Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 210250

Area Forecast Discussion
National Weather Service Salt Lake City UT
850 PM MDT Sat Apr 20 2019

A mild storm system will cross the state late tonight through
Monday, followed by high pressure for the middle of next week.


Convection across the northern two thirds of Utah is overall
taking a downward trend in terms of strength and lightning
activity with the loss of solar insolation this evening. Most of
today`s shower and thunderstorm activity was associated with an
opening shortwave that is ejecting to our east this evening. As we
get into the overnight hours, the focus for forcing will
transition to the wave seen on WV imagery splitting over
California and Nevada. The northern half of this split will the be
of interest to the forecast area, as it slows down and merges
with another wave speeding in off the west coast. This will
promote a closed mid-level low that will slowly meander across the
Great Basin and into the western Utah dessert through Sunday,
while the main trough digs into Arizona through Monday.

The closed, meandering mid-level circulation will help focus a
swath of heavier precipitation near the central Nevada border
late tonight and tomorrow, traveling toward the northeast, due to
falling heights ahead of a shortwave lifting into southwest Utah.
Showers with some rumbles of thunder possible will track across
the Wasatch front Sunday afternoon. Snow levels will be around
9000 feet. Most high elevation snowfall will be spotty, but one
possible exception is near the Uintas tomorrow afternoon and
evening. Easterly wrap-around precipitation should support heavier
and widespread precipitation during this time.

Rising heights, warming aloft, loss of diurnal heating and
anticyclonic curvature will support the dissipation of showers
for good by Monday night.

Cooler tomorrow and Monday, before a warming trend begins Tuesday.

Global models are in good agreement depicting a ridge building
over the forecast area Wednesday and Thursday. This will lead to a
warming trend with generally dry conditions. However, a few weak
terrain-based showers will be possible during peak daytime heating

Models begin to diverge after that. The GFS deterministic and
ensemble mean forecasts maintain an amplified pattern on Friday with
a trough crossing California and Nevada while Utah remains under a
warm and breezy southwest flow. Meanwhile, the EC deterministic and
ensemble mean forecasts have a more zonal flow over Utah downstream
of a split flow pattern with a trough over the British Columbia
Coast and a low over the Pacific near 30N 135W. The difference in
sensible weather would be that Utah would be slightly warmer and
drier compared to the EC on Friday. However, in the GFS solution, a
cold front associated with the approaching trough would then bring a
period of showers to the area Friday night.

By Saturday, the differences continue to increase with time with the
GFS building a shortwave ridge over the area behind the departing
trough while the EC brings in a period of weak cyclonic flow as the
trough over British Columbia moves by to the north.

Bottom line, warm and dry conditions midweek will yield to
potentially more moist conditions for the later portions of the
week. Even so, the airmass will remain on the mild side for Friday
and Saturday and any precipitation will likely remain showery with
high snow levels.


Isolated rain showers may continue to bring erratic winds to the
SLC terminal through around 05Z. Outside of any passing showers,
winds will mainly be out of the south through the night. VFR
conditions are expected to prevail.




SHORT TERM...10/Church

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