Area Forecast Discussion
Issued by NWS Boise, ID

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FXUS65 KBOI 251528

Area Forecast Discussion
National Weather Service Boise ID
928 AM MDT Tue Jul 25 2017

.DISCUSSION...Today through Wednesday...A shortwave exiting to the
northeast continues to support scattered showers, mainly over the
Central Idaho Mountains,Magic Valley, and lower Treasure Valley. A
few buildups are visible on satellite, but no lightning yet.
Extensive cloud cover over our Idaho zones should retard
thunderstorm development until late afternoon today. Also, less
coverage is expected, so we updated the West Central Idaho Mountains
and Boise Mountains from scattered to isolated this afternoon and
tonight. Tomorrow the weak upper level trough currently centered
over the Northern California coast will lend better dynamic support
for thunderstorms, mainly during afternoon and evening, as it edges
inland. Temperatures will be a few degrees lower today, and a couple
more degrees lower on Wednesday, but still above normal.


.AVIATION...Mostly VFR. Showers currently pressing NE through SW
Idaho. Showers and thunderstorms will increase in coverage after 18z
and remain mostly in SE Oregon south of KBNO and throughout the
Owyhee Mountains. A few stray thunderstorms may linger into the
valley. Surface winds, variable 5-10 kts with gusts in and around
thunderstorms up to 40 kts. Winds aloft to 10k feet MSL, variable 5-
15 kts.


SHORT TERM...Today through Wednesday...SE Oregon and SW Idaho
reside on the northern fringes of monsoon moisture which extends
into the Great Basin. The moisture is being directed into our
area from an upper trough near the northern California coast. The
highest precipitable water values of around an inch exist across
the southern parts of the forecast area. This also where the
models are indicating the best instability and therefore the
greatest potential for thunderstorms with heavy rain. A Flash
Flood Watch is in effect for these areas this afternoon and
evening. The upper trough is projected to track very slowly to the
northeast through northern California tonight and Wednesday. The
moist unstable southwest flow will continue to support a chance of
showers and thunderstorms on Wednesday, especially near the
Nevada border and in the Boise Mountains. Temperatures will be
near normal.

LONG TERM...Wednesday night through Tuesday...Upper level trough
will track over the CWA Wednesday night into Thursday. This is
expected to continue showers and thunderstorms during the
overnight hours and through Thursday afternoon. With precipitable
water values near an inch, heavy rain will be a threat, despite
storm motions of 20 kts or more. By Friday, the upper ridge to the
southeast will begin to build in once again. The GFS and ECMWF
differ on the extent of monsoon moisture making its way into the
area, but temperatures will nonetheless be above normal through
the period.


ID...Flash Flood Watch noon today until midnight tonight south
portions of Harney and Malheur Counties OR, Owyhee Mountains,
Southwest Highlands, Southern Twin Falls County ID.




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