Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 190822

Area Forecast Discussion
National Weather Service Pocatello ID
222 AM MDT Tue Sep 19 2017

.DISCUSSION...Today through Wednesday...A fairly active weather
pattern is on tap for the week and already noticeable outside. A
surface cold front has passed through Idaho yesterday, making for
a colder temperature forecast, only climbing into the low to mid
50s across the Snake Plain, or low 40s in the mountains for today.
Bands of precipitation are evident on radar, while snow levels are
forecast to drop toward 6500 ft or so this morning and will stay
there, making snow probable in portions of the Central Mountains
today. Anywhere from 1 to 3 inches are currently forecast with a
possible 4 inches above 8000 ft. This will not be the only area
where snow will be possible. Portions of the Upper Snake
Highlands, Caribou Highlands and Eastern Highlands may also
experience a bit of snowfall as well. Snow levels in these areas,
however, are still dropping this morning and will settle around
the 7000 to 7500 ft range. Another concern today will be windy
conditions from the enhanced pressure gradient. Expect wind speeds
in excess of 25 mph through early evening hours across the Snake
Plain and for portions of the Eastern and Caribou Highlands. A
Lake Wind Advisory will go into effect for the American Falls
Reservoir at noon today as a result.

There is somewhat of a break in between weather systems later this
evening into the overnight hours; however a small portion of the
western Salmon-Challis NF won`t feel much of a break at all (if
any). The next wave of rain and snow appears Wednesday morning
with initially similar snow levels to today, then climbing fairly
substantially around 8000 ft. Wednesday will also be another
windy day, with persistent 20 to 25 mph winds across SE Idaho.


.LONG TERM...Thursday through next Wednesday...For Thursday and
Friday, our focus shifts to the Southeast corner/Eastern portions
of Idaho, after the passage of another cold front sweeps through
Idaho. Precip chances will be especially enhanced in this area and
now the snow levels will be dropping to their lowest on Friday
morning, around 5500 to 6000 ft levels. We could therefore see
snow in places there has not been any yet, though amounts will be
very light with little/no impacts. There will remain a chance for
rain/snow across the remainder of SE Idaho, but the chances are
reduced during this time.

Over the weekend, the positioning and progression of an upper low
will determine our forecast. For now, a continued chance for
showers remains in the forecast, particularly on Saturday. Cool
temperatures remain with highs in the 50s on Saturday and upper
50s/low 60s on Sunday.

Temperatures begin to rebound at the start of next week as the
upper low ejects to the east and precip clears out of the area.


.AVIATION...An upper level trough sweeps through the region today
with accompanying low VFR/MVFR CIGS and precipitation. Snow levels
fall to around 6500 ft MSL by this afternoon which may aid in lower
CIGS at KDIJ although this notion is not supported in model time
sections. In fact, the time sections generally show the lowest CIGS
early this morning at all terminals with improving low VFR CIGS
through the day and evening. KSUN may return to MVFR CIGS by
Wednesday morning as moisture from the next upstream system begins
to sneak into the CNTRL mountains. KDIJ may see partial clearing
later tonight which might promote the development of lower IFR CIGS
in fog and/or stratus. Huston


.FIRE WEATHER...Cool, wet, and windy conditions will prevail today
as a low pressure trough gradually migrates east along the Canadian
border. We may see a brief respite tonight as todays system shifts
east into south-central Canada and the next upstream Pacific storm
system sets up off the NW coast. This next system will dig a little
farther south as it slowly shifts through the region Wednesday
through Saturday night bringing widespread valley rain and mountain
snow to southern Idaho. The models continue to wiggle around on the
placement of the upper ridge rebounding along the coast Sunday
through Tuesday and for now it looks as if they are settling on the
idea of keeping the ridge along the coast which leaves southeast
Idaho prone to a clipper-like system topping the ridge and digging
sharply SSE along the continental divide. Yesterdays model runs were
showing such a system impacting the Montana divide region on Tuesday
and we are seeing something very similar this morning but not quite
as strong. Temps fall well below normal with the passing storms and
never really recover even with the ridge along the coast Monday and
Tuesday. Huston


Lake Wind Advisory from noon today to 8 PM MDT this evening for


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