Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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390
FXUS65 KSLC 150300
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
900 PM MDT Fri Jul 14 2017

.SYNOPSIS... A weak disturbance will continue to lift slowly
northward across Utah through tonight. High pressure will build
across the region for the weekend bringing hot temperatures.

&&

.DISCUSSION...Thunderstorms are beginning to dissipate this
evening, as the sun sets on Utah and southwest Wyoming. Coverage
of storms today was once again isolated to widely scattered, with
most storms being pulsy and short-lived. Otherwise, it was another
hot day, with the string of above normal temperatures continuing
unabated through the first two weeks of July.

The strongest storms of the day were along the Wasatch Mountains;
formation of thunderstorms aligned along the Wasatch crestline is
relatively rare, but does occur in light easterly flow
situations, which was in place from about 700mb to 500mb across
far northern Utah this afternoon. These storms generally produced
heavy rain, and perhaps some small hail in the strongest storms,
and then produced a good easterly outflow from Salt Lake County
northward as the storms died. These easterly wind gusts have
generally been 25-45 mph, though a couple of gusts in the 50s have
been observed in far northern Utah. Some of these easterlies
could persist into the overnight hours, particularly near canyons,
as a mesohigh has developed over the Wasatch.

The ridge will amplify over the weekend, leading to even hotter
temperatures in most locations. Convective activity should be even
less than the last couple of days, but enough moisture will
continue to linger under the ridge that at least some afternoon
development on the higher terrain is expected. Moisture will
likely increase quite a bit across the forecast area in the first
half of next week; see the previous long term discussion (copied
below) for more details.

Updated the forecast earlier this evening to add gusty easterly
winds to northern Utah, and kept them in place near canyons
through 09Z. No further updates are currently anticipated.

.LONG TERM (After 12Z Monday)... The mid-level ridge axis will
shift east into the four-corners region during the day on Monday.
This along with the encroachment of a Pacific trough will result
in southwesterly flow/improved moisture transport into the area.
Consequently max temps will likely drop a few degrees and
afternoon precip chances will increase Monday relative to Sunday.
The enhanced moisture transport on the periphery of the ridge will
continue Tuesday with widely-scattered precip developing over the
higher-elevation "spine" of Utah with chance precip over
southern/central valley locations.

Guidance begins to diverge mid-week as the GFS more-or-less
maintains/enhances the early week regime while the EC noses a
mid-level ridge directly over the fcst area. The resulting
dynamic subsidence combined with unfavorable moisture trajectories
essentially squash precipitation chances Thursday/Friday. On the
other hand the moist GFS and Canadian solutions would be favorable
for moisture transport resulting in widespread precip over the
mountains and scattered precip over the valleys. Went with a blend
this package with the caveat that PoPs will almost certainly be
either higher or lower depending if the GFS/CMC or EC verifies
respectively. Additionally decided to blend the cooler GFS/CMC max
temps with the drier/warmer EC, because at this point there is no
clear reasoning to prefer one solution over the other.

&&

.AVIATION...Gusty easterly winds will likely continue at the SLC
terminal through at least 04-06Z, with a slight chance that these
easterlies persist past 06Z. After the easterlies dissipate,
southeasterly drainage winds should take over, though continued
light and variable winds are possible.

&&

.FIRE WEATHER...Low level moisture remains in place across the
southern half of the area and therefore isolated heavy rainfall
is possible. Min Rh values will remain somewhat elevated with
readings in the teens. Farther north, isolated thunderstorms are
also expected through this weekend with an increase possible by
Monday as the ridge relocates to the east and allows a southerly
flow to resume.

Models diverge by middle of next week which lowers confidence
drastically. The GFS model shows a moisture plume intensifying
from Tuesday into Wednesday across the southern half of the area,
while the EC model shows a drier west southwest flow behind a
shortwave disturbance that moves across the Northern Rockies. The
southeast portion of the fire district looks to remain rather
moist in either scenario, while the biggest difference in models
will occur over the Northwest.

&&

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

$$

PUBLIC/AVIATION...Schoening
LONG TERM...Carr
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



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