Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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227
FXUS65 KSLC 210252
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
852 PM MDT Tue Jun 20 2017

.SYNOPSIS...High pressure will remain in place across the eastern
Great Basin into Wednesday. A series of dry cold fronts will
start a gradual cooling trend after Wednesday, primarily for
northern portions of the forecast area.

&&

.DISCUSSION...Showers and thunderstorms are dissipating across
much of Utah and southwest Wyoming as of 03Z, as the sun goes
down. Organized convection was able to form across the northern
half of the CWA earlier this afternoon, which produced widespread
wind gusts in the 45-65 mph range. Combined with some brief
rainfall, this helped cool off some areas from the record or near
record highs from this afternoon, though temperatures overnight
should remain quite warm under the strong ridge and lingering
cloud cover.

Tomorrow should be a similar day, though perhaps with less
instability and DCAPE available for strong, gusty thunderstorms.
Temperatures will remain hot, with record breaking highs possible.
The hottest temperatures will be in the south and southeast, where
heat warnings/advisories remain in place through Thursday. Winds
will increase the next couple of days as a shortwave moves through
the area; see the previous fire weather discussion below for more
details on how this will impact fire growth potential.

Made a minor update earlier in the evening to the point-and-click
forecast, increasing the thunderstorm coverage before 00Z.
Otherwise, the ongoing forecast looks good, and no further updates
are anticipated. The previous long term discussion follows.

.LONG TERM (AFTER 00Z FRIDAY)...
A shortwave trough will dig southward across the Northern Tier
Friday afternoon flattening out the upper level ridge across the
Southwest. Meanwhile, a weak cold front located across south-
central Utah, will continue to push through southern Utah into
Arizona Friday afternoon into Saturday morning, but given the lack
of moisture, little to any shower activity is expected.

H7 temperatures will cool a few degrees Friday afternoon
across northern Utah, with highs returning to near-normal readings.
Meanwhile, southern Utah will remain unseasonably warm, with high
temperatures 10-15F above average, with a few locations potentially
recording record highs.

Model guidance begins to diverge Saturday as the shortwave trough
continues to dig into Wyoming. The EC and GFS bring the shortwave
trough across central Wyoming, while the CMC pushes the trough
further to the east. Thus, H7 temperatures among the EC and GFS are
about 2C cooler than in the CMC.

The upper level ridge is expected to slowly amplify once again
across the Southwest Sunday through early next week as a shortwave
trough approaches the Pacific Northwest. A few weak vort. maxes
rotating within the upper level ridge along with an increase in mid-
upper level moisture will allow for isolated thunderstorms to
develop across the higher terrain Monday and Tuesday afternoons.
High temperatures will continue  to run about 10F above average
across southern Utah Sunday into early next week, while northern
Utah sees high temperatures about 5F above average.

&&

.AVIATION...

&&

.FIRE WEATHER...
ERC values across southern Utah in the 70th-89th percentile have
been steady for the past 3 days, while northern Utah remains below
the 50th percentile most locations, though ERCs are trending
higher.

A ridge is dominant across the region during the next couple of
days. Excessive heat, single digit RH, and a Haines of 6 will be
common across southern and even parts of central Utah. Across the
North it will remain quite warm and dry, but less so.

Southwest winds increase enough to warrant critical fire weather
conditions Wednesday. On Thursday gusty westerly winds will impact
central and eastern Utah providing another day of critical fire
weather conditions.

A slight cooling trend, especially north, will occur at the end
of the work week with the arrival of several cold fronts. These
boundaries will struggle to reach south central Utah. Low RH
however will carry through the work week across the region.

Thunderstorm activity will be more isolated after today and work
from north to south as the aforementioned cold front makes better
progress into south central Utah.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Excessive Heat Warning until 10 PM MDT Thursday for UTZ019-021.

     Fire Weather Watch from Thursday afternoon through Thursday
     evening for UTZ482-484-488-489-493-494-496-498.

     Red Flag Warning from noon to 10 PM MDT Wednesday for UTZ495-496.

     Heat Advisory until 10 PM MDT Thursday for UTZ013-020.

WY...None.
&&

$$

PUBLIC/AVIATION...Schoening
LONG TERM...Lukinbeal
FIRE WEATHER...Rogowski

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



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