Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 252114

Area Forecast Discussion
National Weather Service Spokane WA
214 PM PDT MON MAY 25 2015

A slow moving low pressure system will bring scattered afternoon
and evening thunderstorms to the Inland Northwest through
Wednesday. Locally heavy downpours, frequent lightning, and small
hail will be possible the next several days. Low pressure will
gradually depart by Thursday, bringing a decrease in precipitation
chances, but chances may increase again by early next week across
the region. Temperatures warm back above normal from Wednesday
into the end of the week, with highs pushing into 80s Thursday


Tonight and Tuesday: The Inland Nortwest will be under the gun for
unsettled late spring weather as an upper level low slowly
meanders across the region. Anticipate showers and thunderstorms
especially during the afternoon and evening hours. Temperatures
will remain mild but not as warm as previously experienced, and it
will be muggy with light winds. Currently the mid level frontal
band will slowly depart from Idaho panhandle into Montana by this
evening. Then the track of the low center will help dictate the
path and coverage of convection. Currently the low center is
residing just north of the Cascades in BC as a shortwave rotates
southward and is helping ignite convection across the Okanogan
Highlands and upper Columbai Basin. This activity will gradually
spread eastward. The main concerns with the thunderstorms will be
frequent lightning, heavy downpours, small hail and gusty winds.
This activity will sweep eastward toward the northeast Washington,
north Idaho and Spokane/Coeur d`Alene area early this evening and
overnight as the low center takes this similar path. The low will
gradually fill and remain parked over eastern Washington through
much of the day on Tuesday. With pwats remaining near three
quarters of an inch and circulation spinning over the region,
anticiapte another round of thunderstorms rotating from east to
west across the northern mountains. This will bring a renewed
concern with heavy downpours as thunderstorms increase during the
afternoon and evening hours on Tuesday. /rfox.

Tuesday night through Monday: Low pressure exits and temperatures
begin to warm, but the threat of showers and thunderstorms
continues. First between Tuesday night and Wednesday night low
pressure migrates from the southeast WA/OR border to the
ID/southwest MT border. Without any real influx of drier air,
PWATs remain around 150% of normal (or 0.50 to 0.75 inches). In
addition there are pockets of elevated instability (CAPE and high
level total totals) during the night and early morning and
expansion of SBCAPE in the afternoon. The north-northeast flow on
the backside of the low and smaller scale impulses in that flow
will work with the moisture and instability to bring the threat of
showers and thunderstorms. These will be most numerous in the
afternoon hours. However there are two limiting factors. First the
large-scale pattern shows broader subsidence in the DIV-Q fields,
which may limit coverage away from the higher terrain.
Additionally, models show there is modest CIN across the deeper
Columbia Basin to overcome during the afternoon.

With the lack of significant sheer most storms are not expected
to be well-organized and without a strong steering flow it the
850-700mb layer, storms are expected to be relatively slow-moving.
So the main concern will remain locally heavy downpours and if any
cross a burn scar we will have to monitor for possible flash
flooding or debris flows. Storms may also produce some small hail
and gusty winds, and perhaps abundant lightning.

From Thursday to Monday the region transitions from a northerly
flow to west-southwest flow. Another low drops south across BC and
a deeper trough deepens off the Pacific coast. Impulses ride into
the region in this evolving flow. The precise timing and track of
these features is apt to change over the next several days. With
instability expanding each afternoon there will be some threat of
showers and thunderstorm each day, especially around the mountains
through Friday and potentially expanding to a broader area going
into early next week as models try to bring more a substantial
trough in. This latter set-up will be monitored for possible
organized/stronger thunderstorms for early next week, but it is
too far out to have high confidence yet. /J. Cote`


18Z TAFS: A mid level cold front will exit north idaho by midday,
allowing the band of showers with embedded thunderstorms to push
east into Montana. The moist boundary layer and dewpoints in the
mid 40s to lower 50s will aid in the redevelopment of convection
behind the front. The best areas for convection will be across the
northern mountains, but as the storms drift south-southeast,
expect some activity reaching the TAF sites this afternoon and
early evening. Isolated to scattered showers will persist over
much of the region through 18Z Tuesday as the low center remains
over the region. /rfox


Spokane        51  70  52  75  54  81 /  60  60  30  30  20  20
Coeur d`Alene  48  70  48  75  51  80 /  60  60  30  40  20  20
Pullman        45  68  48  71  49  78 /  20  40  30  40  20  20
Lewiston       53  74  55  76  56  84 /  20  50  40  40  20  10
Colville       49  73  49  80  51  84 /  60  70  40  30  20  30
Sandpoint      47  68  48  75  50  78 /  60  70  40  50  30  40
Kellogg        46  67  47  71  49  78 /  60  80  50  60  30  40
Moses Lake     52  79  52  82  55  88 /  30  40  20  20  10  10
Wenatchee      57  77  58  82  60  87 /  20  40  30  20  20  10
Omak           49  76  51  83  52  86 /  40  50  40  40  20  20



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