456
FXUS65 KSLC 081024
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
424 AM MDT Mon Jul 8 2024

.SYNOPSIS...High pressure will gradually shift eastward over the
next seven days, bringing increasingly warm temperatures first to
southern Utah early in the week, then spreading across the
remainder of Utah and southwest Wyoming.

&&

.SHORT TERM (Through 12Z/6AM Wednesday)...Mid level ridging
centered across central California continues to induce a deep
layer north-northwesterly flow downstream across the eastern Great
Basin/Colorado Plateau region. This flow has allowed slightly
cooler air to remain in place across northern Utah/southwest
Wyoming, and despite the airmass modifying a bit trending
temperatures slightly warmer, daytime highs will remain near to
slightly above climo today. Meanwhile, far southwestern Utah
remains under the influence of a very hot airmass associated with
the upstream ridge. Temperatures across lower Washington County
will cool slightly today, but still approach the 110F mark around
St George and Zion Canyon.

The upstream ridge will nudge eastward Tuesday, trending max
temperatures up 3-5F across the forecast area. This will push
daytime temperatures into the upper 90s across lower valleys of
northern/central Utah including the Wasatch Front/Cache Valley.
Meanwhile St George/Zion Canyon, where an Excessive Heat Warning
is in effect, will exceed the 110F mark Tuesday afternoon.


.LONG TERM (After 12Z/6AM Wednesday)...High confidence continues
to be maintained on the forecast pattern from midweek on into the
start of the weekend, with the dominant influence coming from an
anomalously strong ridge of high pressure characterized by H5
heights around 2 sigma above normal. This ridge will initially be
centered from the Desert Southwest into east Nevada and west Utah
Wednesday, gradually migrate northeastward and become centered
more or less atop Utah by Friday, and then very slowly begin
shifting east through the weekend. With H7 temps generally about
18C to 22C, almost all of the forecast region will be looking at
surface temperatures challenging record values for several days.
Given the slow progression of the ridge, the cumulative day-to-day
effect of both hot daytime temperatures and little night time
relief due to very mild overnight lows will pose dangerous. The
overall message remains the same that heat safety will be critical
over the coming days. Drink plenty of fluids, and avoid outdoor
activities during the hottest portions of the day if at all
possible. If not, limit exposure by taking frequent breaks
(ideally in an air conditioned location) and by wearing
lightweight and loose fitting clothing. Learn to identify signs of
heat exhaustion and heat stroke and appropriate actions to take
accordingly. Never leave children or pets in unattended vehicles.
While there are many types of hazardous weather, heat is the
number one cause of weather related fatalities.

Digging into forecast temperatures a bit more shows some
impressive numbers. For KSLC, NBM probabilities show a greater
than 95% chance to see highs exceed 100F Thursday, Friday, and
Saturday, and a greater than 70% chance as well for Wednesday and
Sunday. That said, it would take 6 or more days (at KSLC
specifically) to crack the top 10 runs of 100F or more, and for
most other days the odds fall to around a 30% chance.
Unsurprisingly, the day to day spread is also fairly tight, with
25th percentile values of 103F and 75th percentile values of 106F
Thursday through Saturday when the heat looks to peak. NBM
probabilities carry around a 10% to 15% chance to hit or exceed
107F at KSLC Friday and Saturday, which marks the all- time record
high for KSLC. For KSGU, Wednesday through Friday NBM
probabilities carry around 80% to 90% chance for daily highs
exceeding 110F, falling to around 60% chance by Saturday. For the
moment, the forecast shows a very low (but still non-zero) chance
of breaking the all-time Utah state heat record of 117F. Elsewhere
around the area, deterministic forecast values are quite
anomalously hot as well. This includes higher elevation valleys
from the Wasatch Back to the Bear River Valley as well as
southwest Wyoming, which will see afternoon highs from the upper
80s to low/mid 90s, though will see a bit more relief overnight
with cooler lows.

As early as Saturday, the ridge may begin to shift far enough
east that it in addition to a trough approaching the Pacific coast
may help advect some mid level moisture into the area within
stronger southerly flow. As a result, will see some isolated to
scattered shower/thunderstorm chances creep back into southern
Utah. That said, the likely higher based nature to any convection
will limit wetting rain chances, and may actually manifest as more
of a dry lightning threat. By Sunday and Monday, ensemble
consensus shows PWAT values pushing back above 100% of normal for
mid July (generally 0.50" to 0.80" or so), and diurnal
thunderstorm chances creep northward accordingly. Temperatures by
Sunday also look to begin to fall from the peak of the heatwave as
the ridge shifts, though temperatures will still remain quite hot
all things considered. Some guidance also suggests the ridge may
be more stubborn to shifting, in which case lower PoPs and more
prolonged heat will be possible, but for now opted to keep NBM
values with the aforementioned forecast logic.

&&

.AVIATION...KSLC...No significant weather expected at the
terminal, with VFR conditions and clear to mostly clear skies
persisting. Winds anticipated to follow typical diurnal
directional pattern with southerly drainage flow shifting
northwesterly ~18Z Monday, and back southerly ~04Z thereafter.

.REST OF UTAH AND SOUTHWEST WYOMING...Largely expect a quiet TAF
period with most terminals seeing a continuation of clear to
mostly clear skies and VFR conditions. The one exception will be
potential for some smoke/haze related obscurations at any
terminals downwind of area fires, particularly stronger and larger
ones with more notable plumes. High resolution guidance suggests
south central Utah as the most likely area to see any such
smoke/haze advection. Winds anticipated to more or less follow
something of a typical diurnal directional pattern.

&&

.FIRE WEATHER...A very dry (north) to extremely dry (south)
airmass will remain in place throughout the upcoming week,
resulting in very low daytime RH and marginal to poor overnight
recovery across most zones. A strong area of high pressure
centered over California will maintain northerly flow across the
area today and again Tuesday. Winds will not be quite as strong as
what was observed over the weekend, however gusts in the 20-25
mph range can be expected across exposed areas of the central and
southern mountains along with the western valleys. With these
lighter winds, conditions are expected to remain just below
critical fire weather criteria, with isolated pockets of critical
fire weather conditions possible in central and southern Utah.

The high centered over California will slowly move east, becoming
centered across the region during the middle to latter portion of
the week. The resultant warming trend will push high temperatures
near daily records, and in some cases may challenge all time
records. The extended nature of these record challenging
temperatures will create potentially dangerous heat for those with
prolonged exposure. By late in the week into next weekend,
confidence is increasing in high based moisture spreading into at
least southern Utah, and potentially points north, resulting in a
chance for high based showers and thunderstorms as early as Friday
afternoon.

&&

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

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

WY...None.
&&

$$

Seaman/Warthen

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