Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 210945

Area Forecast Discussion
National Weather Service Salt Lake City UT
345 AM MDT Sun May 21 2017

.SYNOPSIS...A weak weather disturbance will move across the state
today. High pressure aloft building across the western states
will bring a warming and drying trend to the area through the
middle of the week.


Water vapor loop shows a strong disturbance dropping southeast
over southern Idaho, with areas of subsidence to its northwest and
another over Montana. AMDAR 400mb-200mb wind observations reveal
a 60kt-75kt cyclonic jet extends from Idaho over the Eastern Great
Basin and into the Four Corners. GOES/HRRR/00Z KSLC RAOB indicate
precipitable water values range from 0.15"-0.30" mountains to
0.40"-0.60" most valleys.

Scattered showers and thunderstorms will affect northern Utah and
southwest Wyoming this morning into the afternoon. As the
aforementioned wave progresses toward the southeast over Utah
today, convection will develop across portions of central and
southern Utah this afternoon, lingering across the south and east
tonight. This scenario continues to be depicted well by the
Convective Allowing Models. Northwest Utah will be drying out due
to subsidence behind the wave by later in the afternoon.

SREF indicates a good probability of modest instability today to
support deeper convection, with the possibility of 30kt of
effective shear for storm organization. BUFKIT model forecast
soundings indicate a deep enough inverted-v signature to support
modest DCAPE, potentially leading to a few strong gusty/erratic
dry microbursts. Best threat appears to be this afternoon between
Interstates 80 and 70.

With drying anticyclonic flow building in tonight and tomorrow,
possibility of terrain circulations initializing convection is
remote tomorrow afternoon.

Today the warming/drying trend is paused across the north and
central areas, relegated to southern Utah. The warming/drying
trend will then occur across the entire area beginning again

The western CONUS ridge continues to slide eastward Tuesday and
Wednesday, leading to a continued warming trend. Wednesday will
likely be the warmest day of the week in most locations, with
increasing west-southwesterly flow ahead of a trough over the
Pacific Northwest.

The low level cold front associated with this trough is currently
forecast to push into northern Utah Wednesday evening, bringing
cooler temperatures and the possibility of isolated convection. That
said, the forecast area largely remains on the southern fringes of
this trough as it lingers over Idaho/Montana late Wednesday through
at least Friday, with the best moisture/instability never looking to
make it far into the forecast area. For now, have maintained slight
chance POPs across the northern half of Utah through the end of the
week, with temperatures generally around climatological normals
after the cold front comes in.

Model details begin to differ some heading into the weekend, but the
general idea at the moment appears to be general troughiness
lingering across the Intermountain West, with near normal or
slightly cooler temperatures potentially lingering through the end
of the month.


There is a 60 percent chance of showers impacting the SLC
terminal this morning and early afternoon, with gusty erratic
winds and brief ceilings below 7000 feet as the most likely
impacts. Away from showers, winds are expected to switch to the
northwest around 14-16Z, with only a slight chance that
southerlies hang on through 18Z.


Weak transport winds will limit clearing to the fair to good
categories across many valleys during the next several days.
Mixing also becomes limited across the western valleys Monday.

A disturbance dropping south from Idaho today will trigger
scattered showers and thunderstorms. This activity is expected
across the north mainly though mid afternoon, before developing
across portions of central and southern Utah late today, lingering
tonight. In addition to lightning, they carry the risk of
gusty/erratic winds associated with dry microbursts, and low
probabilities of a wetting rain.

The warming and drying will accelerate for the first half of the
work week as a ridge builds over the region. A cooler and more
moist trough may impact the area during the second half of the





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