Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 270841

Area Forecast Discussion
National Weather Service Boise ID
241 AM MDT Tue Jul 27 2021

.SHORT TERM...Today through Thursday night...The upper high
center will shift east to Wyoming and Colorado today and into
the high Plains Wednesday. As a result, monsoon moisture will
play a more prominent role and smoke a less prominent role in
our CWA the next several days. Flow aloft will change from
smoky southwest today to less smoky southerly Wednesday, and
the southerly flow will tap more directly into the monsoon
moisture source, especially in Idaho. For this afternoon and
evening, however, skies will continue smoky with a chance of
thunderstorms in western Harney and Baker Counties in Oregon,
and also near the NV/ID border. Models develop gusty outflow
winds from the Oregon storms and into the Treasure Valley this
evening. On Wednesday and Thursday few if any thunderstorms will
still occur on the Oregon side, but a better chance will exist
in south-central Idaho and the central Idaho Mountains. Humidity
will also increase on the Idaho side and clouds will limit high
temperatures to the 90s in the valleys and 80s in the mountains.
Meanwhile, with few if any fires in northern Nevada, southerly
flow aloft should improve air quality Wednesday.

.LONG TERM...Friday through Tuesday...The upper level ridge over
the central U.S. will drive an increase in southerly flow and
moisture through the weekend. Precipitable water values will
approach the high end of the climatological distribution, which
would support heavy rainfall in showers and thunderstorms on
Saturday and Sunday. Many ensemble runs also show an easterly wave
from the Gulf of Mexico merging with an upper level low from the
Pacific, providing a bit of focus for the convection late Saturday
and Sunday. Still a ways off, but certainly have the potential
for significant precip over parts of the forecast area on Saturday
and Sunday. Flow will become a bit more southwesterly and drier
late Monday and Tuesday, but still enough moisture remaining for
some afternoon and evening showers and thunderstorms over the
mountains. Temperatures will drop below normal over the weekend
with all the clouds and showers.


.AVIATION...VFR with areas of MVFR and terrain obscuration due to
wildfire smoke. Significant visibility restrictions aloft due to
smoke layers. Scattered showers and thunderstorms developing this
afternoon and evening, mainly south of KTWF and west of KBNO.
Surface winds: variable 5-10 kts, except gusts 25-35 kts possible
near thunderstorms. Winds aloft at 10k feet MSL: S to SW 10-20 kts.
Hot temperatures will increase density altitude.





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