Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 241043
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
443 AM MDT Sat Jun 24 2017

.SYNOPSIS...A generally dry west to northwest flow aloft will exist
across Utah today. Strong high pressure aloft will return to the
region tomorrow. A brief surge of moisture will move through the
area Monday, followed by a cooler airmass.

&&

.SHORT TERM (Through 12z Monday)....The predominant large scale
feature to note this morning is a SE-NW ridge axis that remains in
place across the southwestern CONUS stretching from the desert
southwest across California. A slight cyclonic flow continues to
impinge on the north largely due to a deepening trough over the
northern Plains states. Heights have begun to build across the north
over the last 24 hours but only subtly so, this maintaining a
slightly cooler airmass than that which is more closely tied to
ridge across southwestern Utah. Dixie remains in an excessive heat
warning through Sunday as minimal change to the gross pattern is
anticipated, with the north remaining near status quo today (roughly
seasonal) prior to becoming a few degrees warmer Sunday beneath a
further building of heights.

Have maintained a mentioned of areas of smoke across portions of the
south through the short term period, with areal extent tied closely
to the flow both near the surface and aloft. Subtle changes of the
winds and Brian Head fire plume will likely occur, but this can be
fine tuned by later shifts.

.LONG TERM (After 12z Monday)...Monday should be the warmest day of
the next few for many areas due to the ridge axis being overhead in
the morning, then shifting east in the afternoon allowing for
southwesterly flow to develop. There is still a chance that the
Excessive Heat Warning for Dixie may need to be extended into Monday
as temperatures remain hot and expected to change little from Sunday.

The southwest flow is still expected to bring a plume of midlevel
moisture into the area. Convective development will be possible on
Monday due to this moisture as well as instability owing to the very
warm airmass. This development is expected to be more terrain-based
in the afternoon, but by late in the afternoon and into the evening
hours, a shortwave trough moving into northern Utah will aid
increasing shower/thunderstorm coverage through the northern Utah
valleys as well. This convection will likely be high-based, however,
producing gusty winds with generally little rain.

Said shortwave trough will push a shallow cold front into northern
Utah Monday night. Some drying will occur behind this boundary, and
as a result convection may remain confined to the northeastern zones
on Tuesday. However, temperatures are expected to be cooler,
especially across the north. The cooler temperatures will likely
remain steadfast through the rest of the week. This is because a
nearly zonal flow will be in place through midweek, then the pattern
is expected to amplify, putting Utah under a cooler cyclonic flow.
The GFS, with its more consolidated trough, remains stronger and
faster in this transition than the EC. However, the EC has been
trending more in line with the GFS, as 24 hours ago it was showing
more of a zonal flow and 48 hours ago there was a ridge for this
period.

&&

.AVIATION...VFR conditions under clear skies are expected
at the SLC terminal through the valid TAF period. Light south winds
are expected to transition to northerly winds by 17-18z.

&&

.FIRE WEATHER...An upper level ridge stretching from the desert
southwest across California coupled with a dry northwesterly flow
aloft on the downstream side of the ridge will maintain dry and
stable conditions across the district through this weekend. Wind
trends will continue to decrease both at the surface and aloft as
this ridge continues to build NE over the next 24 hours, becoming
largely diurnal in nature. A Haines of 6 will remain across the
south today, but trends do support these levels expanding north into
central Utah this afternoon and all but far northern Utah come
Sunday.

The approach of a weak mid level disturbance on Monday is expected
to kick up west to southwest winds across the southwestern tier by
Monday afternoon, with speeds looking to reach or exceed critical
fire weather thresholds at that time. Something to take note of as
headlines will likely be needed for Monday, while conditions
supporting a Haines of 6 will overspread the remaining portions of
the district.

The aforementioned mid level disturbance combined with increasing
mid level moisture from the south looks sufficient to produce
isolated showers and thunderstorms of the mixed wet/dry variety over
the terrain Monday afternoon, then much of the north Monday night.
At this time instability looks meager, but at least some lightning
remains a potential, especially Monday evening.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Excessive Heat Warning until 10 PM MDT Sunday for UTZ019.

WY...None.
&&

$$

Merrill/Cheng

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