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fxus65 kslc 270532 cca 

Area forecast discussion...corrected
National Weather Service Salt Lake City Utah
1035 PM MST sun Feb 26 2017

Corrected synopsis

Synopsis...the next cold Pacific storm system will reach Utah on
Monday, then impact much of the state through at least Tuesday
evening. An increasingly dry and mild westerly flow aloft will set
up for the latter half of the week.


Short term (through 12z wednesday)...the cold core upper trough
over the Pacific northwest will take a turn to the east and move
east across the western Continental U.S. Through Tuesday night. This storm
looks to have to distinct pieces, the first arriving Monday,
followed by the second for Tuesday through Tuesday evening.

The first feature will evolve out of the upper low embedded in the
trough along the Oregon coast. This circulation center will eject
east as an open trough and focus mainly over the western/northern
Great Basin Monday through Monday evening. Ahead of this trough
low-level warm advection this evening with steadily cooling mid-
level temps will lead to an expansion of light to moderate precip
across northwest Utah overnight. This precip will become
widespread as strong low-level cold advection moves into western
Utah immediately ahead of the mid-level trough.

Anticipating a period of intense snowfall along and for a brief
period behind the near 700mb front during the morning through
early afternoon hours. Further intensification of this baroclinic
zone over central Utah during the afternoon could result in a
period of heavy snow over west-central Utah and through the
central mountains, then across the southwest valleys and southern
mountains as the baroclinic zone shifts south later in the
afternoon and evening.

Up north a rather cold and somewhat unstable air mass could
maintain some orographically enhanced snow along mainly the
Wasatch Range Monday evening. A brief break in organized snowfall
will come late in the night, then energize once again as the
second piece of the storm drops into Utah from the northwest early
Tuesday. This second dynamic feature will have a very cold and
conditionally unstable air mass to work with over mainly the
northern half of the forecast area through early Tuesday evening.
This second round of potentially heavy snow may require the
extension of the current suite of warnings and advisories beyond
the late Monday night end time.

Lingering instability should maintain snow showers across the
Wasatch Range and adjacent valleys late Tuesday night. Additional
accumulations are expected, though amounts should remain on the
light side in the valleys.

Previous long term (after 12z wednesday)...the GFS and NAM show
lingering quantitative precipitation forecast into Wednesday across northern Utah and southwest
Wyoming due to weak warm advection at 700mb. The ec shows this
warm advection also although it does not produce any quantitative precipitation forecast. Have
leaned towards the GFS and NAM solution and threw some chance and
slight chance pops in the Cache Valley, northern Utah mountains
and southwest Wyoming.

The ridge builds in Wednesday night through Thursday night but the
GFS showed a weak brush-by feature Friday and Friday night along the
Idaho border. Added some minimal pops over the northern mountains,
but this may not have been needed as the GFS 18z has backed off and
no longer supports any pops being needed. If this trend continues
with the 00z run then these pops will likely be removed.

By Saturday night the GFS and ec are about 60 meters difference in
the 500 mb heights across Utah. The GFS is lower than the
operational ec run but the ec ensemble mean is more like the GFS so
have leaned towards the GFS for the Saturday night and Sunday
period. Although this may not sound like much, the resultant weather
and temperatures are quite significant. The GFS shows that the 700mb
temp will be down to -12c degrees at slc by Sunday evening vs the ec
showing -6c degrees. The GFS shows much more in the way of dynamics
and therefore more quantitative precipitation forecast. As a result have much higher pops than
previous forecast for Saturday night through Sunday night.


Aviation...the cold front developing across far northwest Utah
this evening will bring increase south winds to the terminal after
midnight. Precip for the most part should remain north and west of
the terminal, though ceilings will continue lower overnight.

Precip will bring to work into the area after around 12-14z, with
MVFR ceilings/vsbys possible in snow. Heavy snow will accompany
the front through the terminal between 15z and 17z with IFR or
LIFR expected through early afternoon along with gusty northwest


Slc watches/warnings/advisories...
Utah...Winter Weather Advisory until 4 am MST Tuesday for utz001>003-

Winter Storm Warning until 4 am MST Tuesday for utz004-008>010-

Wyoming...Winter Weather Advisory until 4 am MST Tuesday for wyz021.




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