587
FXUS65 KSLC 191023
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
423 AM MDT Wed Jun 19 2024

.SYNOPSIS...Temperatures will trend warmer across the area through
Thursday before anomalous moisture spreads into eastern Utah late
Thursday through Friday, bringing showers and thunderstorms with
locally heavy rainfall and an associated flash flood risk. Drier
conditions are expected over the weekend and into early next week
with hot temperatures.

&&

Key Messages:

* Anomalous moisture will work into eastern Utah, mainly along and
  east of I-15 by Thursday night and Friday. This moisture will
  support locally heavy rainfall and an associated flash flood
  risk Thursday night and Friday. Areas most as risk include
  recent burn scars, slot canyons, normally dry washes and
  slickrock.

* Heat re-surges across the forecast area, allowing high and low
  temperatures to rise to 10-15 degrees above average by Sunday.
  Hot temperatures combined with warm overnight lows will bring an
  increasing risk of heat related illness through at least
  Monday, especially for the urban areas.


.SHORT TERM (Through 12Z/6AM Saturday)...Early Wednesday morning,
increasing deep-layer southwest flow was commencing across the
region in advance of a trough in place across the western CONUS
coastline. As a result of the developing southwest flow, a warming
trend will develop today, with temperatures returning to seasonal
normals for mid-June. On Thursday, the above-mentioned trough
will strengthen as it progresses eastward into the Great Basin.
Meanwhile, the remnant moisture associated with Potential Tropical
Cyclone 1 over the Western Gulf of Mexico will advect
northwestward across the Four Corners. The leading edge of this
anomalous moisture will reach southeast Utah late on Thursday.
Along the leading edge of the moisture field, scattered showers
and thunderstorms will develop over southeastern and eastern Utah
late Thursday afternoon. Initially, the low-levels will remain
quite dry, so isolated dry lighting and gusty outflow
winds/microbursts will be the main threat. HREF wind probabilities
show widespread convectively-induced gusts in the 50-60kt range
from south-central Utah through eastern Utah, with a 30%
probability contour for gusts reaching/exceeding 50kts having
appeared in the 19.00Z run.

Total column moisture advection will persist Thursday night and
Friday, especially along and east of the I-15 corridor. At the
same time, the above-mentioned trough and associated jet will
promote an area of upper divergence across the area. Forecast
soundings and plan views show the presence of a modest low-level
jet nosing into SE Utah as well, providing mid-level convergence.
Finally, PWAT values are forecast to increase to around 1.2" or
250% of normal (nearly 4SD), which is near-record for this
typically dry time of year. GEFS QPF probabilities are in the 99th
percentile for the time of year, and EFI reaches 0.8 with SoT
values above 2. Model QPF shows a couple of corridors of 1-2" on
Friday. As a result of these ingredients, and after collaboration
with WPC and Grand Junction, a slight risk (level 2 of 4) was
added to the Excessive Rainfall Outlook (ERO) for Day 4 (Friday).
In addition, MUCAPE values surge into the 1000-2000J/kg range
Friday, and 0-6km bulk shear increases into the 35-45kt range.
These ingredients also point to the potential for a few organized,
strong thunderstorms. As is typically the case in these very
moist environments, there is lingering uncertainty regarding the
total cloud cover. Thick cloud cover will limit SBCAPE generation,
leading to weaker convection with a limited heavy rainfall
threat. Indeed, models do indicate significant cloud cover during
the morning, but tend to thin it out by afternoon. Thus, the
strongest cells may actually form on the edge of the cloud shield
(along the differential heating boundary) from Zion through
central Utah. This will need to be watched. A Flood Watch may also
be considered for Thursday night and Friday.

What does this all mean for you? Know that given the ingredients
will be in place to support strong thunderstorms capable of
damaging winds, hail and locally heavy rainfall that could lead
to a couple of instances of flash flooding. Areas where the
vulnerability is highest include slot canyons, recent burn scars,
normally dry washes and slickrock. Those with plans to recreate
across Utah on Friday, especially along/east of I-15 may consider
alternate plans. West of I-15, increasingly hot temperatures will
return, with highs returning to 5F to 15F above normal for Friday,
with the greatest departures across northern Utah.

.LONG TERM (After 12z/6AM Saturday)...Heading through the weekend
models maintain solid agreement on an area of high pressure building
back into the forecast area. This area of high pressure will allow
temperatures to rise back up to around 10-15 degrees above normal
across the area, especially across the northern half of the area.
This will be record challenging heat. For example, the high
temperature forecast for SLC on Sunday, June 23 is 100 degrees while
the record for the day stands at 101 degrees (set back in 2012). In
addition to the daytime heat, overnight lows will remain fairly
elevated in the low- to mid-70s, particularly across urbanized areas
of northern Utah. For southern Utah, particularly lower Washington
County, lows may not even drop below 80 degrees. The combination of
the high daytime temperatures and minimal relief during the
overnight hours raises concerns for those who are sensitive to heat
and those with insufficient cooling methods. Will need to continue
to assess the need for heat related headlines through at least
Monday as this is the period where temperatures will be highest.

Precipitation-wise, much of the northern half of the area will
remain dry under the influence of the high, however, moisture will
linger over the southern half of Utah and bring a chance for showers
and thunderstorms through at least Monday. Ensemble guidance from
the EPS and GEFS still shows precipitable water values of upwards of
175-225% of normal along roughly the southern half of Utah. There is
still some uncertainty revolving around how far north this moisture
will creep, which is dependent on how much an active northern jet
stream will suppress the high early in the week. Nonetheless, should
still see at least isolated to scattered showers and thunderstorms
over southern Utah late in the weekend/ early in the work week.
Higher than normal PWAT values will bring increased concern for
flash flooding in the typical problem areas. Will need to see how
models trend through the week... but the potential is there.

&&

.AVIATION...KSLC...Minimal operational concerns are forecast for the
KSLC terminal today. Light and variable flow will prevail through
the mid-morning, transitioning to a light northerly flow around 15-
16Z. North winds prevail through the day, returning to southerly
drainage flow in the evening.

.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions under high
level cloud cover across the northern area will prevail through the
day. Winds will be generally light and terrain driven across most
terminals through the day.

&&

.FIRE WEATHER...A warming trend will get underway today with
temperatures returning to seasonal normals for the middle of
June. The warmup will be courtesy of strengthening southwest flow
in advance of a developing trough near the California coast. Very
dry air remains in place, especially across central and southern
Utah. Pockets of near critical fire weather conditions will
develop this afternoon, particularly over those areas of southern
Utah where critically dry fuels, southwest wind gusts near 25 mph
and humidities below 15 percent overlap.

Moisture will gradually stream into the area from the southeast
on Thursday. Enough moisture will work into the area to foster the
development of isolated to eventually scattered showers and
thunderstorms. Initially on Thursday afternoon, dry air will
remain in place in the low levels, supporting isolated dry
lightning and gusty thunderstorm outflow winds. Showers and
thunderstorms will become increasingly wet Thursday night as
moisture continues to flow into the area from the southeast. On
Friday, the upper trough will be located just west the area. This
will combine with the continued increasing moisture to support
widespread showers and scattered wet thunderstorms for mainly
areas along and east of I-15. Some of this activity will be
capable of producing heavy rainfall and isolated flash flooding.

Drier air will quickly move back into the area this weekend, but
lingering low level moisture over eastern areas will promote
isolated showers and thunderstorms. Hot and dry conditions will
overspread the state on Sunday, with highs around 100F for
northern valleys. Early next week, enough moisture lingers over
southern Utah to promote isolated showers and thunderstorms.
Otherwise, hot and dry conditions will persist, especially over
central and northern areas.

&&

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

$$

ADeSmet/Webber

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