Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 231100
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
500 AM MDT Sun Jul 23 2017

.SYNOPSIS...A limited amount of moisture will remain across the
region today, before deeper moisture spreads northward into the
area early in the upcoming week.

&&

.SHORT TERM (Through 12Z Tuesday)...Early morning water vapor
imagery and objective analysis depict an elongated mid level
ridge extending from central NV eastward across central UT and
into CO, while an upper low spins off the northern CA coast. A
shortwave trough/closed circulation is noted rotating around the
northern periphery of this ridge axis through southwest ID, while
a more subtle convective induced feature is noted across southern
UT. Meanwhile further south, a better defined easterly wave is
evident translating through southern AZ, and will be a player
later in the short term.

Surface dew point values are currently running in the mid to upper
40s across most of the forecast area south of I-80, with low 50s
noted along the AZ border. As a result, PW values are near 1 inch
along the AZ border, and generally 0.5-0.8 across the remainder of
the area.

Primary change to the going forecast was to introduce
showers/thunderstorms to northern Utah from the central/southern
Wasatch Front northeastward this afternoon. This is in
association with the southern UT circulation which should begin
to lift north/northeast this morning, as the deep layer flow
temporarily transitions to southerly. This is supported by several
recent runs of the HRRR, which initiates convection across this
area by early afternoon. As the southwest ID circulation passes
north of the area later this afternoon, may see drying try and
work back into these areas, so the window for convection may be
somewhat small. Additionally, lowered max temps a bit over the
north given anticipated convection.

Further south, moisture will remain sufficient for convection
across central and southern Utah, however most convective
allowing models are hesitant to produce much more than perhaps
slightly better than isolated terrain based convection this
afternoon. This may be a result of subsidence in the wake of the
aforementioned wave, as well as warming in the upper levels of the
column depicted in model BUFR soundings, which would
significantly limit the depth of instability. As a result, have
left most of these areas in the 20-30% range this afternoon and
evening.

The easterly wave across southern AZ is forecast to slowly lift
northward tonight through the day Monday, but the associated
moisture surge may not reach southern Utah until late Monday
afternoon or Monday evening. With the mid level ridge remaining
situated across the forecast area until late in the day, may see
only terrain based convection through much of the day. Left chance
PoPs across central and southern Utah for the afternoon,
although the greatest potential looks to be late, with even less
coverage across the north.


.LONG TERM (After 12Z Tuesday)...The broad upper ridge becomes
flattened out as a trough passes by to the north of Utah Tuesday
into Wednesday, compressing the flow to more southerly drawing
moisture northward. The high pressure center aloft becomes
positioned south and east of the Great Basin, and under an
anticyclonic flow aloft draws ample moisture northward into the
Great Basin. Mid level mixing ratio values Tuesday soar to 12 - 14
g/kg. In observation, values greater than 10 can lead to heavy
rain producing storms, and values greater than 12 can lead to
flooding potential heavy rain storms. This paired with more
favorable steering flow from the west-southwest across southern
Utah and instability across the southern two thirds of Utah are
pointing to an active weather day Tuesday. The moisture surge
northward continues into Wednesday and begins to wane Thursday
with the high slowly moving west and the flow aloft becoming more
westerly around the ridge.

Going into the following weekend, the best moisture becomes shifted
eastward over Colorado as the high shifts farther west. As the
moisture lessens and begins a subtle drying trend late in the week
into the weekend, temperatures once again warm several degrees into
the upper 90s across the lower elevations.

&&

.AVIATION...Southerly winds at the KSLC terminal will prevail until
a switch to the northwest settles in between 19z and 20z. There is a
20 percent chance afternoon thunderstorms nearby create gusty
erratic winds at the terminal. Winds are expected to switch to the
southeast late by 05z this evening.

&&

.FIRE WEATHER...Sufficient moisture will be in place across the
region today to support afternoon and evening showers and
thunderstorms. Across central and southern Utah, these storms
will likely remain tied to the terrain much of the day, while
across the north a weak weather disturbance is expected to
cross the area this afternoon, which may push some of these storms
into the adjacent valleys. Temperatures are expected to run roughly
5 degrees or so above normal.

A stronger push of monsoonal moisture is expected to arrive in
the south late Monday into Monday night, then spread northward
across much of the remainder of the area Tuesday. This will bring
a better chance for showers and thunderstorms to most areas, along
with cooler temperatures and higher daytime RH with better
overnight recovery.

&&

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

$$

Seaman/Dewey

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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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