Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
411 AM MDT Fri Sep 10 2021

.SYNOPSIS...The ridge of high pressure over central New Mexico
will continue to be flattened as a trough moves from northern
California this morning to across the Northern Rockies late
tonight through Saturday. A zonal flow with embedded disturbances
is expected to stream across the northern Great Basin Sunday into
the middle of next week.

&&

.SHORT TERM (Through 12Z/6AM Monday)...Moisture is increasing over
western portions of the CWA this morning with a few rain echoes
showing up across the western valleys overnight. With a dry sub-
cloud layer, these radar echoes are not resulting in rain at the
surface but they are producing gusty isolated outflow winds. This
trend is expected to continue today with the areal coverage
increasing over the mountainous spine of Utah from Boulder
Mountain northward to the Uintas. Gusty winds and frequent
lightning will be the main hazard from these storms today.

The winds over western valleys will be quite breezy this afternoon
as the 700mb winds increase to about 30kts. The good news is that
the southerly winds will bring in smoke free air into all of Utah
and southwest Wyoming by this afternoon, which will be nice for a
change. Although the winds aloft shift to the west Saturday, smoke
is not expected to be readily available initially so another day
of little if any smoke likely.

A trough moving across northern California this morning will
sweep NE into northern Idaho by this evening. The associated cold
front with very little upper dynamic support will move into NW
corner of Utah this evening and then begin to fade due to lack of
dynamical support. Although the main dynamics will remain north of
Utah, the lapse rate between 700 and 500mb will be about 18C
which is sufficient to create instability from about I-80
northward tonight. In addition, the GFS brings PWs up to about 1
inch across GSL desert and Wasatch Front tonight so the forecast
of likely showers appears reasonable. As the remains of the
associated cold front sags farther south and east into southwest
Wyoming, it should be a focusing mechanism for showers and
thunderstorms Saturday from the central mountains NE across the
Uintas into SW Wyoming. Precip amounts once again are not expected
to be more than 0.10 of an inch for most places. This area of
instability will dissipate Saturday night, but enough moisture
will remain over the Uintas for isolated showers on Sunday.

The south will largely remain rain free, other than isolated
showers mainly over the mountains Saturday afternoon.

Temperatures will be 8-12 degrees above normal today across the
board, but with cooling of about 4 to 5C at 700mb over the
northern portions by Saturday, temperatures will be about normal
in the north, but the cooling will be marginal at best in the
south. Similar temperatures are expected across the south Sunday,
but they should increase a couple of degrees by Sunday due to less
clouds.

.LONG TERM (After 12Z/6AM Monday)...Remnant energy in zonal
flow will keep a chance for rain showers in southwest Wyoming and
northeast Utah Monday morning. Isolated to scattered convection is
expected in the afternoon in the same region. The ridge that has
resulted in warm and dry conditions this week will be oriented more
east-west, which will keep zonal flow in place. There are
differences in ensemble guidance in shortwaves within the mean flow
moving through. Some minor temperature differences are likely going
through the week as they move through southwest Wyoming and northern
Utah. Those could bring enough dynamics for an isolated shower or
thunderstorm, but the zonal flow won't have much moisture within it.
Therefore, most places will remain dry through through the week.
With zonal flow, temperatures will remain right around average in
the north. With more influence from the elongated ridge, the south
will have temperatures near or slightly warmer than average.

&&

.AVIATION...KSLC...VFR conditions are expected through the
valid TAF period. South winds will increase, with gusts likely
exceeding 25 knots in the afternoon. Isolated to scattered showers
and thunderstorms are likely in the afternoon, with the best chances
after 21Z. The main threat will be gusty, erratic outflow winds.
Winds will diminish in the evening, but isolated to scattered
showers and thunderstorms will last into Saturday.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected
through the valid TAF period. Gusty southwest winds will likely top
30 knots at many locations. Isolated to scattered showers and
thunderstorms are expected after 18Z. Southwest Wyoming and northern
Utah have the best chance for showers and thunderstorms. Gusty,
erratic outflow winds will be the main threat. Winds will diminish
in southwest Wyoming and all of Utah in the evening, but isolated to
scattered showers and thunderstorms will last into Saturday in
southwest Wyoming and northern Utah.

&&

.FIRE WEATHER...The dominant ridge of high pressure will move farther
east today allowing an increase of mid level moisture to work its
way northward across the region. Isolated to scattered mainly
high-based thunderstorms will develop over the mountain spine of
Utah this afternoon, as well as over the northwest corner of Utah
ahead of an approaching trough. This trough will increase
convection this evening and through tonight across northern Utah
north of about I-80. Showers will be likely in this area, but rain
amounts are expected to be rather light at under 0.10 of an inch
in general, but locally more is possible. Southern Utah valleys
are expected to remain rain free through tonight, but isolated
showers could reach into zones 492 and 494 Saturday. The RH values
are expected to remain above 15% today after several previous
days of lowering into upper single digits. Temperatures will still
be about 6-12 degrees above normal today but lower to near normal
across the north Saturday and be 4 to 8 degrees above normal
across the south. Temperatures Sunday through middle of next week
will be near to about 4 degrees above normal in the north and
remain about 4-8 degrees above normal across the south. Min RH
values will gradually lower from the upper teens and lower 20s
Sunday to the lower to mid teens by Thursday, while the south will
have RHs in the teens Sunday but then drop into the lower teens
to near 10% by midweek.

&&

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

SHORT TERM...Struthwolf
LONG TERM...Wilson
AVIATION...Wilson
FIRE WEATHER...Struthwolf

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php

Hazardous Weather Outlook
National Weather Service Salt Lake City UT
417 AM MDT Fri Sep 10 2021

UTZ101>131-WYZ021-111200-
Great Salt Lake Desert and Mountains-Tooele and Rush Valleys-
Eastern Box Elder County-Northern Wasatch Front-Salt Lake Valley-
Utah Valley-Cache Valley/Utah Portion-Wasatch Back-
Bear Lake and Bear River Valley-Wasatch Mountains I-80 North-
Wasatch Mountains South of I-80-Western Uinta Mountains-
Wasatch Plateau/Book Cliffs-Western Uinta Basin-
Western Millard and Juab Counties-Eastern Juab/Millard Counties-
Central Mountains-Sanpete Valley-Sevier Valley-Castle Country-
San Rafael Swell-Southwest Utah-Lower Washington County-
Zion National Park-Southern Mountains-Upper Sevier River Valleys-
Bryce Canyon Country-South Central Utah-
Capitol Reef National Park and Vicinity-Western Canyonlands-
Glen Canyon Recreation Area/Lake Powell-Southwest Wyoming-
417 AM MDT Fri Sep 10 2021

This Hazardous Weather Outlook is for the western two thirds of
Utah and southwest Wyoming.

.DAY ONE...Today and Tonight

Gusty winds from mainly high based showers and thunderstorms will
be the main hazard today. An increase in shower and thunderstorm
activity is forecast to develop tonight over northern Utah in
conjunction with a cold front.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Isolated showers and thunderstorms will likely continue across
central and northern Utah and SW Wyoming through Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please relay any information
about observed severe weather to the NWS while following all
local, state, and CDC guidelines.

For more information from NOAA/s National Weather Service visit...
http://weather.gov/saltlakecity

For information on potential road travel impacts visit...
http://www.udottraffic.utah.gov/roadweatherforecast.aspx

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