Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
349 PM MDT Sat Aug 27 2016
Synopsis...moisture will remain in place over southern Utah
today. Drier air will gradually spread into the area from the
north over the weekend and into early next week.
Short term (before 06z tuesday)...a short wave trough currently
over northern Arizona/southern Nevada will continue to be the
focus for short term weather concerns through tonight, before
gradually weakening in the vicinity of the 4-corners tomorrow. The
mid level circulation of this trough has slowly worked into
extreme south central Utah this afternoon with a deformation axis
extending north and west from Boulder Mountain to Utah's Dixie
where numerous showers continue to exist. Daytime cloud cover and
a modestly cool airmass has suppressed much in the way of deeper
convective initiation thus far, but with instability parameters
becoming more sufficient suspect some isolated cells to develop
along this northwestern periphery later this afternoon into this
evening. Outside of this area across the south, largely clear
skies and pleasant conditions exist outside of isolated terrain
based convection along the mountains spines in central/eastern
Focus of any nocturnal showers or isolated storms will continue to
focus along this deformation axis as it slowly works east into
southeastern Utah tonight. This said, coverage and significance is
expected to wane as both differential heating and net forcing will
be as well.
Heights will rise across the area beginning tomorrow as both the
trough over the 4-corners weakens and the upstream ridge amplifies
north and east across the state. Increasingly stable and drier
conditions will spread across the area through Monday as such,
though have continued to retain an isolated mention for shallow
convection along the mtn spines.
Long term (after 06z tuesday)...medium range begins with an upper
level ridge centered over the Rocky Mountain region and an upper
level trough situated off of the West Coast. On Tuesday, both the
operational GFS and European model (ecmwf) indicate a shortwave moving up the east
side of the trough from the western Great Basin into the northern
intermountain region. Southerly flow increases a bit ahead of
this wave bringing the potential for a bit of an increase in south
winds, especially across western Utah on Tuesday afternoon.
Moisture return looks to be minimal at this time as deeper
moisture is confined to the lower deserts of Arizona at the
beginning of the week. May see a bit of an increase on Tuesday,
but likely only enough for isolated convection over the higher
terrain of southern Utah.
Gefs and European model (ecmwf) ensemble means are in very good agreement that
upper level trough moves slowly east into the western U.S. During
the middle of the week. The majority of members from both
ensembles lift the primary forcing with the trough through the
northern intermountain region as the end of the week approaches.
Southwest flow increases across the eastern Great Basin ahead of
this feature and this will likely result in more breezy conditions
across western and southern Utah on Wednesday and Thursday. The
southwest flow also allows for a return of deeper moisture. At this
time is does not look like a significant moisture surge, although
there is plenty of time for that to change. Still, the moisture
surge looks to bring the threat of isolated showers and thunderstorms
to most valley location with more scattered coverage over the higher
terrain. The exception to this will likely be the northwest portion
of the state which may once again remain dry through the period.
As the upper level trough moves through the northern intermountain
region the flow aloft looks to become more westerly leading to a
drying trend heading into next weekend.
Temperatures at the beginning of the medium range will be above
normal in most areas. As the trough moves inland heights over the
region lower bringing temperatures down to near normal for the
middle to latter portion of the week.
Aviation...operational weather concerns are minimal at the slc
terminal through the taf period. Winds will Switch Back to the
southeast around 02-04z.
Fire weather....an upper level circulation over northern Arizona
continues to drive wetting rains across south central portions of
the district this afternoon...with isolated storms developing over
the terrain of central mountains. Continued shower and storm
activity is expected to continue into this evening with activity
largely south of I-70...and the greatest wetting rain potential
across the southwest. This upper low will fill tonight and weaken
tomorrow over The Four Corners as high pressure builds in from the
High pressure will be the dominate weather feature tomorrow through
Tuesday allowing a warming and drying trend across the district.
Winds both at the surface and aloft will be rather light owing to a
relatively quiet fire weather period through that time.
The next Pacific storm will lift northeast of the area mid/late
week...but increased winds and another round of scattered storms
appears likely beginning Wednesday.
Wyoming...red flag warning in effect until 800 PM MDT this evening for
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