River Flood Warning 9, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
359 AM MDT Mon May 1 2023

.SYNOPSIS...High pressure will slowly shift east over the next few
days. A cooler, more unsettled pattern is expected Thursday into
the weekend.

&&

.SHORT TERM (Through 12Z Wednesday)...Morning upper air and
satellite analysis indicates the upper level ridge responsible for
the arrival of summer (seemingly) over the last few days is
gradually shifting east. A ~546 dam upper level low is shifting
south along the Pacific Northwest coast. Southerly flow is
developing over the region ahead of this low.

Temperatures are quite elevated especially across portions of
northern Utah early this morning. Gusty southerly winds have been
reported in some locations, indicating these areas are remaining
relatively well mixed.

Starting the day quite warm, particularly for the Wasatch Front,
introduces the potential for the 90 degree mark to be crossed this
afternoon and evening. While there is around a 1 in 5 chance Salt
Lake City will reach 90, regardless of whether the high is 88 or
90, it will be quite warm; near record warm in some locations
this afternoon and evening. This will continue to accelerate
snowmelt and the potential for additional flooding will continue
to be monitored.

Expect modest mid-level moisture advection this afternoon and
evening across portions of northern Utah. HREF ensemble mean
SBCAPE is forecast to range from around 400-500 J/kg. Inverted-V
type profiles will allow for the development of high-based showers
and potentially a few thunderstorms. The biggest threat with any
convection will be gusty, microburst winds. The highest threat
area will be across northeastern Utah but adjacent areas of the
Wasatch Front and Cache Valley should be prepared for isolated
microburst potential.

A similar set up can be expected Tuesday as the upper level low
continue to shift southward down the coast. Expect another threat
of microbursts across northern Utah Tuesday afternoon and evening.

.LONG TERM (After 12Z Wednesday)...The long-term period will
begin largely hot and dry, similar to early in the week but
slightly cooler. Precipitation chances and cooler temperatures
will return overnight into Thursday, with the active pattern
continuing through the weekend and into early next week.

The low pressure system along the West Coast is expected to begin
pushing inland on Wednesday, bringing unsettled weather and
cooler temperatures for the rest of the long-term. Southern Utah
will begin to cool off first, with highs on Wednesday nearing
normal. In contrast, northern Utah high temperatures remain 10-15
degrees above normal, though it won't last much longer. By
Thursday, and especially into Friday, expect temperatures to drop
to 10-15 degrees below normal, given H7 temperatures plummeting to
an ensemble mean of -4C. This is less than the historical 25th
percentile at KSLC for early May.

This low pressure system will bring precipitation to much of, if
not all of, our forecast area. Besides some initial high-based
showers possible on Wednesday afternoon, the first shortwave will
bring more more widespread PoPs beginning early Thursday. This
precipitation will come in the form of mountain snow in valley
rain, with snow levels dropping on Thursday and into Friday
morning to near 7000- 8000ft. Expect little snow accumulation.
Subsequent waves will produce more precipitation, though mostly
focused on northern/central Utah and southwest Wyoming...unlike
the first which will bring precipitation to southern Utah, too.
The details of these waves, such as timing and intensity, still
hold a lot of uncertainty. However, most ensemble members suggest
persistent wet weather for northern areas through the long-term
period, with low thunderstorm chances each afternoon. Southern
areas are likely to remain dry, except for isolated showers across
higher terrain.

Additionally, it's worth noting increased southerly flow on
Wednesday and Thursday, especially across southern Utah. Expect
gusts around 25-35kts across southern and central valleys.

&&

.HYDROLOGY...River flood warnings are now in effect for Emigration
Creek and the Little Bear River at Paradise. Flood watches remain
in effect for East Canyon Creek near Jeremy Ranch to East Canyon
Reservoir, and the Weber River near Plain City. Due to a
combination of reservoir releases and snowmelt, an areal flood
watch is in effect for areas near the Little Bear River in Cache
County below Hyrum Reservoir to Cutler Reservoir.

An areal flood advisory is in effect for portions of Thistle
Creek from the headwaters to near the US-89/US-6 junction (Thistle
Junction). Law enforcement reported up to 2 feet of water on
US-89 and at least one car was stuck and then flooded. If your
travel would normally take you on this route, check in with UDOT
for updated closure information.

Rapid warming will continue to accelerate snowmelt across the
state. All area rivers, creeks and streams will be running very
high, fast and cold. Please continue to monitor future statements
including potential upgrades to warnings and keep children and
pets away from rivers, creeks and streams. Let's keep everyone
safe during this runoff season.

&&

.AVIATION...KSLC...Southerly winds will prevail, becoming gusty
after 16z and diminishing after 02-03z. There is a 10% likelihood
of high-based showers producing a brief period of gusty and
erratic winds. VFR conditions will prevail.

.REST OF UTAH AND SOUTHWEST WYOMING...Expect gusty southerly flow
across much of the forecast area during the afternoon, especially
across southern and western valleys. Isolated high-based showers
could produce an occasional period of gusty and erratic winds (10%
likelihood adjacent to higher terrain).

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flood Watch through Friday morning for UTZ107.

WY...None.

&&

Kruse/Cunningham

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity