Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 172128
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
328 PM MDT Thu Aug 17 2017

.SYNOPSIS...A warming and drying trend will continue across the
area through Friday. Moisture will increase again from the south
over the weekend.

&&

.SHORT TERM (THROUGH 12Z SUNDAY)...The upstream trough is carving
westward through the southern California coast this afternoon as it
pinches off into a closed low. Meanwhile, over Utah, a drier
northwesterly flow has settled into the area with PWATs now
generally in the 0.6-0.7 inch range. Despite some cumulus blowups
over the higher terrain, mesoscale analysis shows very limited
instability, and as a result this shallow convection is amounting to
just a few weak showers that are hardly electrified. These showers
are expected to wane this evening with the loss of daytime heating.

Expect most of tomorrow will be similar to today but even less
convection may be in store for northern Utah where it will continue
to trend drier. However, weak disturbances rotating around the
southern California low could start to impact the area by late in
the afternoon. The GFS and NAM indicate that an ejecting wave could
enhance convection across southwest Utah late in the day tomorrow
and could potentially keep a few nocturnal showers going into
central Utah tomorrow night. This wave will then focus convection
across central Utah on Saturday. However, moisture will remain
limited during this time so any thunderstorms that develop are not
expected to be very strong and rainfall will remain light.

.LONG TERM (After 12z Sunday)...The upper level low is forecast to
remain mostly stationary off the California coast through mid week,
while moisture is transported northward into southern and central
Utah through the week. With several shortwaves rotating up from the
southwest through southern and central Utah starting Monday, the
overall pattern through the week looks quite unsettled for
convection each day.

Overall upward trend in the PoP forecast through the extended. The
slowness of the GFS to eject the upper Low from the
Nevada/Utah/Arizona tri-point area and the ECMWF similar pattern
through Thursday, differences aside, made me lean towards a more
unsettled solution. The previous model runs of the GFS seem to be in
better agreement compared to the previous versions of the EC, so
leaned a bit more towards the GFS, which ironically is a bit of a
wetter solution. Confidence of timing and exact location of the best
opportunity for precipitation and convection is low, but the pattern
definitely has more moisture drawn northward into Utah from the
monsoon pattern. Temperatures in the extended seem to remain mostly
unchanged even with this pattern; just enough daily instability and
convective cloud cover to help temperatures remain near seasonal
normals.

&&

.AVIATION...VFR conditions will prevail at SLC throughout the
TAF period. Northerly winds will shift to the southeast around 03Z.

&&

.FIRE WEATHER...The airmass continues to trend drier and more stable
across the fire district with some weak showers coming off the
higher terrain through this evening. Much of the same is expected
tomorrow, although convective activity could be even less across
northern Utah. A weak disturbance is expected to lift across
southern and central Utah on Saturday which could increase the
chances of showers and thunderstorms, although the chance of wetting
rain will remain on the low side. Moisture will then increase from
the south beginning Sunday and linger through the middle of next
week.

&&

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

$$

Cheng/Dewey/Carr

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