Flash Flood Warning 43, NWS Salt Lake City, UT

163 
WGUS75 KSLC 172051
FFSSLC

Flash Flood Statement
National Weather Service Salt Lake City UT
251 PM MDT Thu Aug 17 2023

UTC017-055-172215-
/O.CON.KSLC.FF.W.0043.000000T0000Z-230817T2215Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Garfield UT-Wayne UT-
251 PM MDT Thu Aug 17 2023

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 415 PM MDT THIS 
AFTERNOON FOR NORTHEASTERN GARFIELD AND SOUTHWESTERN WAYNE 
COUNTIES...

At 251 PM MDT, Capitol Reef National Park rangers reported heavy 
rainfall producing flash flooding, with Sulphur Creek reaching the 
Visitor's Center and the Fremont River overflowing its banks at 
Fruita Campground. Between 0.5 and 3 inches of rain have fallen, 
with the heaviest totals falling over the Fremont River Basin.

HAZARD...Life threatening flash flooding. Thunderstorms producing
         flash flooding.

SOURCE...Capitol Reef National Park rangers reported.

IMPACT...Life threatening flash flooding of creeks and streams,
         normally dry washes, and slot canyons.

Some locations that will experience flash flooding include...
  Capitol Reef National Park, Torrey and Fruita.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Remain alert for flooding even in locations not receiving rain. Dry 
washes, streams, and rivers can become raging killer currents in a 
matter of minutes, even from distant rainfall.

&&

LAT...LON 3840 11144 3836 11124 3828 11109 3830 11104
      3829 11102 3824 11110 3820 11110 3815 11117
      3810 11132 3822 11136 3830 11145

FLASH FLOOD...OBSERVED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

JAC

801 
WGUS75 KSLC 172208
FFSSLC

Flash Flood Statement
National Weather Service Salt Lake City UT
408 PM MDT Thu Aug 17 2023

UTC017-055-172218-
/O.EXP.KSLC.FF.W.0043.000000T0000Z-230817T2215Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Garfield UT-Wayne UT-
408 PM MDT Thu Aug 17 2023

...FLASH FLOOD WARNING WILL EXPIRE AT 415 PM MDT THIS AFTERNOON FOR 
NORTHEASTERN GARFIELD AND SOUTHWESTERN WAYNE COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose a 
threat. Flows near SR-24 and Fruita Campground have receded. Please 
continue to heed remaining road closures.

LAT...LON 3840 11144 3836 11124 3828 11109 3830 11104
      3829 11102 3824 11110 3820 11110 3815 11117
      3810 11132 3822 11136 3830 11145

$$

JAC

Area Forecast Discussion
National Weather Service Salt Lake City UT
422 AM MDT Thu Aug 17 2023

.SYNOPSIS...Monsoonal moisture will remain in place across the
region, bringing daily chances for showers and thunderstorms
across the area. A moisture surge from Tropical Storm Hilary is
slated to move across the Great Basin region and may bring
significant impacts to the forecast area late in the weekend/
early next week, but there are still some forecast challenges to
work through in that regard.

&&

.SHORT TERM (Through 12Z/6AM Saturday)...The eastern Great Basin
region remains sandwiched between two large scale synoptic
drivers; an offshore low near California and a developing high
over the central Rocky Mountains. Deep atmospheric moisture is
noted between these two features and will continue to drive
diurnally driven showers and thunderstorms across the forecast
area. High terrain and adjacent valley areas from roughly Zion NP
north-northeastward through Uinta Co., Wyoming will see the
greatest chances for seeing any sort of significant precipitation
with scattered storms, whereas areas in eastern and northwestern
Utah will see more isolated storms. Storm motions are expected to
be relatively slow (10-20kts) and on a SW-NE trajectory. For areas
sensitive to heavy rainfall (i.e. slickrock areas, dry washes,
slot canyons, and recent burn scars), the threat of flash
flooding will be elevated... especially for areas like Capitol
Reef NP, Grand Staircase-Escalante NRA, and the various large burn
scars of central and northern Utah. Temperatures will remain near
seasonal today, however, any passing showers will bring potential
to drop temperatures 10-15 degrees cooler than forecast.

Moisture will remain spread across the region through the end of
the week, and into the weekend, keeping chances for showers and
thunderstorms in the forecast for Friday. The caveat here is that
Friday will feature a bit more support from the offshore low,
which will increase the overall coverage of storms, especially
across the southern half of the forecast area. The risk of flash
flooding will remain elevated on Friday and spread a little
further north into northern Utah, where areas featuring steep,
rocky terrain or recently burned areas will see an increased
threat.

.LONG TERM (After 12Z/6AM Saturday)...A complex pattern will be in place
to start the long term period. A ridge over the central CONUS and a
cutoff low off the coast of California will keep a moist southerly
flow advecting into the entire CWA. This will help to develop
afternoon convection on Saturday with the highest probabilities
across southern Utah.

In addition to the typical monsoonal moisture plume, tropical storm
Hilary will be moving up the Baja of California coast with impacts
to portions of the desert SW Sunday through Tuesday. The highest
confidence track currently keeps a bulk of this tropical moisture
across California and Nevada. However, any deviations further east
would result in a greater flash flood potential to Utah and SW
Wyoming. A further track west/east would also result in temperatures
near normal/below normal. Currently there is a marginal risk of
flash flooding across Utah Saturday and Sunday, according to WPC's
excessive rainfall outlook.

Once the remnants of this tropical cyclone passes by to the north
Tuesday the focus returns to a more typical monsoonal moisture plume
that will be moving in from the south/southeast as the
aforementioned ridge remains in place across the center of the
country. This southeasterly flow will be drawing moisture up from
the Gulf of Mexico as tropical moisture will be moving into northern
Mexico/southern Texas. This moisture will remain in place through
the end of the period as ensemble mean PWATs across northern Utah
remain ~1" with near 1.15" PWATs across southern Utah. Expect
temperatures to remain near normal, if not slightly below normal.

&&

.AVIATION...KSLC...Mostly VFR conditions will prevail for the KSLC
terminal through the remainder of the period. Monsoonal moisture
will result in isolated afternoon convection that could briefly
reduce flight categories. Gusty and variable outflow winds could
result from any nearby convection. Otherwise, winds will likely
remain southerly for most of the day with only a brief window of
northerly lake breeze winds in the afternoon.

.REST OF UTAH AND SOUTHWEST WYOMING...Mostly VFR conditions will
prevail for most terminals as a monsoonal plume moving through the
entire region will result in afternoon convection that could create
brief flight category reductions. Additionally, winds will primarily
be out of the south with gusty variable winds associated with any
nearby convection. Convection over the terrain could lead to brief
mountain obscuration.

&&

.FIRE WEATHER...Deep atmospheric moisture will spread across a large majority
of the region today, bringing increased risk of showers and
thunderstorms across Utah. Storms will be diurnally driven and
will favor higher terrain areas, as well as adjacent valley areas.
Due to increased atmospheric moisture content, wetting rain
chances will be anywhere from 30 to 60 percent across the high
terrain (excluding northwest Utah). Heavy rainfall with isolated
flooding, lightning, and gusty outflow winds will be the primary
threats in passing storms. Outside of storm chances, humidity will
continue to be moderated across a majority of Utah with the
exception of portions of northwest and eastern Utah. In these
areas, humidity may drop as low as 20%.

Deep layer moisture will remain in place tomorrow with coverage
of showers and thunderstorms expected to increase across the
southern half of Utah. CWRs will see a significant increase in the
southern and central mountains, as well as the Uintas and
southern Wasatch, and adjacent valley areas with minimal change
expected across far northern Utah.

A much more significant surge of moisture is expected to push
into Utah this weekend, bringing much higher daytime humidity
values, coverage of showers and thunderstorms, and increased
chances for widespread wetting rains. Moisture will remain in
place through at least mid-week next week, keeping the chance for
daily showers and thunderstorms in the forecast.

&&

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

Webber / Mahan

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