Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 161631
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
1031 AM MDT Fri Apr 16 2021

.SYNOPSIS...Unsettled conditions will continue across much of Utah
again today...shifting to mainly southern Utah Saturday. High
pressure will build into the region Sunday. Another disturbance
will impact mainly northern and eastern Utah Monday.

&&

.UPDATE...Previous forecast remains on track this morning, haven`t
made any notable changes with this current update. The primary
focus this shift will key in on downslope/canyon wind potential
tonight into Saturday morning for the northern Wasatch Front.
Initial look at available 12z guidance, including latest Hi-Res,
hasn`t shifted thinking much. In large, a modest strong wind
event remains forecast with most bench/canyon mouth areas
anticipated to see gusts in the 40-55mph range, strongest around
and just after daybreak Saturday morning...focused Weber/Davis
Counties.

Will have more detail in this afternoon`s package after full
perusal of 12z suite. Previous discussion below...

&&

.SHORT TERM (Through 12Z Monday)...A broad area of low pressure
remains across the Interior West this morning. A continental
shortwave trough is currently shifting southward into northern
Nevada. This trough will continue to move southward through
eastern Nevada through the day today...beginning to cut-off near
St. George Saturday...and then finally shifting away from the
state Sunday. Meanwhile, high pressure remains in place along the
Pacific Coast.

Lake enhanced valley rain/mountain snow showers have been
impacting portions of the Salt Lake and Utah Valleys through much
of the night. Salt Lake City Airport and northern Salt Lake County
experienced periods of moderate to heavy rainfall at onset. Expect
showers to continue to develop in this area through morning.

With relatively steep lapse rates overhead...expect additional
showers to develop across much of the state this afternoon and
evening. The best forcing for precipitation will be shifting south
through the day, so the best chance for showers will be from
roughly I-80 southward. Occasional winter driving conditions can
be expected across most higher terrain routes through this
evening.

With the loss of daytime heating, expect shower activity to
largely diminish across most of the state.

Attention then will turn to the canyons of northern Utah. The
position of this shortwave trough will support enhanced easterly
700mb winds. This combined with modest low-level cold air
advection from southwestern Wyoming into northeastern Utah will
set up at least a moderate canyon wind event across the Cache,
eastern Box Elder Counties as well as Weber, Davis and
northeastern Salt Lake County. Much of the model guidance
indicates 700mb flow near 25-30kts. Given this, expect canyon
winds to range from 40 mph near most canyons to 55 mph near the
most prone locations such as Centerville to Farmington late Friday
into Saturday morning.

There is a small subset of the guidance which would suggest
potentially wind gusts up to 60 or 65 mph or so at these
locations. Given these solutions are an outlier in the bulk of the
guidance, did not have the confidence to issue a high wind watch
but rather will let another round of model data come in for the
dayshift. Regardless, the appreciable difference to most between
gusts to 55 mph versus 60 mph is somewhat academic and those in
the canyon wind prone areas should once again consider securing
outdoor items such as trampolines, garbage cans, and other items
that may become airborne in stronger winds.

With the low gradually cutting off from the mean flow overhead
across southwest Utah Saturday...another round of afternoon and
evening showers is expected...this time mainly impacting southern
Utah. Localized critical fire weather conditions are possible
Saturday afternoon and evening across eastern Utah. See the fire
weather discussion for more information.

Sunday will be largely clear and somewhat warm across much of the
state before the next system approaches.

.LONG TERM (After 12z Monday)...The long term forecast continues
to advertise a glancing blow across northeastern Utah and
southwest Wyoming on Monday. A quiet and dry day Tuesday will be
sandwiched between the Monday trough and the potential of a
trough/closed low, pending on what model solution verifies,
impacting Utah by Wednesday.

Although the majority of Utah will see a quiet and dry day with
seasonal temperatures on Monday, portions of the Wasatch Back, SW
Wyoming and Uinta Mountains will the chance of some precipitation
in the form of snow showers. The apex of an eastward moving ridge
axis will extend into the Great Basin, and nose just enough east
to keep back end of the trough and surface cold front far enough
east to keep the bulk of the precipitation across the
aforementioned areas. The net effect of increasing heights across
the west and falling heights across the east, will be a tightening
of the pressure gradient which could bring some breezy conditions
across central and northern Utah. For the areas that see
precipitation expect the coverage to increase during the late
morning/afternoon when the surface reflection will be at its
closest proximity to Uinta County. Not expecting a long duration
of the precipitation so accumulation amounts look light for most
areas.

Rising H5 heights move across Utah on Tuesday, but right on the
heels is the next system moving across southern Oregon. Tuesday
will be dry across Utah with another day of seasonal temperatures.

Heading into Wednesday and toward the end of the week, model
variations regarding this next system come into play. Most of the
GFS/GEFS continue to show a closed low moving across central
California before moving into southern Nevada Wednesday night. At
this same timeframe, the EC and associated ensemble members have a
weak open wave pattern across this area and this trend in model
differences continue into Thursday. Pending on what solution pans
out, will impact the PoP forecast Wednesday and Thursday. Forecast
approach was to stick close to the NBM guidance until better
agreement in the handling of this next period of unsettled becomes
clear and adjustments are likely in subsequent forecast packages.


&&

.AVIATION...VFR conditions are largely expected through the valid
TAF period at the SLC terminal. Areas of light rain will continue
through about 18Z, causing brief periods of MVFR conditions. VCSH
will continue this afternoon with a 30% chance of an isolated shower
before clouds and showers diminish early this evening. Winds will be
northwest 5-10 knots, but rather variable through 19-20Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.

&&

$$

UPDATE/AVIATION...Merrill/Burghardt
PREVIOUS DISCUSSION...Kruse/Woodward

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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