Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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854
FXUS65 KSLC 221543
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
943 AM MDT Sat Jul 22 2017

.SYNOPSIS...Drier air will gradually spread back into the area
from the northwest through Sunday. Deeper moisture will return to
Utah early next week.

&&

.DISCUSSION...A mid level high circulation oriented over the
UT/ID border will maintain north/northeast flow aloft across the
forecast area today. Drier mid level air advecting in from the
northern/eastern peripheries of this low has spread into southern
UT overnight, though PWATs near an inch and dewpoints in the low
to mid 50s across remain in place across the southern third. A PV
anomaly exists over the 4-corners attm and will slowly face west
along the the UT/AZ border riding the return flow easterly
trajectories.

Focus for convection today will remain across the south coincident
with the remnant deep moisture and greatest potential for modest
diurnal destabilization. The westward translation of the PV
anomaly this afternoon may aid initiation, though anticipation is
for yet another airmass TS day initiating over the terrain then
phasing SE into lower elevations while riding weak outflows later
in the afternoon. Isolated heavy rain potential remains a threat
across the far south today, but not as much so as the last few
days.

Updated earlier to largely remove morning PoPs across the SW as
remnant nocturnal convection has since waned. Tweaked sky cover to
follow recent clearing trends as well. Previous discussion
below...

PREVIOUS DISCUSSION...As the ridge center slowly shifts eastward,
the deeper moisture that had been sitting over Arizona looks to
begin moving north into Utah starting Sunday afternoon/evening,
though the best push will likely hold off until Monday morning.

The broad upper level ridge will shift slightly eastward
beginning in the extended period as a trough meanders up the
Pacific Coast through the first half of the week. The cyclonic
flow will pull moisture from the Gulf into southern Utah and the
southern Great Basin Monday into Tuesday. Forecast precipitable
water across southern Utah (the more favored moisture rich
environment) soars from 0.8 inch to 1.0 inch previously, to near
1.5 inch by Tuesday. The 1.0 inch contour shifts northward across
western and northern Utah. The mid-level steering flow becomes
unsettled and disturbed Tuesday, lending to an active storm day
across the area. Trended PoPs upward late Monday through early
Wednesday for this pattern shift. Mid level mixing ratios jump to
12-14 g/kg across southern and eastern Utah through Wednesday,
pointing to a very moist environment with rather weak steering
flow This should point to an enhanced threat for flooding concerns
Tuesday into Wednesday. The timing of the moisture surge may play
a part into diurnal heating and storm evolution, but the
ingredients are in place. Will have to keep an eye on how this
pattern evolves.

As the trough feature shifts inland and through the Northern Rockies
late in the week, the high shifts eastward with the best moisture
also moving east and a drying (subtle) moving in from the west.
Perhaps a brief break in the thunderstorm and rain shower activity
to end the week. Temperatures aloft change very little day to day,
and suspect the moisture and cloud cover will play a bigger role in
how the temperatures react. Have kept a pretty minimally changing
day to day temperature trend through the going week ahead.


&&

.AVIATION...Operational weather concerns will remain minimal at
the KSLC terminal through the valid TAF period. Southeast winds
currently in place are expected to switch to the northwest between
18-19z per norm. VFR conditions will be maintained under largely
clear skies.

&&

.FIRE WEATHER...A drying trend from the northwest is continuing across
Utah today, with mostly sunny skies expected across much of the
north. In the southern half of the state, isolated to widely
scattered showers and thunderstorms will again be possible, but
only locations near the Arizona border will have a great chance
for wetting rain. Storms will be fairly similar on Sunday, before
deeper moisture returns to the entire state Sunday night through
Monday. Apart from storms, winds in most locations will remain
fairly light through the weekend and into the beginning of next
week.

&&

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

$$

DISCUSSION/AVIATION...Merrill
PREVIOUS DISCUSSION/FIRE WEATHER...Schoening/Dewey

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