Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 291531

Area Forecast Discussion
National Weather Service Salt Lake City UT
931 AM MDT Thu Jun 29 2017

.SYNOPSIS...Dry and stable conditions will be in place today, with
high pressure poised to rebuild over the area over the next 24
hours. A weakening trough will cross namely northern Utah Sunday
prior to high pressure rebuilding once again early next week.


.DISCUSSION...A low amplitude trough over the northern Rockies
states this morning will maintain a dry near westerly flow aloft
today (cyclonically oriented). A weak short wave can be noted in
water vapor over southern ID and is poised to dive SE across
northeastern portions of the area over the next 12 hours. This
said, with PWAT ranging from .3-.4 inches and only modest lapse
rates in place across the area, do not expect much more than
shallow cu formation over the eastern terrain this afternoon.

A suitable N-S MSLP gradient exists for breezy northwesterly winds
across namely eastern/southern Utah, especially across the ridges
of the central mtns and adjacent downslope areas. These winds
coupled with a bone dry airmass will primarily impact fire weather
concerns (more detail below).

As a whole, temps across the northern 2/3rds of the area will be
running some 5 degrees below yesterdays highs in wake of the
shallow boundary that set the aforementioned gradient up. Little
to no change in sensible weather is expected through Friday, even
with height trends rising coincident with reamplification of the
western conus ridge. Seasonal and dry.

No updates made or planned this morning. Previous long term
discussion below...

PREVIOUS LONG TERM...A stretched out low-amplitude trough is
moving into the Great Basin and will translate eastward through
the remainder of the weekend. Weak falling heights ahead of this
trough, along with weak cooling aloft is advertised by forecast
models. Dry and stable conditions will be present behind this
trough. Any instability looks to be confined primarily to high
terrain, and weak at that. Have kept very light mention of
convection in the mountains through the weekend.

Very modest cooling at the mid-levels will rebound by Monday as the
shortwave progresses eastward and heights once again build in across
the Great Basin with 700mb temperatures warming above 14C across our
county warning area. High pressure will build over the region and be
the dominating feature, or so one model thinks. The ECMWF however
has other ideas. By late Wednesday, the ECMWF has a deepening upper
level trough off the Pacific Northwest coast carving through the
Northern Rockies and up through Canada, all while the GFS still
thinks the ridge is the main feature. As that feature is forecast by
the EC, the southern tier does not seem to make many ripples across
Utah and southern Wyoming, if anything some minor cooling.

With this mostly dry and stable airmass in place, temperatures will
continue to run warm or hot across the state, some 10-15 degrees
above seasonal normal. Mostly dry, with some afternoon instability
convection possible though not looking too favorable, any mention of
activity was limited to afternoon time and terrain based.


.AVIATION...The dry/stable air mass in place across northern Utah
will maintain VFR conditions throughout the TAF period. Light
northerly winds will develop between 16z and 17z, then gradually
increase around 21z. Northerly winds will become light early this
evening, then switch to light southeast after 04z.


.FIRE WEATHER...ERC values have risen to between the above their
90th percentile across southern and central Utah, with a few
reporting stations above their 97th percentile. Far northeast Utah
remains below 50th percentile, but the remainder of northern Utah
is climbing above the 50th percentile.

Cooler and not quite as bone dry today behind the cold front.
However RH will remain in the 5-10% range and areas that are
favored in northwest flow downslope winds such as the eastern
valleys will see critical fire weather conditions. Haines will be
a 6 across southern and parts of central Utah today, decreasing a
bit for tomorrow. Lighter and more northerly flow tomorrow due to
high pressure building in.

A ridge builds for Saturday, increasing Haines Index to 6 again,
along with a warming and drying trend. There could be some
isolated showers and thunderstorms in the mountains each afternoon
and evening this weekend.


UT...Red Flag Warning until 10 PM MDT this evening for UTZ482-484-488-




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