Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 222131
Area Forecast Discussion
National Weather Service Salt Lake City UT
331 PM MDT MON AUG 22 2016
.SYNOPSIS...Moisture will remain in place across all but the
northwest third of Utah tonight and Tuesday, as an upper level
disturbance drifts slowly across the southern reaches of the
region. A northwest flow will usher in drier air across the
forecast area on Wednesday.
.SHORT TERM (THROUGH 06Z THURSDAY)...A weak trough axis
stretching across the southern half of the area combined with a
weak mid level wave over extreme southeastern Utah is providing
subtle enough forcing to drive convection this afternoon across
central/southern/eastern Utah. This said, lack of deep instability
within a somewhat suppressed environment and marginal moisture has
limited updraft strength, and the bulk of the aforementioned
activity has thus far remained over the terrain. With the peak
heating hours still in place for the next few hours, do expect
some cells to eventually become outflow dominated providing an
additional trigger to move off the terrain, but threats from
locally heavy rain should largely remain minimal unless passing
over one of the more prone flashy basins in the far south.
An upper level trough now over southern Alberta and the associated
cyclonic flow around its periphery will be the next focus to usher
in drier air into the north on Tuesday. A weak surface trough
already exists across northern Utah, and guidance supports a net
strengthening of the northerly gradient tonight providing a solid
push of dry air to advect south across the northern third of the
area tomorrow. Outside of of drying conditions, some northerly
breezes, and slight downtick in temps, this push should largely go
unnoticed over the next 24 hours. With time however, this boundary
will dry most if not all of the area further through Wednesday. CAA
in wake and continued reinforcement from secondary waves rotating
around the back side of the trough will also yield further cooling
into the mid week period.
.LONG TERM (AFTER 06Z THURSDAY)...With a westerly flow aloft, a dry
air mass will be over the region to start the period, with
precipitable water values from .25" north to .50" south.
GFS and ECMWF models in general agreement in digging a trough
southward into California and the western Great Basin on
Thursday, with upper level disturbances ejecting northeast from
trough into Great Basin late Thursday through Friday. With
southerly flow developing, moisture will spread into southern Utah
on Thursday and across bulk of forecast area by Friday afternoon.
With upward lift from system and adequate moisture, precipitable
water values around .75", will go with a slight chance to chance
for showers and thunderstorms over southern Utah on Thursday and
over much of forecast area Friday.
ECMWF sweeps trough of low pressure across the forecast area
Saturday and Saturday night, while GFS is approximately 12 hours
slower. Either way, will need to continue with chances for showers
and thunderstorms Saturday and Saturday night.
Residual moisture supports slight chance for showers and
thunderstorms southern and eastern Utah on Sunday, mainly across
Generally dry weather conditions will prevail on Monday as much
drier air advects into region.
.AVIATION...Northwest winds at KSLC will prevail into the evening
before switching back to the south during the 03-04Z timeframe.
VFR conditions will prevail through the TAF period.
.FIRE WEATHER...A storm system extending south into the northern
Rockies will continue to usher in drier air from the northwest over
the next 48 hours. As this occurs across northern Utah tomorrow
gusty winds combined with low humidity are expected to create
critical fire weather conditions across northern portions of FWZ
479, specifically in the Bear River Valley and Bordering mountain
areas. Deeper moisture over central/southern/eastern Utah will
remain in place through tomorrow providing another day of scattered
showers and thunderstorms with an increasing potential of wetting
rains, especially south of I-70, with the stronger cells carrying the
potential of gusty and erratic outflow winds. As the dry air
continues to work south the threat of additional thunderstorm
activity will rapidly diminish for Wednesday.
Moisture looks to return Thursday afternoon and may linger through
UT...Red Flag Warning from noon to 9 PM MDT Tuesday for UTZ479.
WY...Red Flag Warning from noon to 9 PM MDT Tuesday for WYZ277.
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