Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 140753

Area Forecast Discussion
National Weather Service Pocatello ID
153 AM MDT Thu Sep 14 2017

.DISCUSSION...Upper low in southern California continues to weaken
and lift as a sharp upper trough approaches the PAC NW. The upper
low is shooting some short-wave energy into northeast NV and
northern UT, with some activity crossing into our southern zones.
The surface cold front associated with the PAC NW trough will pass
into our western zones around 6 to 9 pm this evening. Models are
pushing in some much cooler temps behind the front, with snow
levels dropping below 10,000 ft tonight across much of the area.
Snow levels continue dropping through Saturday as low as 6000 ft
over the Central Mountains to 8000 ft in our southern zones. This
means some areas will see their first snow of the season. Current
forecast is around 3 to 5 inches above 8000 ft, with up to 1 inch
from 6000 to 8000 ft in the Central Mountains across to the Island
Park area. Cool temperatures over the weekend may bring frost
headlines for the Snake River Plain into consideration.

The upper trough should lift out of the area Saturday afternoon,
leaving us with some drier weather while warmer temperatures
briefly fill into southeast Idaho before the next weather system
nudges into the Central Mountains Monday afternoon, bringing much
below normal temperatures through the middle of next week.


.AVIATION...Scattered showers were advancing across SE Idaho early
this morning ahead of a developing Pacific trough. Numerical models
show the trough spreading onshore this afternoon and into WRN Idaho
Friday morning with increasing shower activity across the region.
Model cross sections favor lowering VFR CIGS late this afternoon and
tonight with perhaps some TEMPO VIS and CIG restrictions in heavier
shower activity. KDIJ is the only terminal at this point where the
models were showing lower CIGS after midnight tonight. Gusty daytime
winds will be a factor at most terminals today and again Friday.

.FIRE WEATHER...A low pressure trough will sweep into the region
this evening with an attending surface cold front working from west
to east across SE Idaho through the evening and overnight hours.
Gusty winds are expected today with elevated daytime humidity
precluding any red flag issuances for wind. We will see increasing
shower activity advancing across the region late this afternoon with
embedded thunderstorms. The models do show some fairly decent
instability out ahead of the cold front today and for now we are
only advertising "Isolated Thunderstorm" activity although the
reality is we may see scattered thunderstorms especially near the
front where forcing will be greatest. Stability increases rapidly
behind the front Friday with ongoing showers and lowering snow
levels across the CNTRL (6500-8000 MSL) and ERN mountains (8500
MSL). Strong gusty winds are also expected with elevated humidity
levels. The Snake Plain and SRN Mountains will likely remain dry as
the low tracks east through the CNTRL mountains and WRN Montana. By
Saturday, dry and stable conditions are anticipated as the storm
system pushes rapidly east toward the Great Lakes. Dry and
seasonably mild temperatures are expected Sunday and Monday as the
next Pacific storm system loads up and moves onshore sweeping into
the region Monday afternoon/night for another round of showers
followed by much colder temperatures. Huston



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