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987
FXUS65 KSLC 262133
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
333 PM MDT Wed Jun 26 2024

.SYNOPSIS...
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Deep layer sub tropical moisture spreading across the
state will support enhanced thunderstorm potential for the
majority of the forecast area through this evening. This moisture
combined with passage of an upper level disturbance will on
Tuesday will enhance the potential of organized thunderstorms for
namely central and eastern Utah. A drying trend will ensue on
Friday.
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&&

.SHORT TERM (Through 12z Friday)...
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Afternoon water vapor and H5
analysis indicate the core of an upper level high over southern
NM/AZ, this coincident with a late season trough impinging on the
local region from the NW...current location along the PacNW.
Quite the set up for late June as the aforementioned high pressure
continues to tap abundant sub-trop moisture, and enhanced
streamlines associated with the trough encroaching is allowing
much of that moisture to be drawn northeastward across the state
this afternoon. PW`s on the rise as such, with lowest values near
.80" in the northeast, highest pushing 1.3" in the southwest.

Initiation of diurnal convection has ensued over the elevated heat
sources across the southern mountains quite similar to the last
few days, but have noted the local environment in this region will
enable ability for more efficient rain with trends in LCL`s
lowering and surface dewpoints on the rise. Highest probability
for localized heavy rain and potential flash flooding extending
from the Bryce Canyon Region east across Escalante and into
Capitol Reef, but not ruling out the lower Grand Staircase Powell
region through this evening.

To the north another area for focused convective potential exists
from east-central Nevada northeast into northern Utah later this
afternoon and evening. Noting a well-defined confluence zone for
convective initiation/downstream maintenance, and modest shear
oriented near the UT/NV border region. Trends in CAMs holding
pat, with scattered convection likely impacting the Wasatch Front
from the WSW after roughly 22/23z. Gusty winds and brief heavy
rainfall anticipated with these storms.

A net downtick in convection will ensue with loss of solar later
this evening (per norm), but further encroachment of the
aforementioned trough will maintain isolated/scattered showers
and the potential for a nocturnal storm over the northern third of
Utah.

Lining up for quite an active day Thursday across central/eastern
Utah with introduction of a dry air impingement aloft (from the
west), and additional forcing/shear/convergence of residual sub-
trop moisture along the downstream side of an attendant boundary.
Higher potential for organized convection midday/afternoon. SPC
already placing the region from Salt Lake southeast to the
4-corners within a marginal risk for wind and hail...efficient
rainers as well...though enhanced storm motions will aid to limit
residence time outside of a training scenario. CAMs introduce
higher probs for excessive rainfall east of the Green River where
WPC places a slight risk over Grand Junction`s forecast area.

.PREVIOUS LONG TERM (After 12Z Friday)...Much drier and cooler
air will move into the region behind a departing trough. This
cooler air will help bring temperatures back closer to normal for
Friday. The cooler air will be fleeting, however, as shortwave
ridging builds back in over the weekend with a return to above
normal temperatures (upper 90s for most valleys with mid 100s
across southern Utah).

A PNW trough starts to approach by Sunday with southwest flow
increasing. This will result in increasing southerly surface winds
Saturday-Monday with winds particularly strong on Sunday with
widespread gusts 30-40 mph. This will increase the fire weather
risk, but guidance has started to introduce a little more moisture
compared to previous runs, so RH values are now forecast to stay
>10% Sunday afternoon as opposed to single digits that were being
forecast in previous runs.

As the trough approaches on Monday there will be a slight chance
(<20% chance) for some afternoon high based thunderstorms
developing. Anything that is able to develop will be capable of
producing microbursts given the dry sub cloud layer. A frontal
passage associated with the trough will scour out the higher
moisture content as drier and cooler air advect into the region.
This will bring the temperatures down closer to normal for early
next week. Winds aloft will remain elevated as the jet stream stays
positioned across the area with a resultant westerly flow. These
elevated winds will mix down during the afternoon so expect breezy
conditions to continue through most of next week with low relative
humidities that will pose a fire weather risk.
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&&

.AVIATION...
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KSLC...Vicinity shower and thunderstorm activity will
increase over the terminal through the mid- to late-afternoon hours,
bringing about a 30 to 40 percent chance of storms impacting the
terminal between about 23-01Z. A drop to MVFR visibility will be
possible with passing moderate to heavy rainfall, as well as gusty
and erratic outflow winds in excess of 25kts. Periods of vicinity
showers will continue through the overnight. Otherwise, northerly
winds will prevail through the evening hours, becoming southerly
after 03Z.

.REST OF UTAH AND SOUTHWEST WYOMING...Scattered showers and
thunderstorms are expected across Utah and southwest Wyoming over
the next 12 hours, with coverage decreasing overnight but still
remaining at least isolated over west-central to northern Utah
through 14Z Thursday. Gusty and erratic outflow winds in excess of
25-30kts are expected near passing showers, with moderate to heavy
rainfall under said showers reducing visibility into the MVFR
category. Outside of erratic winds near showers, winds will be
generally terrain driven and follow typical diurnal trends.
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&&

.FIRE WEATHER...
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The combination of sub-tropical moisture rotating around
high pressure over New Mexico and an upper level storm system
moving on shore over the PacNW has allowed deep moisture to spread
across the entirety of the district this afternoon. Scattered
storm develop will continue to expand across western/northern Utah
through this evening with gusty winds/lightning associated with
storm passages. Likelihood of wetting rains higher with storms
across the south where risk of flash flooding exists from Bryce
Canyon Country eastward.

With further encroachment of the upper low tonight into Thursday,
areas on the western fringe of the district will begin to see a
notable drying trend by the p.m. hours, but central and eastern
portions will retain deep moisture and an increased potential for
strong storms capable of heavy rain and hail.

The drying trend will continue for all areas in earnest leading
into Friday with a significant drop to RH, and increased near
surface winds across the west. Potential exists to flirt with
critical fire weather conditions across the southwest Friday
afternoon. Trends in drying and gustier conditions will increase
each day through Sunday when critical fire weather conditions look
to peak across western portions of the district.

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

$$

Merrill/Mahan/Webber

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