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557
FXUS65 KSLC 212131
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
331 PM MDT Fri Jun 21 2024

.SYNOPSIS...
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As a trough exits the area this evening, drier air
will move in over the weekend and into early next week. However,
enough moisture will linger to support isolated showers and
thunderstorms over southern Utah. With high pressure building,
temperatures will be on the rise over the weekend, particularly
over northern Utah.
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.SHORT TERM (Through 12Z/6AM Sunday)...
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Southerly flow has drawn
deeper moisture northward into eastern Utah, with satellite
derived PWs in the 0.7 to 0.8 inch range. A weakening trough with a
good upper jet associated with it is tracking across the state,
providing ample instability and shear. Conditions have not only
been favorable for flooding, with multiple confirmed flash floods,
but for severe weather as well. Many storms have produced large
hail, with a storm near Big Water reportedly being accompanied by
golf ball sized hail. The rare Severe Thunderstorm Watch
highlighted the threat well.

As the trough exits early this evening, the flow aloft will shift
to the west, allowing drier air to quickly advect in. Thus, the
strong storms will tend to diminish during that time, with drier
conditions anticipated for the weekend. That being said, enough
moisture will linger over southern Utah to produce isolated
convection, with gusty winds possible with any storms that
develop. With high pressure in place, temperatures will be on the
rise.

.LONG TERM (After 12Z/6AM Sunday), Issued 418 AM MDT...Heat and
isolated to scattered convection remain the primary story of the
long term forecast through the middle of next week. Towards the
latter half of the work week, longer range guidance hints at
potential for increasing trough influence and slightly cooler
weather.

Starting with the heat, Sunday continues to look very warm across
much of the forecast region, especially northern Utah, as a strong
ridge extending from the southern Plains into the Desert Southwest
yields H7 temperatures around 16C to 19C across the area. With this,
afternoon highs from the Wasatch Front into the Great Salt Lake
Desert look to push near to maybe slightly above 100F. While it`ll
hot more or less everywhere, HeatRisk product particularly
highlights the urban corridor from the Salt Lake Valley northward
roughly through to Brigham City, as well as much of the Great Salt
Lake Desert to Wendover. As such, opted to issue an Excessive Heat
Watch for these areas with this package. Held off on including the
Toole/Rush and Utah Valley zones where temperatures look just
marginally cooler, but subsequent expansion to heat headlines
definitely remains possible. A shortwave trough passing through the
northern jet will brush by Monday, helping to flatten the ridge a
bit, and nudge temperatures down a few degrees accordingly. However,
following the passage of this feature, the ridge rebounds
Tuesday/Wednesday, and afternoon highs and overnight lows will once
again push to potentially dangerous levels. HeatRisk once again
highlights this period for potential heat headlines, but given a bit
more spread in guidance and still several days out, holding off on
any issuance.

For southern Utah, temperatures will also start off very warm Sunday
with afternoon highs at lower elevations spanning generally from the
mid 90s to mid 100s. Given these temperatures are more reasonable
for southern Utah from a climatological perspective (around 5-10F
above normal), HeatRisk isn`t as aggressive, thus no headlines
planned at the moment. That said, the aforementioned flattening
effect from the northern stream trough will be too weak to have much
impact across southern Utah, and instead will see temperatures trend
upward into midweek, likely peaking Wednesday or Thursday. Tuesday
through Thursday, forecast highs for lower elevations of Glen Canyon
NRA are around 100-105F, and for Lower Washington County around 105-
110F. With overnight lows near 80F offering little relief in these
areas, this appears a more likely time range where heat headlines
will need to be considered.

In any case, it will be hot across the vast majority of the forecast
region from Sunday through midweek, and naturally more heat can be
expected as we push deeper into summer. Remember to keep heat
related safety in mind, whether outside recreating, working, or just
in general. Drink plenty of fluids, take frequent breaks (ideally in
an air-conditioned area), wear lighter and looser fitting clothing,
and recognize the signs of heat exhaustion or heat stroke. Never
leave young children and pets in unattended vehicles.

Despite the strong ridge exerting the dominant influence over the
forecast region, precipitation chances remain non-zero as
anomalously high moisture (PWAT values ~0.75" to 1.00") for this
time of year periodically surges northward into the area. While the
subsident effect of the ridge should limit widespread precipitation
potential, daily isolated to scattered convection looks to fire
during the afternoon. Southern Utah appears more favored to see
these low end daily convective chances, though further north
especially along high terrain and adjacent valleys, at least a few
showers and thunderstorms can`t be ruled out, particularly by
Wednesday. While the day to day coverage will be a bit isolated in
nature, those planning on recreating in any rain sensitive areas
(slickrock areas, typically dry washes, slot canyons, etc.) should
remain weather aware for potentially quickly changing conditions.

Thursday or Friday continue to offer the next opportunity for some
relief from the heat, as a deepening Pacific trough moving inland
may help to weaken the influence of the stout ridge. By Thursday,
around 25% of ensemble membership shows some increasing trough
influence, and by Friday membership increases markedly. That said,
there`s still a small grouping of around 10% of ensemble members
showing continued strong ridging holding on into Friday, which would
yield a continuation of heat if that scenario ultimately pans out.
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.AVIATION...
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KSLC...Winds continue to compete between convective
outflows and southerly background flow turning westerly through the
evening... but should see a return to more typical southeasterly
flow this evening around the usual 03-04Z as high pressure builds
back in from the west. Cloud cover should also rapidly dissipate.
Expect more typical quiet weather conditions and wind shifts for
Saturday.

.REST OF UTAH AND SOUTHWEST WYOMING...Lingering showers and
thunderstorms through the evening will slowly shift east past the
Green River. While quiet conditions return for the overnight,
lingering moisture and a weak shortwave trough could kick off an
additional round of showers and thunderstorms in central eastern
Utah midday Saturday, ending by the early evening with high pressure
building in statewide and rapid drying throughout.
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&&

.FIRE WEATHER...
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An unusually moist and unstable airmass over Utah is
resulting in good coverage of showers and thunderstorms capable of
producing heavy rain, large hail, and gusty winds, particularly
over eastern Utah. Drier air will move in early this evening, and
showers and thunderstorms should diminish. Drier and warmer
conditions overall are anticipated through the weekend, though
enough moisture will remain for isolated showers and thunderstorms
over southern Utah each day.
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&&

.SLC WATCHES/WARNINGS/ADVISORIES...
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UT...Excessive Heat Watch from Sunday morning through Sunday evening
     for UTZ101-103>105.

     Flood Watch until 9 PM MDT this evening for UTZ113-120-121-
     128>131.

WY...None.
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$$

SHORT TERM/FIRE WEATHER...Traphagan
LONG TERM...Warthen
AVIATION...Wessler

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity