Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 171041

Area Forecast Discussion
National Weather Service Salt Lake City UT
441 AM MDT Mon Jul 17 2017

.SYNOPSIS...A ridge of high pressure will remain in place across
the region over the next couple of days, resulting in continued hot
temperatures. Lingering moisture will continue to bring a few
showers and thunderstorms to the area today, followed by a drying
trend Tuesday. Deeper moisture will spread into the area Wednesday
and Thursday.


.SHORT TERM (Through 12Z Thursday)...Latest analysis and satellite
imagery show the high pressure is centered in the general area of
south-central Utah and north-central Arizona. Lingering moisture
combined with a few very weak disturbances has continued to fuel a
few weak showers overnight and which will continue this morning.
Expect showers and thunderstorms to develop again this afternoon
mainly across the higher terrain and adjacent valleys to the east.
However, models suggest a weak vort max and associated convection
will develop across the western valleys this afternoon and progress
east into portions of the Wasatch Front by early this evening. Any
thunderstorms, as in the past few days, will be capable of producing
locally heavy rain and gusty winds.

The airmass will trend a bit drier tomorrow, especially across the
north, owing to a flattening of the ridge. Thunderstorms are
expected to be a bit more limited as a result, and confined mainly
to the spine of Utah as well as the south.

With the ridge having shifted east of Utah by tomorrow night,
moisture will be able to finally spread north from Arizona. Both the
GFS and NAM indicate PWATs will increase above 1.25 inches across
portions of the area on Wednesday. Expect Wednesday to be much more
active and wet where convective activity is concerned. The bulk of
this activity will remain across southern and central Utah, although
a few thunderstorms may be possible over the northern mountains and
adjacent valleys. Given the moisture and associated cloud cover and
precipitation expect a cooling trend to begin on Wednesday as well.

.LONG TERM (After 12z Thursday)...Deep moisture continues to surge
northward on Thursday, with precipitable water values remaining
above 1 inch across most of the CWA. Thursday should be another
active day for convective activity, though there is some concern
that instability could be limited somewhat by widespread cloud
cover. Have lowered max temperatures on Thursday to account for this
increased cloud cover and chance of precipitation.

A mid-level trough pushes into the Pacific Northwest on Thursday,
and then slides across the Montana/Canadian border on Friday. In the
lower levels, this looks to be enough to push drier and somewhat
cooler air into far northern Utah during the day Friday. This trend
then potentially continues through the weekend, as the parent trough
digs southward across the Great Plains. Have kept this north-to-
south drying trend in the forecast through the weekend, with only
the southern third of Utah having mentionable POPs by Sunday/Monday.
Have also kept temperatures closer to climatology through much of
the extended, though a warming trend could start back up again for
the beginning of next week, as a ridge re-builds and re-centers over


.AVIATION...Winds at the SLC terminal are expected to switch to the
northwest around 19-21Z, with a 30 percent chance that southerlies
persist past 21Z. There is also a 30 percent chance that the
terminal could be impacted by showers/thunderstorms today, with
gusty erratic winds as the most likely impact.


.FIRE WEATHER...A few showers this morning will yield to increased
shower and thunderstorm activity by this afternoon. While most
thunderstorms will remain terrain-based and drift east into adjacent
valleys, models indicate a weak disturbance may spread some
thunderstorms into the western Utah valleys this afternoon and into
portions of the Wasatch Front by the early evening hours.
Locally heavy rain will remain possible with a few storms especially
across the south, and gusty winds will be possible with many storms
areawide. Tuesday will be a bit drier so expect decreased areal
coverage of storms. A surge of moisture is still expected on
Wednesday which will bring more widespread thunderstorms and a
greater chance of wetting rain. This moist airmass will remain in
place through late week, after which a drying trend is expected to
occur for the weekend.





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