Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 191035

Area Forecast Discussion
National Weather Service Salt Lake City UT
435 AM MDT Sat Aug 19 2017

.SYNOPSIS...Moisture will slowly increase again from the south
this weekend and continue into early next week, bringing a general
increase in showers/thunderstorms and possibly hampering eclipse
viewing Monday. The chance of storms then lingers next week.


.SHORT TERM (Through 12Z Monday)...Zonal flow extends across the
Pacific Northwest/northern Rockies region this morning. Meanwhile
further south, and upper low is noted spinning along the southern
California coast while a mid level ridge is noted over the
southern Rockies of New Mexico. A mid level deformation axis
between these large scale features extends across the Great Basin,
where a few showers have maintained overnight. Moisture associated
with this axis is largely high based, as surface dew points remain
in the 30s. As this axis slowly lifts northward today, will likely
see isolated convective development along the terrain of
northern/central Utah this afternoon. Have maintained 20-30 PoPs
despite the fact few if any hi-res models are producing much if
any convection this afternoon and evening.

This deformation axis is expected to dissipate Sunday as the
southern Rockies ridge expands northwestward across the forecast
area. This will likely suppress convection for the most part,
although isolated storms will remain possible over the terrain. A
tongue of higher PW is expected to spread into the lower Co River
Valley later Sunday into Sunday night, and may impact
southwestern Utah by Sunday evening. As such have maintained
slight chance PoPs for this area.

.LONG TERM (After 12Z Monday)...A trough progressing across the
US/Canada border has trended faster with the last few model runs.
The net impact for portions of the CWA with this outcome will be
dry air advection and less cloud cover across northern Utah during
the solar eclipse period Monday morning into early Monday
afternoon. Decreased cloud cover from Logan south to about Salt
Lake City to coincide with these changes in the models. Reduced
pops in the northern mountains as well for similar reasons.

A weak wave/convergence zone will gradually move north across the
state from the southeast Tuesday morning through Wednesday
afternoon. This should help to provide sufficient lift for
convection both afternoons, even outside the typical favored
terrain areas.

Another round of convection Thursday is expected to be followed
by a drier southwesterly flow Friday. There is a significant model
to model discrepancy regarding the depth/timing of a trough
crossing the northern Intermountain Region. The EC favors a weaker
solution and thus mid-level moisture remains more robust over the
CWA Friday, whereas the GFS favors a stronger, faster wave and
more drying across the CWA Friday. Leaned toward the GFS solution
for now Friday. Drier conditions continue into the weekend.


.AVIATION...Light and at times variable winds at the SLC
terminal will become southerly between 13-15Z.  A shift to the
northwest is expected between 17-19Z.


.FIRE WEATHER...A weak weather disturbance coupled with mid level
moisture will bring a small threat of high based showers and
thunderstorms to the area through this evening. High pressure
will strengthen a bit on Sunday resulting in a bit of a drying
trend, and maintaining above normal temperatures and low daytime
RH. By Monday this ridge will shift east, with southerly flow
allowing for an increase in moisture, which is expected to
linger through at least mid-week.





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