826
FXUS65 KSLC 042140
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
340 PM MDT Thu Jul 4 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
Tuesday. A few disturbances passing well to the east will help to
increase winds across the eastern valleys Saturday and Sunday.

&&

.SHORT TERM (Through 12Z Sunday)...It`s going to get quiet hot,
however, that is covered well in the long term forecast
discussion. For the immediate short term, afternoon upper air and
satellite analysis indicates a strong, broad upper level ridge off
the California Coast. A longwave trough is currently centered
across the northern High Plains. Most of Utah is under northwest
flow.

This northwest flow will continue to bring weak fronts through
northern and eastern Utah over the weekend. The main impact will
be an increase in gusty winds across eastern Utah...bringing the
potential for critical fire weather conditions Saturday to the
San Rafael Swell and the western Uinta Basin. By Sunday morning,
the upper level ridge will be centered near the central
Sierras...and the heat will be on for southern Utah.

.LONG TERM (After 12Z Sunday), Issued 418 AM MDT...Main theme of
the long term portion of the forecast will be very hot and dry
conditions. Global deterministic and ensemble forecast systems are
in excellent agreement in their relative depictions of the
presence of an unseasonably strong high pressure ridge into the
region. While there remain some minor strength and positioning
differences among the model solution space, this doesn`t take away
from the fact that temperatures may approach record values in the
Sunday through Tuesday timeframe across Utah. By Sunday, EFI
values and anomaly plots suggest the most likely location for
unseasonably hot temperatures reside across SW Utah, with this
extreme heat then expanding into northern valleys by Tuesday and
persisting through the end of the workweek, coincident with the
center of the ridge migrating overhead. Existing Excessive Heat
Warnings will likely need to be expanded in both geographical
extent and temporal extent as we get closer to the event. There is
some uncertainty as to how far out to extend these at this
juncture, as temps may ease ever so slightly across southwest Utah
by mid-week, but still remaining above normal.

So, how hot are temperatures likely to get? In St. George,
temperatures will reach or exceed 110F each day from Saturday
through at least Thursday (with lows in the upper 70s to around
80F), with a 10% chance of tying the State`s all-time record high
of 117F on Sunday, per latest NBM probabilities. Thus, forecast
temperatures in terms of magnitude through the period have some
potential to rival the extreme heat wave of early to mid July
2021. Excessively hot temperatures will also overspread Zion NP
and the Glen Canyon area where warnings are in effect. Farther
north, the hottest days are most likely to begin on Tuesday and
persist through the workweek, where high temperatures are forecast
to meet or exceed 100F. Here, latest NBM advertises nearly a 30%
chance of tying SLC`s all-time record high of 107F by Thursday or
Friday of next week. Day- to-day variations in temperature trend
as well as the magnitude of the temperatures can be explained by
the subtle differences in the strength and positioning of the
ridge through this time.

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, which adds to the vulnerability. Avoid
strenuous outdoor activities during the hottest time of the day,
drink plenty of water and limit exposure to the sun.

Towards the end of the workweek, an increasing portion of the
model solution space advertises an increase in PWAT across the
region, with this moisture originating from the western Mexican
coastal region and the Gulf of California. Latest consensus
advects this moisture to the north and into the Great Basin in the
Thursday- Sunday timeframe next week. The trajectory of this
moisture plume will ultimately be dictated by the position of the
ridge by this time, which ensemble means generally suggesting the
vicinity of the Four Corners region. It`s too early to conclude
whether this moisture will be limited to the mid-levels (tending
to favor dry lighting assuming sufficient instability) or will be
manifest in an increase in sensible low-level moisture all the way
through the precipitation-bearing layer, which would be more
supportive of more widespread rains. Either way, moisture does
appear sufficient to begin to support at least low-end probability
for precipitation across high-terrain areas of southern Utah as
early as next Thursday/Friday, with the potential gradually
increasing with time. Uncertainty does exist surrounding the
timing and extent of any moisture, which will dictate where and
when precipitation chances will appear in the forecast as we
approach this period of time.

&&

.AVIATION...KSLC...No significant weather expected at the
terminal. VFR conditions persist with clear to mostly clear skies.
NW winds anticipated to shift SSE ~04-06Z this evening, and back
to NW ~16- 18Z Friday. Some periods of more light and variable
flow possible near times of diurnal wind shifts.

.REST OF UTAH AND SOUTHWEST WYOMING...In general, no significant
weather is expected at area terminals through the TAF period, with
VFR conditions and clear to mostly clear skies persisting. Only
noted exception is a small potential for any terminals downwind of
area fires to experience brief VIS drops due to smoke plume
advecting through. Otherwise, anticipate winds to follow a fairly
typical diurnal pattern.

&&

.FIRE WEATHER...A strong upper level ridge will gradually shift
eastward through the next 7 days. A mean trough remains across
the northern High Plains, with occasional disturbances shifting
south into the High Plains. Eastern Utah will remain close enough
to this stronger northwest flow to allow for periods of critical
fire weather conditions for the eastern valleys Saturday and
Sunday.

Meanwhile, as the upper level ridge shifts east, very hot
temperatures will build into southern Utah Sunday...gradually
shifting north through the remainder of the state for Tuesday.
This long duration heat wave will bring near record temperatures,
single digit daytime RHs for many locations, and very poor
overnight recoveries. Current models suggest this extended heat
wave may last through the next weekend...and beyond...though mid-
level moisture may begin to increase across portions of southern
and eastern Utah as early as next Thursday. While this may bring a
slight improvement to humidities...there is also the potential
for an increased threat of dry lightning.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning until 9 PM MDT this evening for UTZ482-489.

     Fire Weather Watch from Saturday afternoon through Saturday
     evening for UTZ482-489.

     Excessive Heat Warning from 9 AM Sunday to 9 PM MDT Tuesday for
     UTZ123-124-131.

WY...None.
&&

$$

Kruse/Warthen/ADeSmet

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