Discussion...
today and tonight: the inland northwest will be in a progressive
northwesterly flow with a few cloudy periods, isolated shower
chances and below normal temperatures. Yesterday's shortwave is
shifting southeast and a weak ridge of high pressure is building
in this morning. Patchy fog, locally dense, will linger around the
sheltered northeast valleys early today under this ridge. The
onshore flow and approach of the next system will keep shower
chances alive near the Cascade crest today and along the Canadian
border late today into this evening. That next system was diving
southeast across British Columbia this morning and models bring it toward
northeast Washington/north Idaho late this afternoon into tonight. The brunt
of the lift and moisture remains north of the Canadian border,
hence the main threat of showers will linger near the immediate
US/British Columbia border. But look for some increased middle to high clouds
this afternoon and evening throughout the region, before some
clearing develops overnight. The incoming wave will also lead to
an increase in winds again this afternoon and evening. Nothing
too strong, but noticeable in the 10 to 15 mph range with local
gusts near 20 mph. Cooler air will continue to seep into the
region on the northwesterly flow. With 850mb temperatures in the
middle to upper singles (celsius), regional temperatures will
remain below average. I added some patchy fog again across the
sheltered northeast valleys overnight into Thursday morning.
Abating winds, low level inversions and cooling overnight, behind
the exiting middle to high clouds, will allow for this potential.
/J. Cote'

Thursday through Saturday...this will generally be a dry weather
period as the upper level jet retreats to our north and east with
the initial building and then the persisting upper level ridge
over central portions of British Columbia. On Thursday the ridge
is expected to make a swift easterly shift and amplification into
west central British Columbia and move toward the British Columbia/Alberta
border on Friday. The ridge axis is still expected to contain a
nicely defined atmospheric river extending from just west of
Hawaii to the British Columbia coast through Friday. This will likely bring very
wet conditions to western British Columbia...but little weather activity this
far south. In fact the main impact will likely be increasing high
clouds late Thursday into early Friday associated with a weak mid-
level warm front. Temperatures will warm steadily through this
period with high temperatures in the 60s on Thursday and upper 60s
to mid 70s on Friday..

For Saturday...previous model was showing the flattening of the
upper level ridge with the atmospheric river surging south of the
British Columbia border. By this point...the surge of moisture become much less
coherent with most of it located above 10000 ft. Meanwhile 500 mb
heights are quite lofty...578 dm or higher which is almost 2
Standard deviations higher than normal for this time of year. The
trend has been one of a slower flattening (ie more ridging) and
consequently less precipitation. In fact...for the 00z
models...the only strong precipitation signature was showing up
near the west-facing slopes of the Cascades. The remainder of the
inland northwest was showing dry conditions. Given such lofty 500 mb
heights...this premise seems logical. We will back off pops
further from previous forecasts, and leave most near the Canadian
border. If this trend continues we may need to eliminate pops
completely. Temperatures on Saturday will warm further with most
valley highs in the 70s and even a few lower 80s over the lower
Columbia Basin. Fx

Saturday night through Tuesday night: extended portion of the
forecast looks rather benign due to the jet stream remaining north
of our area thanks in part to a ridge of high pressure near the
area. Models are continuing to show the brunt of the moisture
flowing along the jet stream leading to a prolonged period of rain
for the British Columbia coastal area while we remain dry just to the southeast. The
only chance of mentionable precipitation would be along the
Cascade crest as small amounts of moisture stray away from the
main flow into British Columbia. The majority of the region will only see mid
and high clouds from the atmospheric river to our north. The main
feature of note throughout this period would be the continuing
above normal temperatures. The warm subtropical airmass from the
central Pacific will keep our daytime highs 8-15 degrees above
normal with widespread 70s and some 80s for lower areas expected.
Overnight lows also remain above normal for this part of the year
as the warm airmass coupled with increased cloud cover diminishes
our amount of overnight radiative cooling. Overall the early part
of next week can be summarized as warm and dry, a scenario all to
common to the inland northwest this year. /Fliehman

&&

Aviation...
12z tafs: clearing skies and diminishing winds overnight will
allow fog to form along lakes and waterways in the valleys of NE
Washington and north Idaho. This may produce low stratus or patchy fog near
geg/sff/Coe/puw. Most likely to be affected is Coe and sff where
greater amounts of precip will provide a source of low level
moisture. Any stratus that develops will dissipate by 19z. After
19-22z winds are expected to increase, along with middle to high
clouds, with the next system swinging toward NE Washington/north Idaho. The winds
will abate after 02-06z along with the clouds, bringing another
potential for patchy fog across the northeast valleys and higher
Palouse toward early Thursday morning, perhaps just beyond this
taf period (i.E. Beyond 12z thursday). Confidence is low around
taf sites but better over the sheltered northeast valleys again,
such as near szt. /J. Cote'



&&

Preliminary point temps/pops...
Spokane 63 39 64 39 70 46 / 0 0 0 0 0 0
Coeur D'Alene 62 38 63 38 69 45 / 0 0 0 0 0 0
Pullman 63 38 64 38 72 45 / 0 0 0 0 0 0
Lewiston 70 44 70 43 77 49 / 0 0 0 0 0 0
Colville 67 37 67 35 71 44 / 10 10 0 0 0 10
Sandpoint 61 35 61 31 66 40 / 10 10 0 0 0 0
Kellogg 56 40 58 37 65 46 / 10 0 0 0 0 0
Moses Lake 71 40 69 39 76 49 / 0 0 0 0 0 0
Wenatchee 70 45 69 44 76 53 / 0 0 0 0 0 0
Omak 67 38 67 40 73 47 / 0 0 0 0 0 10

&&

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

$$

National Weather Service Glossary of Abbreviations