Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
914 am MDT Sat Jul 4 2015
Synopsis...high pressure aloft across the Great Basin will
settle into the southern rockies later in the weekend. Abundant
moisture along with weak weather disturbances moving through the
region will generate showers and thunderstorms into early next
Discussion...morning water vapor and 500 mb analysis depict a slight
eastward shift of the dominant ridge that has been residing over
the eastern Great Basin for the last several days. Circulation
center now shifting from eastern Utah into western Colorado. Deep
subtropical moisture exists across much of southern and western
Utah...with trends increasing rapidly across the west as position
of high is allowing precipitable water in excess of an inch to surge north.
Additionally a middle level wave within the return flow resides over
far northwestern Arizona lifting northwest. The northern periphery
of this wave is expected to provide focus for convection as the
day wears on and into tomorrow.
Noted spotty showers this am beneath the shifting ridge axis over
portions of the southern/central Wasatch front/mountains and
southwest Wyoming. Added isolated shower mention those areas for
the morning hours though any precipitation will be minimal at best. This
afternoon should be relatively quiet as the environment...though
increasingly moist...will remain quite suppressed. Expecting bulk
of forcing/instability will move north into the Wasatch
front/northern Utah this evening and overnight...with an uptick
in activity arriving towards sunset...and nocturnal convection a
potential overnight. Focus in the short term will be on this
potential on this Holiday weekend.
Copious cloud cover across the south should prohibit much
convective potential until this afternoon. Dropped thunder wording
for the morning hours most areas outside of the most prone mountains
such as Boulder Mountain area as such. Heating of the day and a net
thinning of the middle level deck will promote an increased convective
potential during the afternoon hours as the aforementioned wave
lifts into east central Nevada. Localized heavy rain remains a
threat due to a somewhat favorable warm cloud layer...minimal
shear and precipitable waters over an inch.
Previous discussion follows...
Aforementioned wave shears out over the Idaho border region Sunday.
This should provide the focus for convection as drying aloft begins
to thin out more diurnal activity across southern Utah.
With heights building back in behind the disturbance Sunday night
believe convection will decay by Monday morning. However diurnal
convection is expected to redevelop across the region Monday
afternoon and evening given the amount of instability in place under
The increase in cloud cover...and a little more moisture should take
the edge off of temperatures during the next several days.
The ridge over the Great Basin continues to weaken Monday night
due to storm systems crossing the northern rockies. A west-
southwest flow over Utah downstream of a closed low approaching
the California coast will result in a gradual drying trend.
However...the Monday night through Tuesday timeframe could remain
somewhat active in terms of convection as models indicate a weak
disturbance crossing northern Utah. Otherwise...the drying trend
from southwest to northeast will be more noticeable for the second
half of the week.
The aforementioned closed low is prognosticated by the global models to
eject across the Great Basin Friday through Friday night...weakening
as it rides north around the ridge which will strengthen again over
the Texas Panhandle. There could be some dynamic forcing over
northwest Utah Friday night and Saturday with the storm grazing the
area...but the airmass is expected to be too dry by this point to
allow for much if any precipitation.
Otherwise...expect southerly winds to increase across the area
coincident with the approach of the storm. These stronger winds
could begin as early as Wednesday across southwest Utah then become
more widespread heading into the end of the week. Temperatures are
expected to remain close to normal throughout the period.
Aviation...VFR conditions are expected to continue through this
afternoon at the slc terminal with occasional ceilings well above
7000ft. Southeast winds will switch to northwest between 18-19z. An
increasing chance of showers and lower ceilings is expected late evening
and continuing overnight.
Fire weather...isolated to scattered showers and thunderstorms will
be the rule through the middle of next week. New lightning starts
are the primary concern...with wetting rain only gradually
increasing in coverage during the time period. The increase in
convection will trend temperatures down a notch and humidity up a
An abrupt pattern shift is currently advertised during the middle of
next week. A dry and very gusty southwesterly flow develops trending
humidity lower. Convection will still be around...though wetting
rain becomes less of a possibility as activity becomes higher
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