Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 170354

Area Forecast Discussion
National Weather Service Salt Lake City UT
954 PM MDT Tue May 16 2017

.SYNOPSIS...An unseasonably cold Pacific storm system will push a
strong cold front through northern Utah tonight, then into
southern Utah by Wednesday morning. This center of this storm
system will settle into the area Wednesday, and remain over the
area through the end of the week.


.SHORT TERM (Until 00z Thursday)...The cold core upper low
currently over the Pacific Northwest will continue southeast into
the Great Basin by early Wednesday. This low will settle into
northern Utah during the afternoon hours.

The leading cold front sits just off the northwest corner of Utah
at mid-evening. This front is in the early stages of rapid
cyclogenesis, which will continue as the front sweeps through
northern/western Utah and southwest Wyoming later tonight through
early Wednesday.

Excellent baroclinic structure exist with this storm with strong
and deep layer cold advection tilting back towards the upper low
and strong dynamic lift generate by this feature. Convection will
also get a boost with strong upper divergence in the left exit
region of the jet along the back side of the upper low.

Anticipating at least a couple of hours of intense convective
precip along and behind the front, with this convection likely to
hug the higher terrain through around mid-morning. Precip will
almost immediately turn to snow in the mountains down to around
6500 feet, with elevation below that seeing mostly rain with some
snow at times in the heavier precip. Significant accumulations are
expected for the higher terrain, with bench areas along the
Wasatch Front along with the Cache valley and Wasatch Back
possibly picking up a few inches of accumulation.

Model guidance make an attempt at bringing a dry slot into the
southern flank of low Wednesday morning. The 00Z guidance in so
far has backed away a little bit on the drying, with the dry slot
cutoff by the afternoon. Convection should fill in again with
accumulating snow to continue in the mountains. Valley locations
will see more of the short duration heavy squalls during the
afternoon. Not anticipating accumulations from these squalls due
to their short duration.

.PREVIOUS SHORT TERM (Thursday 00z through 06z Friday)...The
upper low will slowly settle south and east overhead Wednesday,
with convective showers becoming more numerous once again during
the afternoon hours. Steep lapse rates beneath the H5 cold pool of
-23 to -27 C (south to north) do look sufficient for some
convective squalls as well. Any squall that does form would likely
allow graupel to fall to lower valleys tomorrow
afternoon/evening, but limited duration should limit much of any
impact from these intermittent pulsers. This said, mountain areas
may see brief accumulation impacts (slush on roads), and feel the
Snow Advisory is well on track for this time of the year (though
totals accums may be smaller than normal winter advisories).

It continues to look like most valley areas will escape from Hard
Freeze conditions Wednesday night (outside of the mountain
valleys and potentially the Cache depending on cloud cover). Will
let later shifts continue to monitor this potential moving

The upper low will remain overhead through the end of the short
term period, with any organized precipitation likely remaining
confined to areas west of I-15 Wednesday night into Thursday,
while the remainder of the area will more than likely rely on
more showery convective precip, trending more and more diurnal in
nature in time.

.LONG TERM (After 06Z Friday)...The upper level low that has
remained across the Interior West for days will finally begin to
pull away from the area by early Friday. One last vort max rotating
along the west side of the low will bring a threat for precipitation
across portions of southern Utah through early Friday morning.
Meanwhile, areas of light wraparound precipitation will be possible
across the northern mountains.

In the wake of the upper level low, a shortwave ridge will build
into the area Saturday, followed by a weak shortwave crossing the
area Sunday. Northwesterly flow will build into the area in this
shortwave`s wake. A series of weak shortwaves will move across the
area through the remainder of the long term forecast period. This
will mainly bring the threat of isolated to widely scattered
afternoon/evening convection each day across mainly northern Utah
and perhaps the central mountains.

The main story for much of the long term forecast period is a
progressive flow will be maintained through next week, bringing the
threat of precipitation to at least the northern mountains each
afternoon and evening. Temperatures will show a gradual warming
trend, reaching near normal levels for mid-May by Saturday. Beyond
day 7, global models are still holding off on developing a more


.AVIATION...The strong cold front advancing toward northwest Utah
will enter the state between 04z and 05z. This front will
strengthen prior to its arrival at the terminal between 09z and
10z. Ahead of the front scattered rain showers will exists, with
winds becoming west-northwest and gradually increasing. The
frontal passage will bring a few hours of intense showers or
thunderstorms with MVFR and/or IFR conditions in the heavier
showers. Winds will become northwest and will be strong and gusty
for 1 to 2 hours behind the front. Snow could briefly mix in with
the rain Wednesday morning.

Precip will taper off beginning late Wednesday morning. The
terminal could see an uptick in snow squalls during the afternoon,
with brief periods of IFR conditions if any of the snow squalls
hit the airport.


UT...Winter Weather Advisory until midnight MDT Wednesday night for

     Wind Advisory until 9 AM MDT Wednesday for UTZ005.

     Wind Advisory from 3 AM to 9 AM MDT Wednesday for UTZ004.

     Winter Weather Advisory from 5 AM Wednesday to midnight MDT
     Wednesday night for UTZ518.




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