Scientific Forecaster Discussion
fxus65 kslc 251021
Area forecast discussion
National Weather Service Salt Lake City Utah
421 am MDT Mon Sep 25 2017
Synopsis...warmer and drier conditions will develop today and
continue into midweek. Another upper low will develop over western
Arizona tomorrow. This low will lift north and impact much of
southern and eastern Utah during the latter half of the week.
Short term (through 12z thursday)...Utah remains under a cyclonic
north to northwesterly flow aloft this morning with the mean trough
axis still cutting through Utah, despite the closed circulation now
lifting northeast across Wyoming. The deeper moisture associated
with this low has exited the forecast area, but a fairly extensive
stratus layer across northeast Utah has been left in its wake. Not
seeing any noticeable fog development yet per surface obs and
satellite imagery, but with dewpoint depressions within a degree or
two celsius in some western and central Utah valleys, have left the
mention of fog in place for this morning.
Stratus and fog should gradually clear out through the day, with
warmer and drier conditions expected. An upper jet noted along the
southern British Columbia coast will dive south along the West Coast
states today and bring a developing shortwave disturbance into the
Desert Southwest. This disturbance will develop into a closed low
across far southeastern California tomorrow, then drift into western
Arizona by Wednesday. With the storm largely avoiding Utah during
this time, the warming and drying trend across Utah will not be
The low is expected to start lifting northeast Wednesday afternoon.
Moisture from the southeast will be drawn into the low and should
start to spread into Utah ahead of it, with showers affecting
southern Utah beginning Wednesday afternoon and spreading north
through eastern Utah Wednesday night. Due to the southeasterly flow
bringing the moisture, temperatures should remain on the mild side
with high snow levels.
Long term (after 12z thursday)...a cut-off upper level low will be
near the Utah/Arizona border region Thursday morning. As an upstream
trough approaches the Pacific northwest, this low will finally eject
and move away from the area by late Friday morning. Through the day
Thursday, expect sufficient synoptic scale lift for periods of rain
on the northern and western periphery of this low, mainly across
eastern Utah. Started increasing pops a bit more, but if the current
GFS and ec solutions remain consistent, pops will need to be
Enough lift may remain in place Friday afternoon for a few showers
across the northern Wasatch and western uintas but any precipitation
should end near sunset Friday.
The previously mentioned upstream trough will begin to impact the
Great Basin Saturday afternoon/evening into Sunday. The GFS solution
would indicate a more widespread threat of precipitation...whereas
the ec solution is more of a brush-by system. For now, kept pops
near to slightly above climo as a nudge toward the wetter GFS
Much of the global model guidance develops a substantial
ridge...keeping high pressure in place through at least
Tuesday/Wednesday of next week.
Main takeaway: upper low will bring the threat of precipitation to
eastern Utah Thursday into Friday, with another storm possibly
impacting northern Utah Saturday into Sunday. Temperatures will
largely remain near normal through the long term forecast period and
will feel much warmer than the last few days.
Aviation...southerly winds with ceilings at or above 7000 feet will
continue through the morning hours at the slc terminal. Winds are
expected to shift to the northwest between 18-19z.
Fire weather...clouds will continue to linger across northeast Utah
this morning behind the departing storm system. These clouds should
gradually clear out through the day as warmer and drier conditions
spread across the fire district through the middle part of the week.
The next storm system will develop into Arizona Tuesday night. This
storm system is expected to then lift across the eastern portions of
the fire district, spreading moisture across southern and eastern
Utah Wednesday through Thursday. Temperatures will remain on the
mild side with this storm, so snow levels should be high.
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