Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 280241

Area Forecast Discussion
National Weather Service Boise ID
841 PM MDT Thu Jul 27 2017

.DISCUSSION...Air mass is drying and stabilizing from the west
this evening as the monsoon moisture and the upper trough from
northern California exit into Montana and Wyoming.  Drier zonal
flow aloft will bring mostly clear skies and normal temperatures
Friday, but high pressure aloft will intensify in the Great Basin
Saturday and bring hotter weather.  Latest models continue to
intensify the Great Basin high through next week and move the
high center to northern Nevada.  If that happens temperatures
will become extremely hot late next week.  For now, our forecast
keeps our area only a few degrees above normal.  Monsoon moisture
will stay generally south of our CWA through the week but enough
moisture will be present for isolated thunderstorms each day.
Current forecast already has this.  No updates.


.AVIATION...VFR. Lingering showers over the higher terrain this
evening will dissipate before midnight. Isolated showers and
thunderstorms will redevelop over the higher terrain after 28/18Z.
Surface winds: variable 10 kts or less, except up to 30 kts near
thunderstorms. Winds aloft near 10 KFT MSL: south to southwest 5-15


SHORT TERM...Tonight through Saturday...The main instigator of
showers and thunderstorms, an upper-level trough, is currently
tracking eastward across central Idaho. Moisture, heating, and
terrain influences are combining with the trough to generate
convection over eastern Oregon and central, southern, and eastern
Idaho. The best forcing is moving just east of our area, with
convection over SW Idaho and SE Oregon being driven mainly by
terrain. This will be the case into the evening with storms
remaining in/around higher terrain. The best chance for lower valley
impacts will be in the Magic Valley later on this evening and the
Baker Valley through early evening. Storms may produce brief periods
of moderate to heavy rainfall, along with gusty winds.

Overnight through Saturday the trough will move east of the area
with high pressure building northward into the northern Rockies
and Pacific Northwest. Enough moisture will linger to allow for
higher terrain showers and thunderstorms each afternoon and
evening, but coverage will be isolated at best. Temperatures will
remain above normal, creeping up toward the century mark for lower
valleys by Saturday.

LONG TERM...Saturday night through Thursday...The very warm upper
level ridge over the western states will gain amplitude through the
long term, resulting in even hotter daytime temperatures, but record
highs are not expected. Models are in good agreement on the overall
pattern, but there are the usual differences in coverage of
convective precipitation. Monsoon moisture circulating within the
ridge will fuel isolated afternoon and evening thunderstorms most
days, triggered by surface heating and orographic lift.





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