Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 252125
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
325 PM MDT Tue Jul 25 2017

.SYNOPSIS...Monsoonal moisture will remain in place across the
region through Wednesday. A gradual drying trend is expected for
the latter portion of the week. Guidance begins to diverge on the
evolution of this weekend`s pattern.

&&

.SHORT TERM (Through 00Z Saturday)...Disturbance moving northeast
from NW Arizona will bring widespread showers and isolated
thunderstorms across south central and eastern portions of the CWA
this afternoon into this evening. Although hard to find other
disturbances of note, the air mass is very moist with near record PW
values across the region so have at least slight chance or chance of
showers in remainder of CWA through this evening. The GFS shows a
disturbance at 500mb moving across NW Utah after midnight, but none
of the other models pick up on this feature so have gone with only
slight chance there for after midnight.

The air mass remains very moist through Wednesday and Wednesday
night with mainly terrain driven thunderstorms in the afternoon and
evening hours although outflow boundaries will also promote shower
and thunderstorm development so blanketed most areas with at least
slight chance PoPs.

The upper level ridge will flatten and shift southeast
of the Four Corners Thursday afternoon as a shortwave trough ripples
across northeast NV into southeast Idaho.  As the ridge shifts
southeastward, dry air will invade Utah from the southwest, with the
mid to upper levels drying out Thursday into Friday afternoon across
Utah.

Northern Utah will see the best coverage of storms Thursday
afternoon as the presence of a shortwave trough and upper level
diffluence associated with the right front jet entrance region will
provide enough lift for isolated to scattered thunderstorms to
develop, with the best coverage over the higher terrain. Meanwhile,
lingering low level moisture across central and southern Utah will
allow for only isolated afternoon convection across the higher
terrain. The atmosphere will continue to dry out Friday, with mainly
isolated showers and thunderstorms expected across the higher
terrain. High temperatures Thursday and Friday afternoons will
hoover near-normal values across much of Utah.

.LONG TERM (After 00Z Saturday)...A mid-level ridge will be
centered just SE of the fcst area near the four corners at the
start of the long term period. Additionally a shortwave trough
will be centered near the California coast. This setup will place
the fcst.area under southwesterly flow at mid-lvls with weaker
more terrain- driven/erratic flow at lower lvls. Enough residual
moisture remains over at least the southern/eastern parts of the
fcst.area to spark at least isolated convection Friday and
Saturday afternoons. Weak waves breaking off from the larger
Pacific trough will potentially provide enough dynamic lift to
generate some cumulus or weak t-storms over Northern Utah Saturday
afternoon, but think this area will be too moisture-starved to
include higher PoPs at this time.

Heading into Sunday guidance diverges considerably with the
EC/Canadian building a mid-lvl ridge over Nevada while the
deterministic GFS slowly propagates the four-corners ridge
northward ultimately centering it over the eastern portion of
Utah. The GFS solution would allow for fairly good moisture
transport on the western periphery of the ridge and the GFS is
quite bullish on PoPs/QPF for Sunday and Monday and is also cooler
with regards to max-temps due to precip/cloud cover The EC/CMC
solution would keep the area on the eastern periphery of the
amplifying Nevada ridge which would result in a much drier
northerly flow likely squashing precip chances over most of the
region. Leaned towards the drier/warmer EC/CMC solutions this
package because there is also support for this solution from a
number of members of the GFS ensemble. It seems probable that a
large source of the current model divergence is due to the
possible (difficult-to-model) interaction between EPAC tropical
cyclones (Hilary and Irwin) the mechanics of which may have
significant impacts on the evolution of the western US synoptic
pattern.


&&

.AVIATION...A few weak showers may linger near the SLC terminal
through around 00-01z under high CIGS, but the chance of
thunderstorms impacting the terminal will only be around 10 percent.
Northwest winds are expected to develop around 22-23z with south
winds returning after 03z, but there is a 30 percent chance that the
north winds will not become established and winds will remain light
and variable.


&&

.FIRE WEATHER...Wetting rains occurred across most of zones
496-498 past 24 hrs as well as in portions of central and
other southern zones. Wetting rains will continue to spread
NE across zones 489 and 494 this afternoon and evening as a
disturbance ejects northeast. Although showers will be isolated
or scattered elsewhere, the relative humidity will be much higher
than normal. RH values will gradually decrease this week as
temperatures rise back to slightly above normal as the ridge
builds back in across the Great Basin.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch until 9 PM MDT this evening for UTZ010-012>016-
     019>021-517-518.

WY...None.
&&

$$

SHORT TERM...Struthwolf/Lukinbeal
LONG TERM...Carr
AVIATION...Cheng
FIRE WEATHER...Struthwolf/Lukinbeal

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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