Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 182222
Area Forecast Discussion
National Weather Service Salt Lake City UT
422 PM MDT THU AUG 18 2016
.SYNOPSIS...The airmass will slowly become drier from north to
south through Friday. A dry cold front then will settle into
extreme northern Utah and southwest Wyoming for Friday night
through Saturday. Moisture will spread back into much of the area
late in the weekend through early next week.
.SHORT TERM (through 06z Sunday)...A well defined mid level
circulation is noted in afternoon satellite imagery crossing
southwest Wyoming, with a trailing pool of cooler and more stable
air trailing back across northern Utah. Convection which fired
over the Uintas earlier has since weakened, although much further
upstream weak convection has formed across the Raft River range
westward into northeast Nevada. Given the stable airmass in place
across most of the north have gone with a dry forecast for the
Wasatch Westward while holding onto isolated showers and
thunderstorms over the Uintas/Wasatch Plateau. In addition, drier
air around the southern periphery of this circulation has advected
into central Utah where convection has really struggled and dew
points have fallen into the 20s. Held onto the Red Flag Warning
for now, but may end up cancelling early if activity does not
increase over the next hour or two, which given the dry
conditions seems unlikely.
Further south, moisture has been sufficient for scattered
convection which originated across the higher terrain, but is
gradually propagating southward into the lower elevations of
southern Utah. Given surface dew points are running in the mid 30s
to low 40s the threat of heavy rain/flash flooding is minimal
across this area, even with the storms slowly propagating
downbasin. Radar estimates appear to be significantly
overestimating rainfall amounts. This activity should slowly
continue shifting southeast through the evening while weakening
with the loss of daytime heating.
Meanwhile the broad trough which encompassed much of the Great
Basin/Sierras region has sagged south and is in the process of
retrograding back along the CA coast. This is in response to a
shortwave dropping south out of Canada, which will dig through the
northern Rockies Friday. Although the cold air with this system
will remain well off to the east, a shallow backdoor cold front is
forecast to sneak into northern Utah/southwest Wyoming Friday
evening, potentially bringing some gusty easterly canyon winds
along the Wasatch Front overnight Friday through early Saturday.
At this point any winds which develop would appear to remain below
This drier northwest flow will act to further dry the airmass,
and convection will become increasingly isolated and confined to
the terrain Friday through Saturday. With the cooler northerly
flow temperatures should fall below climo Saturday, remaining in
the upper 80s across most northern and central valleys.
.LONG TERM (after 06z Sunday)...The upper low which is forecast to
have retrograded along the CA coast will gradually spread back
inland over the weekend into early next week. This should pull
moisture back northward into southern Utah Sunday, then northward
into the remainder of the area Monday.
A northern stream trough is forecast to swing through the Pacific
Northwest/northern Rockies Monday into Tuesday, likely sweeping
any moisture across northern Utah back south by midweek.
Temperatures through the extended period are expected to warm
initially with southerly flow returning, but exhibit a cooling
trend by midweek as the northern stream trough gradually pushes
cooler air into the region.
.AVIATION...The SLC terminal will see VFR conditions through the
evening with some high and mid level clouds. Northwest winds are
expected to shift to the southeast between 03Z and 05Z. The chance
out outflow causing periods of gusty and/or erratic winds is 10
.FIRE WEATHER...Lingering moisture will maintain showers and
thunderstorms into the evening across central and southern Utah.
The airmass will remain drier across central portions where a Red
Flag Warning remains in effect through this evening. Drier air
will move into the area from the north beginning Friday, and
continuing through Saturday. Thunderstorms will become
increasingly isolated and confined to the mountains of central and
southern Utah during this time. Moisture will begin to return
northward as early as Sunday, with showers and thunderstorms
increasing across much of the area early next week. These storms
may initially be dry, but should quickly transition to wet across
central and southern Utah.
UT...Red Flag Warning until midnight MDT tonight for UTZ488-489-492-
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