Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 210905
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
305 AM MDT Sat Apr 21 2018

.SHORT TERM...Today through Mon night. High pressure with its
clear skies and much warmer temperatures is expected to last at
least into Sun morning; that is when the GFS and the NAM diverge
in solution, with the GFS bringing in moderate precipitation while
the NAM brings in none to much lighter. The GFS has had a little
more consistency, with the NAM having very narrow precipitation
bands streaming from southwest to northeast across the forecast
area. The precipitation is more convectively based to be sure, as
the instability of the colder air behind the front on Sun moving
over the warmed ground, enough so that thunderstorms are a
possibility. So have biased closer to the GFS, but still trend
lower than GFS PoPs. The associated upper level low is very slow
to move out, still bringing a threat of precipitation even on Tue
night. Likely category continues in the mountains now through Tue
afternoon. Wind with the front will be breezy to windy (15 to 30
mph sustained), so do not expect any Wind Advisory. Right now, the
precipitation accumulation only has a very small area in the
central Idaho mountains where it reaches 6 to 10 inches; so do not
expect any sort of winter weather advisory, but it will be snowy
on that day. A Special Weather Statement may be in order, but
there is a high degree of uncertainty at this point, and should
wait at least 12 hours, if not a full 24 before the GFS and NAM
come to some better agreement. Messick

.LONG TERM...Tuesday night through next Saturday night. A Ridge of
High pressure is forecast to build into the region on Tuesday night,
resulting in a warming and drying trend across the region. A weak,
dry Cold Front is forecast to drop across the region Wednesday night
into Thursday, bringing a round of gusty, northerly winds along with
a temporary halt to the warm-up. The Ridge of High Pressure is then
forecast to further strengthen across the region late Thursday
through Saturday, bringing the warmest conditions of the year so
far, with highs some 10-15 degrees above Climatological averages. By
early next weekend, an organized area of Low Pressure is forecast to
drift into the CA/OR vicinity -- ejecting NE propagating
disturbances across our region. As such, an attendant increase in
Shower/Thunderstorm is expected as next Weekend unfolds. Pattern
recognition suggests this is a favored pattern for potentially
strong Storms. This will bear watching as we head into the weekend.
The bottom line is that Spring appears o be making its arrival this
week. AD/Messick

&&

.AVIATION...Expect VFR conditions through the period as High
Pressure reigns supreme. Breezy conditions expected this Afternoon
as the pressure gradient strengthens in response to a trough
sweeping Eastward across MT. As such, SW/W winds in the 15-25kt
range expected from 18-06Z for BYI, IDA and PIH. AD/Messick

&&

.HYDROLOGY...Releases from Palisades Reservoir are expected to
decrease and reduce the flow on the Snake River, including the
Lorenzo area. Expect the Flood Warning for this stretch of the
river to be canceled once the lower levels reach this far
downriver of the dam. Messick

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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