Weather Service Report


912 
FXUS65 KBOI 230255
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
855 PM MDT Wed Mar 22 2017

.DISCUSSION...Pacific system moving across the region this 
evening, bringing light shower activity to areas in the region. 
Instability is low and showers unorganized, with only one 
lightning strike noted this evening over southeast Oregon. Shower 
activity will continue to move east with the upper level trough, 
tapering off by midnight. Expecting patchy fog to develop
overnight in sheltered mountain valleys; will dissipate before 
noon. Mild and dry tomorrow ahead of the next system, set to move 
into the region early Friday morning. Forecast is on track. 
Updates made for patchy fog.

Several flood warnings are still in effect across the 
region, with streams running high. Please see the hydrologic 
section below for more details.


&&

.AVIATION...VFR with broken-overcast mid and high level clouds. 
Isolated showers and thunderstorms will end by 06Z. Patchy fog is 
possible in the northern mountain valleys after 09Z, including KMYL. 
Surface winds: Mainly Northwest 5-15 kts. Winds aloft at 10k ft MSL: 
Northwest 10-20 kts.


&&

.HYDROLOGY...Drier and slightly cooler weather overnight and 
Thursday will ease the situation on all rivers, but more rain is 
expected Friday and Friday night. For now, the Payette River at 
Emmett and the Weiser River at Weiser are expected to come below 
flood stage tonight. Fields and low-lying areas along the Silvies
will remain flooded, as will areas around the Snake River at
Weiser and the Boise River at Glenwood. See flood products for 
details.


&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Friday...Clear conditions noted 
across much of western Idaho, and portions of eastern Oregon. The 
next Pacific moisture push associated with a trough axis is moving
into central Oregon this afternoon, and will begin to bring 
shower activity across the area. Instability with these showers is
anticipated to be weaker than that experienced with showers on 
Tuesday, leaving a diminished thunderstorm threat across the area.
Additionally, models indicate instability moving off quickly this
evening, with most potential ending just around sunset. A few 
showers will linger across western Idaho into the overnight hours,
though activity will simultaneously weaken as it progresses 
eastward. Building northwest flow expected with the passage of the
trough axis, helping to dissipate shower activity.

Dry northwest flow associated with a transitory ridge will leave 
benign conditions across the area on Thursday. Temperatures will be 
slightly cooler tomorrow in response to the trough passage, but will 
still be seasonably mild. These conditions will provide some 
hydrologic relief across the area. The ridge axis will move through 
the area through Friday evening, with a return of a southwesterly 
flow. An Alaskan area of low pressure will spread moisture across 
the area Friday morning, with showers moving into eastern Oregon 
before sunrise Friday morning. Shower activity will spread through 
Friday, with widespread shower activity possible by Friday 
afternoon. Instability with this next push is negligible, with 
thunderstorms not anticipated. Regardless, moisture with this system 
may be plentiful to cause rivers across the area to rise.

LONG TERM...Friday night through Wednesday...The unsettled 
pattern will continue through Monday. The first of two Pacific 
weather systems will cross the Intermountain Region Friday night and 
Saturday. The second system is forecast for Sunday night and Monday. 
Models have been agreeing well on timing. A drying trend is 
indicated for Tuesday and Wednesday as an upper level ridge builds 
over the area. Temperatures will average a few degrees above normal, 
with overnight lows showing the the greatest departure due to cloud 
cover. 

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.

&&

$$

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DISCUSSION...AB
AVIATION.....BW
HYDROLOGY...AB
PREV SHORT TERM...KB 
PREV LONG TERM....JT

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Western Regional Climate Center, wrcc@dri.edu