Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 191955

Area Forecast Discussion
National Weather Service Pocatello ID
155 PM MDT Wed Apr 19 2017

.SHORT TERM...Tonight through Saturday. The low pressure system
positioned off the NW coast this afternoon is expected to send a
fairly significant chunk of energy inland tonight which will result
in a negatively tilted trough spreading over the region Thursday.
These types of troughs typically produce severe weather, but the
current suite of numerical models continues to show marginal
instability but with decent shear development over the Southern
Highlands Thursday afternoon. For now, it looks like a good shot of
spring showers for everyone followed by lowering snow levels
Thursday night with lingering showers over the Eastern Highlands
through the day Friday. A ridge of high pressure will build into the
region Saturday ahead of the next Pac trough advancing toward the NW
coast resulting in dry conditions and warmer temperatures. Huston

.LONG TERM...Sunday through next Wednesday night. 500mb long wave
pattern has low amplitude ridge at coast slowly moving into the
Pacific Northwest and de-amplifying by Wed. Thus expect a
progressive pattern dominated by the shortwaves. So no really big
storms but no huge ridge either. Expect large swings in forecast
times of arrival of any given shortwave event, with potential for
little agreement between product suites. For the first trough during
this period, there is good agreement between the GFS and ECMWF on
timing and intensity, for Sun. The same goes for another shortwave
on Mon Night. By Tue, though, the ECMWF brings in another trough
right on the heels, while the GFS delays this feature another 12
hours. Either way, the wet spring continues. Messick

.AVIATION...Not expecting a return of any stratus tonight. Showers
may continue in the extreme northeast corner of eastern Idaho, but
otherwise very stable conditions. CIGs will start to develop again
after midnight for the western airdromes and close to 20/18Z for the
three eastern airports. KSUN, KBYI, and KIDA most susceptible to
marginal VFR prior to 20/18Z, KPIH and KDIJ should see it by
afternoon. Light wind for all airports. Messick

.HYDROLOGY...Another round of widespread precipitation is expected
Thursday coupled with warming temperatures heading into the weekend
will support forecast rises on rivers through the latter half of the
week and into the weekend. The Portneuf at Pocatello will remain in
flood stage throughout the weekend. The Snake at Blackfoot is
expected to continue falling as releases from Palisades have been
scaled back and increases in flows coming off the Henry`s fork will
be modest. The Bear river at the Wyoming 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
reached 7.38ft back on March 20th and it looks as if by Thursday
afternoon we may be running near that level again per the latest
river forecast. An advisory remains current for that area and we
will be making calls tomorrow to see how things are shaping
up. Huston


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