Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 252153
Area Forecast Discussion
National Weather Service Salt Lake City UT
353 PM MDT Tue Apr 25 2017
.SYNOPSIS...High pressure briefly builds across the region tonight
then gives way to a series of progressively colder systems through
the remainder of the week.
.SHORT TERM (Thru 12Z Friday)...A broad upper trof is shifting
into the central US this afternoon with the axis extending from
wrn SD to nrn NM. A short wave dropping into the back side of the
trof crossed UT today bringing fairly widespread showers to the
north and scattered showers to the south and east along with a few
lightning strikes. Lingering showers in the wake of this wave
continue over the mtns and portions of the south and east.
The showers will end quickly by sunset as short wave ridging just
upstream over NV starts to build in.
The cool airmass in place will allow temps to get chilly tonight
dipping to near or below freezing in some valleys especially swrn
and central UT. Don`t expect hard freeze conditions as there will
be some lingering eve clouds, and moisture at low levels from the
precip today will persist overnight.
The ridge will shift east by Wed morning as the next short wave
trof begins to slide in from the northwest. This wave is currently
tapped into the atmospheric river that extends across the Pac and
is forecast to bring some of this moisture inland with it. Warm
advection precip develops across the northern CWA in the morning
spreading south in the afternoon and continuing overnight as a
cold front crosses the area.
The airmass warms enough Wed to lift snow levels above most passes
but the cooling that begins Wed night lasts thru Thu. It appears
precip turns more showery by Thu morning with a lesser threat of
accumulation as snow levels drop to the nrn valleys floors.
Even colder air spreads in Thu night as a broad upper trof deepens
again over the Rockies and Great Basin downstream of an amplifying
ridge in the ern Pac. Expect precip to fill back in across the
north overnight in a wrap around environment. Precip will be all
snow with some potential accumulation in the nrn valleys...mainly
off pavement surfaces.
.LONG TERM (After 12Z Friday)...The airmass continues to cool
through the day Friday as the upper level trough deepens and
slides south through the Rockies. Additional snow showers are
expected for the valley locations and mountains through Friday
evening as the low wraps around across northeast and east central
Utah before sliding south into the four corners region Saturday.
The GFS is currently the colder of the forecast solutions for
Friday morning, and of note in the 30 year climate record database
this ranks as occurring less than 1 percent of the time at this
time of year. In other words, this very cold airmass is anomalous
for this time of year.
Extended forecast models are in decent agreement with the low
cutting off and sliding east and south by Saturday, with minimal
spread among the ensembles. While heights are building in with the
ridge Saturday, the cool air aloft remains overhead through the
weekend. The moisture train becomes shut down late Saturday into
early Sunday as the flow aloft turns more north and even slightly
Ridging is short-lived with another shortwave cold front dropping
south Monday and brushing across the northern extent of the CWA.
Several waves of energy are upstream in the far extended and look
to brush through the Great Basin in the first week of May,
continuing the unsettled weather pattern for the Intermountain
.AVIATION...MVFR conditions at the SLC terminal are expected to
improve to VFR by about 23Z, but there is a 20 percent chance of
MVFR conditions persisting as late as 01Z. After going above VFR,
cigs should move above 6000 feet AGL by 01Z, but there is a 30
percent chance lower cigs hang on later than expected. Northwest
winds are expected to shift to the southeast between 03Z and 05Z.
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