Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 262143
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
343 PM MDT Mon Jun 26 2017

.SYNOPSIS...A weak upper trough will cross the region tonight and
Tuesday. Additional weak troughs will clip northern Utah through
Thursday.

&&

.SHORT TERM (Through 12Z Thursday)...High pressure has shifted
just east of the forecast area this afternoon ahead of a trough
currently moving onshore along the Pacific coast. Increasing
southwest flow has drawn some high based moisture into the
forecast area, which has combined with the increasing instability
ahead of the approaching system to result in some showers, with
the greatest coverage currently over the higher terrain of
northern and central Utah as well as the northwest desert. The
threat of showers continues for all but southwest Utah (where a
dry slot is moving in) through the evening. Increasing winds ahead
of the system are combining with the dry airmass to produce
critical fire weather conditions over central and southern Utah.
See the fire weather section of the AFD for more details.
Temperatures have warmed about 5F over northern Utah and southwest
Wyoming compared to yesterday with maxes running up to 15F above
seasonal normals, as temperatures over southern Utah remain
similar to yesterday.

The trough is expected to graze northern Utah tonight into
tomorrow, bringing a mostly dry front into Utah and southwest
Wyoming. This will result in noticeable cooling (maxes tomorrow
will be more like 5-7F above seasonal normals) and will also
stabilize the airmass somewhat, limiting the convective threat
tomorrow. However, gusty west to southwest winds will result in
critical fire weather conditions over a broader area than today.
The zonal flow will continue through midweek, with a slow cooling
trend as additional mostly dry fronts cross northern Utah Tuesday
night and Wednesday night.


.LONG TERM (AFTER 12Z Thursday)...The axis of the main long wave
trof is forecast to be east of UT and over the western Plains at
the start of the long term period with a short wave dropping into
the base of this trof crossing nrn UT. This wave reinforces the
cool air over the north while little if any of this cooling makes
it into the south.

Models hint at a small threat of weak convection along the stalled
frontal boundary across central UT Thu aftn but don`t see much if
any threat of actual showers. Weak short wave ridging with
building heights is forecast for Fri and little if any threat of
convection. It will stay cool again north with some slight cooling
south.

Med range guidance diverges Sat with one more short wave digging
down from the north in the GFS flattening the ridge while a weak
wave moves in from the southwest in the EC with the ridge
remaining in place but shifting into ern UT. Both would bring an
increase in the threat of convection altho it ends up in different
parts of the CWA by Sun aftn. So confidence drops off in the
forecast rapidly over the weekend.

&&

.AVIATION...Winds at the KSLC terminal will remain from the south
through the evening. There is a small chance of a wind shift to
the north before 03z, however confidence is low and was taken
out of the current TAF. Isolated showers and thunderstorms are
possible across northern Utah into this evening, and will create
gusty and erratic winds likely impacting the terminal.

&&

.FIRE WEATHER...Ridge axis has moved east of the district this
afternoon ahead of an approaching trough, allowing for an
unstable southwest flow to develop with increasing high based
moisture. This flow is resulting in gusty winds over central and
southern Utah, which are combining with the already dry conditions
to result in critical fire weather conditions. Fire danger is
elevated across the entire district with a Haines index of six
today. The increase in moisture is also resulting in isolated high
based thunderstorms across portions eastern portions of the
district as well as northwest Utah which will continue into the
evening.

A cold front will move across northern Utah tonight, reducing the
Haines index there as it remains a six over central and southern
Utah. A somewhat unstable zonal flow will be dominant over the
district during the middle of the week as dry conditions persist.
Winds will be strong enough over southern and eastern portions of
the district tomorrow and Wednesday to result in severe fire
weather conditions, so have expanded and extended the Red Flag
Warning. High pressure is expected to return Friday through the
first part of the weekend.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Red Flag Warning until 10 PM MDT Wednesday for UTZ493-495-496-
     498.

     Red Flag Warning from 10 AM Tuesday to 10 PM MDT Wednesday for
     UTZ479-482-484-488-489-494.

     Red Flag Warning until 10 PM MDT this evening for UTZ492-497.

WY...None.
&&

$$

SHORT TERM/FIRE WEATHER...Traphagan
LONG TERM...Wilensky
AVIATION...Dewey


For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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