Area Forecast Discussion
Issued by NWS Spokane, WA

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FXUS66 KOTX 220542
AFDOTX

Area Forecast Discussion
National Weather Service Spokane WA
1042 PM PDT Mon May 21 2018

.SYNOPSIS...
A risk for showers and few thunderstorms will linger Idaho and
southeast Washington through Tuesday evening. A significant
warming trend is forecast this week. A broader area of showers and
thunderstorms is possible Wednesday into Thursday. Friday should
be a dry day, before shower and thunderstorm chances increase at
least for the first half of the Memorial Day Weekend.


&&

.DISCUSSION...
Tonight through Tuesday: THe upper level trof will continue to
push further East as a ridge builds in along the coast. This will
continue to the dry, warming trend through the period. The early
evening showers over the IDaho Panhandle will continue to
dissipate as the region stabilizes and cools from the daytime
heating. Tuesday is expected to warmer than today with highs into
the 80s and ranging around 10 to 15 degrees warmer than normal.
Afternoon convection and isolated thunderstorms in Southern Idaho
Panhandle is still possible, but with less moisture and more
stable atmosphere, isolated rain showers are more probable. /JDC

Wednesday and Thursday: The upper-level low currently over the Great
Basin will begin to weaken and drift northward into the region. A
moist and muggy air mass accompanying the low along the subtle
cooling aloft will allow the threat for thunderstorms to expand
westward into the Columbia Basin, Cascades and eventually Northern
Mountains. Forcing will remain very weak so coverage will remain
isolated to scattered with activity firing in the mountains during
the early afternoon and potentially expanding into the Basin
during the hottest part of the afternoon as the CIN layer weakens.
The main threat with these storms will remain heavy downpours and
localized flooding given the high moisture content, low to
moderate CAPE, and little to no steering flow. Burn scars and
urban areas will need to be monitored closely and cannot rule out
small scale washouts in areas of hilly terrain.

The next shortwave coming across the Ern Pac will begin to move onto
the CA Coast Thursday. Heights will increase over the Inland NW
and the threat for showers and thunderstorms will migrate eastward
back into Idaho and the eastern third of WA with a decreasing
threat over the Cascades.

Friday through Monday: Models continue to waver regarding the details
for the upcoming holiday weekend but trends have been toward a
great risk for showers and storms early (Friday into Saturday) and
drier weather for Sunday into Monday. These changes can be
attributed to a massive shift with the track of a deep low
pressure system which was progged to lift through WA and now
passes south of Oregon. This leaves a weaker northern branch
shortwave over the NW ushering a weak but moist laden frontal
boundary through this neck of the woods. How fast this moves
through carries moderate uncertainty and thus the uncertainty when
to trim back pops throughout the weekend. As such, the forecast,
using a blend of models keeps a small mention of precipitation
through most days but will likely be fined tuned in the coming
days. Temperatures will also begin to cool much quicker in the
weekend with the hottest day now Friday and temperatures cooling
back toward seasonal readings Saturday into Sunday. /sb


&&

.AVIATION...
06Z TAFS: VFR conditions thru the night. Cumulus builds again
Tues aft 17Z with showers possible aft 21Z in the ID Panhandle
(impacting COE-LWS aft 23Z). Some thicker clouds are expected
around PUW and LWS thru the day.



&&

.HYDROLOGY...
Mountain snow melt issues continue to promote mainstem flooding
on a couple rivers. Temperatures will warm through the week to
well above normal for this time of year resulting in additional
snow melt and high levels on most area rivers/streams.

Flood warnings remain in effect for the following rivers and
lakes

Lake Pend Oreille AFFECTING Bonner County
Pend Oreille River below Albeni Falls AFFECTING Bonner and Pend
Oreille Counties
Okanogan River near Tonasket AFFECTING Okanogan County

An Areal Flood Warning continues for the following areas:
In Okanogan County for the lake shore of Lake Osoyoos...and the
possibility of runoff flooding on the Salmon Creek from Conconully
to Okanogan.
In Bonner County for the Warren Beach area of Priest Lake.


&&

.PRELIMINARY POINT TEMPS/POPS...
Spokane        54  82  59  82  59  81 /   0   0   0  20  30  20
Coeur d`Alene  53  81  55  81  56  80 /   0   0   0  20  30  20
Pullman        53  78  55  79  56  77 /   0  10  20  30  40  20
Lewiston       58  83  59  83  60  84 /  10  10  20  40  30  30
Colville       52  84  56  88  55  84 /   0   0  10  10  30  30
Sandpoint      50  81  52  82  53  78 /   0  10   0  10  40  30
Kellogg        51  78  52  78  53  76 /  20  10   0  30  60  40
Moses Lake     52  86  59  88  58  88 /   0   0   0  10  20   0
Wenatchee      58  85  60  86  60  86 /   0   0   0  20  20   0
Omak           56  84  58  86  57  86 /   0   0  10  10  20  10

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...None.
WA...None.

&&

$$


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