Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 271042
Area Forecast Discussion
National Weather Service Salt Lake City UT
442 AM MDT Thu Apr 27 2017
.SYNOPSIS...The cool and moist northwest flow aloft will remain
over Utah today. A colder and more northerly flow aloft will
develop late Friday as an intensifying weather disturbance moves
south through the eastern Great Basin. High pressure aloft will
return to the western states for late in the weekend.
.SHORT TERM (Until 00z Monday)...The cold deep layer northwest
flow aloft across the Great Basin will persist through this
evening. Shortwaves embedded in this mean flow will serve to
maintain showery precip, and bring increasingly colder air aloft
into the region. For this morning, showers look to be fewer and
less organized behind the shortwave that moved through the region
overnight. Anticipating an increase in showers again this
afternoon as the air mass becomes a bit colder and more unstable
with subsequent shortwaves supplying dynamic lift. Can not rule
out a thunderstorm or two with the upper jet extending through
west-central Utah southeast toward the four corners region.
Amplification of the upper ridge over the eastern Pacific
beginning later today will result in an increase in the cyclonic
west-northwest flow aloft over the Basin tonight/early Friday.
Further development in the form of a closed circulation center
across the eastern Great Basin during the day Friday will result
in increased synoptic-scale lift and more widespread precip during
the afternoon through early evening hours. This precip will
gradually focus along the wrap around in the north and west flanks
of the upper low, with the best chances for precip extending from
the the northeast mountains south into south-central and southwest
Utah into early Saturday.
The upper low will gradually work southeast into the southern
Rockies Saturday night/Sunday. The deep layer northerly flow in
its wake will bring drier and somewhat warmer/stable air across
the area for late in the weekend.
.LONG TERM (After 00Z Monday)...Northwest flow remains over Utah and
southwest Wyoming late Sunday, with a couple of weak disturbances
moving through the area Sunday night and Monday. This could bring
some light showers to the northern third of the CWA, but the best
cold air and instability looks to remain well northeast of the area.
The parent trough begins to move southward on Tuesday, though models
have generally trended weaker and further east with this system
(i.e.- the GFS and Canadian have trended toward the ECMWF solution
from the last couple days), which means the bulk of the forcing goes
through Colorado and points eastward. There is still a somewhat
increased chance of precipitation across the northern half of the
forecast area Tuesday in the moist, cold advection northwest flow,
but instability is fairly meager. This weaker solution also means
that 700mb temperatures only get down to -2C, a far cry from last
night`s GFS solution of -8 to -10C.
The trough exits the region Tuesday night and Wednesday, and models
are still promoting the idea of a high amplitude ridge moving over
the Intermountain West late Wednesday and Thursday. Have increased
afternoon temperatures for Wednesday and Thursday, and they may need
to be increased even more on future shifts. Current runs don`t have
this ridge hanging around very long, though, with the next trough
pushing into the Great Basin next Friday or Saturday.
.AVIATION...Ceilings at the SLC terminal are expected to lift above
7000 feet between 17Z and 20Z today. However, isolated to widely
scattered showers are still expected across northern Utah through
the afternoon, so briefly lower ceilings should be expected under
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