Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 202139

Area Forecast Discussion
National Weather Service Salt Lake City UT
339 PM MDT Sun Aug 20 2017

.SYNOPSIS...Southerly flow aloft early this week will bring an
increase in mid-level moisture, leading to an increase in shower
and thunderstorm chances. Eclipse viewing on Monday will likely
be hampered by clouds in southern Utah.


.SHORT TERM (Through 12Z Wednesday)...Midlevel moisture continues to
increase slowly across the CWA this afternoon due to an upper level
trough off the coast of southern Cal. With southerly winds on the
east side of this trough moisture over Arizona is being tapped and
transported northward. Most of the convection today has been
concentrated over the southern mountains but it is moving northward
into the central mountains this afternoon. So far, eastern adjacent
valleys have not reported any precip and this should remain the same
through this evening as low levels rather dry with dew point values
in the lower 30s.

Low level water vapor showing an increase of moisture over west
central Utah this afternoon so have added slight chance of showers
and thunderstorms for this evening. The HRRR model is now showing
some convection in this area for this evening as well.

The dew points begin to climb over southern Utah Monday and then
more so on Tuesday. Should see a higher threat of showers reaching
the ground over southern Utah Tuesday as well as making their
presence known across northern Utah. Temperatures will be a few
degrees above normal through midweek.

.LONG TERM (After 12Z Wednesday)...After a disturbance moves south-
to-north through Utah and southwest Wyoming on Tuesday and Tuesday
night, the big question is how much moisture remains in place to
allow for convective development Wednesday and Thursday. The ECMWF
continues to be more aggressive with drying on Wednesday, while the
GFS and Canadian continue to linger moisture over the area through
Thursday. For now, have kept slight chance POPs in place, leaning a
little more toward the GFS/Canadian solution.

Either way, models begin to re-converge a bit starting
Thursday/Friday. An upper level trough is expected to push through
the Pacific Northwest on Thursday, then through Montana on Friday.
On the southern edge, this trough will likely push a drier airmass
into the Great Basin for the end of the week. A ridge is then
forecast to amplify over much of the western CONUS next weekend,
which should lead to a warming trend across the area. Have kept
these drying and warming trends in place for the extended, and there
is a chance that temperatures will have to be warmed even more for
next weekend in future forecasts.


.AVIATION...VFR conditions will continue through the TAF period at
the KSLC terminal. Northwest winds this afternoon are expected to
switch to the southeast between 0200-0400 UTC. However, there is a
20 percent chance that the switch to southeast winds will hold off
until after 0400 UTC.


.FIRE WEATHER...An upper level low located off the southern Cal
coast will remain in place through mid-week before shifting inland
late in the week. Early on it will be importing moisture up
from Arizona to bring a threat of showers and thunderstorms.
However, by midweek, it will tap drier air and a downward trend
in showers and thunderstorms will occur.




LONG TERM...Schoening

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