Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 251035
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
435 AM MDT Tue Jul 25 2017

.SYNOPSIS...Monsoonal moisture will remain in place across the
region through midweek. A gradual drying trend is expected for
the latter portion of the week.

&&

.SHORT TERM (Through 12Z Thursday)...South-southwesterly flow
aloft sandwiched between an upper low along the northern
California coast, and a mid level ridge over the southern High
Plains, has allowed deep boundary layer moisture to advect
northward into much of the forecast area. Surface dew points this
morning are currently running in the low to mid 60s across the
lower elevations of southern Utah, and mid to upper 50s across
most other valleys.

A couple of features embedded within this flow have maintained
widespread precipitation with isolated embedded convection across
southern and central Utah overnight. One such feature is currently
lifting through east central Utah, and has resulted in an increase
in precipitation over the past couple hours near Price and across
the terrain to the north and west. A second feature across
northwest AZ continues to fire convection which has been spilling
into southwest UT. Anticipate both of these features to continue
into the morning hours, and as a result have maintained high PoPs
along with the going Flash Flood Watch.

Further north, precipitation has been lighter and more
disorganized, and appears to be associated with a mid level
deformation zone associated with the east central UT wave. This
activity will likely continue northward and out of the area this
morning, however the upstream AZ wave is forecast to lift through
central UT later this morning, and may help to spark additional
convection across northern UT. This has been advertised by several
recent HRRR runs as well as the 00Z ARW/NMM and NAM Nest convective
allowing models. As such have maintained likely PoPs across the
central/southern Wasatch Front for the morning, decreasing
slightly and becoming focused across the northeast CWA this
afternoon.

As these features exit the area this afternoon, may see
redevelopment of convection with daytime heating, however fairly
stable profiles and subsidence may preclude much more than
scattered coverage. That said, ample boundary layer moisture would
support a heavy rain threat with any convection which does
develop.

Ample boundary layer moisture will remain in place across the
forecast area Wednesday with PW values expected to remain near 1
inch across most areas. However, poor mid level lapse rates owing
to warm 500mb temps will significantly limit instability, and
with a lack of an obvious forcing mechanism  any convection which
does fire may struggle, and remain anchored to the higher
terrain. As such have cut back on PoPs for the Wednesday into
Wednesday night period.

&&

.LONG TERM (After 12z Thursday)...The upper level ridge flattens out
and weakens Thursday as a trough scoots by to the north sliding
through the Northern Rockies. This will help to suppress the
southerly flow (and turning it more westerly) that has previously
advected in so much moisture. A subtle drying trend will take place
late in the week, with precipitable water values retreating below
the one inch contour across most of Utah going into the weekend.

As the high becomes amplified once again by Sunday, moisture becomes
drawn northward once again with southern utah highlighting 1-1.5
inch precipitable water. Models to diverge on the solution through
the weekend into next week, with the GFS being the wetter solution
where the ECMWF has the high displaced much farther west and an
overall more dry solution. Nonetheless, with the drying taking place
temperatures will be allowed to warm over the weekend above normal
before coming back down near normal into early next week. A less
active period of showers and thunderstorms late in the week going
into the weekend as models are showing, however have kept mention of
afternoon showers and thunderstorms across the south central and
eastern mountains for the typical diurnal buildups.

&&

.AVIATION...A brief break in shower activity near the KSLC
terminal will come this morning before becoming more widespread late
this morning and gradually tapering off this afternoon. Brief MVFR
is possible with low CIGs in heavier rain showers. Southeast winds
are expected to shift to the northwest between 19z and 20z.

&&

.FIRE WEATHER...Monsoonal moisture which spread across the region
Monday through Monday night will remain in place through
midweek. A weather disturbance crossing the area today will
help enhance coverage of showers and thunderstorms capable of
producing wetting rains. Locally heavy rainfall will be possible
with the strongest storms. Although moisture will remain in place
Wednesday, warm temperatures aloft will limit instability, and
may reduce coverage of storms. Nonetheless, the increase in
moisture will result in higher afternoon minimum RH values
along with good to excellent overnight recovery. A gradual
drying trend is expected during the latter portion of the week.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch through this evening for UTZ010-012>016-
     019>021-517-518.

WY...None.
&&

$$

Seaman/Dewey

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visit...
http://weather.gov/saltlakecity/general/afd_faqs.php


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