193
FXUS65 KSLC 071011
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
411 AM 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)...High pressure centered
across central California is inducing a very dry northwesterly
flow downstream across the forecast area this morning. A shortwave
trough embedded within this flow is brushing by the forecast area
this morning as it digs through the central Rockies. This will
result in gusty northwest winds this afternoon, particularly
within downslope favored areas across southern and eastern Utah
such as Castle Country. This passing trough will also keep
temperatures across northern Utah "cooler" and near climo, while
+20C 700mb air across far southern Utah pushes the St George area
to near 110F this afternoon. An Excessive Heat Warning goes into
effect this afternoon for lower elevations of southern Utah, where
record challenging heat will continue through much of the
upcoming week (see Long Term for more details). The upstream ridge
will begin building east into the Great Basin Monday, allowing
for a slight warming trend across northern Utah.

.LONG TERM (After 12Z/6AM Tuesday)...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...VFR conditions are forecast with high based
clouds throughout the day. Southeast winds early this morning will
shift to the northwest a bit earlier than normal, with the shift
expected to occur between 14-16Z, with some afternoon gustiness.
Winds will also shift to the southeast this evening slightly later
than normal, likely not until 04-06Z. Brief periods of variable
winds will accompany the wind shift windows.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are
forecast throughout the forecast across the region, with a few high
clouds over central/southern Utah this afternoon with a few high-
based cumulus over the Unitas and SW Wyoming. Gusty NW winds
expected once again this afternoon, strongest over wind-prone areas
of central, south-central and southeast Utah, where there is a 90%
chance of gusts to 30-35kts after 18Z. Localized reduced visibility
will be found near and downwind of central Utah fires as well.

&&

.FIRE WEATHER...A dry (north) to extremely dry (south) airmass
resides across the region today, and will remain in place
throughout the upcoming week and likely beyond. A weak weather
system brushing by the region will enhance northwest flow today,
with the gustiest winds across southern and eastern Utah where
fire weather conditions will be critical anywhere fuels are
sufficiently dry.

An expansive area of high pressure across California will
begin building eastward Monday, and reside across the eastern
Great Basin into the Colorado Plateau region through much of
the upcoming week. The result will be a prolonged period of
hot weather, with daytime temperatures challenging records and
running 10 to 15 degrees above normal across southern utah
beginning today, and across northern Utah by midweek. With
the high in place winds will become generally light and
terrain driven Monday through Wednesday. By late in the
week high based moisture looks to begin to spreading into
the region, bringing a threat for dry thunderstorms across
southern Utah as early as Friday, with a better chance
heading into the upcoming weekend.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning until 9 PM MDT this evening for UTZ482-489-493-
     496.

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

     Red Flag Warning from noon today to 9 PM MDT this evening for
     UTZ494-497-498.

WY...None.
&&

$$

Seaman/ADeSmet

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