Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 192204

Area Forecast Discussion
National Weather Service Salt Lake City UT
404 PM MDT Wed Jul 19 2017

.SYNOPSIS...Monsoonal moisture will persist over most of Utah
through Thursday. Drier air will spread back into the area from
the northwest Friday into Saturday.


.SHORT TERM (Through 12Z Saturday)...Utah and southwest Wyoming
are on the back side of a ridge, allowing for increasing southerly
flow. Because of this, monsoonal moisture has spread northward
across the forecast area this afternoon, with satellite derived
PWs in excess of 1.0 inch well into northern Utah. Shortwave
energy moving through this flow has moved into central Utah,
acting as a focus for shower and thunderstorm activity. This
shortwave will lift slowly northward through the evening. Though
the deep moisture in place will result in a threat of at least
scattered convection for all but northwest Utah, the best coverage
should continue to be in association with the shortwave energy.

The deep moisture will remain in place through tomorrow, allowing
for a continued threat of showers and thunderstorms. A weak
shortwave is expected to impact far southwest Utah tomorrow
afternoon, but otherwise overall instability will be less compared
to today so have kept POPs primarily in the scattered range except
over the higher terrain.

By Friday, the flow aloft is expected to become more westerly as the
ridge flattens in response to a trough moving over the top of it.
This will allow for a drying trend to commence, primarily over
northern Utah and southwest Wyoming.


.LONG TERM (After 12Z Saturday)...The flat ridge in place at the
start of the long term period is forecast to be centered over
central UT with deep moisture remaining across the south in a
light easterly flow. This should keep a threat of convection going
across the south thru the weekend with a few cells possible over
the Uinta mtns.

Med range models start to differ after Sun with the EC indicating
a wave rotating around the high Sun night thru Mon night bringing
the deep moisture back into the CWA with an increase in
convection. The GFS does not really show this feature but does
shift the high east on Mon and also spreads moisture back into the

The moisture is slow to depart and have raised coverage of
convection for Mon thru Wed, but limited coverage to scattered at
most due to low confidence in guidance details.


.AVIATION...Northwesterly winds at the SLC terminal are expected
to switch back to southerly by 00-01z this evening with outflow
from storms to the south. These south winds could be gusty at
times. There is a chance that showers could form in the vicinity
of the terminal after about 01-02z and bring occasional erratic
winds this evening.


.FIRE WEATHER...Monsoonal moisture has spread over much of the
district this afternoon, with only northwest Utah remaining somewhat
dry. A large area of showers and wet thunderstorms will continue
into the evening, with the best coverage over the higher terrain and
over central Utah. Locations over northwest and far northern Utah
will be on the northern fringe of this moisture and could see storms
on the dry side that have the potential to produce gusty outflow
winds. The moisture will remain in place across much of the area
Thursday except for a bit of drying across far northwest Utah during
the afternoon. The increased moisture will lead to cooler
temperatures and much higher humidities for much of the fire

More robust drying from the northwest will take place Friday and
Saturday, limiting the bulk of showers and thunderstorms to southern
through east-central Utah. Latest models indicate some moisture will
return to northern Utah for the early part of next week.


UT...Flash Flood Watch until midnight MDT tonight for UTZ010-012>016-

     Red Flag Warning until 10 PM MDT this evening for UTZ478.




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