Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 211018
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
418 AM MDT Mon Aug 21 2017

.SYNOPSIS...Southerly flow aloft will draw moisture north across
the forecast area early in the week. Somewhat drier air will
return to the south midweek.

&&

.SHORT TERM (Until 12z Wednesday)...The upper low still parked off
the southern California coast will continue push moisture north
through the Great Basin the next couple of days. PWAT values
remain the highest over extreme southern Utah this morning. This
moisture will begin to work north into central Utah later today,
then continue north into northern Utah Tuesday.

Cloud cover for this mornings eclipse remains issue one at this
time. The most extensive cloud cover will remain at the core of
the moisture plume through south-central and central Utah, then
arcing northeast into northeast Utah. Some early mixing may
briefly thin out some of this cloud cover, though many areas of
south-central and central Utah could see a persistent 50%+
coverage of opaque clouds today. Southwest and southeast Utah
which are on the fringe of the moisture plume will see clouds thin
a bit early this morning, with a gradual increase returning late
morning. The visibility of the eclipse will be somewhat
restricted, with the best viewing likely near the Nevada border.

Up north a weak deformation axis extending west-to-east from near
Wendover to Vernal will focus scattered cloud cover early this
morning. Anticipating that early mixing will thin out some of the
clouds, with cloud development confined mainly to higher terrain
mid-morning. Overall, viewing of the eclipse looks to be good
across the north.

Now back to the precipitation forecast. Scattered loosely
organized convection today will center on the moisture plume
across southern/central Utah, with a secondary maxima across the
northeast mountains later today as the moisture profile improves.
A shortwave ejecting north from the coastal southern California
low will move slowly north across the forecast area beginning
Tuesday afternoon for the south, then reaching central/northern
Utah Tuesday evening. This convection will remain active
overnight, with the greatest areal coverage tied to the shortwave
across the northern third of the state

.LONG TERM (After 12Z Wednesday)...Models in good agreement with
timing of upper level disturbance lifting northward through northern
reaches of forecast area at start of period, and in bringing one
last weak disturbance across northern sections of eastern Great
Basin Wednesday afternoon and evening.  With residual moisture still
in place, precipitable water values near three quarters of an inch,
will continue chance wording for showers and thunderstorms northern
Utah and extreme southwest Wyoming, with just slight chance wording
for central and southern Utah, where have scaled chances for
precipitation down a bit.

With continued drying on Thursday, potential for showers and
thunderstorms will primarily be limited to mountains.

GFS indicates a weak upper level disturbance will graze northern
sections of forecast area Friday afternoon and evening, while
Canadian and ECMWF are much weaker with this feature.  Given low
confidence, will limit chances for precipitation to high terrain of
forecast area, with best potential over northern sections.

Globals models in excellent agreement with building a ridge of high
pressure over the Great Basin over the weekend, with a generally
west to northwest flow promoting a very dry air mass over region.
With 700 millibar temperatures warming to 16 degrees Celsius, should
see readings several degrees above normal.

&&

.AVIATION...VFR conditions will prevail through the TAF period at
KSLC.  Expect southeast drainage winds to shift to the northwest
around 18Z, though there is a 20 percent chance the switch will not
take place until 19Z.

&&

.FIRE WEATHER...Moisture concentrated across southern Utah will
work north across the state through Tuesday. This increase in
moisture will lead to an increase in shower/thunderstorm activity,
especially across southern, central and northeast Utah through
Tuesday. Wetting rains are possible, particularly for
southern/central Utah through Tuesday.

Somewhat drier air will work into southern Utah by Wednesday,
bringing an end to most if not all of the showers/storms through
the end of the week. Up north the drying trend will be slower with
lingering moisture confined to the far north by the end of the
week.

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

$$

SHORT TERM/FIRE WEATHER...Conger
LONG TERM/AVIATION...Barjenbruch


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