Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 200517 CCA

Area Forecast Discussion
National Weather Service Salt Lake City UT
1015 PM MST Tue Feb 19 2019

.SYNOPSIS...A potent winter storm will settle into the Great Basin
Wednesday, then remain over the region through late in the week.
Heavy snow associated with this storm will concentrate across the
southern two-thirds of Utah late Wednesday through early Friday.


.SHORT TERM (THROUGH 00Z SATURDAY)...The upper trough moving south
along the BritCol coast is still on track in the global models to
slowly evolve into a fairly broad upper low centered across the
western Great Basin by Wednesday evening. The center of this newly
developed upper low will settle into southern Nevada by early
Thursday, where it will be in a favorable position to generate
widespread and likely heavy snow through early Friday.

Northern Utah will be first up to see snow from this developing
storm system. Solid low-level warm advection along with fairly
rapid mid-level cooling of the air mass will lead to sufficient
thermally-driven lift for widespread snow returning for late
tonight through Wednesday. The very cold temps aloft and fairly
strong lift suggest several inches of new snow and little water
content from the early portion of this storm.

The focus of heavy snow will shift away from the north and into
southern/central Utah by late Wednesday. A vorticity maxima
currently along the Pacific Northwest coast will continue
southeast into the far western Great Basin early Wednesday, then
weaken as it turns east into southwest Utah late in the day.

A similar scenario of low-level warm advection and colder mid-
level air along with dynamic support for lift from the weaken
vorticity max will generate a fairly rapid increase in snow across
southern/central Utah during the late afternoon/evening.
Increasing synoptic-scale lift from the now formed upper low will
keep widespread snow going well into Thursday night. Anticipating
significant accumulations across the southern two-thirds of the
state with low water content due to the very cold temps aloft.
Areas not accustom to snow such as the St. George area will likely
see several inches of snow for the second time in less than a

The center of the upper is expected to drift south into central or
southern Arizona by early Friday. Snow will begin to decrease in
areal coverage by that time, with much of the remaining snow
transitioning to showers and remaining over/near the higher
terrain and across the eastern valleys.

.PREVIOUS LONG TERM (AFTER 00Z SATURDAY)...Though precipitation
winds down by Friday evening as the trough exits, an unsettled
pattern will persist for the northern portion of the forecast area
through at least early next week. Global models show a trough
moving through the Pac NW/BritCol region, which advects a moist
airmass into northern Utah and SW Wyoming by late Saturday. Solid
jet streak support and continued cold 7H temps will promote snow
showers primarily in the higher terrain, into the remainder of the

Models remain inconsistent as the work week begins, with the ECMWF
suggesting ridging into midweek, which would cut off the moisture
tap for the aforementioned northern events. The GFS, however, is
much slower on the weekend trough passage and surges another storm
into the northern region as the trough axis passes late Monday. Have
bumped Pops a bit in anticipation of this event but confidence low
as of yet. Models do agree thus far on ramping temps up toward
seasonal norms by the end of the forecast period.


.AVIATION...Snow showers in vicinity to the KSLC terminal earlier
this evening have for the most part shifted off to the north at mid-
evening. This snow should return south for late tonight through
Wednesday. Ceilings will generally run between 3500 and 4500 feet
overnight, then lower into MVFR/IFR conditions as snow returns for
Wednesday. Light south winds overnight will increase and turn to the
southeast Wednesday morning. Prevailing winds will remain out of
the south but weaken Wednesday afternoon and evening.


UT...Winter Storm Warning from 5 PM Wednesday to 9 AM MST Friday for

     Winter Weather Advisory from 3 AM to noon MST Wednesday for

     Winter Weather Advisory until noon MST Wednesday for UTZ002.

     Winter Weather Advisory from noon Wednesday to 4 PM MST Friday
     for UTZ010-517.

     Winter Storm Warning from noon Wednesday to 4 PM MST Friday for

     Winter Weather Advisory from noon Wednesday to 9 AM MST Friday
     for UTZ014.




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