Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 191018

Area Forecast Discussion
National Weather Service Salt Lake City UT
418 AM MDT Mon Mar 19 2018

.SYNOPSIS...High pressure aloft will expand across the region
during the first half of this week. A new series of weather
disturbances will first impact Utah midweek, and continue into the
upcoming weekend.


.SHORT TERM (Until 00Z Friday)...Heights are beginning to build
across the Great Basin in the wake of the exiting trough pressing
east into the central/southern plains. The broad low amplitude
upper ridge over Utah during the first half of the week will
maintain dry conditions across the forecast area with a warming
trend developing the next couple of days. Mid and high level
moisture moving through the ridge will not offer up any real
chance for precip, but will serve to inhibit warming a bit today
and Tuesday.

The next series of weather disturbances will develop out of the
strengthening upper trough digging south along the BritCol coast
Wednesday. This trough will eventually settle in along the BritCol
through Pacific Northwest coasts and will be centered around a
closed low near 50/130W.

Initially, the atmospheric river (AR) to the south of the
advancing trough will focus across southern/central California,
with some of this moisture breaking off and extending into the
Great Basin Wednesday. Only looking at limited showery precip with
this early moisture as dynamic/thermal support for convection will
be weak at best. The areal coverage/intensity for precip should
increase Thursday as shortwaves ejecting out of the coastal trough
will draw in additional moisture and generate somewhat stronger
dynamic/thermally-driven lift during the day.

Snow levels look to be fairly high on Thursday, so will keep any
accumulating snows generally above 8000 feet. Will also keep an
eye on far southwest Utah where the persistent southwest flow into
the upslope areas could lead to significant rains extending into
the long term period beyond Thursday afternoon.

.LONG TERM (After 00Z Friday)...A shortwave breaking off from the
main Pacific Northwest storm system is expected to slide across the
forecast area Thursday night into Friday. Associated precip in the
very most airmass is initially expected to cover the majority of the
forecast area, but the focus is expected to shift into southern Utah
Friday afternoon as the associated frontal boundary shifts the flow
over northern Utah to a more W/NW direction as the wave exits,
resulting in a drier and more stable airmass there.

The main storm system is then expected to pass across Utah and
southwest Wyoming Saturday into Sunday. The system is now stronger
in the GFS compared to the EC, which shows it grazing northern Utah
as it splits. Despite this, global models all indicate the best
moisture will be confined to northern Utah, though moisture is
somewhat limited with this system, especially compared to the
exceptional moisture with the previous system.

The system and its associated front should, however, cause
noticeable cooling with respect to temperatures with 700mb temps
currently progged to drop into the -12C to -13C range by Sunday.
Have kept POPs primarily in the isolated to widely scattered range
over the weekend as guidance has been overall inconsistent in the
evolution of the Pacific Northwest system and its associated waves.
The GFS indicates high pressure returning by day seven while the EC
keeps things unsettled with some shortwave energy still impacting
the forecast area. Have included some isolated POPs through the end
of the forecast period to account for this.


.AVIATION...VFR conditions are expected at the SLC terminal through
the morning with some scattered clouds. Light southeasterly winds
are expected to shift to the northwest between 17Z and 19Z.





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