Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 261028

Area Forecast Discussion
National Weather Service Salt Lake City UT
428 AM MDT Wed Jul 26 2017

.SYNOPSIS...Monsoonal moisture will remain in place across the
region through Thursday. A gradual drying trend is expected late
in the week as high pressure aloft strengthens across the region.


.SHORT TERM (Through 12Z Friday)...Southwesterly flow aloft
prevails across the Intermountain region this morning, upstream
from an upper ridge centered cross the southern Plains, and
downstream from an upper low spinning over northern California. A
moisture rich airmass remains in place across the forecast area,
with GOES-derived PW values in the lower elevations running in the
1.00-1.25 range, and surface dew points in the mid 50s to lower

A weak shortwave traversing through the larger scale southwesterly
flow has been maintaining a cluster of showers and thunderstorms
overnight. This activity is currently making its way through the
Wasatch Front, and may linger through sunrise or so as the wave
continues to slowly meander northeastward.

Despite ample boundary layer moisture, marginal mid level lapse
rates will significantly limit instability across the forecast
area this afternoon and evening, and in the absence of an obvious
larger scale trigger, convection will likely remain fairly
scattered in nature and tied to the higher terrain. This seems to
be supported by most 00Z hi-res convective allowing guidance, and
as such have left only a slight chance of precipitation across
most valleys, and a chance in the mountains.

The upper low over northern CA is forecast to slowly eject across
the northern Great Basin and into the Snake River Plain of
southern ID tonight through Thursday. As this wave brushes by
northern Utah, it may provide enough forcing for a better chance
of showers/thunderstorms Thursday through Thursday evening, while
convection across the south largely remains terrain based.

.LONG TERM (After 12Z Friday)...As the upper level ridge slowly
builds back west and then north, a very brief and subtle drying
trend will take place across the southern Great Basin. Just enough
of a trend to lower afternoon chances for convection for a day or
so. By late in the weekend the flow aloft turns more southerly
drawing up moisture from the south. Paired with a shortwave moving
in from the west, increasing chances for convection return to the
area. Generally tweaked PoPs upward through the period, but
focused on the south and south central areas.

By Monday and into Tuesday, long range models have a hard time
deciding how to resolve the tropical storm system off of Baja
California. This will determine how much moisture is advected
northwards and what the flow does going into next week.
Temperatures aloft continue to be mostly persistent and will
largely depend on the amount of moisture and cloud cover each day,
but for the most part will remain above seasonal normal through
the period.


.AVIATION...Nearby showers will affect the KSLC terminal through
13z or so with MVFR ceilings. Winds may be erratic during this
time, while favoring the north, but should swing back to the
southeast until 18z or 19z. Ceilings will lift by late morning
above 7000 feet and continue through the TAF period.


.FIRE WEATHER...A weather disturbance generating showers and
isolated thunderstorms will exit northern Utah this morning.
Monsoonal moisture will remain in place across the region today,
however the airmass will remain fairly stable, which will limit
thunderstorm coverage for much of the day, and largely confine
this activity to the higher terrain. A low pressure system along
the California coast will brush by northern Utah Thursday,
potentially bringing an increase in thunderstorm activity. With
the moisture in place, daytime RH values are expected to remain
elevated with good to excellent overnight recovery through at
least Thursday. A gradual warming and drying trend is expected
for the end of the week.





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