496
FXUS65 KPIH 062049
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
249 PM MDT Mon May 6 2024

.SHORT TERM...Tonight through Tuesday night. Active northwest flow
pattern continues with series of shortwave troughs moving through
the mean trough over the northern Rockies. Satellite imagery shows
first shortwave shifting east of the region this afternoon, with
weak ridging ahead of next negatively aligned shortwave. Strong
upper jet just south of the region helping to amplify winds across
the southern half of East Idaho, while still providing for mainly
orographically induced showers over higher terrain. With the
transition mainly to more convective influence, both QPF and
subsequent snow totals through the short term tail off
significantly with last night`s system shifting out of the region.
Have dropped the remainder of the Winter Weather Advisories and
Winter Storm Warnings for today. Additional snowfall is expected
Tuesday into Tuesday night over mainly higher elevations, but even
at the 90th percentile (1 in 10 chance of exceedance) higher end
snowfall totals with potential travel impacts stay at or below 6"
accumulation. Winds and temperatures remain the far greater story
for impacts. Very strong winds continue mainly across the southern
portions of the Snake Plain, southwest of US-26. Observations show
widespread gusts over 45 mph, which should continue into the
evening with support from strong mid-level flow, steepened surface
gradient, and enough sunshine to mix to the stronger winds aloft.
Have dropped the Wind Advisory for the Arco Desert/Mud Lake zone
as most of the northwest winds across the region are struggling to
reach minimum thresholds. Elsewhere, expanded the Wind Advisory
into Tuesday evening, with the caveat that the winds should
briefly subside this evening below minimums, but still windy at
around 20 mph sustained. Guidance suggests that the winds will
increase well before sunrise, generally in the 2-4am timeframe,
and could be stronger than today. The strongest winds Tuesday
should remain from the Eastern Magic Valley into the Raft River
region and Lower Snake Plain. 90th percentile NBM favors
widespread region with gusts over 50 mph, possibly exceeding 60
mph in the typically overperforming Raft River region and I-84
south of the I-86 interchange. A High Wind Warning may be needed
in that area if the winds overperform from todays readings.
Lastly, temperatures tonight and Tuesday night will continue to be
well below normal. A Frost Advisory has been issued for the
entirety of the Snake Plain growing zones, with some potential to
drop below freezing in outlying areas that see a more significant
drop off in winds overnight. A Hard Freeze is not anticipated
tonight. Similar temperature profiles are expected Tuesday night,
with less wind, but the NBM ensemble probabilities do indicate a
potential trend of a degree or two cooler Tuesday night. This
could tip the scales toward a Freeze Warning with localized
potential for a Hard Freeze. DMH


.LONG TERM...Wednesday through next Monday.
Seasonably cold and unsettled weather will continue into Wednesday
as a H5 low situated over the NRN Great Plains brings colder,
northerly flow overhead and isolated to scattered light rain/snow
showers throughout the day further north and east. While heavier
rain/snow will exist north and east of the Continental Divide, this
flow regime will keep our area mostly shadowed with lesser amounts.
As that H5 low over the Plains ultimately splits Wednesday night
into Thursday, a secondary H5 low will begin to work SW through the
Great Basin. This will keep very isolated precipitation chances
going south and east of the Snake River Plain but what will be more
noticeable will be the warmer temperatures. Highs in the 40s/50s on
Wednesday will increase to the 50s/60s on Thursday as a ridge of
high pressure begins to shift inland over the PacNW and NRN Rockies.

High confidence amongst ensemble, deterministic, and cluster models
shows a broad, positively tilted H5 ridge building in from the
Pacific to round out this week. What this means will be the warmest
airmass of the season lifting NE into our area as predominant SW
flow ushers in highs back in the 60s/70s with even some low 80s
across our lowest elevations as soon as Saturday. Our current
forecast continues to represent the NBM 50th percentile high
temperatures well in this regard which remains in line closest to
the EPS.

While warm and dry conditions are expected Thursday through Monday,
as that H5 jet overhead becomes more zonal by early next week, we
may begin to see some moisture working overtop this ridge feature
helping to re-introduce some slight chances for precipitation. The
GEFS and EPS both support this solution helping to bring in some
rain shower/thunderstorm potential as we head into next week.
Temperatures however look to remain relatively unaffected as highs
in the 60s/70s prevail. MacKay


&&

.AVIATION...For the 18Z TAFS through 18Z Tuesday.
A mix of VFR/MVFR conditions continue this afternoon with a mix of
rain/snow showers around KIDA and KDIJ as strong winds persist
across the Snake River Plain and Magic Valley. Winds are slightly
less at KSUN and KDIJ but still expect gusts to around 20-25 kts. As
a shortwave trough begins to build in from the west this evening
through the overnight hours, isolated precipitation chances will
continue into Tuesday with MVFR/IFR CIGS/VIS possible at times
associated with heavier bands of rain/snow. Strong winds will
persist into Tuesday of which will be strongest at KPIH and KBYI
around 25-35 kts with gusts to 30-45 kts. Marginal instability this
afternoon and evening will support a nonzero chance of thunderstorms
around KBYI and KSUN but with the HREF model probability of thunder
now staying less than 20%, have kept the mention out of thunder out
of the TAFs at this time. MacKay


&&

.HYDROLOGY...Area rivers remain elevated today, with the Portneuf
and Blackfoot Rivers remaining the trouble spots of the day with
Flood Warnings continuing. Cool temperatures and ongoing periods
of showers (snow at higher elevations) will continue to slightly
mitigate snowmelt runoff. Periods of showers will continue to
provide additional water into the basins, mainly snow at mid slope
and higher elevations. Blackfoot River levels look to stay at
Minor Flood for the foreseeable future. Portneuf forecast trends
continue to produce a temporary nudge back into the low- end
Moderate Flood category, then drop back into persistent Minor
Flood for several days. The cold temperatures and consistent
unsettled conditions should keep East Idaho waterways high, fast
and cold through the week. DMH


&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 8 PM MDT Tuesday for IDZ051-054>057.

Frost Advisory from 8 PM this evening to 9 AM MDT Tuesday for
IDZ051>055.

&&

$$