Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 232052
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
252 PM MDT Tue May 23 2017

.SYNOPSIS...High pressure will shift east of the region
Wednesday. This will allow a series of weather disturbances to
impact Utah late Wednesday, through the first half of the
upcoming weekend.

&&

.SHORT TERM (Through 12Z Friday)...A mid level ridge extending
across the northern Rockies through the northern Great Basin
will continue to weaken as it shifts east tonight, in response
to an upper low currently digging along the British Columbia
coastline. This low is forecast to carve out a longwave trough
across the interior Pacific Northwest/northern Rockies region
during the day Wednesday, with the associated surface front
forecast to cross northern Utah late Wednesday afternoon
through Wednesday evening, before eventually stalling across
central/southern Utah Wednesday night into Thursday.

Ahead of this front, strengthening southwesterly flow should yield
a very mild day across most of the forecast area. By late in the
afternoon, mid level moisture associated with an upper low
currently spinning off the CA coast near 130W is forecast to
spread into the area, interacting with the surface boundary as it
pushes south. Model soundings suggest perhaps an initial round of
high based convection with gusty microburst winds just
along/ahead of the front Wednesday afternoon into early Wednesday
evening, followed by a better chance for measurable rainfall
across northern and central Utah Wednesday evening as the boundary
layer continues to cool and moisten.

The surface boundary is expected to remain stalled somewhere
across central/southern Utah Thursday, depending on the model run,
and a secondary shortwave rotates into the mean longwave position,
and helps to re-ignite showers along this boundary. Given
uncertainty in placement along with the convective nature of the
precipitation, have left PoPs generally in the slight chance to
low chance category. Temperatures Thursday are expected to run
approximately 10 to 15 degrees cooler across the north, and
perhaps 4 to 8 degrees cooler in the south, when compared to
Wednesday`s max temperatures.

.LONG TERM (After 12Z Friday)...Global models remain in good big
picture agreement regarding evolution of the northern Rockies long
wave trough, and the associated short wave energy rotating
through it late week. With the remnant cold front stalled over
central Utah to begin the long term period, encroachment of the
next short wave into northern Utah Friday will tighten thermal
packing across northern/central Utah providing a focus for
scattered convection by midday. Vertical profiles in BUFRS suggest
the bulk of convection will need to be forced due to limited
instability, so anticipate showers/storms to largely remain
confined to the frontal zone, gradually shifting south/east into
Friday night as the short wave sags into central Utah overnight.
Made subtle changes to PoPs, namely continuing a slight increasing
trend across Castle County Friday night due to the anticipated
forcing in place at that time.

Downstream progression of the short wave and attendant cold front
Saturday will limit additional convective potential, but have
maintained slight chance PoPs over the terrain due to remnant low
level moisture supporting an opportunity for shallow convection to
form over the mtns.

Beginning Sunday a transition period will begin with encroachment of
a mid level ridge building in from the west. Globals continue to
portray a notable warming trend beginning Sunday and lasting through
the end of the long term period within an increasingly stable
environment as such. Temps by midweek will most likely be pushing 10
or more degrees above climo as a negatively tilted ridge axis
positions overhead.

&&

.AVIATION...VFR conditions will prevail at KSLC through the
evening and overnight hours. Northwest winds are expected to
switch back to the south by 03Z, then increase and become gusty
during the morning hours Wednesday.

&&

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

$$

Seaman/Merrill

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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