Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 250142

Area Forecast Discussion
National Weather Service Salt Lake City UT
742 PM MDT Wed Apr 24 2019

High pressure aloft over the Great Basin will weaken as a series
of weather disturbances move east across the northern Rockies and
impact northern and western Utah through the end of the week. Warm
weather each day is expected through the end of the week.


Updated to extend PoPs into central Utah as convection taking a
while to decay this evening, especially near the Nevada border
where instability and shear are maximized.

Instability diminishes significantly overnight, so continued with
the idea that all convection decays by around midnight. Increased
clouds this evening to account for convective debris, which should
diminish later tonight.

Otherwise only minor changes to temperatures/RH utilizing the
latest observations and model guidance.


Radar analysis this afternoon shows rain shower and thunderstorm
activity has blossomed over far northwest Utah. Per convective
forecast models, this has panned out well. Available instability
is confined to the far north, where the best advertised wind shear
also resides and available precipitable water increased to
0.60-0.70 inches. As the shortwave pushes through northern Utah
this evening, expecting the convection to come to an end after
sunset this evening. The showers and isolated thunderstorms are
expected to extend as far south as northern Utah county by early

After the weather disturbance shifts to the east overnight,
ridging builds in for Thursday but this won`t mean quiet weather.
There are several disturbances embedded in the large scale flow
that will continue to introduce daily convection Thursday
afternoon and more so Friday afternoon. With regards to Thursday
evening, one interesting note in the models today was the
artifact of an area of higher instability and precipitation along
the Nevada/Utah border into Juab/Millard counties. This was seen
in the 06z and also the 12z model runs. As this trend continues,
will have to watch for late afternoon convection to get going and
perhaps continue into the evening hours. Precipitable water values
have a maximum late Thursday afternoon coincident with a swath of
high instability. PoPs were increased during most of the short
term to better fit potential convective activity.

Moving on to Friday, as the shortwave from Nevada/Utah late
Thursday afternoon moves to the northeast, a northern branch
trough feature will further create favorable conditions and lift
for more scattered to widespread rain showers with thunderstorms
possible. Friday looks to be the best opportunity for more
thunderstorms in the area, coming after several days of mostly
clear skies and substantial daytime heating. Saturday has a break
in the active weather pattern as the flow becomes more zonal and
weaker with drier air moving in from the north behind the
departing trough feature.

Some destabilization is expected Sunday afternoon over mainly the
higher terrain as moisture ahead of a close low off the SoCal
coast squirts northward and increases our PWs to a little over
0.50 of an inch. As the closed low moves into southern CA on
Monday the jet circulation over Utah will become diffluent
creating good lift over mainly the southern and eastern portions
of the state.

The main event comes Tuesday as the longwave trough strengthens into
the western US. The deterministic GFS is the coldest of the models
and looks to be an outlier, so have leaned toward the EC and GFS
ensembles, which are still plenty cold and could bring the snow
levels down to 5500 ft across northern Utah. Have lowered temps for
Tuesday and Wednesday across mainly northern Utah due to the -4 to -
8 degrees C accompanying the precipitation. Gusty winds are expected
ahead of the front across southwest and south central Utah on

Temperatures will fall to about 15 degrees below normal Tuesday and
Wednesday across northern Utah while the south will be more in the 5
to 10 degrees below normal range.


Convection continues to decay across north central Utah this
evening. Debris clouds expected into the middle of the night.
Otherwise southeast winds have become established at the KSLC
terminal for the night.





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