Area Forecast Discussion
Issued by NWS Pocatello, ID

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FXUS65 KPIH 210856

Area Forecast Discussion
National Weather Service Pocatello ID
256 AM MDT Fri Apr 21 2017

.SHORT TERM...Tonight through Sunday.

Low pressure system will swing through the Island Park area today.
This will bring a continued threat for showers to the eastern
highland communities although the Snake Plain and central Idaho
mountains may see a stray shower as well. Snow levels are relatively
low, ranging from about 5000 feet this morning to around 6000 by
afternoon. Snow amounts however are unimpressive, generally a
dusting. Skies will clear quickly this evening and with light winds
expect cold sub-freezing temps tonight for most of the area.
Saturday looks dry and temps should rebound nicely into the mid 50s
and lower 60s. Next system arrives Sunday. This will produce a good
chance for showers for the central Idaho mountains. Showers and
isolated thunderstorms will be possible elsewhere as well,
especially across the southern highlands into the eastern highlands
during the afternoon on Sunday.


.LONG TERM...Late Sunday through Friday...It will be hardpressed to
find a dry day next week as prolonged zonal flow sets up. Embedded
shortwaves within the flow to enhance periods of heavier rainfall,
and be the lifting mechanism for thunderstorms at times. Snow will
fall above 6500 ft Tuesday with snowfall accumulations in the 1 to 4
inch range. Snow will persist in the forecast throughout the rest of
the week, with varying snow levels each day. Temperatures will not
change much throughout the week, with high temperatures in the mid
to low 50s across the Snake Plain and 40s in the higher elevations.
By Thursday, the GFS model chooses to close off an low in the upper
atmosphere to our south. This would shift flow more NW`ly and cool
temperatures off a bit. ECMWF brings in a closed low to the region
by Friday, a bit of a different solution compared to the GFS, which
at that time brings the flow NW`ly. There is no end in sight for
precip production at this time. NP/Valle


.AVIATION...As of 3:00 AM MDT...As we work on slowly clearing
out Thursday`s low pres system, radar continues to show persistent
showers in our far ERN zones, esp near Driggs. Temps are supporting
all snow, but precip is light enough that ceilings/vsbys at KDIJ are
mostly staying at MVFR per obs. Expect MVFR and occasional IFR to
cont for the next few hrs while slowly diminishing/trending toward
VFR toward 12Z. Low clouds at KPIH are also producing MVFR due to
ceilings below 2,000 ft. These should slowly thin out this AM and
suspect we will return to VFR by or shortly after daybreak.

Low confidence forecast today, but the silver lining for aviation is
that all scenarios should result in VFR at all sites. Precip and
clouds in the short term model guidance early this AM appear quite
overdone compared to radar/sat/obs. GFS/HRRR generate showers again
this afternoon as far west as KPIH, while RAP keeps all TAF sites
dry, and NAM lies in between with slight shower potential at KIDA
and KDIJ. Our CWA will be in close proximity to a mid-level low
sliding SE into WY, so this is certainly possible. However, with the
models overdoing precip last night and this AM, have low confidence
in this scenario. Will cont to monitor guidance leading up to 12Z
TAF issuance and may include VCSH at KIDA and KDIJ, but CIGS and VIS
should remain VFR, even with temps marginal for RN/SN at KDIJ.
Meanwhile, slowly clearing skies and VFR should be the rule of the
day at all other airports with a ridge of high pres building into SE
Idaho. Winds today/tonight should be fairly light out of the SW,
except for the usual diurnal wind shifts at KSUN and KDIJ.

Looking ahead past the TAF period, high pres should hold on for Sat
as well with dry conditions and VFR at all sites. Not seeing any
strong indications of low stratus or fog concerns at this time.


.HYDROLOGY...Flood warning continues for the Portneuf at Pocatello
and will remain in effect for quite some time as wet weather is
expected for much of the next week or so. Flood advisory continues
along the Bear River from Montpelier to the border where some minor
spillover continues and will likely continue for some time.
Otherwise, high flows continue for many streams and rivers.




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