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Area forecast discussion 
National Weather Service Spokane Washington
515 PM PDT Wednesday may 6 2015

Synopsis...
low pressure will bring isolated showers around the western
Columbia Basin and over the mountains this evening with more
showers possible overnight to the southeast. The weather remains
generally dry and warm through the end of the week, except for a
small shower threat over the Idaho Panhandle mountains Friday. In
addition expect occasionally breezy conditions, again especially
on Friday. Temperatures moderate by the beginning of next week as
a weather pattern change occurs. This change will bring a return
to cooler temperatures and a chance of precipitation.



&&

Discussion...
tonight and thursday: the upper level low over the region is
beginning to drop south into central or late this afternoon. The
cold pool aloft associated with this low is positioned over the
southern Washington Cascades. This is where the deepest convection has
been observed this afternoon with thunderstorms developing over
the higher terrain. Showers further north have not been as deep
and have looked fairly weak based off of radar data. Precip
amounts are likely on the lighter side due to the amount of dry
air in place across the region as well. Expect much of this
shower activity across the northern mtns and over into the
Cascades to begin to wane as we lose the surface heating this
afternoon.

The region will not stay completely dry tonight though. There is
a vorticity maximum rounding the base of the upper level low this
afternoon. This energy will push toward the southern Panhandle
this evening into tonight. Moisture will wrap around with this
energy and should produce showers as far north as the Camas
Prairie, Palouse and into the central Panhandle. The Camas Prairie
stands to see the most precip in our region with between 0.05 and
0.10 inches possible. Skies will clear out across the northern
portion of the region and become progressively more cloudy to the
southeast where the wrap around moisture will be located. Winds
will also remain breezy down the Okanogan Valley with northerly
winds increasing through the Purcell Trench tonight as well. All
these factors has made for a tricky low temperature forecast for
tonight. In general, we should see milder low temperatures tonight
compared to last night with the increasing northerly winds and mid
level clouds moving up from the south.

Thursday will be significantly warmer compared to today and climbing
back above normal. Temperatures at 850 mbs will Jump Up from
around 6 celsius today to around 10 celsius tomorrow. This will
translate into high temperatures in the upper 60s and 70s for
tomorrow afternoon. /Svh

Thursday night through saturday: the inland northwest will be in a
northerly flow this period, with low pressure to the south and
high pressure to the north. This will lead to some breezy
conditions and only minor shower chances around the eastern
mountains, with slightly above normal temperatures. The mid-week
trough sags south through Friday. At the same time a trough
crosses central Canada and a shortwave rounding its backside skims
by the northern rockies. The brunt of the lift, moisture and
instability associated with it remains east of the Idaho/Montana border.
However a bit brushes north Idaho late Thursday night into Friday, so
I cannot entirely rule of some showers around the mountains of
Pend Oreille County and north Idaho, with confidence higher closer
to the British Columbia and Montana borders. However any that may develop are
expected to be isolated or few and far-between. Otherwise the
forecast is dry.

The more notable forecast issue will be the winds. High pressure
takes hold over western Canada behind that shortwave, while low
pressure lingers over the Great Basin and central rockies. This
puts the inland northwest in a modest pressure gradient and the result
will be some breezy to windy conditions. As models depict it now
the north-to-south gradient is strongest late Thursday night into
midday Friday, giving the Okanogan Valley southward some of its
strongest winds. The gradient turns more northeast to southwest
Friday afternoon into evening. In theory this will allow speeds to
slacken some over the Okanogan Valley, while remaining modest
through the northern Idaho valleys out into the Columbia Basin.
There are some model differences with regard to the precise
speeds; however at this time loose agreement suggests they should
remain sub-advisory speeds. Overall speeds then abate through the
evening, but the gradient still remains somewhat tight across the
basin through Saturday. So expect marginally breezy condition for
the start of the weekend especially across over Washington south
and southwest of downtown spokane; but overall speeds are expected
to lower as compared to Friday. /J. Cote'

Saturday night through Wednesday...Sunday will continue to be
dry and warm with high pressure over the region. The weather
pattern becomes rather messy toward the beginning of next week with
the high pressure ridge becoming influenced by an offshore low
pressure trough off the West Coast diving south and a retrograding
closed low moving in from the east. This effectively pinches off
the ridge over Canada and opens the door for shower activity to
increase day to day starting Monday. Models are not in full
agreement on exact location and timing of the effects of chaotic
pattern but do agree mostly that the ridge will be replaced by
lower heights and better chances of showers, more significant
cloud cover and cooler temperatures by the middle of next week.
With no significant moisture fetch Monday only a few mountain
showers can be expected with high temperatures in the 70s still
about 5 degrees above normal for this time of year. Going into
Tuesday and Wednesday, the Pacific trough may become the main
feature as it enters the southwest U.S. Imparting a more
consolidated southerly flow into the region. With potentially a
better moisture tap and stronger flow aloft, this may open the
door for better chances of showers and isolated thunderstorms. Tc



&&

Aviation...
00z tafs: VFR conditions expected at all taf sites through 00z
Friday. An upper level trough of lower pressure will remain over
the region tonight. This will result in scattered showers across
the mountains and isolated showers into the western basin through
this evening. Some showers may become strong enough to develop
into thunderstorms over the Cascades and over the Okanogan
Highlands. The upper level low will drift south of the region
tonight with some wrap around moisture possible into klws and
kpuw after midnight. The threat of showers will end by mid-morning
Thursday as the low sinks south of the region. /Ek



&&

Fire weather...
low afternoon humidity and breezy wind conditions from the north are
in the forecast, especially Friday. A tightening pressure gradient
between low pressure exiting to the south and high pressure to the
north will lead to some breezy to locally windy conditions from
the north. Initially, through Thursday, these higher gradient
winds are expected to be localized to the Okanogan Valley. However
as a secondary system swings east of the region and high pressure
becomes more established across western/central Canada, this will
lead to increasing gradient winds over a broader region especially
going into Friday morning and afternoon. The Okanogan Valley is
expected to see north winds peaking between 5am and 2 PM, in the
north- to-south gradient. Thereafter models show the northeast-to-
southwest gradient through the afternoon, shifting the main focus
for higher winds to the north Idaho valley out through the
Columbia Basin. In the northerly flow drier Canadian air is
expected infiltrate the region, leading lower minimum relative humidity values
from day-to-day between Wednesday and Friday. This means minimum
relative humidity values potentially around the mid to upper teens or lower 20s.
This translates to potential concerns for the fire weather
community, with combination of low relative humidity and winds. However without
any other significant trigger and it still remaining early in the
fire weather year, we will just go with a heads-up headline and
advise keeping vigilant should any fire activity does occur. /J.
Cote'

&&

Preliminary point temps/pops...
Spokane 41 69 42 69 42 71 / 10 0 0 0 0 0
Coeur D'Alene 40 68 39 68 39 70 / 10 0 0 10 0 0
Pullman 40 67 38 69 38 69 / 20 10 0 0 0 0
Lewiston 44 73 44 74 44 74 / 30 10 10 0 10 10
Colville 41 74 42 73 40 75 / 20 0 0 10 0 0
Sandpoint 36 67 36 66 34 69 / 10 0 10 10 0 10
Kellogg 39 66 38 66 37 67 / 10 10 0 10 0 10
Moses Lake 43 76 46 77 44 77 / 20 0 0 0 0 0
Wenatchee 44 75 48 78 48 79 / 20 0 0 0 0 0
Omak 42 74 42 75 42 77 / 10 0 0 0 0 0

&&

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

$$

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