Scientific Forecaster Discussion
fxus65 kslc 191236
Area forecast discussion
National Weather Service Salt Lake City Utah
500 am MDT Thu Apr 19 2018
Synopsis...southerly flow will strengthen today ahead of an
upper low which will cross the region through tomorrow, bringing
rain and snow to portions of the forecast area. High pressure and
resultant warm/dry weather will follow for the upcoming weekend.
Short term (before 12z sunday)...infrared satellite imagery early
this morning shows several features set to affect our weather over
the next couple days: a deformation zone moving over Utah in
advance of a circulation center over the southern Great Basin, and
another circulation center moving down the socal coast. These two
lows are progged to merge into a single closed low and track
through southern Utah later today and Friday.
Water vapor imagery shows a notable dry slot currently sliding
into southern Utah. Models suggest this dry slot will keep the
eastern third of our forecast area dry through tonight, while
areas west of around I-15 and south of I-80 should see showers
fill in by late today. Temperatures meanwhile will be fairly warm
for areas east of I-15 as 700mb temps reach or exceed 0c. Gusty
south winds are expected for the higher terrain of southern Utah
today. Winds at lower elevations should pick up as well by late
in the day as the surface pressure gradient tightens, especially
for areas near the Arizona border such as Lake Powell.
As the upper-level closed low pushes eastward tomorrow, models show
a notable trowal signature from around the uintas north into
southwest Wyoming, suggesting that this area could see more
significant and widespread precipitation (in comparison to the more
showery and generally lighter precip elsewhere in our forecast
area). One area that could struggle to see any precip is the Wasatch
front, especially slc northward, which will be downsloped by the
easterly mid-level flow. Snow levels will be higher in comparison to
recent storms, around 6,000 to 7,000 feet in the most active portion
of the event.
Ridging and associated subsidence will move into our area by early
Saturday, bringing clear skies and a warming trend.
Long term (after 12z sunday)...the ridge axis over Utah heading
into Sunday slowly shifts eastward through the day, with a warm day
expected in lightly increasing southwesterly flow. This is ahead of
a trough over the Pacific northwest that is expected to brush by
northern Utah Sunday night into Monday. This could produce some
precipitation across the far north, but 80% of the area will likely
just see an increase in cloud cover.
The trough continues eastward out of the region Monday night, with
heights and temperatures rebounding for Tuesday. Beyond Tuesday,
global models begin to get wildly out of phase, as they struggle
with how to handle a closed low off the West Coast. As such, details
beyond Tuesday are very low confidence.
Aviation...the wind forecast at the slc terminal is low confidence
today. The most likely scenario is for winds to switch to the
northwest around 20-22z, but there is a chance southeasterlies
persist through at least 23z. These southeasterlies could become
gusty at times, especially 15-19z, but gusts greater than 30 mph are
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