363
FXUS65 KSLC 262146
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
346 PM MDT Fri Jul 26 2024

.SYNOPSIS...Moisture will be in place across the entire state
through Friday night, resulting in the threat of showers and
storms areawide through this time. Drier air will move in for the
weekend with increasing winds, resulting in critical fire weather
conditions for central and southern areas. Dry conditions with
lighter winds and gradually warming temperatures will greet us for
early next week, and continue through at least midweek.

&&

.SHORT TERM (Through 00Z Monday/6PM Sunday)...Early Friday
afternoon analysis depicted a departing shortwave propagating
northeastward across central Wyoming, with an upstream shortwave
tracking across southern Nevada. Behind the northern-most
shortwave, mid-level subsidence was delaying the onset of
convection across northern Utah and SW Wyoming (with the exception
of the Uintas), while the southern-most shortwave was aiding in
convective initiation across eastern Nevada and southern Utah. In
general, latest guidance has shifted main area of highest
probabilities for convectively-driven winds southward through
this evening, as well as the highest probabilities for heavy
rainfall. Earlier guidance was in good agreement that northwest
Utah would have the greatest potential for gusty winds, but that
has now shifted to mainly central and southern Utah, although
while probabilities still exist for northern Utah, they have
certainly fallen since yesterday. This lowers confidence in
expected convective evolution this evening. Sifting through the
guidance, and based on trends, it appears convective initiation
has largely been terrain-based, with best shear across northwest
Utah. Given this, would expect central/southern Utah convection
will gradually diminish after sunset, however CAMs do indicate
some form of northward-propagating cold pool across central Utah
this evening, perhaps fizzling out by the time it reaches the I-80
corridor. As we head through the evening and overnight, upstream
shortwave will propagate across southern and central Utah,
reaching northern Utah Saturday morning. As a result, focus for
convective activity will shift across northern Utah and SW Wyoming
overnight into early Saturday morning. Main threats with any
activity will continue to be gusty, erratic outflow winds, briefly
heavy rain and frequent lightning.

On Saturday, expect a lull in activity from mid-morning through
early afternoon as subsidence will be in place in the wake of the
above-mentioned shortwave. However, yet another, more potent
shortwave and associated modest jet streak will track across
northern Nevada Saturday afternoon, and through southern Idaho
through Saturday night, with another, loosely-defined shortwave
tracking across central Utah. As a result, expect scattered
thunderstorms to develop across northern Utah later Saturday
afternoon through the evening, with isolated thunderstorms for
eastern areas. HREF max wind plot is quite bullish on its wind
gust output Saturday afternoon and evening, with 30% probability
contour of 58 mph wind gusts appearing across eastern Utah.
Digging into the details, this has merit as winds will increase to
around 30kts at the top of the boundary layer, and mid-level dry
advection will give an extra boost to downdrafts. In addition,
ensemble max QPF shows some impressive values (1-2" in 1 hour)
across portions of northern Utah, thanks to lingering anomalous
moisture and aid of large-scale ascent, so can`t rule out some
localized flash flood concerns here, especially where
thunderstorms with heavy rain cores train. Showers and
thunderstorms are then expected to continue near the Idaho border
for much of Saturday night before diminishing towards sunrise
Sunday morning.

Outside of convective potential Saturday, impressive dry
intrusion across central/southern Utah will team up with 30kt
winds at the top of the boundary layer to support a well-mixed
boundary layer, with afternoon gusts in the 30-40 mph range across
much of central and southern Utah. This will result in critical
fire weather conditions when combined with minimum afternoon/early
evening humidity values less than 15% along with critically dry
fuels.

.LONG TERM (After 00Z Monday/6PM Sunday), Issued 357 AM MDT...
There is strong agreement in a dry stretch of weather starting
Sunday and continuing through most of the week. For the end of the
weekend, a broad, weak trough will be positioned in the western
U.S. That will keep a powerful ridge to the southeast. With that
synoptic set up, as what`s likely prior to that, gusty southwest
winds are forecast. The pressure gradient will be a bit weaker
Sunday, so wind speeds and gusts will be slightly lighter. Minimum
relative humidity will be in the single digits, so enhanced fire
danger will continue. Temperatures will be near normal, with low
to mid 90s for most valleys.

Minimal change is likely Monday, as the broad trough will be in
place to the west. The ridge will likely build slightly to the
northwest, which would allow for slightly lower wind speeds and
gusts.

Ridging will build northwest Tuesday. That will allow for lighter
winds throughout southern Utah, with similar speeds from Monday for
southwest Wyoming and northern Utah.

The ridge will build into the Four Corners area Wednesday.
Precipitable water values will be slightly higher throughout
southern Utah, with an isolated shower or thunderstorm capable of
gusty, erratic outflow winds.

Models bring increased moisture late in the week as the ridge builds
more northwest, but with a lack of strong forcing, showers or
thunderstorms will be isolated and during the afternoon and evening.
Temperatures will increase to the mid to upper 90s for most valleys,
with lower Washington County around 105F Thursday and Friday.

&&

.AVIATION...KSLC...The lake breeze, currently sitting over the
northern half of the runways, is likely to push southward, producing
northwesterly winds (instead of northerly over the north half and
southerly over the south half). These winds will then transition to
S around 02-03z as outflow reaches the terminal from some showers at
the south end of the valley. Scattered showers/isolated
thunderstorms are likely overnight, beginning around 09-10z, likely
exiting the area by 15z. With these showers, winds may be gusty and
erratic at times, with a 25% chance of lightning. Wind direction
after 15z continues to be low confidence due to gusty outflow.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms will continue to develop this afternoon across
portions of central and southern Utah, slowly shifting northward.
These showers could produce gusty and erratic winds, especially
further north; there is a 5% chance of winds exceeding 50kts across
northwestern Utah. More showers and thunderstorms will move into
northern Utah overnight along an upper-level disturbance. These
showers will reach the Wasatch Front as early as 08z (KPVU),
gradually pushing northward. KLGU in particular could see some
heavier rain and gustier winds as the showers strengthen after
sunrise.

&&

.FIRE WEATHER...A moist airmass remains in place across much of the
area today, although drier air will start to move into southwest
Utah tonight. Expect another evening of scattered showers and
thunderstorms, with some of the stronger storms capable of
producing wetting rain. Another weather disturbance crossing into
Utah tonight will maintain showers and thunderstorms through the
night across portions of northern Utah. By Saturday, increasing
southwest flow will bring more significant drying to much of
southern and central Utah where afternoon relative humidities are
expected to lower to 15% or below, with relatively poor overnight
recoveries. Meanwhile, isolated to scattered showers and
thunderstorms will continue across northern and eastern portions
Utah through Saturday evening before the dry air overspreads the
entire area, remaining in place through at least the first half of
next week. The increasing southwest winds on Saturday will
combine with the low humidities to result in critical fire weather
conditions across much of southern and central Utah. Some areas
will continue to see critical fire weather conditions through
Sunday and potentially beyond, although winds will be a bit weaker
compared to Saturday. Pockets of critical fire weather conditions
will persist across portions of southwest Utah on Monday and
Tuesday, but currently it appears too marginal for a fire weather
headline. Otherwise, expect steadily warming temperatures through
the week with generally poor overnight recoveries. A return to
isolated thunderstorms is expected across southern Utah by
Thursday and Friday.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning from 10 AM Saturday to 10 PM MDT Sunday for
     UTZ482>484-488-489-492>498.

WY...None.

&&

$$

ADeSmet/Cunningham/Wilson

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