Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 272204
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
404 PM MDT Thu Apr 27 2017

.SYNOPSIS...An cold weather disturbance will move into the
Intermountain West tonight, bringing a threat of snow showers to
many areas Friday morning. Quieter weather will return for late
in the weekend as the disturbance exits the region.

&&

.SHORT TERM...An unseasonably cold upper-level is on track to
develop over the Intermountain West tonight and persist through
Saturday, before pulling eastward by Saturday into Sunday. 12Z
model runs today continue to show a core of 700MB temps
approaching -12C moving into Northern Utah tonight, with 500MB
temps nearing -30C. This will easily push snow levels to valley
floors for nearly all of Utah by Friday morning, except Utah`s
Dixie and the Lake Powell vicinity.

Colder air pushing southward through Utah this evening will set
up a strengthening north-south pressure gradient, leading to gusty
northerly winds are expected in north- south oriented canyons of
southwest Utah tonight. Have issued a winter weather advisory for
marginal advisory- criteria winds in that area. Will need to
monitor tomorrow, as another surge of cold air into that area will
set up another favorable situation for gusty winds again tomorrow
night.

The big forecast question today is whether the Wasatch Front
metro area will see impactful snow Friday morning. Many
ingredients are there in model guidance, including good synoptic
support, column saturation, an unstable lower-atmosphere with
steep lapse rates, and sufficiently cold temperatures. However,
high resolution models indicate that precipitation will be
strongly convective in nature with scattered coverage at best,
limiting the potential for widespread snow accumulations. The
Great Salt Lake effect is another question mark, with many
ingredients in place (mostly notably the temperature difference
from the lake surface to the lower atmosphere), but wind
convergence may not be favorable for banding. Considering all
this, have opted to not issue "winter" weather highlights, but
subsequent shifts will need to keep a close eye on fresh model
guidance. If precipitation becomes more organized and widespread,
there is potential for slushy roads near the morning commute time,
and perhaps power outages due to downed tree limbs.

The mountains of northern Utah can expect another 6-12" of snow
meanwhile. Not issuing any advisories for those areas as recent
storms have brought plentiful snow lately while roads have
remained mostly just wet, so impacts are expected to be limited.

The parent closed low is expected to drift towards the Four
Corners region later Friday, with potential isentropic wrap-around
precipitation extended through southwest Wyoming and into Utah.
Showers should wind down by Saturday morning as the low pulls east
of our area. Models are hinting at easterly winds and an
associated backdoor cold front early Saturday, which may create
gusty winds in east-west oriented canyons along the Wasatch Front
north of SLC.

One other potential impact is cold temperatures can be expected
the next few nights. While synoptic temperatures will be coldest
tonight, current thinking is breezy conditions and periods of
cloud cover will prevent temperatures from dropping to their full
potential. While temperatures aloft are warming by Saturday,
thinking that calmer conditions and clearing skies would support a
bigger chance of frost that day.


.LONG TERM (After 12z Sunday)...The forecast area is expected to
remain under a somewhat moist and unstable northwest flow through
midweek on the back side of a broad trough over the central United
States. A few weak waves are expected to move through northern
Utah in this flow, one late Sunday into Monday and another during
the day Tuesday. Best instability remains east of the area, but a
few showers will be possible, primarily over the higher terrain of
northern Utah, as they pass through. Temperatures are expected to
remain near to a few degrees above seasonal normals during this
period.

Global models agree that the central US trough tracks east beginning
Wednesday, allowing strong high pressure off the Pacific coast to
move inland, with the ridge axis progged to move overhead by next
Friday. This will result in a rapid warming and drying trend through
day seven.

&&

.AVIATION...Showers will continue in the vicinity of the SLC
terminal through the evening with unstable conditions in place.
Ceilings will occasionally fall to near 5000ft AGL near showers.
Strong northwest winds will continue through the day.

Showers are expected to redevelop later tonight into early this
morning with IFR conditions possible near any snow showers.
Accumulations on untreated surfaces are expected to remain below 1
inch. At this time, the probability of a lake band impacting the
airport is 10 percent or less due to low confidence.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory from 9 PM this evening to 6 AM MDT Friday for
     UTZ019.

WY...None.
&&

$$

SHORT TERM...Van Cleave
LONG TERM...Traphagan
AVIATION...Kruse

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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