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Area forecast discussion 
National Weather Service Salt Lake City Utah
413 am MST Wednesday Jan 28 2015

Synopsis...a weak weather system will affect northern Utah today.
A more potent system will develop across the Desert Southwest late
in the week...impacting central and southern Utah into the
upcoming weekend.

&&

Short term (through 00z sunday)...the upper low which lifted
northward through the Great Basin during the day Tuesday has
evolved into an open wave as it translates eastward across Wyoming. One
last minor shortwave on the back side of this feature is rotating
through northern Utah helping to enhance valley rain and mountain
snow across portions of northern Utah early this morning. In the
wake of this feature anticipate a downward trend in precipitation
through the remainder of the day...although with lingering
moisture and cold air aloft will likely see orographic
precipitation hold on into the early afternoon hours with perhaps
a few lingering showers over the northern valleys.

Temperatures early this morning remain anomalously warm along the
Wasatch front owing in large part to cloud cover. 700mb temperatures are
forecast at near -6c this afternoon...and as such even with the
very warm start will likely not see much diurnal swing with maximum
temperatures should have a ceiling in the lower 50s along the Wasatch
front assuming sufficient clearing occurs.

Middle level ridging briefly builds across the region tonight into
Thursday...before an upper low develops along the Southern California
coastline late Thursday...and slowly meanders inland and across
the Desert Southwest Friday through Saturday. A tropical moisture
tap has already become established off the mx coastline...and this
tap will remain in place through Friday feeding rich moisture
northward and entraining into this system.

A fairly prolongued period of isentropic upglide is forecast to
develop across southern Utah Thursday night through Friday...with
the deformation axis on the north side of the low eventually
crossing the area Friday night into early Saturday. As such have
increased probability of precipitation considerably across central and southern Utah during
this timeframe. Typically these scenarios in late January would
produce widespread heavy snowfall across the southern
valleys...however with the absence of cold air in place preceding
the system. P-type will likely remain rain below 7000 feet through
much of the event with fairly high density snowfall across the
higher terrain of southern Utah. The northward extend of this
moisture surge remains uncertain and as such have left probability of precipitation on the
low side across northern Utah.

As the upper low gradually sags southeast Saturday ridging on the
back side will bring and end to precipitation across the forecast
area.

&&

Long term (after 00z sunday)...with further downstream progression
of the late week trough heights will build rapidly from the
west...this as short wave ridging translates overhead Sat night
through Sunday. Not much in the way of an airmass change however
with 700 mb temperatures hovering near -3 c allowing a continuation of above
normal temperatures within an increasingly stable environment.

00z European model (ecmwf)/06z GFS in quite good agreement thereafter /for now/
through midweek regarding a flattening of this ridge Monday night as
ejecting short wave energy from a weak trough off the pacnw states
translates into the western Continental U.S....this in response to ridge
amplification near 130 west. Said ridge amplification could also aid
whats left of the parent trough to translate across the eastern
basin states Tuesday through Wednesday. Potential exists for a
marked cool down and some precipitation to namely northern/central Utah
within cyclonic northwest flow aloft and coupled with modest moisture and
remnant forcing from trough. Although these latest global runs are
in good agreement for now...would like to see a continuation of
model to model consistency run to run for a few before nudging probability of precipitation
above slight chance during this period.

&&

Aviation...ceilings will likely be the main operational concern
through the morning hours at kslc...and will likely remain below 7
kft through 19z before scattering out. There is a 30 percent
chance these ceilings raise above 7 kft or scatter out before this
time.

Otherwise scattered rain showers near the terminal will remain
light with no visibility restrictions expected. Northerly outflow
winds will likely Switch Back to the south by 13z. A typicaly
diurnal wind shift is expected back to the northwest around 19z.

&&

Slc watches/warnings/advisories...
Utah...none.
Wyoming...none.
&&

$$

Seaman/Merrill

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