Area Forecast Discussion
Issued by NWS Boise, ID

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276
FXUS65 KBOI 291611
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1011 AM MDT FRI JUL 29 2016

.DISCUSSION...Another hot and dry day for southeast Oregon and
southwest Idaho as subtropical high pressure centered over the
southwestern states remains in control. Dry northwest flow is over
the forecast area per the morning upper air sounding. Lower
levels of the atmosphere are a little warmer than 24 hours ago which
will result in afternoon temperatures being a degree or two higher
today.

Latest high resolution model runs continue to show some monsoon
moisture moving into the area late this afternoon and evening with
a threat of isolated thunderstorms near the Nevada border, mainly
on the Oregon side. Thunderstorm threat will expand on Saturday
and we have issued a fire weather watch for lightning Saturday
afternoon and evening for fire weather zones 423, 426 and 637.
High based thunderstorms are expected so strong gusty outflow
winds will be a threat and little rainfall is expected.

&&

.AVIATION...VFR. Smoke layers and MVFR visibilities this morning
in the Treasure Valley KEUL through KMUO through about 18Z,
filtering back in overnight. Also near Lowman ID and surrounding
valleys this evening with obscuration. Isolated thunderstorms near
the OR-NV border this afternoon and evening. Surface winds variable
10 kts or less becoming NW 10-15 kts 18Z-03Z, diminishing
afterwards. Winds aloft through 10k ft msl NW 10-20 kts.

Weekend outlook...Mainly VFR. Areas of smoke will continue in the
Boise mountains, filtering into the Snake River Plain each night.
Expect isolated thunderstorms Saturday afternoon and evening over
the Boise Mountains. Scattered thunderstorms in the higher terrain
south of the Snake River Plain, and southeast Oregon south of a
Burns-Jordan Valley line. Sunday will be dry and breezy.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Saturday...Northwest flow aloft today
keeps most of the forecast area dry, with temperatures about 10
degrees above normal. Monsoon moisture may just be barely able to
squeeze a thunderstorm north of the Nevada border into southeast
Oregon. However on Saturday, developing trough in British
Columbia turns the flow direction just slightly more southerly,
and allows this moisture to creep north. At the same time, the
approaching trough is increasing from the westerly component of
the flow, so moisture wont be in the forecast area very long.
With temperatures so warm, instability should be plenty to
support isolated thunderstorms, and perhaps approaching scattered
coverage on Saturday afternoon and evening. We pulled the
thunderstorm threat a little bit further south, thinking that the
westerly flow will probably win out and keep thunderstorms out of
the northern half of the forecast area.

LONG TERM...Saturday night through Thursday...Isolated
thunderstorms near the Nevada border in Oregon and over the higher
terrain south of the Snake River Valley in Idaho will end Saturday
night as increasing westerly flow aloft transports monsoon moisture
out of our area. An upper level trough moving east across southwest
Canada will bring cooler air to our area on Tuesday, lowering high
temperatures by around 10 degrees. Precipitation with this system is
expected to stay mainly north of the Canadian border. Dry westerly
flow aloft will follow, with near-normal temperatures.
&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Fire Weather Watch from Saturday afternoon through Saturday
     evening IDZ423-426.
OR...Fire Weather Watch from Saturday afternoon through Saturday
     evening ORZ637.

&&

$$

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DISCUSSION...TL
AVIATION.....AB
PREV SHORT TERM...TB
PREV LONG TERM....JT



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