635
FXUS65 KSLC 052147
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
347 PM MDT Fri Jul 5 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 Monday)...Afternoon upper air and
satellite analysis indicates a broad upper level ridge centered
near the northern California Coast. A longwave trough remains
across the northern High Plains and into the eastern United
States. Northwest flow along the edge of the ridge continues
across most of Utah. Several weak shortwaves embedded in this
northwest flow will increase winds to critical levels Saturday and
Sunday for portions of eastern and southern Utah where fuels are
critical. Red Flag Warnings have been issued for these areas.

As far as sensible weather across Utah, with the ridge shifting
eastward, southern Utah will begin to see very hot temperatures
this weekend, with the first of many days above 110F in a long
stretch for St. George by Sunday. Excessive Heat Warnings begin
Sunday and continue well into the long term forecast period for
Zion National Park, Glen Canyon National Recreation Area and lower
Washington County.

.LONG TERM (After 12Z Monday), Issued 423 AM MDT... Main focus of
the long term portion of the forecast continues be very hot and
dry conditions as a heat wave will build across the region. Global
deterministic and ensemble forecast systems remain in excellent
agreement regarding of the presence of an unseasonably strong high
pressure ridge that will slowly build towards and across Utah and
SW Wyoming during the period. 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 Thursday timeframe
across southern Utah, with near record- breaking heat building
into northern Utah Wednesday through next Friday as the ridge
moves overhead. EFI plots and standardized anomaly plots continue
to show an anomalous heat event, with 700mb temperatures forecast
outside of model climatology across portions of the Mojave (and
flirting with the St. George area by early next week). 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 heat
headlines, as temps will ease ever so slightly across southwest
Utah by late- week. Biggest chance from 24 hours ago is that model
consensus has slightly delayed the arrival of moisture to next
weekend, which would allow for an already extended period of heat
to continue. NBM probabilities continue to suggest most likely
windows for St. George to exceed 110F Saturday through next
Friday, with SLC exceeding 100F Tuesday- Saturday. 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.

As we head into next Friday and just beyond into next weekend, an
increasing portion of the model solution space advertises an
increase in total column moisture across the region, with this
moisture originating from the western Mexican coastal region and the
Gulf of California. As hinted at above, the latest ensemble system
means (GEFS, EC and Canadian alike) advect this moisture northward
into the Great Basin 1-2 days later than what was forecast 24 hours
ago, making this moisture push the greatest source of uncertainty in
the long term. We begin to see slight chances for isolated
convection appear across at least south-central Utah by next Friday,
which will likely begin as an isolated, dry lightning threat given
anticipated slow increase in low-level moisture.

&&

.AVIATION...KSLC...Northwesterly winds will transition to light and
southeasterly around 04-05z, becoming light and variable at times
under 5kts through the overnight hours.

.REST OF UTAH AND SOUTHWEST WYOMING...Broadly northwesterly winds
with gusts to 20kts will transition to light and diurnally-driven
after roughly 03-05z. VFR conditions will continue aside from areas
downwind of fires, which may see VIS reductions due to smoke.

&&

.FIRE WEATHER...High pressure will continue to slowly build east
through the next week. With relatively strong northwest flow
across eastern and southern Utah, a series of weak disturbances
will bring critical fire weather conditions to portions of eastern
and southern Utah Saturday afternoon and evening and again Sunday
afternoon and evening. Outside of these areas, very low
humidities this weekend, with poor overnight recoveries.

As the upper level ridge shifts eastward, expect near record to
record temperatures across portions of southern Utah Sunday with
northern and central Utah joining the heat on Wednesday. Daily
humidities in the single digits to low teens will be common along
with very poor overnight recoveries. By next Friday, mid-level
moisture may increase sufficiently for at least isolated dry
lightning.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning from noon Saturday to 9 PM MDT Sunday for
     UTZ482-489-496.

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

     Red Flag Warning from noon to 9 PM MDT Sunday for UTZ494-498.

WY...None.
&&

$$

Kruse/Cunningham/ADeSmet

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