Severe Thunderstorm Warning 20, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
400 PM MDT Wed Jul 13 2022

.SYNOPSIS...Showers and thunderstorms will continue to spread
northward today as moisture increases across area. This moisture
is expected to remain in place into the early part of next week,
bringing daily thunderstorm and flash flooding threats. Meanwhile,
excessive heat continues for northern Utah through at least
tomorrow with some lingering heat through early next week.

&&

.SHORT TERM (Through 12Z/06AM Friday)...A textbook monsoon surge
pattern for Utah is underway with as satellite imagery depicts a
high pressure cell aloft parked over the Four Corners region,
advecting in moisture from the southeast along with weak flow
aloft and an antecedent warm air mass. This afternoon, SPC
mesoanalysis shows 500-1000 J/Kg of MUCAPE, with a bit of a cap on
SBCAPE as of yet over Northern Utah though that should erode
soon. PWATs are just a tick below an inch for most of the area,
highest (a little over 1") in the southwest corner of the state
and lowest in the northwest corner (a little under 0.8"). The flow
direction is favoring convective initiation along the central
spine of mountains in Utah, moving northeastward. Additionally,
recent CAMs are fairly confident in an area of thunderstorms
moving off the higher terrain along the NV/UT border and
translating across the west deserts to the I-15 corridor and the
Wasatch Front this evening. Storms generally east of I-15 and
south of I-80 remain a flash flood threat, while storms elsewhere
are more of a gusty outflow winds threat. For info on the fire
weather implications of this thunderstorm threat, see the Fire
Weather section of this AFD. As is the case for us this time of
year, flash flooding is a threat for any slot canyons, recent burn
scars, and normally dry washes.

As was the case yesterday, expect isolated lingering convective
activity into the overnight hours, bringing continued cloud cover,
limiting overnight decoupling, and promoting another warm night.
KSLC has only had ~5 nights in its climate record with an
overnight low of 80 or higher; the current forecast is 80.
Speaking of heat, the HeatRisk tool shows elevated risks of heat
illness lingering into tomorrow over northern Utah where the
current forecast highs and particularly the lows are abnormal for
many consecutive days. A slight moderation in daytime highs is
expected for the latter portion of this week, partially related to
increased afternoon cloud cover and precip chances, but still
remaining elevated. Will allow the next few shifts to reassess if
we want to continue heat headlines in the form of a long-lasting
advisory. Another record we may approach is the consecutive days
of 100+ for SLC; our current forecast combined with yesterday's
observed high would easily move into the top 10.

Tomorrow looks to be a near carbon copy of today, with a slight
overall uptick in available moisture yet again. One difference is a
better chance of wetting storms for far northern and western Utah
and a slightly reduced  threat of microburst winds.

.LONG TERM (After 12Z/06AM Friday)...The extended forecast period
is expected to be an active pattern of weather with monsoonal like
conditions returning and statewide hot temperatures remaining. An
upper level ridge pattern over the 4 corners area will keep
temperatures across the CWA consistently hot with many areas seeing
100F+ through the entire extended. The ridging pattern aloft also
will help transport a sufficient amount of moisture to the CWA that
will fuel shower and thunderstorm initiation/development. A NW
Pacific trough feature is expected to develop over the extended as
well that could bring a flattened pattern to the ridge, bringing
drier air back to the CWA but there remains uncertainty in the
timing and development of this feature.

Warm temperatures will persist over the CWA through the extended
that could meet excessive heat risk thresholds as forecasted
afternoon highs span from 98-104F for northern valleys and 100-112F
for southern UT while overnight temperatures only fall into the 70s
and low 80s. The moisture being lofted into the CWA could change
these forecasted temps slightly as enough cloud cover could keep
afternoon temperatures cooler from lack of daytime heating but also
keep overnight temperatures warmer from lack of surface cooling.
Anyone with any heat related health issues should continue to
monitor conditions.

Sufficient moisture brought from down south will pool over the CWA
and some guidance is forecasting PWAT values that are 100-200% of
the climatological norm which when combined with proper forcing from
S/SW flow will keep the potential for daily convection to develop
over the CWA. Model guidance currently is pointing towards Friday,
Saturday and Sunday as the most active days as the potential for a
flattened ridge and dry air returning will lessen chances for the
start of the next work week. The best chance for precipitation is
primarily for areas in central/southern UT that are east of I-15
that will get additional forcing from high terrain areas. Strong
S/SW flow will help bring some of this moisture northward leaving
chances for areas in and around the Wasatch/Uinta Mountains to spark
up storms as well. With expected continuous days of precipitation
that will have relatively slow storm motion and potentially moderate
rainfall rates, there will be high potential for flash flooding
situations in many popular slot canyons, national/state parks and
any areas with recent burn scars.

&&

.AVIATION...KSLC...A risk for evening thunderstorms will persist
through approximately 07Z though CIG are expected to be high based.
Any thunderstorms that pass on station have the potential to reduce
visibility temporarily. Meanwhile, southerly wind gusts are forecast
to peak between 02 and 05Z before improving through the overnight
hours. Tomorrow is expected to bring another round of increasing
southerly winds by mid-morning with winds forecast to switch out of
the northwest in the early afternoon. VFR conditions are anticipated
tomorrow.

.REST OF UTAH AND SOUTHWEST WYOMING...A risk for thunderstorms will
continue into the early evening hours before improving overnight.
CIGs are expected to be high based but VIS may temporarily decrease
conditions to MVFR or IFR status on station. Look for diurnally
driven winds otherwise through tomorrow.

&&

.FIRE WEATHER...

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning until midnight MDT tonight for UTZ478-492.

     Heat Advisory until midnight MDT Thursday night for UTZ106.

     Excessive Heat Warning until midnight MDT Thursday night for
     UTZ101>105.

WY...None.
&&

Van Cleave/Selbig/NDeSmet

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

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php

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