Scientific Forecaster Discussion
fxus65 kslc 251045
Area forecast discussion
National Weather Service Salt Lake City Utah
445 am MDT Wed Apr 25 2018
Synopsis...high pressure aloft settling across the interior west
will generate increasingly warm temperatures through the latter
portion of the week. The next Pacific storm system will work slowly
east across the Great Basin this weekend.
Short term (through 12z saturday)...a high-amplitude ridge
continues to build into the Great Basin today, resulting in a dry
airmass with warmer temperatures across the area. An easterly mslp
gradient across northern Utah this morning along with a
northeasterly gradient across the southwest have contributed to
somewhat enhanced winds out of the canyons across the northern and
central Wasatch front as well as in Dixie. The winds have not been
particularly strong, however, as there is no support aloft. The
gradient is expected to weaken midmorning bringing an end to these
A shortwave trough is still progged to dive southeast along the
northern rockies tonight. The only real impact of this trough for
the forecast area is that it will push a shallow cold front into
southwest Wyoming and far northeast Utah, reinforcing the easterly
gradient across the area and bringing another round of enhanced
canyon winds to the Wasatch front late tonight through tomorrow
morning. Otherwise, very little moisture will accompany this trough.
The airmass will continue to trend slightly warmer tomorrow except
for the northeastern zones influenced by the cold front.
The ridge will center itself over Utah late tomorrow afternoon, then
start shifting east of the area Friday. A very warm airmass will
spread into the area Friday, with 700 mb temperatures in the 7-10c
range. Developing southwesterly flow aloft will aid mixing during
the afternoon. Afternoon Max temperatures are expected to run 10 to
nearly 20 degrees above climatological normals. However, the
southwesterly flow will also bring an influx of midlevel moisture.
This will allow clouds to increase over the area as well as aid in
the development of high-based convection which should mostly
initiate off the higher terrain.
Long term (after 12z saturday)...southerly flow will increase over
the forecast area during the day Saturday as the large Pacific low
moves onto the California coast. Overall, global models have come
into better agreement with regard to their treatment of the system
over the weekend, showing the system splitting Saturday afternoon
and the front piece of the system moving through and bringing a cold
front with it Saturday night into Sunday. Ec is slightly slower
bringing the system through and shows this wave a bit stronger and
digging farther south into southern Utah compared to the latest GFS
solution. Impacts remain similar despite these differences: maxes
back near seasonal normals beginning Sunday with showers developing
for primarily northern Utah and southwest Wyoming Saturday night
into Sunday. Overall, have increased pops somewhat with increasing
Beyond the weekend, models start to diverge more significantly. Both
show the back piece of the Pacific trough impacting the forecast
area, but differ on the details. The ec slides it across primarily
central and southern Utah on Monday as it phases back in with the
first piece, that moves back over northern Utah on Tuesday. It then
shows another Pacific low merging with a second Pacific northwest
system over Nevada on Wednesday, bringing this warm but moist and
potentially potent system into northern Arizona by next Thursday.
The GFS digs the back wave south into Southern California on Monday,
merging it with a few other waves before it eventually moves into
Arizona for next Wednesday. All model solutions would keep unsettled
weather over much of the forecast area through day seven with
temperatures near seasonal normals, but significant uncertainty
exists as to the most favorable locations for precip at any time.
Because of this, have generally favored keeping low end pops over a
broader area, focused over the higher terrain.
Aviation...the slc terminal will see VFR conditions and clear skies
through the morning. Southeast winds are expected to shift to the
northwest between 18z and 20z.
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