Flash Flooding and Debris Flow in Utah, March 13 to 16, 2023

Area Forecast Discussion
National Weather Service Salt Lake City UT
348 PM MDT Sun Mar 12 2023

.SYNOPSIS...Unsettled weather will remain over Utah and southwest
Wyoming through Monday. Periods of mainly light valley rain and
snow, along with mountain snow will impact the area. A potentially
significant storm system will bring additional precipitation to
the area late Tuesday through early Thursday.

&&

.SHORT TERM (Through 12Z Tuesday)...A progressive zonal flow
extends across the Great Basin/Desert Southwest region this
afternoon, with a series of weak embedded waves passing through
the flow. One such wave is evident in water vapor imagery crossing
northern Utah, and combined with daytime heating is aiding in
showers from roughly I-80 southward, along with a few
thunderstorms across southwest Utah. As this wave progresses east
and daytime heating diminishes, these showers should quickly come
to and end toward sunset.

Shortwave ridging upstream across eastern NV will quickly build
across the area overnight into early Tuesday, before the next
subtle shortwave trough lifts through the area midday Monday. This
feature will again couple with daytime heating to bring a round of
shallow convection late Monday morning into Monday afternoon. This
activity will again diminish by early evening with the loss of
daytime heating, and the influence of the next shortwave ridge
quickly building into the area.

.LONG TERM (After 12Z Tuesday)...Shortwave ridging over the area is
expected to quickly shift east during the day as a trough moves
onshore along the Pacific coast. Confidence remains a bit higher
than usual for this timeframe in the details of the forecast, which
indicate the arrival of an atmospheric river for the midweek period.
Southwest winds look to become strong and gusty ahead of this
feature Tuesday afternoon and evening where a large portion of
guidance indicates 700 mb winds in excess of 50 kts. This would
normally indicate the potential for advisory level gusts but with
other atmospheric river events as of late, winds have not mixed down
as much as expected which may limit the strength of the strongest
gusts.

Initial shortwave energy makes its way in during the day Tuesday,
allowing moisture and instability to spread across the area.
Location of initial showers will be determined by various shortwaves
embedded in the southwest flow, so there is a bit more uncertainty
in the location of the heaviest snow during this period. However, as
the associated jet streak noses into the area late Tuesday through
Wednesday morning, should see the heaviest snow of the event,
especially for the mountains of northern Utah, which look to be in
the most favorable position for instability. Snow levels at this
time should also be the highest for the event, most likely 7,500 to
8,500 feet, which should limit snow related impacts to the highest
terrain.

Associated cold front is then expected to make its way in with the
main trough during the day Wednesday, shifting the flow to a more
N/NW regime and allowing snow levels to gradually lower, with the
greatest decrease anticipated over northern Utah. Thursday
afternoon, northern Utah precip will be more tied to the terrain
behind the front as the boundary moves into southern Utah through
Wednesday night. The front is expected to exit the area Thursday
morning, with associated precipitation tapering off. Given
increasing confidence in significant snow totals for the northern
Utah mountains, have issued a Winter Storm Watch for that area for
this storm.

Behind the exiting storm, high pressure will move in, likely
bringing a drying trend through the end of the work week. There are
some indications, however, that a more active and unsettled pattern
will return for the upcoming weekend.

&&

.AVIATION...KSLC...Isolated showers decrease in coverage through the
evening. Expect cloud coverage to diminish a bit as well, with VFR
conditions anticipated overnight. Around sunrise Monday, isolated
showers, lowered cloud bases, and increased cloud coverage return.
Could see brief period of -RASN mix in early activity, with temps
supporting all -RA by later in the morning. Isolated precip then
remains possible through the day. That said, aside from precip
directly impacting terminal, expect VFR conditions to prevail.

.REST OF UTAH AND SOUTHWEST WYOMING...Isolated to scattered
precipitation continues through the evening, with a relative lull
expected overnight. Isolated to scattered precip then expected to
redevelop as early as sunrise Monday, and remain a possibility
through the day. While SCT to BKN clouds linger, most locations
should see VFR conditions by evening onward, aside from any precip
directly impacting a terminal. One exception is LGU, where guidance
suggests moderate potential for BR/FG overnight, and correspondingly
lowered VIS. Can't entirely rule out some lowered VIS elsewhere at
northern terminals, but guidance less bullish. Winds generally
expected to be light and diurnally normal to at times variable.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Winter Storm Watch from Tuesday afternoon through late Wednesday
     night for UTZ110>112.

WY...None.
&&

Seaman/Traphagan/Warthen

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
916 PM MDT SUN MAR 12 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0325 PM     SNOW             ROY                     41.18N 112.04W
03/12/2023  M1.0 INCH        WEBER              UT   TRAINED SPOTTER

0340 PM     SNOW             ALTA                    40.57N 111.65W
03/12/2023  M3.0 INCH        SALT LAKE          UT   TRAINED SPOTTER

            SNOWBIRD - 8100 FT

0347 PM     SNOW             PARK CITY               40.61N 111.54W
03/12/2023  M1.5 INCH        SUMMIT             UT   TRAINED SPOTTER

            PARK CITY MOUNTAIN - 9300 FT

0352 PM     SNOW             PARK CITY               40.66N 111.57W
03/12/2023  M2.5 INCH        SUMMIT             UT   TRAINED SPOTTER

            CANYONS VILLAGE AT PARK CITY - 8800 FT

0429 PM     SNOW             ALTA                    40.58N 111.64W
03/12/2023  M4.0 INCH        SALT LAKE          UT   MESONET

            ALTA - COLLINS - 9662 FT

0430 PM     SNOW             BRIGHTON                40.59N 111.58W
03/12/2023  M4.0 INCH        SALT LAKE          UT   TRAINED SPOTTER

            BRIGHTON CREST - 9500 FT

0432 PM     SNOW             BRIGHTON                40.62N 111.59W
03/12/2023  M2.0 INCH        SALT LAKE          UT   TRAINED SPOTTER

            SOLITUDE - 8200 FT

0442 PM     SNOW             POWDER MTN              41.36N 111.71W
03/12/2023  M3.0 INCH        WEBER              UT   OFFICIAL NWS OB

            POWDER MOUNTAIN - 0 FT

0448 PM     SNOW             ALTA                    40.59N 111.64W
03/12/2023  M5.3 INCH        SALT LAKE          UT   TRAINED SPOTTER

            ALTA UDOT - 8799 FT

0521 PM     SNOW             SUNDANCE                40.37N 111.59W
03/12/2023  M3.0 INCH        UTAH               UT   MESONET

            SUNDANCE MID MOUNTAIN - 7450 FT

0555 PM     SNOW             ALTA                    40.64N 111.64W
03/12/2023  M3.0 INCH        SALT LAKE          UT   TRAINED SPOTTER

            BIG COTTONWOOD SPRUCES - 7402 FT

0600 PM     SNOW             ALTA                    40.59N 111.64W
03/12/2023  M5.8 INCH        SALT LAKE          UT   COOP OBSERVER

&&