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628
FXUS65 KPIH 080149
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
749 PM MDT Tue May 7 2024

.UPDATE...

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Will allow wind advisory to expire. NBM shows gusty conditions
continuing through the night with some isolated spots occasionally
reaching advisory levels. But most areas have dropped below
advisory levels.

13
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.PREV DISCUSSION... 
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/issued 224 PM MDT Tue May 7 2024/

SHORT TERM...Today through Wednesday night. Broad area of
rain/snow showers working through the eastern half of the forecast
area this afternoon, with generally isolated to scattered showers
elsewhere. HREF consensus pushes the consolidated stronger band of
showers into the eastern highlands through the remainder of the
afternoon, then showers gradually dissipate through the early
evening. Across the Magic Valley and portions of the Lower Snake
Plain not currently impacted by the showers, winds remain elevated
well into Wind Advisory thresholds over 30 mph sustained and gusts
topping 50 mph in a few locations. The southern portions of the
Lower Snake Plain is marginal for winds, where the band of
showers has squashed some of the potential mixing. With the zone
split by the winds, opted to keep the Wind Advisory in place,
though acknowledging that the winds are marginal here. A brief
break in the precipitation is expected overnight, allowing some
clearing and temperatures once again to drop near freezing.
Another Frost Advisory is in place. Showers redevelop across the
region Wednesday as moisture wraps around the low and spills over
the Divide from Montana. Temperatures should be a few degrees
warmer Wednesday, so expect more rain at lower elevations. The
overnight should be a repeat, though temperatures might be a
couple degrees warmer. Some areas may not need a Frost Advisory,
but differences in the expectations for clearing overnight may
make a difference. DMH

LONG TERM...THURSDAY THROUGH NEXT TUESDAY...
Fear not...warmer/drier wx is ACTUALLY on the horizon! This warming
trend starts in earnest Thu as a sprawling E-W zone of relative low
pressure sinks south across thew Central Plains and 4-Corners
region, allowing a tongue of high pressure to build east on top of
it from the Pacific inland across the nrn Rockies. A few lingering
showers/t-storms can`t be ruled out Thu afternoon across the srn/ern
highlands in best proximity to the departing low, before dry
conditions take hold Fri/Sat. High temps will gradually gain 10-20
degrees over Thu-Fri-Sat, reaching the upper 60s to upper 70s by Sat
to kick off the weekend. Wrn fringes of that low pressure zone to
our south will manifest as a closed low over this period and may be
able to bring a few showers/t-storms back to the forecast Sun
afternoon, before our attention turns back to the potential for
fresh disturbances approaching the region from the NW in our usual
flow. 500mb height cluster analysis is so far in good agreement, but
does weaken the corridor of high pressure near/to the north of our
CWA and strengthen the corridor of low pressure to our south with
time, and both the clusters and 12z deterministic model solutions
suggest uncertainty as to how quickly low pressure to our south
kicks out to the east (if it does at all over the next 7 days). The
clusters also hint at the amplitude of ridging weakening which could
support at least modest disturbances riding in from the NW, but no
strong systems are yet indicated...all of this strikes us as a
somewhat weak overall pattern with plenty of potential for the
sensible wx details in our forecast to change in the days to come.
In the meantime, enjoy the overall warmer/drier pattern compared to
what we have seen over the past week! - KSmith

AVIATION...
Hit-and-miss rain/snow showers are expected (and indeed noted on
radar) across the region this afternoon with the greatest (brief)
cig/vsby hits at KDIJ (otherwise predominantly VFR), but the larger
impact will continue to be strong W to SW winds coming up the Snake
Plain through KBYI (strongest) to KPIH to KIDA (more modest).
Massaged these wind values down just slightly in the TAFs based on
latest NBM guidance (although still gusting 35-40kts at KBYI/KPIH),
with some overall decrease still expected between 02-04z/8-10pm
although conditions will remain abnormally/non-diurnally breezy
overnight. After a brief break in precip chances this eve, our
attention then turns to yet another round of precip gradually
arriving from NE to SW between 05-12z/11pm-6am rotating around the
back side of a low pressure center over the nrn Plains, and new FM
groups have been introduced to account for this with timing based on
the HREF consensus. Temps may be just cold enough to support all
snow with this. Went with predominant -SHSN or -SN as far west as
KIDA/KPIH where simulated reflectivity looks healthiest, and held
with VCSH for now at KSUN/KBYI although these terminals could be
"upgraded" later. HRRR, NBM, and MOS guidance not advertising much
if any vsby reduction, but as long a precip remains snow think
reductions to 5-6SM are likely with some potential to go lower, so
we`ll continue to evaluate how impactful this Wed AM round of snow
may be with future TAF packages. Winds will still be a bit breezy
but much lighter in comparison on Wed. Thu/Fri our wx trends drier
and VFR as some ridging intrudes across the nrn Rockies from the
west. - KSmith

HYDROLOGY...Portneuf and Blackfoot remain the rivers of concern
in East Idaho, though high flows also continue on the Snake River.
Showers continue through Wednesday mainly impacting the eastern
half of the forecast area with generally light precipitation. Very
cool temperatures today begin to moderate some on Wednesday, then
begin to warm significantly into the weekend. For now, weekend
high temperatures look to generally be in the 70s at lower
elevations, so expect snowmelt to restart. Forecast flows remain
high for the Portneuf: Minor Flood for the gage at Pocatello, and
fluctuating right at Minor Flood for the gage at Topaz. Given the
fluctuation, simplified the wording and continued the flood
warning until further notice for that gage. Similar conditions
exist for the Blackfoot, with the river expected to remain at
or fluctuating right around Minor Flood Stage. DMH
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.PIH WATCHES/WARNINGS/ADVISORIES...
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Frost Advisory until 9 AM MDT Wednesday for IDZ051>055.
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