Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 220251 CCA
AFDBOI

Area Forecast Discussion...CORRECTED
National Weather Service Boise ID
851 PM MDT Mon Aug 21 2017

.DISCUSSION...Clear through Tuesday morning as a weak upper ridge
passes through the interior northwest. Later Tuesday an upper low
off southern California will circulate moisture northward into
Harney and Malheur Counties leading to a slight chance of
thunderstorms.  Wednesday looks more threatening for thunderstorms
as stronger southwest flow aloft pulls more moisture in and over a
larger part of our CWA.  Current forecast looks good.  No updates.

&&

.AVIATION...VFR. Increasing mid-high level clouds through the day
Tuesday along the Nevada border and north across SE Oregon for a
slight chance of afternoon/evening thunderstorms. Smoke layers
mainly east of KMYL. Surface winds: variable 10 kts or less. Winds
aloft near 10 KFT MSL: southwest to northwest 5-15 kts.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday...Dry conditions expected
through Tuesday morning, with light wind and warming temperatures.
An area of low pressure off the coast of California will push
moisture across Nevada and into southern OR/ID Tuesday. This will
bring unsettled conditions with the threat of showers and
thunderstorms by Tuesday afternoon. Meanwhile, the ridge axis will
slide to the east, allowing additional Pacific moisture and
instability to impact the area. This will leave slightly cooler, and
generally unsettled conditions across the area through Wednesday
afternoon with continued showers and thunderstorms. Models are in
fair agreement that the most shower coverage is anticipated to occur
Wednesday afternoon.

LONG TERM...Wednesday night through Monday...A cold front will cross
eastern Oregon and southwest Idaho Wednesday night as an upper level
trough from the Gulf of Alaska moves inland over British Columbia.
The front will trigger thunderstorms in the moist and unstable
monsoon air over our area. Instability will decrease following the
front, but surface heating on Thursday is expected to set off
isolated afternoon and evening thunderstorms. Only a slight chance
of measurable rain is expected at lower elevation locations. As the
trough moves east of the Rockies Thursday night, subsidence and
cooler drier air will hinder thunderstorm development across our
area, and Friday is expected to be mostly sunny. The upper level
ridge will rebuild over the western U.S. over the weekend, bringing
a warming trend and mostly clear skies Saturday through Monday.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Fire Weather Watch from Wednesday afternoon through late
     Wednesday night IDZ400>403-421-423-426.
OR...Fire Weather Watch from Wednesday afternoon through late
     Wednesday night ORZ636-637-646.

&&

$$

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DISCUSSION...LC
AVIATION.....AB
PREV SHORT TERM...KB
PREV LONG TERM....JT



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