Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 281513
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
913 AM MDT THU JUL 28 2016

.SYNOPSIS...High pressure will maintain hot and dry conditions
through much of the remainder of the work week. This high will
move east Friday allowing moisture to slowly increase from the
south through the upcoming weekend.

&&

.DISCUSSION...
Water vapor loop shows ridging from the southwest CONUS ahead of a
weak trough over the west coast. MDCARS wind observations show a 50-
105kt westerly jet from northern Utah into the lower Great Lakes.
GOES/HRRR/00Z KSLC RAOB indicate the precipitable water value ranges
from 0.15"-0.25" northern mountains to 0.75"-1.00" southern valleys.

Instability will be greater today with moisture aloft advecting into
the region. Based on SREF instability parameters along with
simulated reflectivity from the HRRR and our WRF models, have bumped
up PoPs across the south through this evening. WRF BUFKIT forecast
sounds are quite high based with a substasntial inverted-v profile,
suggesting little rainfall can be expected though dry microbursts
may bring locally gusty and erratic winds.

Updated sky cover based on new convective potential through this
evening.

&&

.PREVIOUS DISCUSSION...
High pressure firmly in place over the forecast area this morning,
resulting in mostly clear and dry conditions. Another hot day is in
store for Utah and southwest Wyoming with maxes in excess of 10F
above seasonal norms for some locations. It will be hot enough to be
hazardous over lower portions of Utah`s Dixie, including the city of
St. George, where an Excessive Heat Warning is in effect today and
tomorrow. Though the airmass remains dry, it will be warm enough to
allow for a few high based storms to fire off the higher terrain of
southern Utah this afternoon with little rainfall expected.

The ridge is progged to remain in place through tomorrow, keeping
conditions hot and dry. However, the ridge is expected to flatten
some by late Friday as a Pacific Northwest trough moves onshore.
This will allow for a more westerly flow over the area, drawing
moisture into southwest Utah by Friday afternoon, increasing the
chance of afternoon convection. The moisture is expected to continue
to spread northward on Saturday, allowing for an increasing chance
of precip with some cooling of temperatures over southern Utah.
Given the dry airmass over the area, storms will initially produce
little if any rainfall.

With the ridge axis shifting slightly to the east, midlevel moisture
will continue to increase across the forecast area Saturday night
into Sunday and Monday. This will continue to bring an increasing
chance of showers and thunderstorms to the bulk of the forecast
area. However, some of the storms on Sunday, especially those across
northern Utah along the edge of the moisture plume, may remain high-
based and produce strong gusty outflow winds but little rain. The
moisture will remain in place through Monday, helping temperatures
to gradually trend downward.

A shortwave trough crossing the PacNW states and tracking into the
northern Rockies on Tuesday will flatten the ridge and push a weak
cold front into Utah Tuesday night into Wednesday. This will not
only continue to bring slightly cooler temperatures to the area, but
drier air will spread in from the northwest as well. The moisture
and associated showers will become increasingly confined to the
south and east through the midweek period.

&&

.AVIATION...Operational weather concerns will remain minimal at the
KSLC terminal through the valid TAF period. Light and variable winds
currently in place will transition to a light northwest between 17-
18z, with speeds increasing above 6 knots between 18-19z. VFR
conditions will prevail under largely clear skies.

&&

.FIRE WEATHER...
Primary concerns revolve around new starts due to lightning during
the next several days. Headlines will likely be required.

Yesterday`s ERC values were above the 90th percentile for Central
and Northern Utah, with areas greater than the 80th percentile
across Southwest Utah.

Lightning will be most likely across zone 496 today, sneaking into
498 by evening. A significant increase is expected for tomorrow with
the threat including much of central and southern utah.
Saturday this threat includes much of Utah.

Otherwise hot conditions will begin to receed this weekend due to
the greater coverage of convection. The same can be said about RH
values, very dry today will trend a bit more moist each coming day
through the weekend.

&&

.SLC Watches/Warnings/Advisories...
UT...Excessive Heat Warning until 9 PM MDT Friday for UTZ019.

WY...None.
&&

$$

PUBLIC...Rogowski/Traphagan/Cheng
AVIATION...Merrill
FIRE WEATHER...Rogowski

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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