926
FXUS65 KSLC 101009
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
409 AM MDT Thu Oct 10 2024

.SYNOPSIS...Southwesterly flow will maintain unseasonably warm
and dry conditions through Saturday. A weak weather system will
bring a cooling trend late in the weekend into early next week.

&&

.SHORT TERM (Through 12Z/6AM Saturday)...Southwesterly flow aloft
will maintain dry and very warm conditions across the forecast
area through the short term period. Max temperatures across
northern Utah will continue to run 15 to 20 degrees above
climo, and challenge daily records. Wednesday saw KSLC tie the
daily record of 88, and the official forecast of 88 today and 87
Friday would tie daily records as well. Max temps across southern
Utah will continue to run 10 to 15 degrees above climo, which
runs slightly warmer this time of year than northern Utah. The
Yellow Lake Fire will continue to result in smoke setting into
portions of the Wasatch Back near Heber/Kamas as well as the
western Uinta Basin during the overnight/morning hours. This
smoke should continue to mix out by early afternoon within these
areas.

.LONG TERM (After 12Z/6AM Saturday)...The axis of a stubborn mid-
level ridge will translate downstream of the area on Saturday,
opening the door to a weakening low moving in from the east Pacific.
The overall trend through the weekend will be an introduction of
cooler, yet still solidly (+10F) above average temperatures for this
time of year. As the low translates into the region, southwesterly
winds will increase ahead of the main trough, bringing elevated fire
weather conditions to portions of southern Utah. In addition, low
end chances (10-20%) for precipitation are expected across central
and northern Utah will exist from Monday morning through early
Tuesday morning, though there is still some uncertainty on the
precise timing of this weak shot of precipitation. Realistic high-
end precipitation amounts from this system don`t even come close to
a wetting rain (0.1") for the higher terrain of central Utah,
however, there is about a 10% chance for 0.1 inches or more in the
mountainous terrain across Utah. Bottom-line is that this system
will be weak and bring minimal concerns for impactful weather...
really just introduces slightly cooler temperatures.

Past early Tuesday, models remain in solid agreement that the
aforementioned ridge axis will continue to shift from the
Intermountain region eastward to the Plains, with a deeper trough
developing offshore in the northeast Pacific. Moreover, there is
generally good agreement on this trough progressing through the
western U.S. through the latter half of the week. A few things,
however, remain uncertain about this trough. First off, how deep
will the trough be as it progresses through Utah? Ensemble guidance
output of 700mb temperatures range from about +8C to -12C on
Thursday evening (warm enough to maintain above normal temperatures
vs. cold enough to support snowfall in the valley areas across
Utah). Secondly, what is the timing of the potential cold air? Model
guidance shows potential for 700mb temperatures to begin falling as
early as Wednesday night whereas some guidance hold off until
Thursday afternoon. Thirdly, how much precipitation are we looking
at potentially falling, what form at what elevations (if we need to
consider that), and where specifically? Current model output for
50th percentile QPF appears to favor northern Utah mountains and
southwest Wyoming with generally less than 0.05" liquid
precipitation. However, increasing thresholds to 75th percentile
depicts much more widespread precipitation producing over 0.1" for
terrain features, while decreasing to 25th percentile reveals little
to no precipitation chances. Taking a look at 90th percentile
reveals widespread 0.25-0.5 inches liquid precipitation, with
upwards of 1 inch in the mountainous terrain (mostly focused in
northern Utah).

Needless to say, there is plenty of uncertainty to work through
going forward. Could this be our first taste of winter/ true fall? A
break from well above average temperatures? Snow in the air? Future
model runs will have to be monitored closely! For now, trends to
expect are cooler temperatures through the second half of next week
with a chance for a shot of precipitation across the northern areas.

&&

.AVIATION...KSLC...VFR conditions under high level cloud cover will
be maintained over the KSLC terminal through the valid TAF period.
South winds will remain in place through the morning and early
afternoon hours, with gusts up to 20-22kts expected mid-morning.
Winds shift to a northwest flow around 21Z, but may happen as early
as 20Z and as late as 23Z.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions under
increasing high level cloud cover will be maintained across all
terminals through the valid TAF period. Gusty south to southwest
winds are expected across the western half of Utah and southwest
Wyoming mid-to-late morning through late afternoon. A return to
light terrain driven flows are expected after sunset.

&&

.FIRE WEATHER...An unseasonably warm airmass will remain across
the region through the remainder of the week. Afternoon high
temperatures will run 15 to 20 degrees above normal across
northern Utah and challenge daily records, while temperatures run
10-15 degrees above normal across the south. Southwesterly flow
aloft will bring a drying trend across the region today, resulting
in afternoon RH values below 15% across lower and mid elevations,
and near 20% across high elevations. With this dry air in place,
overnight RH recovery will become marginal to poor tonight and
again Friday night, mainly south of I-80. The combination of very
warm and dry conditions along with gusty afternoon winds will
result in elevated fire weather conditions today and again Friday.


A weak area of low pressure will move into the Great Basin
Saturday, then linger into early next week. Limited moisture will
only allow for a slight chance of showers mainly over the higher
terrain Sunday and Monday. The main impact of this system will be
to trend temperatures cooler and increase RH. There are
indications of a potential pattern shift during the latter half of
next week, which would bring cooler temperatures along the first
chance for meaningful precipitation in quite some time. This is
still almost a week out, but certainly bears watching.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Seaman/Webber

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