Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 180913

Area Forecast Discussion
National Weather Service Pocatello ID
313 AM MDT Tue Apr 18 2017

.SHORT TERM...Today through Thursday. Rain and very high mountain
snow is increasing as expected across southern Idaho this
morning. The bulk of the moisture should fall south of an Island
Park-INL-Burley line through the next several hours. Lighter and
more scattered showers are forecast. Round 2 will move through
this afternoon, with the bulk of the showers falling south of an
Ashton-Shoshone line. Coverage of showers will also increase
across the rest of eastern Idaho as we do have some instability
forecast to develop. That instability is also just enough to kick
off isolated thunderstorms, with the potential for small hail and
gusty winds. Snow levels don`t drop much today, around 7500ft in
the central mountains to around 9000ft across the southeast
corner. For this evening and tonight, the focus shifts into the
Upper Snake Highlands and southeast highlands. Up north, it
appears a convergence band develops but doesn`t really get much
farther south than Roberts to the Teton Valley by morning. Across
the southeast, the models show an enhanced area of showers and
evening thunderstorms that should move out by midnight. Snow
levels across the east will hover around 7500ft.

Wednesday should be much drier as weak high pressure moves
overhead and to the east by evening. A few showers are possible
with any moisture that gets caught up in the flow over the ridge.
Yet another storm digs southeast across the state on Thursday.
Showers and afternoon thunderstorms are on tap, with snow levels
at 6500-7500ft. It will be breezy in general, but stronger gusts
likely with any showers and storms. Keyes

.LONG TERM...Thursday night through Monday. Trough on Thursday
slides across this area with snow levels  about 6200 to 69  feet
elevation. Accumulation 1 to 2 inches in the mountains. Airmass
looks unstable and may have thunderstorms with it. A chance of
showers will linger in the Eastern Highlands on Friday. The next
disturbance comes through on Sunday, not as strong as the Thursday
event. A busy pattern continues with another round of precipitation
headed this way next Monday night into Tuesday. RS


.AVIATION...Two embedded disturbances in moist southwesterly flow to
cross Southeast Idaho today. First disturbance tracks through KBYI,
KPIH, KIDA and KDIJ roughly 18/0800Z to 18/2000Z. This first wave
will also bring showers to KSUN 12-16Z. The second disturbance will
also affect all TAF sites 18/2000Z to 19/0200Z. Snow levels near
6800 feet MSL this morning, rising to near 7800 feet this afternoon.
There will be enough instability for isolated thunderstorms 20Z-01Z.
Fairly strong vertical shear present this afternoon. Precipitable
water values up to 0.68 in. RS


.HYDROLOGY...Several rounds of precipitation expected through mid-
week and then warmer temperatures heading into the weekend should
support forecast rises on rivers through the latter half of the
week and into the weekend. Portneuf at Pocatello will remain in
flood stage throughout the week possibly reaching moderate flood
stage by Wednesday morning. The Snake at Blackfoot was running at
flood stage this morning and is gradually expected to recede
Tuesday into Wednesday in concert with flows coming out of the
Henry`s fork. The Bear river at the border is forecast to remain
below the official flood stage of 8.6 feet through the week but we
did notice issues near Dingle and Pegram when the stage was at
7.38ft back on March 20th and it looks as if by Thursday afternoon
we may be running near that level again per the river forecast.



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