Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 241015

Area Forecast Discussion
National Weather Service Salt Lake City UT
415 AM MDT Mon Jul 24 2017

.SYNOPSIS...Moisture will spread northward today, then remain in
place across the region through the mid-week period. A gradual
drying trend is expected for the latter portion of the week.


.SHORT TERM (Through 12Z Wednesday)...The center of the mid level
ridge which has resided across the forecast area over the past few
days is shifting east into the southern Rockies this morning, as
an upper low encroaches on the northern California coast. This
will help to induce a mean south to southwest flow aloft across
the eastern Great Basin through the short term period.

A fairly well defined easterly wave rotating around the southern
periphery of the mid level ridge axis has been gradually making
its way through southern AZ over the past couple of days, and is
beginning to take a northerly turn into central AZ this morning.
This trend will continue through the next 24-36 hours as this wave
lifts across southern and eastern Utah tonight through Tuesday
morning. As it does so, a deep moisture plume will lift northward
across the forecast area, bringing the potential for heavy

Ahead of this moisture surge, anticipate scattered convection
primarily tied to the terrain during the mid-day period today,
with greater coverage across the south where dew points are
currently in the low to mid 50s. This wave will begin to influence
the south late this afternoon through this evening, which should
bring an increase in convective coverage to the southern half of
Utah as moisture continues to increase. BUFR soundings indicate
tropical-type soundings characterized by tall skinny CAPE profiles
and a deep warm-cloud layer, which would support warm rain
processes and very heavy rainfall. As such have issued a flash
flood watch for all of central and southern Utah.

The aforementioned wave is forecast to lift through southern and
eastern Utah tonight into Tuesday morning, which should keep
showers and scattered thunderstorms going into the overnight
hours, with a continued threat for locally heavy rain. The best
chance for precipitation across the north looks to come overnight
into the morning hours Tuesday as deeper boundary layer moisture
finally reaches this area.

As this wave lifts away Tuesday afternoon, warming temperatures
aloft may limit convective redevelopment despite ample boundary
layer moisture, particularly across the south, and have trimmed
PoPs a bit to indicate a downward trend in convective coverage.
Despite this, any cells which develop would have the potential to
produce very heavy rainfall, and maintained the Flash Flood Watch
through Tuesday evening.

The models do suggest convection across NV Tuesday afternoon will
spread into northern Utah Tuesday evening/overnight, and have
increased PoPs for this area.


.LONG TERM (After 12z Wednesday)...The very moist airmass remains in
place as the upper level high slowly expands back westward through
late in the week. Mixing ratio values across Utah range from 12 to
14 g/kg Wednesday and slowly and subtly dry out by Friday to values
near 9 to 10 g/kg. The flow aloft also shifts from a south-soutwest
early in the week to a more westerly by Friday going into the
weekend. Suffice to say, a decent monsoonal moisture surge in place
from early in the week remains through mid week before backing off
by late in the week. Have made little change to the PoP forecast in
place, with subtle upward tweaks across higher elevations Wednesday
and Thursday and some areal coverage Thursday.

Going into the weekend, as the high centers itself more west, the
moisture will be suppressed and a drying trend will take place
across the Great Basin. Temperatures aloft will gradually warm,
allowing surface temperatures to continue reaching into the upper
90s across most lower elevation valley locations of Utah.


.AVIATION...Southeast winds at the KSLC terminal will shift to the
northwest by 17z. Increasing clouds from the south and west
throughout the day and evening should not impact aviation
operations. Showers expected to develop nearby and south of the
terminal after 03z this evening.


.FIRE WEATHER...Moisture across Arizona will spread northward
into the region beginning this afternoon, and remain in place
through midweek. A weather disturbance will bring an enhancement
in showers and thunderstorms this evening through the day Tuesday.
Wetting rains will be common with these storms, and locally heavy
rain will be possible. With the moisture surge, daytime RH values
will be elevated with good to excellent overnight recovery.


UT...Flash Flood Watch from noon MDT today through Tuesday evening
     for UTZ010-012>016-019>021-517-518.




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