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Area Forecast Discussion (AFD)

Issued by Boise, ID (BOI)

FXUS65 KBOI 230237

Area Forecast Discussion
National Weather Service Boise ID
837 PM MDT Mon Oct 22 2018

.DISCUSSION...Skies were mostly cloudy over SW Idaho and partly
cloudy over eastern OR this evening. Isolated showers continued to
move northwest across parts of SW Idaho, mostly in the mountains
and foothills, but there is an area of showers from near Mountain
Home AFB stretching northwest into southern Ada County as of 835
pm MDT. This area is decreasing in size and intensity, but may
still put down one or two hundredths of an inch of rainfall.
There will be additional showers and isolated thunderstorms Tue,
mainly in the higher terrain of southwest Idaho. All this is
handled well by the current forecast, and no changes are planned
at this time.


.AVIATION...VFR. Showers will linger in southern portions of SW 
Idaho through the night then increase for the central Idaho 
mountains Tuesday morning. Surface winds will be light and 
variable. Winds aloft to 10k feet MSL, southwest 10-15kts.


SHORT TERM...Tonight through Wednesday...Showers and a few 
lightning bolts noted across the forecast area today as unsettled 
conditions remain over the area. Opted to keep thunder across 
southern Idaho into the evening hours, with most locations 
switching to showers this evening. Shower coverage will continue 
into the overnight hours as the trough axis lifts north through 
the forecast area. Drier conditions noted across the area with the
departure of the axis on late Tuesday. Expect gusty wind to 
develop over Oregon Tuesday afternoon and evening as a dry cold 
front approaches the area. The front is not anticipated to hold 
together well into Wednesday, with dry conditions expected. 
Temperatures will cool over the next couple of days under the 
influence of these systems.

LONG TERM...Wednesday night through Monday...A split flow continues 
over the region Thursday morning which further weakens the cold 
front. Therefore little if any precipitation is expected. An upper 
ridge briefly builds to the northeast from southern California into 
Idaho Thursday afternoon bringing continued near or slightly above 
normal temperatures. The next cold front pushes into the Pacific 
Northwest Thursday night. Models have this system very wet with PWAT 
values over an inch. As the front moves into eastern Oregon and the 
Idaho Panhandle values are around 0.75, which makes it about the 
75th percentile. So POPS should likely be on the increase as the 
event unfolds. The front is expected to remain nearly stationary 
over the Salmon River region, and therefore the best threat of 
precipitation. The ridge off the West Coast begins to amplify 
northward for the weekend, which pushes the storm track towards 
northern Idaho. Potential big changes going into next week as the 
ridge weakens. This drives a strong storm system into the Pacific 
Northwest bringing much cooler temperatures and lowering snow levels.