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628
FXUS65 KPIH 211951
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
151 PM MDT Tue May 21 2024

.SHORT TERM...
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Tonight and Wednesday
Afternoon satellite imagery shows gradually increasing CU field
across the eastern half of the region. To the northwest, beginning
to see clouds and precip associated with our next weather system
moving into the Pacific northwest this afternoon. Not expecting
too much in the way of precip throughout the remainder of the day.
Could see some isolated showers, maybe a thunderstorm, across the
eastern highlands but the majority of the region will be dry.
Temperatures today have been a touch warmer than yesterday but
still running close to 10 degrees below normal for late May.

Expect increasing cloud cover overnight and certainly throughout
the day Wednesday as an upper low moves over the area tomorrow.
Expecting widespread precipitation and increasing winds. May need
a wind advisory for the Arco Desert zone but held off for now.
Forecast precipitation amounts of around a tenth to a third of an
inch are expected tomorrow, maybe a bit higher totals in the
highest terrain. As a front sweeps through the area tomorrow
afternoon, temperatures and snow levels will drop to support a few
inches above 6000 feet. Frost and/or freeze products will likely
be needed for Wed night into Thu AM as it looks to be quite chilly
once again across the growing region. McKaughan

.LONG TERM...Thu through next Tue night
The massive low from the near-term forecast period has shifted to
the east, bringing northerly to northwesterly air flow and still
quite a bit of precipitation along the border with MT, including
the northern end of the Snake River plain, and the eastern
highlands. It is still going on to a lesser degree in the central
Idaho mountains. The low continues to move on, and by late night
Thu night it should be over. This makes Thu the coldest day of the
week, with afternoon highs 12 to 17 degrees F below normal for
the time of year. Likewise, the overnight low on Thu night will
likely mean Frost Advisories at a minimum, perhaps Freeze Warnings
if the cold air is currently being underplayed, or the skies
clear faster on Thu evening. The cool unstable air means a risk of
showers and thunderstorms, mainly in the north and east, along
the MT and WY borders. A second shortwave trough is expected Sat,
knocking down the warm up that occurred from Thu to Fri. All the
clusters have it over eastern Idaho on Sat, but its departure
timing is less confident as 20-25 percent of the clusters have an
early departure with warming. However, the majority solution is
for the trough to linger and for conditions to turn colder, just
not as cold as Thu.

Wind during this first part of the extended forecast is strong on
both Thu and Sat night/Sun with the two troughs featured during
the period. Enough for possible Wind Advisories, and at a minimum
a Lake Wind Advisory.

There is strong improvement for the actual holiday, Memorial Day,
as an upper level ridge axis is directly overhead, or just to the
west. Temperatures are just slightly below normals, and a risk of
frost/freeze returns. By Tue afternoon this ridge amplifies and
is much stronger with strong warming to above normal temperatures.
Wind is much less being under the ridge. Messick
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.AVIATION...
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Incoming trough will shift wind to the south in addition to
increasing gustiness even tonight. SHRA are expected this evening
at the northern airdromes, KIDA and KDIJ. TSRA also a threat at
KDIJ. Overnight, the incoming trough will bring strong upper level
support for gusty south and southwest wind, SHRA, and high
elevation SHSN. Looks like the SHSN should stay above most
airdromes, with only KDIJ getting cold enough to have SHSN, if the
moisture arrives earlier than expected. KSUN is the only area
threatened with marginal VFR for CIGs, but it must be watched
there; if the snow level is forecast too high at this time, then
SHSN could reduce VSBY at KSUN. TSRA threat from this trough will
be at all airports during the afternoon, so only KSUN is currently
forecasted with TSRA. KBYI should have the strongest wind from
the trough, around 20G30KT. Wind should also start early to mid-
morning. Messick
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&&

.HYDROLOGY...
Elevated river levels continue on the Portneuf River at Pocatello
and Topaz. River levels are expected to gradually recede over the
upcoming week but will likely remain high enough to warrant
continued flood products for much of the week. McKaughan

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