Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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479
FXUS65 KSLC 230039
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
639 PM MDT SUN MAY 22 2016

.SYNOPSIS...An elongated upper level trough stretching from
southern Canada to the California coast will maintain a mostly
dry and mild southwest flow over Utah early in the week. Cool
and unsettled conditions will return midweek as the trough
shifts east through the Great Basin.

&&

.DISCUSSION...Water Vapor loop shows an expansive trough firmly in
place across the Western CONUS. AMDAR 400-200MB wind observations
place a 100-125kt cyclonic jet from West Central Utah into the
Northern Rockies. GOES/HRRR/00Z KSLC RAOB indicate the
precipitable water value ranges from 0.10"-0.20" Southwest
Valleys and mountains to 0.30"-0.50" most valleys.

Early update this evening to account for convective evolution per
regional radar. Threat of convection has been increased for the
Cache Valley and Northern Wasatch front, but little chance is seen
from Salt Lake southward. Still favor convection decaying by
midnight given waning instability and as shortwave ridging moves
overhead per RAP.

Another area of mid and upper clouds are expected to expand into
Northern Utah later tonight in advance of the next wave nearing
the western Utah border by sunrise.

Little other changes were made to the previous forecast.

&&

.PREVIOUS DISCUSSION...
The shortwave lifting northeast across northern/central Utah will
maintain scattered convection across northern Utah/southwest
Wyoming through early this evening. Subsidence trailing this
dynamic feature will bring an end to most convection...with any
lingering activity confined to the Idaho border region and
possibly over far northeast Utah and southwest Wyoming later
tonight.

Monday looks to be a relatively quiet day in terms of convection.
Suspect that convection will be confined to the northern third of
the forecast area...with the model guidance suggesting that a weak
shortwave could ripple across the far north during the afternoon
and early evening hours. Southern and eastern Utah will be under
the influence of an increasingly strong and dry southwest flow
aloft. Do not see any real threat of convective precip in those
area...even in the higher terrain Monday afternoon.

The shortwave diving south along the west coast Monday will serve
to elongate the mean trough across the western CONUS. This trough
axis will extend from south-central Canada to the California
coast by Tuesday. A shortwave ejecting northeast from the base of
the now elongated trough will lift northeast through Utah Tuesday
afternoon/evening. This feature will find adequate moisture to
work confined to northern Utah/southwest Wyoming. Will limit Pops
to the areas with the best moisture...and keep QPFs on the low
side for now.

Cooler conditions will shift east into Utah Wednesday as the axis
of the still elongated trough settles along the Utah/Nevada
border. Precip will expand across a good portion of western and
northern Utah Wednesday afternoon/evening...though QPFs will
still remain towards the low side as PWAT values stay low outside
of the far northwest portion of the state.

With the elongated trough draped southwest across Utah and into
southeast California by late week, the unsettled and wet pattern
continues. Forecast models trend the trough into a cut off low for
a brief period, though it remains south of Utah in southern
Arizona through Friday. The southwest flow will change to west-
northwest across much of Utah with this progression by the end of
the week.

Models diverge on solutions by Saturday with the next upper low
developing off the Washington State coast and descending through the
Pacific Northwest. While the GFS solution wants to hold on to this
cut off low wobbling into California by the end of the weekend, the
ECMWF has changed ideas with the latest model run and now keeps an
open wave pattern and moves the trough east through Montana.
Needless to say confidence is a bit low into this next system, so
the forecast was changed very little in the far extended.

&&

.AVIATION...Light and variable winds will continue at the SLC
Terminal through 02Z...becoming predominately southerly at that
time.

&&

.SLC Watches/Warnings/Advisories...
UT...None.
WY...None.
&&

$$

PUBLIC...Rogowski/Conger/Dewey
AVIATION...Kruse

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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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