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FXUS65 KPIH 202002

Area Forecast Discussion
National Weather Service Pocatello ID
202 PM MDT Wed Sep 20 2017

.DISCUSSION...Satellite imagery shows moist southwest flow aloft
digging toward the Great Basin early this afternoon as shortwave
rotates northeast through OR/WA. Plenty of sunshine in eastern 
half of the forecast area though low orographic stratus remains in
place over most of the higher terrain. Winds remain strong,
especially through middle of Snake Plain and wind advisory will 
remain in place as planned across the region. Precipitation 
continues to push into the central mountains, with area web cams 
showing some accumulation above valley floors, mainly east of 
State Route 75. Expect shortwave, cold front and precipitation to 
sag southeast across the remainder of the region this evening. 
Models have been very consistent in holding heaviest precip band 
along southeast highlands for quite some time as upper low sags 
toward Southwest Idaho. Band sets up late this evening, and 
NAM/GFS keep band in place into Thursday evening. Total QPF does 
appear to approach or exceed an inch in some places, but snow 
levels don't drop until during the day Thursday. Best snowfall 
appears to be above 6000 ft elevation, and mainly late Thursday 
into Thursday night. Have already messaged the threat of snowfall 
above valley floors but near passes, so will hold off on a formal 
headline for now. Wrap around moisture also becoming a factor at 
this time, as precip works east along the Divide toward the 
central mtns late Thursday through Friday. Meanwhile, colder air 
has fully filtered into the Snake Plain, and temperatures by 
Friday morning are expected to drop to near or below freezing. 
Will hold off one more day on a freeze headline. 

Upper low opens and begins to shift east late Friday into
Saturday. Any precipitation remaining associated with the trough
likely to remain either along the WY border, or along the Divide
where wrap around precipitation is slow to break. Temperatures
remain cool, but trend will be drying from west to east late
Friday into Saturday. Weak upper ridge in place in general
northwest flow Sunday into Tuesday, with next shortwave dropping
out of the PacNW into the region during the day Tuesday. Unclear
at this point how much precipitation may be associated with this
feature, but models continue to keep the region dry. Should see
moderation of temperatures late in the weekend into mid week next
week as ridge continues to build over western coastal states. DMH


.AVIATION...Another strong system will impact the area the next 
couple of days starting this afternoon/early evening. Expect rain 
showers to start first at KSUN later this afternoon and then expand 
to the other terminals with time. Expect MVFR conditions with rain 
showers. KPIH, KIDA, and KDIJ may see IFR conditions with heavier 
showers later this evening into tomorrow morning. KDIJ may see a 
rain/snow mix tomorrow morning. Also, expect moderate to strong West 
Southwest winds for TAF sites this afternoon into early evening, 
particularly for KPIH and KIDA where gust of 35 to 45 mph are 
likely. Wyatt


.FIRE WEATHER...Cool, wet, and windy conditions will continue 
through the remainder of the week with a strong, slowing-moving 
upper level low system moving into the area.  Expect moderate to 
strong wind with widespread valley rain and mountain snow as well as 
well below normal temperatures. High pressure ridging builds in over 
the weekend bringing drier conditions and gradual warming 
temperatures, approaching near normal by the middle of the week. 



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