Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 212112

Area Forecast Discussion
National Weather Service Pocatello ID
212 PM MST Tue Feb 21 2017

.SHORT TERM...Today through Thursday...Rain, snow showers and isolated
thunderstorms encompass Southeast Idaho this afternoon. At 2 p.m.
MST, a line of showers extended from Teton County to Cassia
Country with embedded thunderstorms across southern Power County.
These lines are progressing to the northeast. Through the evening
hours, expect additional rain, snow and thunderstorms to persist
across the Interstate corridor, and fill in through the Southeast
corner of Bear Lake Country. Heavy snow is expected in the Idaho
portion of the Wasatch Mountains this evening and overnight,
therefore a Winter Weather Advisory has been issued for this area
until 6 am MST tomorrow morning. Three to six inches of new snow
is forecast. Rain and snow is expected in area like Montpelier,
Soda Springs and Preston with thunderstorms possible. Meanwhile,
thunderstorms are possible this evening for the southern Snake
Plain areas, with small hail and gusty winds the primary threat.
Wind gusts may exceed 60 mph at times. The threat for severe
weather will diminish greatly after 8 p.m. MST. The other concern
for this afternoon and evening is regarding winds and wind gusts
that are not associated with thunderstorms. Wind Advisories will
continue for the lower Snake and Southern Highlands tonight, along
with a High Wind Warning, due to forecast strong gusty winds from
the southwest and west.

The forecast for Wednesday brings winds out of the west to
northwest around 10 mph and quite a temperature drop. High
temperatures in the mid to upper 30s are forecast in the Snake
River Plain while below freezing temperatures are expected at
higher elevations. More snow showers are expected Wednesday
afternoon and evening for the Southern Highlands in particular,
with a chance for snow showers for the rest of SE Idaho.
Confidence is very low for the rest of SE Idaho to see much
accumulation tomorrow. Thursday is looking more favorable for snow
across the region and valley locations even look to pick up some
accumulation. At this time, over an inch is forecast for most
locations except for the Southern Highlands and the Eastern Magic
Valley. Three inches or so is forecast in the Sawtooth Mountains
and Caribou Highlands. NP/DMH


.LONG TERM...Friday through next Tuesday. SE ID remains under
influence of broad upper trough over western US early in the period.
Exiting shortwave keeping showers lingering over mainly eastern half
of region Friday. By Saturday, next shortwave drops along coast into
base of trough but retrogrades westward off the coast, merging with
close low near 140W. Consolidated trough does drive into the Great
Basin during the day Monday, mainly in response to next shortwave
dropping along PacNW coast. Model differences manifest in which
feature takes precedence. GFS favors southern (first) low, with
moisture tap. ECMWF favors moisture remaining limited and further
south. Have blended toward the middle given timing similarities
between the models with greatest upward nudge Monday into Monday
night, particularly eastern highlands. DMH


.AVIATION...Widespread weak convection occurring across SE Idaho
this afternoon ahead of surface cold front. Winds struggling this
afternoon but convectively enhanced, but convection also locally
dropping snow levels. Still seeing widespread VFR/MVFR but locations
could drop to IFR as ceilings drop with influence of snow. Main
precipitation band ends this evening, so return to VFR/MVFR
expected. However, models show low level moisture around sunrise and
guidance continues to hint at possibility of fog/stratus, so leaned
into that potential after 10Z. DMH


HYDROLOGY...Moderate precipitation amounts and mild low to mid
elevation temperatures the past several days have maintained and
potentially worsened low land flooding threat across the region.
Minidoka county has, in particular, seen increased low land
flooding. Will continue all low land flood headlines with
exception of Central Blaine county and Butte county where no
flooding is occurring. With moderate to heavy rain expected this
afternoon through this evening for areas below 6500 feet, some of
the flood advisory areas may see increased flooding. These areas,
to include Jefferson, Southwest Caribou, Western Bonneville, and
Western Madison counties, may need to be upgraded to flood
warnings. Some rises have been seen in area creeks as well as some
small responses to rivers. Have also continued the flood warning
for Portneuf River at Pocatello with the river forecasted to rise
to flood stage this evening. Current trend is to increase the
crest and maintain the time the gauge spends above flood stage,
dropping below flood stage early Saturday afternoon.

A cool down Wednesday through most of the weekend will aide to the
slow down and possible elimination of some flooding, though it may
take some time to see the full effect.


Wind Advisory until 8 PM MST this evening for IDZ017-021-022.

High Wind Warning until 6 PM MST this evening for IDZ020.

Winter Weather Advisory from 5 PM this afternoon to 6 AM MST
Wednesday for IDZ025.


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