408
FXUS65 KSLC 051023
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
423 AM 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
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)...Utah remains in a dry
northwesterly flow aloft, in between strengthening high pressure
over the West Coast and a mean longwave trough over the central
CONUS. This general pattern will change little through Saturday
other than further strengthening of the upstream high pressure.
Several embedded disturbances will continue to graze northeast Utah
and southwest Wyoming, bringing at times enhanced winds to far
northern Utah and the eastern valleys. Saturday afternoon and
evening, these winds will be strong enough that, when combined with
low humidities, will result in critical fire weather conditions where
fuels have cured. Areas of greatest impact will be the western Uinta
Basin, portions of Castle Country and the San Rafael Swell, and more
marginally so along the Idaho border.


.LONG TERM (After 12Z/6AM Sunday)...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 and heat dome move 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...VFR conditions expected through the period under
mainly clear skies. NW wind shift expected between 16-18Z, more
likely closer to 16Z. This evening, SE wind shift expected between
04Z and 06Z. Friday night into Saturday morning, periods of variable
wind expected with an easterly pressure gradient, but winds will
remain largely less than 7kts overnight, making direction less
operationally significant.

.REST OF UTAH AND SOUTHWEST WYOMING...No significant weather is
expected at area terminals through the TAF period, with VFR
conditions and clear to mostly clear skies persisting, with only
some cumulus anticipated over the Uintas. 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 northwesterly flow aloft remains in place across
the area through the weekend. As a series of embedded disturbances
graze northern Utah, expect winds to increase at times. Winds today
are not expected to be particularly strong, but will increase on
Saturday across far northern Utah through the Uinta Basin and parts
of the San Rafael Swell area. On Sunday, the winds will focus
farther south, across the San Rafael Swell and into south-central
and southeast Utah. These winds will combine with low humidities to
result in critical fire weather conditions where fuels have cured.
The other main weather issue will be the dry and very hot conditions
that will encompass the area through next week. Midlevel moisture
may then start to make its way into the area late next week which
could potentially bring some microbursts and/or dry lightning
activity.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...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.
&&

$$

Cheng/ADeSmet

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