Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 250936
Area Forecast Discussion
National Weather Service Salt Lake City UT
336 AM MDT Sat Mar 25 2017
.SYNOPSIS...The upper level trough will move east across the
Great Basin today. High pressure aloft will return briefly on
Sunday, followed by another storm system for early in the upcoming
.SHORT TERM (THROUGH 12Z MONDAY)...
Water Vapor Satellite shows the ridge axis has shifted east as
the next storm approaches from Nevada. 400-200mb MDCARS wind
observations place a 115-135kt cyclonic jet from off the Pacific
Northwest coast into the Northern Rockies. GOES/SLC 00Z RAOB/HRRR
indicate that precipitable water values vary from 0.20"-0.30"
mountains to 0.40"-0.65" valleys. Blended Precipitable Water
product shows an atmospheric river from the tropics into southern
There are many things going for today`s precipitation event.
During the next 24 hours a strong height fall/rise couplet crosses
overhead. Far northern Utah may benefit from lift associated with
the right entrance region of an upper level jet, at least this
morning. The system has a moisture tap back to the tropics. There
is enough cold advection to foster instability development today
per SREF. In fact SREF indicates a high enough chance for thunder
to include this afternoon and evening across southern Utah.
Snow levels fairly consistent near 7kft today, perhaps lowering in
areas of higher precipitation rates. Snow levels fall below 6 kft
tonight, but this is mostly after precipitation ends. A Winter
Weather Advisory has been issued for most mountain zones as winter
driving conditions will likely be widespread above 7000 feet.
Height rises, warming aloft and increasingly anticyclonic flow
should shut off precipitation processes tonight.
Next storm system drops into the Pacific Northwest Sunday. As a
result of lowering heights, increasing 700-500mb lapse rates, and
the approaching cold front crossing into northern Utah Sunday
night, carrying slight chance to chance PoPs heading into Monday
.LONG TERM (AFTER 12Z MONDAY)...
The next storm system is expected to dive into the Great Basin
during the day Monday before tracking southeast into Arizona
Monday night/Tuesday morning. This will drop a cold front through
western Utah during the day Monday and across the rest of the
state by Tuesday morning. Moisture and instability look good in
association with this boundary, so it should bring a nice initial
brand of precip with showers continuing into much of Tuesday. 700
mb temps are a little warmer in guidance this morning compared to
yesterday, primarily in the -5C to-7C range. This would keep snow
levels above most northern Utah valley floors but could have some
impacts as low as bench locations. Precip is progged to taper off
from west to east during the day Tuesday as the trough tracks away
from the forecast area. Overall, have raised POPs given increased
confidence due to model agreement and good run-to-run
High pressure is then expected to return for Tuesday night/early
Wednesday but after that guidance diverges a bit. GFS holds onto the
ridge through much of Thursday but the EC brings a weak shortwave
and associated cold front into Utah and southwest Wyoming. As a
result, there is a noticeable difference in 700 mb temps in the
models by Thursday morning with the EC showing -3C to -5C and the
GFS much warmer at +2C to +4C, which makes the Thursday MaxT
forecast a bit problematic. Have favored the GFS somewhat as it has
been more consistent in its solution.
All models indicate a potent Pacific Northwest storm system
impacting the forecast area late Thursday through Saturday. EC is
about twelve hours faster bringing the initial front through
compared to the GFS but both take the low on a similar track through
southwest Utah and into Arizona and New Mexico. GFS showers a colder
front with 700 mb temps as low as -11C. EC looks to keep the coldest
air just to the west of the forecast area but still drops 700 mb
temps as low as -8C. High pressure is then expected to return behind
this system for the end of the forecast period.
VFR conditions are expected at the SLC terminal through the
morning. Cigs are expected to fall to or below 6000 feet AGL
between 12Z and 14Z with rain developing over the terminal. There
is a 30 percent chance of MVFR conditions developing in heavier
rain, primarily before 18Z. West to northwest winds are expected
to continue through the day.
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