Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 241121

Area Forecast Discussion
National Weather Service Salt Lake City UT
521 AM MDT Sat Mar 24 2018

.SYNOPSIS...Cold trough off the Pac NW coast will eject a weak
disturbance with its associated cold front across northern Utah
this afternoon. The cold trough itself will move into northern
and western Utah Sunday and then exit the area later Monday.


.SHORT TERM (Through 00Z Tuesday)...Cold trough off the Pac NW
coast will eject a weak disturbance northeast across Nevada early this
morning and across northwest Utah by midday. The associated
surface cold front near Elko Nevada at 4am will likely reach the
northern Wasatch Front by mid to late morning and to SLC about
late morning to midday. South winds have been increasing across
the western valleys and northern mountains overnight and should
continue to increase in the valleys until the cold front arrives.
Currently there is a narrow broken band of showers associated
with this cold front. The EC is the most bullish in bringing
widespread precip in across northern Utah today while the HRRR
has basically nothing. With decent looking convergence associated
with the 700mb baroclinic zone moving into far NW Utah this
afternoon believe the HRRR is underdone while the EC is making the
precip too widespread since its a narrow band of dynamics. Have
backed off on the PoPs to a basic midpoint between the extremes of
the EC and HRRR. This baroclinic zone will stall and weaken some
over far northwest Utah overnight.

Temperatures across northwest Utah will likely peak late morning
through midday ahead of the cold front while south of the front
temperatures will continue to warm into the afternoon with near to
slightly above normal temperatures under mostly sunny to partly
cloudy skies.

The cold trough itself will move into the Great Basin Sunday and
tighten the 700mb baroclinicity from about northern Utah County
southwestward towards Delta between midday and late afternoon.
However, The latest satellite imagery shows a strong jet down the
backside of the trough near 140W which could cause the trough to
dig a little more and be slower than models which would result in
the baroclinic zone becoming nearly stationary early Sunday
afternoon. If this occurs, snow amounts will be greater in a strip
from just north of Delta to SLC. Have increased the QPF in this
region for this potential as well as both the 00Z and 06Z runs of
the GFS indicate a few 700mb circulations trying to form along
this baroclinic zone from central Millard County to Salt Lake

As far as road impacts there may not be much during the day even
if grassy surfaces receive several inches because road surfaces
are in the mid 40s. However, if the snow intensity increases then
slush or snow build up is possible.

The cold front will slide down into southwest Utah by Sunday
evening but precip should be showery as the low cold air is out
running the cold air aloft and there is only a narrow window for
instability to occur right with the cold front. The 500mb
temperatures begin to warm over west central and southern Utah
Sunday night while the 500mb cold trough moves across northern
Utah. With the cold trough snow showers are expected to continue
over the northern mountains and adjacent valleys Sunday night
with a chance of snow lingering into Monday as a secondary cold
thermal trough keeps the air mass somewhat unstable.

.LONG TERM (After 00z Tuesday)...The upper low will continue to
amplify south Monday night while orienting over the lower Colorado
River valley, becoming a closed system by dawn Tuesday. Do expect
some residual light snow shower activity to linger through Monday
evening, but as a whole precipitation potential is expected to
largely dissipate with sunset that evening. With the orientation of
the upper low, do expect enhanced gap winds in Washington County
overnight and through much of Wednesday as modest north-
northeasterly H7 winds coupled with a favorable N-S MSLP gradient
and weak low level CAA should support this.

Thereafter globals continue to depict eastern Pacific ridge
amplification through late week, with the local area remaining
beneath anticyclonic oriented northwesterly flow aloft. Do have to
note a weak short wave that is resolved within this flow that
remains progged to clip far northern/eastern portions of the area
Wednesday into the overnight hours however. Said wave will have a
continental track and looks quite benign dynamically, but just
enough forcing/diurnally driven instability appears present to
produce isolated to widely scattered showers across the north/east
during that window, while remaining largely orographically favored
in areal coverage.

Dry and increasingly stable conditions are expected for the late
week period as the upstream ridge remains the dominant feature. Do
note a net flattening of the ridge beginning Friday, with a stronger
more zonal flow orientation to winds aloft, but the mean storm track
will remain well to north (at least for the time being).


.AVIATION...South winds are expected to continue to increase
at the KSLC terminal through late morning, becoming moderate
after 13-14Z. A cold front is expected to cross the terminal
between 17-18Z switching winds to the northwest, while lowering
cigs to or just below 6000ft AGL for the afternoon hours. Widely
scattered or isolated light showers are anticipated this afternoon.




SHORT TERM...Struthwolf
LONG TERM...Merrill

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