Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 282155
Area Forecast Discussion
National Weather Service Salt Lake City UT
355 PM MDT THU JUL 28 2016
.SYNOPSIS...High pressure will maintain hot and dry conditions
through much of the remainder of the work week. This high will
move east Friday allowing moisture to slowly increase from the
south through the upcoming weekend.
.SHORT TERM (THROUGH 00Z SUNDAY)...
Water vapor loop shows ridging from the southwest CONUS ahead of a
weak trough over the west coast. MDCARS wind observations show a 50-
105kt westerly jet from northern Utah into the lower Great Lakes.
GOES/HRRR/00Z KSLC RAOB indicate the precipitable water value ranges
from 0.15"-0.25" northern mountains to 0.75"-1.00" southern valleys.
Instability remains sufficient across southern Utah for isolated
to scattered showers and thunderstorms. Large Dewpoint Depressions
and inverted-v profiles suggest locally strong gusty winds will
remain the primary threat through the evening hours. SREF
indicated enough elevated instability to keep isolated showers in
the forecast after midnight.
Leaned pretty heavily on simulated reflectivity guidance from our
local WRF models which indicate scattered thunderstorms across
much of west central and southern Utah. This lines up fairly well
with SREF instability parameters as well.
As we head into Saturday the threat of thunderstorms will increase
across the entire region. This will take a bit off of the
temperatures given increased cloud cover as well. Storms both
Friday and Saturday will carry a risk of locally gusty and erratic
.LONG TERM (AFTER 00Z SUNDAY)...
The mean ridge position will continue to shift south through
Sunday with center of the mid level circulation positioning over
SoCal by 00z Monday. Favorable westerly trajectories within the
return flow environment will aid to maintain modestly deep
moisture over the area with average PWATs running between .80-1.00
inch across the area into early week. Vertical profiles in BUFRs
do suggest the airmass will gradually moisten from the top down
promoting a decreasing threat of high based and largely dry
storms, but an increased potentially of locally heavy rain early
next week from scattered diurnal convection...especially across
the south and higher terrain.
Mid level flow across the eastern Great Basin will gradually become
more confluent through midweek as northern branch energy begins to
descend out of Britcol and into the northern Rockies region. With
this, the mid level high will trend to reposition over the 4-corners
region by Wed as drier and weakly cyclonic flow begins to impinge on
north. Focus of convection as such will begin to shift south, but
likely with heightened moisture convergence and slightly deeper
instability potential. GFS suggests peak PWATs midweek with values
in the 1.00 to 1.20 range across southern/central Utah, potentially
aiding a higher risk of convective cells ability to produce locally
heavy rain there.
Outside of minor tweaks to previous grids, maintained a similar
thinking to previous long term forecast.
.AVIATION...Northwest winds...at times gusting to 15KT...will
continue at the SLC terminal through about 03-04Z this evening
before shifting to the southeast. VFR conditions will prevail
through the TAF period.
Primary concerns revolve around new starts due to lightning during
the next several days. A Red Flag Warning has been issued for
portions of central and southern Utah Friday and Saturday, and a
Fire Weather Watch has been issued for northern Utah Saturday.
Yesterday`s ERC values were above the 90th percentile for Central
and Northern Utah, with areas greater than the 80th percentile
across Southwest Utah.
Lightning will be most likely across zone 496 today, sneaking into
498 by evening. A significant increase is expected for tomorrow with
the threat including much of central and southern utah.
Saturday this threat includes much of Utah. Many of the
thunderstorms will contain little rainfall, but gusty and erratic
winds. This combination will not only support new fires, but also
lead to explosive fire growth potential.
Otherwise hot conditions will begin to recede this weekend due to
the greater coverage of convection. The same can be said about RH
values, very dry today will trend a bit more moist each coming day
through the weekend.
UT...Red Flag Warning from noon Friday to 10 PM MDT Saturday for
Fire Weather Watch from Saturday morning through Saturday
evening for UTZ478>484-488-489.
Excessive Heat Warning until 9 PM MDT Friday for UTZ019.
SHORT TERM/FIRE WEATHER...Rogowski
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