Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 252009

Area Forecast Discussion
National Weather Service Pocatello ID
209 PM MDT Sat Mar 25 2017

.SHORT TERM...Tonight through Monday night. Early afternoon
satellite imagery was showing a split upper trough migrating through
the WRN states with the NRN branch trough axis near Boise. Numerical
models continue to show some weak convective buildups across SE
Idaho this afternoon and evening ahead of the advancing trough with
clearing skies late tonight as the trough moves into Wyoming. The
next storm system sets up off the NW coast late tonight before
spreading inland Sunday afternoon.  The leading edge of the
associated precipitation shield is expected to spread into the CNTRL
mountains and ERN Magic Valley late Sunday afternoon and then the
remainder of SE Idaho Sunday night and Monday while the main body of
the splitting trough moves into and through the Great Basin Monday
and Monday night. Precipitation totals look a little better than
what was advertised on yesterdays progs but the focus for the best
totals will be across Utah as the SRN branch of the split digs SE
through Nevada Monday. Strong gusty winds are anticipated Monday as
a decent surface pressure gradient sets up across SRN Idaho under
the passing upper trough. Near normal day highs continue to be
advertised on the statistical guidance and have strayed
very little from this line of thought. Huston

.LONG TERM...Tue through next Sat night. 500mb 5-wave indicates very
little change from low amplitude, nearly zonal flow until Thu
night/Fri. At that point an upper level longwave ridge builds in,
which amplifies but is never very strong, with a trough developing
to its south over the desert southwest. Thus have low confidence in
what may actually happen, as the weather will all be short wave-
driven, so expect quite a bit of disagreement among product suites
and from run-to-run. At first, the differences between the ECMWF and
GFS are small, with the ECMWF about 6 hours faster with the main
storm during the period, bringing something in on Wed night, while
the GFS waits until Thu. Very wet, with snowy weather at night,
continues into Thu night/Fri. The differences are greater by Sat
night, with the ECMWF bringing in another low, while the GFS stays
dry. this was a considerable drop in PoP for Sat/Sat night from
previous thinking. Messick

.AVIATION...KIDA and KDIJ are struggling to stay VFR, so have kept
marginal VFR in the forecast through the mid-afternoon. All
airdromes expected to develop nearly clear skies with the low level
wind enough to keep fog and stratus away for the morning hours.
Hardest airport to figure out is KDIJ, which should have abundant
moisture in the boundary layer until at least 26/14Z, but it has
occasionally popped up to good VFR, so not sure what is going on
there, and is the least confident forecast of the five. CIGs should
re-develop sometime shortly after 26/12Z. Very stable atmosphere for
this afternoon, looking at the Theta-E profile, so have removed
gusts. Messick

.Hydrology...Cooler, near normal temperatures are expected over the
remainder of the weekend and early next week as a second Pacific
storm system makes its way through the area Sunday night and Monday.
The benefit of the cooler temperatures will likely be offset some by
additional rainfall below 6000 feet MSL and thus an Areal Flood
Watch continues for the mountains along with various flood
advisories where low land flooding continues. Main stem flooding
will continue on the Portneuf river for the foreseeable future while
the Bear River at the Border slowly recedes benefiting from the
cooler temperatures within its headwaters. Above normal temperatures
return late in the week with a resumption of areal snowmelt flooding
expected at that time. Huston

Flood Watch continues until 1 PM MDT Sunday afternoon for IDZ017>019-


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