Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 221045

Area Forecast Discussion
National Weather Service Salt Lake City UT
445 AM MDT Sun Apr 22 2018

.SYNOPSIS...High pressure aloft will maintain warm and dry
conditions across Utah through today. A weak weather disturbance
will bring a few showers to northern Utah and southwest Wyoming late
tonight through Monday.


.SHORT TERM (THROUGH 12Z WEDNESDAY)...The ridge over the area early
this morning will shift east today as an upstream trough currently
over the PacNW coast makes its way inland. The flow aloft over Utah
will turn southerly by this afternoon with the airmass continuing to
trend warmer. Midlevel lapse rates should be a bit steeper today as
well, so overall, temperatures will be warmer than yesterday
throughout the area and well above normal.

Models indicate that the airmass will destabilize just enough to
generate some weak convection this afternoon, initiating over the
higher terrain. However, with the airmass remaining on the dry side,
it is hard to see any convective showers putting down measurable
precipitation. Have allowed a mention of slight chance PoPs over the
Uintas, but even this may be optimistic.

The aforementioned upstream trough will graze northern Utah late
tonight through tomorrow, pushing a cold front into the area. With
the jet axis remaining near the Utah/Idaho border, expect any
precipitation associated with the front to remain over the northern
portions of the forecast area. A second vort max is then progged to
rotate down through northeast Utah and southwest Wyoming on Tuesday
as the main trough exits into the Great Plains. This will bring a
reinforcing shot of colder but drier air into the area. Of course,
colder is a relative term, as this will not mark a return to winter-
like conditions. H7 temperatures only drop to around -5C up north,
bringing Tuesday`s max temperatures closer to normal. The cold front
will be much shallower down south where the extent of cooling will
be less noticeable and temperatures are expected to remain above
normal. A high-amplitude ridge will then build into the area Tuesday

.LONG TERM (After 12Z Wednesday)...High pressure is expected to
remain over the Great Basin heading into Wednesday. There is still
some discrepancy about the placement/depth of yet another shortwave
trough dropping into the Rockies from the north late Wednesday into
Thursday, but on the whole this wave is expected to pass yet again
to the north/east of the forecast area. At most, some minor cooling
is possible as the shallow cold front passes through.

After that wave exits into the eastern CONUS early Thursday, a high
amplitude ridge builds over much of the west for the end of the work
week. Enough moisture could linger under this ridge to allow for
some diurnal, probably primarily mountain-based convection Thursday
and Friday afternoons, but coverage will likely remain isolated at
best. Otherwise, expect a warming trend heading into the weekend.

For the weekend, the big question is the placement and progression
of a large, closed Pacific low as it tries to push slowly inland. It
appears likely that the low will remain west of the Utah/Nevada
border through at least 00Z Sunday, with increasing southerly flow
ahead of it. Combined with 700mb temperatures around 6-10C, Saturday
has the potential to be the warmest day of the year so far in many
locations. Have increased high temperatures for Saturday afternoon,
especially in the northern valleys. Depending on the timing of the
approaching low, Saturday night and Sunday could be fairly warm as
well, though that is where uncertainty in the details begins to
increase a fair amount, as models try to resolve what to do with the
closed low.


.AVIATION...Winds at the SLC terminal are expected to switch to the
northwest around 19-21Z today, with a slight chance that winds
remain southerly or light and variable through 22Z.





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