Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 261936

Area Forecast Discussion
National Weather Service Pocatello ID
136 PM MDT Thu Apr 26 2018

.SHORT TERM...Tonight through Sunday. A ridge of high pressure
continues to expand across the region early this afternoon ahead of
a low pressure system approaching the NRN California/Oregon coast.
It looks as if we peak Friday afternoon with falling temperatures
anticipated through the weekend as the upper low gradually moves
onshore and across the region through Tuesday. Little in the way of
any substantive changes were made to the going forecast other than
to align better with neighboring offices and/or nudge precipitation
potential and amounts higher where necessary. Huston

.LONG TERM...Sunday night through next Thursday night. 500mb
longwave forecast is for weak northwesterly flow to transition on
Tue night to a ridge over the forecast area, which should mean
warmer and drier by mid-week. And that is brought out in the details
as well. The main forecast problem for the period is how much and
where the focus may be in the forecast area. the highest PoP occurs
Sun night and again Tue. Sun night likely PoPs in the central Idaho
mountains, chance elsewhere. Tue is solid chance across the board,
except the southwest corner of the forecast area. There are large
disparities in amounts of precipitation between the GFS and ECMWF;
tried to split the difference in the operational forecast. By the
very end of this period, strong upper level ridging should be
leaving skies clear and a return to above normal temperatures for
Wed/Thu. Snow level and temperatures are somewhat warmer for the GFS
compared to the ECMWF, and this is mainly because the ECMWF is
wetter. Both the Sun/Sun night trough and the Tue trough could bring
some wind, possibly Advisory-level. But confidence in actual timing
from Sun night through Tue afternoon is fairly low and expect large
swings are possible from model run to model run. Messick

.AVIATION...High pressure will keep CIGs and VSBYs unlimited until
Fri night. Except for gusty wind in the eastern Magic Valley (KBYI),
wind should be light northeasterly to easterly, except for diurnal
slope/valley wind at KSUN. Messick

.HYDROLOGY...Warmer temperatures today and Friday will continue
to support enhanced snowmelt. Lower reaches like the Portneuf and
Blackfoot may be seeing their supply dwindling rapidly and thus the
final peaks for them this season. A chance of showers through the
weekend and into early next week will add to runoff while
accompanying cooler temperatures should help to relieve some runoff
pressure. For now, it looks as if the Portneuf, Big Lost, Henry`s
Fork and Snake Rivers will all see high flows either due to
snowmelt or dam operations continue into early next week. Huston

Flood Watch for Henrys Fork near Rexburg for Saturday evening.

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