Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 171524
Area Forecast Discussion
National Weather Service Salt Lake City UT
924 AM MDT Fri Mar 17 2017
.SYNOPSIS...High pressure over the region today will give way to a
very mild southwest flow on Saturday. A more active pattern is
expected to develop for the first part of next week.
.DISCUSSION...Morning water vapor and H5 analysis continue to
indicate low amplitude ridging centered over eastern Nevada, with
a mild near westerly flow in place aloft locally. Latest height
trends do indicate subtle amplification of the upstream ridge,
and models continue to depict this trend will continue over the
next 24 hours as the ridge axis centers over, then shifts
downstream of the area tomorrow.
Near record highs pushing 20 degrees above climo will be realized
today across many portions of the forecast area as H7 temps will push
+4 C in the north and +6 C in the south during peak heating and deep
mixing potential continues to be present. Current forecast handles
this well and have made no updates this morning.
The downstream evolution of the ridge axis tomorrow will allow a
strengthening southwesterly flow to develop over the area, this as
the trough currently located off the NorCal coast (near 140W)
begins to lift northeast into the PacNW. With a very mild airmass
in place, modestly strong southerly winds (both aloft and at the
surface), record breaking temps look likely for many areas across
the area. Current forecast of 79 F for KSLC would shatter the
record for the day, and would be 1 degree shy of tying the all
time record for March. Cirrus filtering overhead from the upstream
trough may at times hold temps back a bit, but guidance does
portray more of a scattered and thinning shield as the sun angle
increases tomorrow afternoon. Feel clouds will have minimal impact
on the temps, but this warrants watching. Previous discussion
PREVIOUS DISCUSSION...A weakening short wave trof ejecting inland
sends a weak cold front into the nrn CWA Sat night that stalls
across central UT on Sun. This front will bring a chance of
showers to the ID border region but see little if any threat of
rain south of about Ogden.
Additional weak waves ejecting out of the offshore trof will
ripple past mainly to our north Sun night into Mon. This will
keep the threat of showers going north of the frontal boundary
into Mon with the chance of rain getting south of SLC. Altho the
front cools the airmass down somewhat it is still forecast to
remain warmer than normal and temps will stay mild.
The large trough just off the Pacific Northwest coast is slow to
rotate inland, though several short waves rotate around the trough
axis before the low center approaches the coast Wednesday. The
overall pattern is quite disorganized and messy, with a split-type
pattern as it progresses through the West coast states. Among the
global forecast models, the general idea is agreed upon, however
glaring differences in details remain.
A warm-advection southerly flow pattern is in place through
Wednesday when a weak baroclinic zone drifts into Utah from the
West. Cooling takes place aloft through Thursday as advertised by
the forecast models, though to what degree is debatable as they
differ. 700mb temps should cool to -5C to -7C from Thursday on
through Sunday, lowering snow levels to bench locations. Take note
of this, since the system is quite moist with precipitation
fields draped across Western Utah Wednesday as the main trough
axis swings through the Great Basin. Modifying a rather warm
airmass, temperatures right now look to keep rain to valleys and
snow confined to mountains and bench locations. The GFS continues
to be the colder of the solutions while the EC is a touch wetter.
.AVIATION...The SLC terminal will see VFR conditions throughout the
day with some scattered clouds. Southerly winds are expected to
shift to the northwest between 18Z and 20Z.
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