Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 210918

Area Forecast Discussion
National Weather Service Pocatello ID
318 AM MDT Thu Jun 21 2018

.DISCUSSION...A Trough of Low Pressure is forecast to track
through the southern Idaho Panhandle and SW Montana today into
this Evening. Forecast guidance has been trending stronger with
this system with each successive run -- and our official forecast
has followed suit by increasing Precipitation chances, amounts and
the potential for an isolated severe Thunderstorm. In fact, the
Storm Prediction center has placed those portions of Idaho
adjacent the Montana border into a Marginal risk for Severe
Thunderstorms this afternoon and evening -- and this looks good.
We have added mention of Gusty winds and hail for these areas. The
best chances for seeing a severe Thunderstorm will be between 12
PM and 6 PM across these areas, as Lapse Rates, Wind Shear and
Instability will be maximized during these hours. Have also
extended mention of isolated Showers and Thunderstorms as far
south as Idaho Falls as the trough, in addition to trending
stronger, has been trending farther south with the forecast track.
This trough will also tighten the pressure gradient across SE
Idaho, and as such breezy SW/W winds will develop across the Arco
Desert and Snake Plain by Noon, with these winds continuing
through Sunset. Winds gusts will likely reach 40 mph across the
INL during the late afternoon/early evening. This could create
some difficult driving conditions due to crosswinds in addition to
creating chop on area waterways such as Lake Walcott and American
Falls. Winds are just below advisory criteria so will not issue
at this time, however impacts will still be present.

The trough is then forecast to dive SE through Wyoming on Friday,
dragging a Cold front across SE Idaho and maintaining Showers and
Thunderstorms in the mix for areas from Monida to Island Park
south to Palisades, with the heaviest activity expected during the
Afternoon and early Evening. An isolated storm may sneak as far
SW as Idaho Falls. Yet another area of Low Pressure will slide
across our area on Saturday, bringing numerous Showers and
Thunderstorms across the Mountains, with chances tapering down to
isolated to scattered across the Snake Plain. Activity will once
again be strongest during the afternoon and early evening.

Drier conditions will gradually build into the region beginning on
Sunday, with perhaps an isolated shower or storm hanging on along
the WY border. Temperatures will surge upward for Monday, soaring
above climatological averages. The warm-up will be tempered
somewhat on Tuesday as a dry, weak Cold front streaks across the
area. Otherwise, dry conditions and seasonable Temperatures are
forecast into the middle of next week. AD/Wyatt


.AVIATION...High pressure ridging moves to the east today as a
trough/system moves through the area. VFR conditions will persist,
but winds should begin to increase by mid to late morning. There is
a chance of VCSH and a lesser degree VCTS for both KSUN and KDIJ
this afternoon into early evening. Wyatt


.FIRE WEATHER...A wave/trough will push through the area today.
Expect mainly west/southwesterly winds gusting around 25-30 mph. Our
southern areas will likely remain dry, but our northern areas will
likely have isolated to widely scattered showers and thunderstorms.
A secondary wave/trough will drop into Lemhi County early Friday
morning, bringing scattered rain showers and possibly isolated
thunderstorms. This wave will continue southeastward toward the
Caribou Highlands mid-day Friday. Thunderstorms will be more likely
in this area due to the warmer daytime temperatures. An upper level
low system will drop into the area from Western Montana on Saturday.
Currently models are showing this system impacting our whole area,
where on previous model runs it was just our eastern areas.   Expect
drier and warmer conditions next week. Wyatt


.HYDROLOGY...Due to decreased releases from Palisades over the
last 24 hours, Rivers have peaked just under previous projections.
Nonetheless, the Snake River at Idaho Falls remains forecast to
hover right around flood stage through today before slowly
falling, and the Snake River at Menan will remain just above flood
stage for at least the next couple of days. The Snake River at
Blackfoot is now forecast to not reach flood stage, however it
will remain just below and will still be running high, fast and
cold. The Henry`s fork at Rexburg has crested, and is forecast to
fall below bankful by later today. Like other Rivers, it will
still be running high and fast. With a couple more rounds of
Precipitation expected through Saturday, we may see some
minor rises on rivers, creeks and streams through the Weekend.



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