Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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000
FXUS65 KSLC 221001
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
401 AM MDT Sat Apr 22 2017

.SYNOPSIS...High pressure will build over the area Saturday
bringing a warming trend into Sunday. A series of fast moving
systems will cross the area through the upcoming week beginning
Sunday afternoon.

&&

.SHORT TERM (Through 00z Wednesday)...Flow aloft continues to
trend more anticyclonic as yesterday`s trough continues to slide
east into the plains, and mid level ridging builds in from the
west. Said ridge will position overhead today through tonight
providing stable conditions across the area.

Have maintained the going Hard Freeze Warnings through mid
morning for some central and SW valleys, with the Sanpete/Sevier
valleys the most likely areas to reach 28F or less. A northerly
gradient across the SW has enabled some enhanced flow across the
SW valleys allowing for a more mixed boundary layer, but this
gradient is showing signs of relaxing and several hours of cooling
is still to come.

The next trough will graze northern Utah Sunday afternoon
driving a weak cold front across the northern half of the area,
while shifting the ridge downstream. EC remains a little
sharper/deeper with this trough, though still not overly
impressive regarding strength of front or breadth of upper
support. Have focused PoPs in the early evening in the post
frontal environment at which time weak H5 cold advection will
steepen lapse rates slightly. Although this trough won`t be
impressive sensibly, it will be the kicker to open up the door to
an increasingly moist near zonal flow.

A strong near zonal jet stretching from the Pac coast west across
most all of the Pacific is forecast to impinge on western CONUS
Monday, with several waves poised to translate across the
central/northern Rockies thereafter. The first comes Monday
evening into Tuesday with focus largely across the northern half
of the CWA. Good agreement exists in globals, though as typical in
flow regimes such as this, subtle timing and amplitude
differences will likely continue over the next few runs. Areal
coverage of precip looks greatest along the I-15 corridor from
Utah Valley north and over the northern/central Mtns under a
fairly strong W-NW flow, with conditions only become more
unsettled heading into the long term period.

.LONG TERM (After 00Z Wednesday)...The large scale pattern is
expected to remain quite active across the region through much of
the long term period, with the general message being wet and cool,
particularly across the north.

The operational models are in general agreement with the idea of a
shortwave trough trekking through the northern Great Basin and
impacting northern and western Utah with valley rain and mountain
snow late Tuesday night into Wednesday, and for the most part have
retained relatively high PoPs and cooler temperatures for this
period, although trimmed PoPs a bit in the south central through
east central valleys, owing to both a slower onset, and strong WNW
flow providing a substantial downslope component in the lee of the
higher terrain.

Beyond Wednesday, the operational models diverge significantly in
breaking down the large scale zonal flow into a more amplified
pattern (as is often the case). The GFS remains the more aggressive
model, amplifying the pattern a full day or more before the EC,
while the Canadian is seemingly somewhere in the middle. As such
have maintained a chance of valley rain and mountain snow through
the end of the week for most areas, with temperatures remaining
roughly 10 degrees below climo, but not as cold as the GFS would
suggest.

&&

.AVIATION...VFR conditions will prevail at KSLC  through the TAF
period, with southerly winds expected to switch to the northwest
around 18Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Hard Freeze Warning until 9 AM MDT this morning for UTZ014-016.

WY...None.
&&

$$

Merrill/Seaman

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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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