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fxus65 kslc 240351 
afdslc

Area forecast discussion
National Weather Service Salt Lake City Utah
951 PM MDT Mon Apr 23 2018

Synopsis...a weak upper level trough across Wyoming will move
southeast across northern and eastern Utah Tuesday. High pressure
aloft will settle across the interior west midweek and produce
very warm temperatures for the latter half of the week.

&&

Discussion...
antecedent conditions...
extreme drought is occurring from Provo south to Cedar City and
to the southeast. Severe drought is occurring surrounding the
extreme drought, in areas south of Ogden and Duchesne to the
Arizona border. Drought conditions scale down to abnormally dry
along the Idaho and Wyoming border.

Big picture...
during the past 5 days, with stronger jets moving into the
western Pacific, the pattern has re-amplified.

Water vapor satellite shows the trough to our northeast is
shearing apart with the better dynamics shifting into the Dakotas,
leaving a weaker cyclonic energy over Idaho. A ridge has built
into the West Coast. 400-250 mdcars wind observations show a
cyclonic 70-90kt jet from Washington across southern Idaho and
nosing into Wyoming.

Local observations and trends...
00z kslc radiosonde observation shows a significant decrease in moisture during the
past 12 hours, with moderate westerly flow in the mid and upper
levels. Precipitable water values range from 0.10"-0.20" northern
mountains, to to 0.40"-0.65" south central Utah. During the past
24 hours, precipitable water has decreased 0.10"-0.30", except
across south central Utah where values are 0.15"-0.25" higher.

A 1036mb surface anticyclone is centered across south central
Montana, with a 1007mb surface cyclone near The Four Corners. This
is supporting a 13mb northerly pressure gradient across Utah.

24 hour trends show temperatures are 5-15f cooler across the
north, and 5-15f warmer across the south. Dewpoint depressions
are 5-10f higher (drier) across portions of northern Utah, and
5-10f lower (moistening) across south central Utah.

Forecast...
going forecast was in good shape, so only a few tweaks this
evening. Still believe high based showers along the frontal zone
in south central Utah will continue to dissipate with the loss of
diurnal heating.

Otherwise touched up the winds, increasing them slightly on the
ridgetops and western valleys due to the pressure gradient. Across
southwest Wyoming and northeast Utah, the pressure gradient pivots
more northeasterly around sunrise, as 700mb cold advection also
increases. This should support an increase in easterly winds in
the aforementioned areas. As of right now we are not expecting
gusts along the Wasatch front near canyons and favored downslope
areas to be too significant. This is due to the current thinking
that the northeasterly pressure gradient does not set up until
several hours after sunrise. Did increase easterly winds in Davis
County between 09-12z, but will allow next shift an opportunity to
monitor conditions instead of updating the forecast to trend higher
beyond 12z.

&&

Previous discussion...
a near 700mb baroclinic zone stretched west-to-east across
southern Utah has become the focus for weak convection this
afternoon. Suspect that a few light mountain showers exist along
this boundary, with additional showers possible before dissipating
with the loss of daytime heating early this evening.

Up north, the dry air that followed this mornings shortwave has
kept afternoon convective cloud cover in check. Clearing skies and
lower dew points should force temps several degrees lower than
this mornings lows for Tuesday morning.

An easterly flow aloft across Wyoming along with a surface high
working south into northern Wyoming will create enhanced canyon
winds along the northern Wasatch front late tonight/early Tuesday.
The support for Strong Canyon winds does not materialize as the
near 700mb flow remains fairly weak, though the surface gradient
is sufficient for gusty, sub-advisory winds late tonight/Tuesday
morning.

The upper ridge building to the west of Utah will begin a warming
trend on Wednesday. This ridge will shift east into Utah by
Thursday, leading to much above temperatures and generally dry
conditions for the latter half of the week.

Upper level ridging will be in place across the west for the
beginning of the long term forecast period. Model to model
consistency regarding the remainder of the long term forecast has
improved over the model runs of the past few days, however
timing/location issues persist. With very warm 700m temperatures
between 8-10c over northern Utah, Thursday is expected to be very
warm.

A cold, large trough off the Pacific coast will be the main story
for the forecast through the weekend. Several shortwaves are
expected to eject across the area ahead of this trough, embedded in
the southwesterly flow. This will likely bring at least periods of
showers/thunderstorms Friday and cooler temperatures (though
remaining well above normal levels for late april).

The upper level low will finally move through the interior west
later Saturday into Sunday (depending on the model). An active
pattern looks to remain in place early next week.

Main point: temperatures are expected to remain above normal
through much of the long term forecast period, although a more
active weather pattern will develop for late this week into
early next week.

&&

Aviation...
north to northwest winds will continue at the slc
terminal through the overnight hours. There is a 30 percent chance
winds will become light and variable or even light southerly (under
6 kts) between 06-14z.

&&

Slc watches/warnings/advisories...
Utah...none.
Wyoming...none.
&&

$$

Public...10/Conger/Kruse
aviation...Kruse

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