Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 062201

Area Forecast Discussion
National Weather Service Salt Lake City UT
401 PM MDT Thu May 6 2021

.SYNOPSIS...Dry and warm southwesterly flow will prevail across
the region through Friday morning. A cold front will move through
northern Utah and southwest Wyoming late Friday, with relatively
cool and conditions continuing for the upcoming weekend and into
early next week.


.SHORT TERM (Through 12Z Sunday)...Utah and southwest Wyoming are
under a warm and dry southerly flow this afternoon on the back
side of a ridge centered near the Utah/Colorado border/ A few
cumulus clouds are bubbling over the higher terrain, most numerous
over central and southern Utah, but skies are otherwise clear.
Temperatures have warmed noticeably compared to yesterday, with
high temperatures approaching 20F above seasonal normals for many

Southerly flow will increase over the area tomorrow as a storm
system moves onshore along the Pacific coast. Breezy winds will
combine with the continued dry conditions to produce critical fire
weather conditions where fuels are dry over southern Utah. See the
fire weather section of the AFD for more details. Temperatures
will remain warm over the state for much of the day, but
increasing cloud cover will result in maxes just a few degrees
cooler than values observed today.

The Pacific storm system will bring a frontal boundary through
northern portions of the forecast area Friday evening through
early Saturday. Frontogenetic forcing will allow for a band of
precip to develop right along the front, though the lack of
moisture will keep accumulations on the light side and the
disorganized nature of the system will limit precipitation outside
of this band. The more noticeable impact of the front will be on
temperatures; maxes Saturday are expected to run in excess of 20F
below values observed Friday across northern Utah. Over southern
Utah, cooling will not be as significant, but highs will still be
10F or so cooler than Friday. The majority of guidance indicates
the second piece of the Pacific system will graze northern Utah
during the day Saturday, bringing a reinforcing shot of cooler air
but little in the way of precipitation.

.LONG TERM (After 12Z Sunday)...A mean trough settling over the
Interior West over the weekend will bring a notable change in the
prevailing conditions across the forecast area through the early
portion of the work week ahead. Thereafter, a ridge builds into the
region, allowing for rebounding temperatures to above average levels
with dry conditions prevailing.

By Sunday, a longwave trough will be centered north of the area,
repositioning itself over the Great Basin region by Sunday evening
as a stout shortwave rotates along the base of the trough. The
net effect of this trailing shortwave will bring a reinforcing
shot of cooler air aloft, and a rather widespread round of showers
as a further moisture tap is introduced. While ensemble means are
in good agreement of moving this feature over the area, there is
some disagreement with the overall depth of the feature. This
discrepancy in the depth of the trough will mainly influence two
parts of the forecast... the first being the overall areal extent
of the precipitation, and the second being the amount of cooling
across the southern half of the CWA. EPS and control solution have
the trough shunted further northward, favoring a large majority
of precip for areas north of I-70 with minimal cooling across the
south. On the other hand, GEFS and control solution continue to be
more in favor of a deeper trough that would favor greater cooling
across the south and a greater extent of precip to areas south of
I-70. With this in mind, best chances for precip look to be for
the high terrain and adjacent valleys (mainly east of terrain)
north (east) of the I-70 (I-15) corridor. Timing-wise, chances for
precip begin to increase Sunday afternoon/ evening, with the most
likely timing looking focused during the afternoon hours on
Monday as the 500mb cold core rotates overhead, allowing
widespread convective showers to take over.

By Tuesday afternoon/ evening, the axis of the mean trough looks to
clear the forecast area, with chances for precip dropping off
quickly by the evening hours as a ridge begins to build over the
eastern Great Basin. As this ridge continues to build into the
region through the latter half of the week, temperatures will rise
back to above normal levels for the entirety of the CWA by Thursday.
Another trough looks to make potential impacts by next weekend, but
details are far to uncertain at this time... more to come as we head
through the week.


.AVIATION...KSLC...VFR conditions are expected at KSLC through the
valid TAF period. Winds will prevail out of the northwest, but
variable winds are expected at times through 03Z. Winds will
prevail out of the southeast after 03Z. Increasing high clouds are
expected into Friday afternoon along with increasing
south/southwest winds, gusting to 20- 25 kts. A cold front moving
through Friday evening could result in virga with enhanced outflow
gusts and scattered rain showers between 00Z-06Z.

Rest of Utah and southwest Wyoming...VFR conditions are expected
through the valid TAF period. Southwest winds gusting over 30 kts
are expected Friday afternoon in southern Utah. To the north, gusts
of 20-25 kts are expected. A cold front moving through southwest
Wyoming and northern Utah Friday evening could result in virga with
enhanced outflow gusts and scattered rain showers between 00Z-06Z.


.FIRE WEATHER...Southerly winds will pick up in earnest tomorrow
ahead of an approaching storm system. The breezy conditions will
combine with the continued dry airmass to produce critical fire
weather conditions for much of the day where fuels are dry.
Because of this, have issued a Red Flag Warning for areas of far
southern Utah. The arrival of a cold front Friday evening will
decrease winds and cool down the airmass, decreasing fire danger
over the upcoming weekend.


UT...Red Flag Warning from 11 AM to 9 PM MDT Friday for UTZ497-498.



LONG TERM...Webber

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