Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 282222
Area Forecast Discussion
National Weather Service Salt Lake City UT
422 PM MDT Fri Apr 28 2017
.SYNOPSIS...A cold upper low will form near the four corners
region late tonight then move southeast into the southern Rockies
later in the weekend. A couple of weak weather disturbances will
graze the area late Sunday into Monday. Strong high pressure
aloft will finally reach the area around the middle of the week.
.SHORT TERM (Through 00z Tuesday)...Afternoon water vapor and H5
analysis continue to portray a more tightly bound circulation of
the mid latitude trough over the 4-corners region. Weak upglide
along the northern/northwestern periphery of this low combined
with adequate moisture have maintained widespread showers across
the north today (snow levels currently hovering near 4300ft),
while southern portions have realized more convective type showers
beneath the upper cold pool.
12z Guidance continues to indicate a backdoor cold front will
track west out of western Wyoming this evening, with low level
forcing aiding to focus a band of snow from SW Wyoming west into
the northern mountains into the overnight hours. Accumulations of
1-2 inches across the Wasatch Back/SW Wyoming look likely with
Models have trended (or continue) to advertise a more easterly
component of near H7 flow across the northern Wasatch in the post
frontal environment after midnight, this promoting more cross
barrier flow across the northern Wasatch through the latter half
of the night. Cold advection in guidance continues to extend a bit
above crest level, and with a modest surface gradient supporting,
expecting enhanced easterly winds to develop from Centerville
north through Ogden after midnight. Would be nicer to see a bit
stronger reflection in the NE-SW oriented surface gradient, but
key factors for mild downslope conditions will be present and
opted to issue a Wind Advisory for the benches along the northern
Wasatch Front. A Wind Advisory also remains in effect across the
gaps of Washington County tonight, with a N-S surface gradient
and strong H7 flow (up to 50kts) supporting north/northeasterly
gusts in the 40-50+ mph in and near the canyons. This does have
the potential be a high end advisory event along I-15 between
Black Ridge and Hurricane.
Winds north of Black Ridge are expected to decouple after
midnight, and with at least partial clearing coupled with the very
cold airmass in place, issued Hard Freeze Warnings for west
central and southwest Utah, as well as the Sanpete/Sevier valleys.
The core of the upper low will slowly churn towards the Texas
panhandle late tonight/tomorrow allowing heights to build in from
the west. With diminished forcing and a stabilizing airmass, any
lingering and or tangible precip will phase away Saturday.
Anticyclonic northerly flow aloft will remain in place as heights
build in from the west Sunday, this as the eastern pacific ridge
amplifies along the west coast. Two weak waves translating through
this ridge will pass the area late Sunday into Monday, but will
have little sensible impact as they do so. A gradual warming trend
will be realized through early week.
.LONG TERM (After 00Z Tuesday)...One last weak shortwave is progged
to move through northern Utah and southwest Wyoming during the day
Tuesday. This will bring through a weak frontal boundary and
another threat of precip, primarily over the higher terrain.
As the trough moves through, a broad Pacific ridge is on track to
move onshore along the California coast before shifting east through
the Great Basin. By Thursday night, the ridge axis is expected to
move overhead over Utah and southwest Wyoming. Therefore, for much
of the extended period the area will see a pronounced warming and
drying trend, with maxes returning to near seasonal normals for
Wednesday and continuing to warm from there.
By Friday, global models are indicating the ridge shifting east of
the area as a Pacific storm system moves onshore, with this
happening more quickly in the EC compared to the GFS. Overall,
models are significantly drier for day seven than the overnight
runs, and have trimmed existing POPs by quite a bit. However,
considerable uncertainty remains for the end of the forecast
.AVIATION...MVFR conditions are expected to prevail at the SLC
terminal for much of the rest of the afternoon in rain showers. The
showers are expected to move out of the terminal between 00Z and
02Z, allowing conditions to move into the VFR range with cigs
primarily above 6000 feet AGL. Northwest winds are expected through
the night, though there is a 30 percent chance of light and variable
developing overnight, primarily between 09Z and 12Z.
UT...Hard Freeze Warning from midnight tonight to 9 AM MDT Saturday
Wind Advisory from 10 PM this evening to 10 AM MDT Saturday for
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