915
FXUS65 KSLC 072055
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
255 PM MDT Sun Jul 7 2024

..SYNOPSIS...High pressure will gradually shift eastward over the
next seven days, bringing increasingly warm temperatures first to
southern Utah this weekend, and then northern and central Utah
Wednesday.

&&

.SHORT TERM (Through 12Z/6AM Tuesday)...It`s an extremely dry and
breezy day across southern/central/eastern Utah today. RH values
are well below 5 percent in several spots and even observed at 1
percent in a few spots. Northwest and westerly winds with gusts of
25 to 35 mph are observed across Castle County, the Central
Mountains and across southern Utah. These winds are expected to
continue until near sunset before they generally diminish. Some
canyon winds in lower Washington County are expected overnight
with gusts around 30 mph along I-15.

An excessive heat warning has gone into effect this morning for
lower Washington County, Zion Canyon and Glen Canyon NRA. This
warning has been extended through midnight Friday as heat
conditions and overnight recoveries in these areas are not
expected to improve. Temperatures tomorrow are forecast to
slightly climb across northern Utah as we continue to lie on the
eastern edge of ridge of high pressure.

.LONG TERM (After 12Z/6AM Tuesday), Issued 411 AM MDT...
Little change in the forecast compared to the past few forecast
cycles as this portion of the forecast will continue to be
dominated by potentially dangerous, excessive and prolonged heat.
Global deterministic and ensemble systems remain in very good
agreement regarding the strength, positioning and progression of
the ridge through the period, the feature responsible for the
excessive heat. On Tuesday, model consensus places the center of
the ridge axis across the Western Great Basin, with the ridge then
shifting only very so slightly eastward to be centered over east-
central Nevada by Wednesday. The ridge is then expected to weaken
only slightly while continuing to propagate very slowly eastward
through Saturday. There remain a small subset of the ensemble
members keeping the ridge in place through Sunday or even early
next week, so we can`t discount the possibility that extreme heat
could linger a bit longer. We do see hints of this showing up in
the temperature forecasts, as temperatures are likely to reach or
exceed 100F in SLC one day later now, extending into Monday. Given
the anomalous nature of the ridge relative to climatology and its
slow eastward progression, surface temperatures will challenge
record values for several days, adding to the cumulative effects
of the hazards associated with this heatwave. Overnight cooling
will be limited as well. The bottom line is that the cumulative
effects of this excessive heat will place significant stress on
people and pets, particularly those without adequate cooling and
those that spend significant time outdoors, adding to the
vulnerability. Avoid strenuous outdoor activities during the
hottest time of the day, drink plenty of water and limit exposure
to the sun.

Temperatures are likely to reach or exceed 110F in St. George from
Sunday through Friday, when probabilities for reaching or exceeding
110F are above the 75th percentile. Low temperatures during this
period will range from the upper 70s to the mid 80s. For SLC,
temperatures are likely to reach or exceed 100F from Wednesday-
Monday, when probabilities for reaching this threshold are at least
75%. We even see 107F (SLC`s all-time record high) in the 75th
percentile of the MaxT distribution on Friday. Low temperatures
during the peak of the heatwave will range from the mid-70s to near
80F in SLC. Relief will be tough to find even for the typically cool
high elevation valleys such as the Bear River Valley, Park City and
Evanston where several days with highs in the low 90s are likely.
Lows here, however, will dip into the 50s, offering a brief
reprieve. This heatwave will rival past heatwaves both in terms of
duration and intensity. EFI values remain elevated and standardized
anomaly 700mb temperatures reach or exceed those in the model
climate, especially over SW Utah early in the week.

We continue to look to the horizon to gauge both the potential for
some increase in moisture and relief from the heat. Ensemble
forecast systems remain in good agreement regarding when the first
hints of increased total column moisture will arrive, with consensus
continuing to suggest increased moisture will reach SW Utah by
Saturday before overspreading the remainder of Utah and SW Wyoming
by Monday, thanks to the development of deep-layer S-SW flow around
the departing ridge. A cross-section of the atmosphere reveals that
much of the increase in moisture will be relegated to the mid-
levels, especially initially, although at least some modest increase
in low-level moisture is forecast, especially over SW Utah by next
weekend and early next week. Thus, the first signs of the moisture
increase will be manifest in the form of mid/high level clouds, with
the first appearances of isolated terrain-based thunderstorms
arriving by Friday and especially Saturday across southern Utah,
with this potential spreading into central Utah by next Sunday.
Initially, main threat with this activity will be dry lightning, and
this is concerning following an extended hot, dry stretch as any
lightning will have the potential to create new wildfire starts.

&&

.AVIATION...KSLC...The SLC terminal will see VFR conditions through
the valid TAF period with clear skies. The return to southeasterly
drainage winds will be slightly delayed this evening to between 05-
06z, with periods of light and variable winds thereafter through the
night. Expect the shift back to northwest tomorrow near the typical
18z timeframe.

.REST OF UTAH AND SOUTHWEST WYOMING...Expect VFR conditions across
the area under mostly clear skies, with the exception of areas
locally downwind of some of the larger wildfires where restrictions
to visibilities in smoke can be expected. Winds will remain out of
the north to northwest, with afternoon and evening gusts 20-30kt,
strongest near lee slopes in the eastern and southern valleys. Winds
relax overnight except in the far southern valleys where northerly
winds may remain enhanced especially near the lee slopes or near the
mouths of north to south oriented canyons.

&&

.FIRE WEATHER...A hot, dry and windy pattern remains will bring critical
fire weather concern across central and southern Utah today. Wind
gusts of 20 to 35 mph and very dry air, less than 5 percent in some
cases, are observed. Much of the flow is northwesterly with a nod
to a westerly wind in a few locations. These conditions are expected
to persist until the sun sets this evening. At that point winds will ease
under 20 mph and drop off overnight. RH recoveries overnight tonight
are not great, at 15% to 25% across Color Country, the Grand Staircase,
Henry Mountains and the Mojave Desert. Similar, or even poorer
overnight recoveries can be anticipated for the next several days
across much of the state.

The positive news here is that the pressure gradient will relax
tomorrow. Wind and wind gusts are not expected to be as strong as
they are expected to be today. Flow will remain generally
northwesterly but only a portion of Color Country and Central Utah
Mountains have about a 30% chance for seeing 30 mph wind gusts or
stronger. Lighter winds are expected tomorrow across southern and
central Utah, around 20 mph.

Mid to late week, a center of high pressure is forecast to gradually
meander closer to Utah which will only assist in warming
temperatures across the region. A few bouts of moisture continue to
show up in forecast models over the weekend, but location placement
and amounts of moisture is still very uncertain at this time.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Excessive Heat Watch from Wednesday morning through Friday
     evening for UTZ101>107-115-116-118-119-122-128.

     Red Flag Warning until 9 PM MDT this evening for UTZ482-489-493-
     494-496>498.

     Excessive Heat Warning until midnight MDT Friday night for
     UTZ123-124-131.

WY...None.
&&

$$

SHORT TERM...NDeSmet
LONG TERM...ADeSmet
AVIATION...Cheng
FIRE WEATHER...NDeSmet

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http://weather.gov/saltlakecity