Scientific Forecaster Discussion
fxus65 kslc 280425
Area forecast discussion
National Weather Service Salt Lake City Utah
925 PM MST Mon Feb 27 2017
Synopsis...the first of two weather disturbances will exit Utah
later tonight. The second system will reach Utah on Tuesday. An
increasingly dry and warmer westerly flow aloft will set up for
the latter half of the week.
Short term (through 00z thursday)...most active area of precip
this evening remains along the near 700mb baroclinic zone
currently stretched west-to-east across southwest through east-
central Utah. Good convergence into the baroclinic zone is
creating decent low-level forcing, with mid-level shortwaves
ejecting out ahead of the main trough axis still to the west of
the state. Synoptic-scale lift also getting a boost from upper
divergence in the right entrance region of the jet over southern
Utah. Widespread and occasionally heavy precip likely along and
north of the baroclinic zone into central Utah as a result of the
favorable synoptic situation.
The near 700mb baroclinic zone will continue southeast late
tonight/Tuesday as the main upper trough presses east into western
Utah. Lift will weaken a bit with the loss of the upper jet
support, though will still remain strong enough to maintain light
precip across the far south along the baroclinic zone early
For northern Utah/southwest Wyoming the air mass will remain
sufficiently moist and unstable to support loosely organized light
showers overnight. This activity will become better organized
and more widespread as the main trough axis advances into western
Utah early Tuesday. A vorticity Max diving into the trough from
the northwest will likely enhance lift and bring a period moderate
to locally heavy snow to the northern third of the forecast area
late Tuesday morning and afternoon.
A still quite moist and cyclonic low-level west-northwest flow
will persist across the northern half of the region Tuesday night.
The mid-levels air mass, though gradually warming will still be
rather cold and will support snow showers over the mountains and
adjacent valleys overnight.
Lingering terrain-tied weak convection will persist across the
northern Wednesday morning through early afternoon. After that
the air mass will rapidly dry and stabilize, with most shower
activity ending before evening.
Issued an earlier update to remove additional zones from the
winter weather highlights list, and to adjust snow numbers a bit
based on the location of the strongest expected lift.
Long term (after 00z thursday)...
Weak ridging and a drying air mass over the western US will bring
a warming trend and generally pleasant conditions for our area
from around Thursday into the first half of the weekend. The
mountains of far northern Utah may see a few lingering showers
Thursday, otherwise the latter half of the workweek will be dry
under northwest flow aloft. Clearing skies with mild days and cool
nights are expected statewide by Friday. Current guidance suggests
daytime temperatures will return to normal across the forecast
area Friday/Saturday (after just over a week of below-normal
highs). By Saturday, the flow aloft buckles to westerly as global
models indicate a broad trough developing along the West Coast. A
few showers may brush the far northern Utah mountains, otherwise
the only changes for US will be increasing high clouds.
For the latter half of the weekend and into Monday, global models
have some disagreements on the timing and amplitude of the
longwave trough as it moves inland, and thus its impacts for our
area are still uncertain. The general message is a chance of
precipitation for roughly the northern half of our forecast area
Sunday/Monday. Stay tuned as forecast details should come into
better focus the next few days.
Aviation...lingering instability snow showers will pass over or
near the terminal overnight. Brief periods of MVFR conditions
could develop in these showers. Otherwise, VFR conditions will
prevail with clouds based between 7 and 9 kft above ground level into early
The next upper trough will cross northern Utah Tuesday. Precip
will return to the terminal area by late morning, with the best
chance of snow and MVFR ceilings/vsbys during the afternoon
through early evening hours.
Utah...Winter Storm Warning until 4 am MST Tuesday for utz010-014-015-
Winter Weather Advisory until 4 am MST Tuesday for utz016-020-
long term...Van Cleave
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