Area Forecast Discussion
Issued by NWS Pocatello, ID

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
000
FXUS65 KPIH 220906
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
306 AM MDT Fri Sep 22 2017

.DISCUSSION...Today through Saturday night. Early morning
satellite imagery reveals an impressive and still strengthening
area of low pressure near Boise. Models struggling with the
evolution of this feature and thus made many manual edits to the
forecast through this afternoon based on Satellite and Radar
trends. Good ol` fashioned forecasting. A gradually strengthening
band of precipitation currently stretches from the Sawtooths south
and east through the Eastern Magic Valley/Southern Snake Plain
southward to the Utah border. This band of precipitation is
forecast to gradually pivot north and east across the region
through this afternoon while becoming more convective/showery in
nature this afternoon. Have added isolated thunder for high
elevation areas, particularly towards the Montana border, with
some support from brand new high-resolution guidance. This may
mean local bursts of heavier Snow this afternoon near the Divide.
Speaking of Snow, saw little evidence to drop the Winter Weather
Advisory, so have allowed that to continue through 6 PM this
Evening due to anticipated impacts to travel at Pass level and
hazardous conditions for outdoor recreation. Will see some snow
mix in around 6,000 feet but the majority of the accumulating Snow
should be relegated to elevations above 6,500 feet or so.
Anticipate anywhere from 1 to 6 inches of additional snow
accumulation through Saturday morning for these areas. The wide
range in forecast accumulations is due to the wide variability of
amounts based on location and elevation. Highest amounts should
fall above 8,000 feet or where heavier convective bursts develop
this afternoon.

Forecast low temperatures this weekend, Saturday morning in
particular, hint at the potential for widespread freezing
temperatures across all of SE Idaho. Have added mention of patchy
frost to the forecast as a result. Held off on issuance of any
Frost or Freeze Advisories for the Snake Plain at this time due to
the uncertainty in how much clearing in the clouds may occur, for
how long, and where. Right now, the best potential for the
greatest clearing is across the Eastern Magic Valley. Those areas
who experience clearing skies for the longest time will see the
coldest temperatures. Models exhibit a high degree of spread
(resulting in lower confidence) in where a harmful Frost or
Freeze may occur. Nonetheless, take steps to protect any
sensitive vegetation for Friday and Saturday nights.

Sunday through next Friday. The area of low pressure is expected
to migrate to Northern Utah by Sunday morning and move northeast
to SW Wyoming Sunday night and Monday. Have thus significantly
increased Precipitation amounts and Potential across far SE Idaho
for late Saturday night through Monday, heaviest later Sunday into
early Monday. This will have to be watched as models tend to be
too conservative in their snow levels in these situations this
time of year. Heavy snow amounts are possible across the higher
elevations of the Idaho portion of the Wasatch/Caribou Highlands
near Bear Lake. Drier conditions overspread all of SE Idaho by
Monday night. A weak wave will provide an opportunity for showers
along the MT border/Island Park region Tuesday. A ridge of high
pressure is then forecast to build into the region by late week
resulting in dry conditions and a rebound in temperatures back to
climatological averages, with 70s returning to the Snake Plain by
Thursday. AD/VP

&&

.AVIATION...A strong upper-level low pressure system will continue
to impact flight conditions across the region today. Scattered rain
showers and isolated afternoon thunderstorms are possible at KPIH
and KIDA producing MVFR to IFR conditions due to lower ceilings..
This morning brief periods of LIFR possible.  To the west expect
MVFR due to lower ceilings all day.  Isolated showers are possible
throughout the day. Those flying over any mountainous terrain today
should use extreme caution for rapidly changing ceiling heights.

VP


&&

.FIRE WEATHER...Cool and wet conditions will continue today and
tonight with a drying trend starting over the weekend. A strong
upper-level low pressure system continues to spin in the
intermountain region. Expect light valley rain and mountain snow
showers in the Central/Pahsimeroi mountains with more widespread
moderate valley rain and mountain showers elsewhere. Expect a
drying trend this weekend as the low weakens and begins to shift
east, leaving lingering rain/snow shower activity over the Central
Mountains and Eastern Highlands. By Sunday these showers will be
mainly over the Eastern Highlands. Temperatures will gradually
warm up this weekend into mid next becoming near normal as high
pressure strengthens.

VP

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM MDT this evening for IDZ018-
019-031-032.

&&

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.