Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 181103

Area Forecast Discussion
National Weather Service Salt Lake City UT
503 AM MDT Sun Mar 18 2018

.SYNOPSIS...A slow-moving storm system will bring cool and
unsettled weather for remainder of the weekend. High pressure
aloft will return for the first half of next week and bring a
warming trend to the region, before another storm system
approaches for the latter half of the week.


.SHORT TERM (Through 12Z Wednesday)...Early morning satellite
imagery and objective analysis show an upper trough translating
across the forecast area. The bulk of the upper level forcing
associated with this trough is passing through northern Arizona
and southern Utah, where areas of snow continue above roughly 4000
feet. As this feature quickly continues eastward this morning
precipitation will likely wane with time across central and
southern Utah. Currently Winter Wx Advisories remain in effect for
the higher terrain as well as higher elevations of the San Rafael
Swell, and this seems reasonable. With snowfall tapering off in
southwest Utah over the next couple of hours expect to be able to
cancel the Advisory for the Cedar City area around or shortly
after sunrise.

Meanwhile, a weaker vorticity maxima further north coupled with
the upper level cold pool should allow for showers to develop
across northern Utah late this morning through the afternoon. Have
bumped PoPs, but given the convective nature of this activity went
with scattered coverage/wording for most valleys, with activity
quickly ending this evening.

Mid level ridging will slowly build across the region during the
early portion of the upcoming week. Initially low level cold air
will remain in place across the region keeping temperatures below
climo, however by Tuesday warming aloft should allow max temps to
rebound to near or slightly above climo area-wide.

.LONG TERM (After 12Z Wednesday)...Southwest flow is expected to
increase beginning Wednesday on the back side of a ridge of high
pressure and ahead of a storm system off the Pacific coast. This
flow is expected to advect a notable amount of subtropical
moisture into Utah and southwest Wyoming with the GFS indicating
PWs of 0.6 to 0.8 inch across much of the area by early Thursday,
which would be near the highest observed for this time of year.

In this moist airmass, EC/GFS indicate a series of shortwaves
ejecting out ahead of the main system into the forecast area on
Thursday as the upper level jet also approaches. This combination
of moisture and favorable dynamics would allow for good coverage
of valley rain/mountain snow across the forecast area on Thursday,
and the global models have come into overall better agreement
with regard to the arrival of the moisture and the timing of the
best precip, which would be during the day Thursday. Have
increased POPs a bit with increasing confidence.

The trough is ultimately progged to slide northeast into the
Pacific Northwest Thursday afternoon into Friday, with a piece
breaking off and sliding a front across northern Utah on Friday.
The resultant shift of the flow to the west would cut off the
subtropical tap, allowing for a significant decrease in coverage
of precip while moving a noticeably cooler airmass. Very mild max
temps are expected to move back near or slightly below seasonal
normals for Friday.

EC/GFS diverge quite a bit after Friday, with the EC bringing a
larger second piece of the Pacific Northwest storm back through
Utah on Saturday, bringing some additional precip and 700mb temps
as low as -13C to -15C for much of the forecast area by early
Sunday. GFS also splits the system but keeps this wave to the
north of the forecast area, resulting in warmer temperatures
overall during this period, with the cooler air confined to
northern Utah. Both ultimately move the main system over the area
shortly after day seven, with significant divergence remaining in
their solutions. Given the differences in the solutions, have
split the difference with regard to temperatures for the upcoming
weekend and maintained isolated to scattered POPs for primarily
northern Utah.


.AVIATION...VFR conditions are expected to prevail at the SLC
terminal throughout the day, with cigs dropping to or below 6000
feet AGL during the afternoon with showers in the vicinity of the
terminal. There is a 30 percent chance of IFR/MVFR conditions in
snow this afternoon. Northwest winds are expected throughout the
day, but there is a 30 percent chance of light and variable or
light southeasterly winds at times before 16Z.


UT...Winter Weather Advisory until noon MDT today for UTZ009>011-013-

     Winter Weather Advisory until 10 AM MDT this morning for UTZ016.




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