Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 222140

Area Forecast Discussion
National Weather Service Salt Lake City UT
340 PM MDT Tue Jun 22 2021

.SYNOPSIS...Gusty southwest winds will continue through today.
Moisture will increase Wednesday into Thursday bringing showers
and thunderstorms to the state through the end of the week.


.SHORT TERM...(Through 12Z Friday)...Broad, deep-layer
southwesterly flow remains in place across Utah and southwest
Wyoming this afternoon as our region remains situated ahead of a
closed area of low pressure located off of the California coast.
This flow regime will largely remain in place through Friday
morning while gradually weakening. As a consequence of the
southwest flow, moisture advection from the southwest is underway,
and this will continue through Friday morning. An anomalously
moist airmass currently resides across the Gulf of California and
the Baja peninsula of Mexico, and this moisture will stream into
the region through the period, peaking on Wednesday. The
combination of increasing moisture and broad-scale lift via
embedded shortwaves and convectively-induced vorticity maxima
will result in the development of shower and thunderstorm
activity, initiating Wednesday morning across southern Utah and
spreading northward into the northern half of Utah by Wednesday
evening. On the northern fringes of the convective activity, dry
and high- based showers and thunderstorms will dominate, but as
moisture increases, showers and storms will become increasingly a
mix of wet and dry with embedded wet cores. Strong microburst
winds will also be possible with any shower or thunderstorm.
Modest steering flow will be in place Wednesday, so convection
should propagate towards the north and east without remaining
over one particular area for an extended period of time. The
majority of this activity should remain on the dry side with a few
wetter cores -- although we can`t rule out an isolated heavy rain

Shower and thunderstorm will become more isolated in nature as
Wednesday night progresses across southern Utah, while the focus
for the most organized/widespread shower and thunderstorm
activity shifts into northern Utah Wednesday night and Thursday
morning. With the influx in moisture and associated cloud cover
and precipitation, temperatures will cool a few degrees for
Wednesday with further cooling expected for Thursday back down to
near seasonal normals for late June. Additional rounds of showers
and thunderstorms are expected for Thursday across Utah and
southwest Wyoming, with all but portions of the west desert in
line to see measurable precipitation. With less cloud cover and
better surface heating on Thursday, instability is expected to be
greater -- and when combined with deeper moisture and weaker
steering winds, locally heavy rainfall will once again be possible
Thursday. With slower storm motions, the threat for flash flooding
will need to be monitored.

.LONG TERM (AFTER 12Z Friday)...A building area of high pressure
across the PacNW and a low pressure area across central California
will shift the flow aloft to westerly flow that will begin to usher
in some dry air advection into Utah. This introduction of drier air
will reduce PoP chances for the valleys Friday, but there should be
an instability axis tied to the higher terrain of northern Utah and
southwest Wyoming that should be enough to initiate some dry

Heading into next week, we are beginning to see signs of yet another
period of very hot and dry conditions emerging amongst a large
majority of the models and ensemble members. A large amplitude ridge
will begin to strengthen and expand across much of the western CONUS
by the weekend. Utah will just be on the eastern fridge of this
ridge through the weekend, but heading into next week, this ridge
will begin to migrate slowly east putting Utah under its influence.
H7 temperatures beginning Monday are expected to jump into the 16-20
Celsius range across Utah with this trend continuing through the
week. Although signs are emerging of another heatwave, details
regarding the evolution of this ridge and any precedent cloud cover
need to be addressed before we begin to message heatwave impacts. At
this point we are confident for a significant warming trend next
week. Stay tuned!


.AVIATION...KSLC...VFR conditions will persist through the TAF
period. Winds will diminish around 03Z and cloud cover will steadily
increase overnight, with bases lowering to around 10kft through the
morning. The potential for convective activity and thunderstorms
impacting terminal operations begins to increase after 21Z Wednesday.

Rest of Utah and southwest Wyoming...VFR conditions will continue
tonight through tomorrow across the forecast area. Cloud cover will
build in steadily overnight, with bases lowering to around 10kft
through the morning. Most convection should hold off until after
18Z, though the potential exists for earlier activity impacting
central southern Utah terminals.


.FIRE WEATHER...Broad and dry southwesterly flow remains in place
across the region this evening, with widespread critical fire
weather conditions in place due to the combination of very low
relative humidity and gusty south to southwest winds in the 30-40
mph range. These winds will decrease by late evening, but may
still remain locally breezy through tonight.

Looking ahead, moisture will continue to increase from the south
through tonight, and enough moisture will be in place to support
the development of scattered thunderstorms by late Wednesday
morning across southern Utah. This activity is expected to
gradually expand northward into northern Utah by Wednesday
evening, while trending more isolated across southern Utah
Wednesday night, and this activity may persist into Thursday
morning across portions of northern Utah. Red Flag Warnings have
been issued to account for this threat. Activity will become
increasingly more wet in nature by Thursday, with a mix of wet and
dry storms expected. We will assess the need for additional Red
Flag Warnings on Thursday for this activity, but at this time
confidence is too low in both coverage and whether storms will be
predominantly wet vs. dry. Locally heavy rain will be possible on
both Wednesday and Thursday, but especially on Thursday. This may
also increase the potential for flows should enough rain
materialize over burn scars.

Additional shower and thunderstorm activity is forecast across
mainly northeast Utah on Friday, with this activity trending
increasingly isolated through Saturday. Otherwise, dry and
increasingly hot temperatures are forecast to build across the
region by early next week, with more record-breaking temperatures


UT...Red Flag Warning from 6 PM Wednesday to 6 AM MDT Thursday for

     Red Flag Warning until 9 PM MDT this evening for UTZ479>484-488-

     Red Flag Warning from 10 AM Wednesday to midnight MDT Wednesday
     night for UTZ489-492>498.




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