Scientific Forecaster Discussion
fxus65 kslc 181052
Area forecast discussion
National Weather Service Salt Lake City Utah
352 am MST Sat Nov 18 2017
Synopsis...high pressure will build across the region over the
weekend. A weak weather disturbance will graze northern Utah
Monday night, followed by strong high pressure aloft returning
Short term (through 00z wednesday)...the shortwave trough which
brought widespread precipitation to much of the forecast area
during the day Friday continues to quickly move off to the east
this morning, allowing mid level heights to rise in its wake.
These height rises are associated with a broad but low amplitude
mid level ridge centered along the West Coast. A surface ridge
remains in place across northern and central Utah at the present
time, and aside from a couple of shallow streams of clouds
emanating off the Great Salt Lake, as well as lingering stratus
banked along the higher terrain, skies remain clear. Could still
see patchy fog develop toward sunrise within the Cache Valley and
perhaps a couple of other sheltered locations in northern Utah,
otherwise a cool and sunny day looks to be in store, as although
temperatures aloft will be warming through the Day, Valley
inversions will likely develop resulting from a cold dense
airmass, light flow, and a low sun angle. As such have lowered Max
temps a bit across the lower elevations.
Warming aloft will continue into the day Sunday, and this will be
most realized at higher elevations, although a warming trend of
lesser magnitude is expected across the valleys as the airmass
modifies a bit.
The GFS and ec both amplify the mid level ridge along the West
Coast Monday, before building it inland during the day Tuesday. A
low amplitude shortwave trough is forecast to dig well east of the
forecast area Monday through Monday night, with a trailing plume
of moisture perhaps bringing a chance of showers within a region
of Theta-E advection. However, with rather warm mid level
temperatures resulting in greater static stability, would not
anticipate much of a response from this forcing, with any real
chance of precip looking to remain confined to the higher terrain
north of I-80 Monday afternoon into Monday evening. Given the weak
forcing have cut back on pops by 10-20 percent for now.
Long term (after 00z wednesday)...the global models are in
remarkable alignment to start this extended period with a strong
ridge over the southwest and Great Basin. The trend of the last 24
hrs is for the ridge to be stronger which will make the weak warm
advection across northern Utah as seen on the GFS more so than
the ec to be more likely a cloud storm rather than much in the way
of measurable precip. Have backed off the pops with only a
minimal chance remaining near the Idaho border vs the old runs
which had pops as far south as Provo.
The ridge strengthens some more through Wednesday night before it
begins to retreat some. The models begin to diverge just a little
at this time with the ec being a little stronger than the GFS on
the Friday into Friday shortwave moving over the ridge. Have
leaned toward the stronger ec and pushed pops up some for Friday
night as the idea of the shortwave trough digging some as it moves
towards the central rockies looks reasonable as it phases
somewhat with the longwave trough extending back into the upper
Midwest from the Great Lakes region.
Temperatures during this extended period will remain several
degrees above normal.
Aviation...scattered to broken clouds near 5000ft above ground level are expected at the
slc terminal through 12 to 13z before dissipating with a 20
percent chance of remaining in place through 15z. Winds will be
light southeast until about 19-20z then become light northwest.
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