Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 190220

Area Forecast Discussion
National Weather Service Boise ID
820 PM MDT Fri Aug 18 2017

.DISCUSSION...Wildfires in central Oregon are sending large
quantities of smoke eastward toward our CWA.  Satellite trends
and model forecast westerly winds at mid-levels indicate this
smoke will spread over most, if not all, of our CWA overnight
and Saturday.  Forecasts have been updated accordingly.  Too
early to tell how long after Saturday it will continue.  No
other updates at this time.


.AVIATION...VFR. Mostly clear with smoke layers. Visibilities could
be reduced to low VFR in smoke on Saturday. Light surface winds,
becoming NW 5-15kt during the afternoon. Winds aloft at 10kft MSL:
West-Northwest 10-20kt.


SHORT TERM...Tonight through Sunday...Dry westerly flow will
continue through Sunday morning, which will keep skies mostly
clear and conditions dry. Smoke from regional wildfires are not
currently creating any major impacts but this will be monitored,
especially if there are new fire starts. By Sunday mid day, models
continue to show a closed low forming near the California coast.
The main change with this feature is that models are now showing
it a but further south, near Los Angeles, rather than near San
Francisco in previous runs. The southerly push of moisture and
cloud cover on Sunday looks to barely reach the southern edge of
the CWA. This will be aided by a weak trough passing to the north
as well. So, as the area is in between these 2 features, it looks
like the CWA will remain mostly dry, with some passing high level
cloud cover through Sunday night. Temperatures are expected to
remain within a few degrees of normal.

LONG TERM...Sunday night through Friday...Overall the extended
period of the forecast appears to be on the active side. Thankfully
for fans of the eclipse the first part of the week looks very nice
across the area. A weak trough of low pressure with very limited
moisture is expected to pass through eastern Oregon and southwestern
Idaho overnight Sunday into early Monday. Models are in good
agreement that dry air will move in within the northwest flow behind
this system early Monday into the evening. This will allow for
mostly clear skies across the area, with maybe a few afternoon
clouds over the mountains late Monday. From there moisture will
begin to creep northward toward OR/ID in response to an upper low
near central California. By mid week this low is expected to
interact with an approaching Pacific trough to generate
showers/thunderstorms Wednesday through Friday. Storms will favor
the afternoon hours, but with the dynamics associated with the
trough, overnight convection may be a good possibility. The timing
and strength of the Pacific trough remains uncertain, but the
forecast looks unsettled Wednesday into late week nonetheless.





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