Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 221611

Area Forecast Discussion
National Weather Service Salt Lake City UT
1011 AM MDT Fri Sep 22 2017

.SYNOPSIS...A cold core upper low to the west of Utah will drift
slowly east into and then across the state this weekend. Below
normal temperatures are expected across the region, with periodic
valley rain and mountain snow concentrating on the northern half
of Utah and southwest Wyoming through the weekend.


.DISCUSSION...Satellite imagery shows the now developed upper low
centered roughly over extreme southwest Idaho this morning. A
vorticity lobe rotating quickly north along the east side of the
upper low should exit northwest Utah shortly, taking any remaining
organized light precip with it into eastern Idaho. Te fairly
stable and moist low-level air mass trailing this feature should
maintain cloud cover and cool temperatures across west-central
and northern Utah this afternoon. A somewhat drier southwest flow
aloft across south-central through eastern Utah will maintain
breezy and mild conditions, with scattered convective cloud cover
but minimal convective precip.

A second vorticity lobe just clearing the Sierras on the southern
periphery of the upper low will turn northeast across western and
northern Utah later this afternoon. This dynamic feature will
bring modestly cooler mid-level air into northwest Utah to
increase elevated instability. In addition, the various model
guidance all show a secondary jet streak forming across northwest
during the late afternoon/early evening hours. The lift generated
in this scenario probably not sufficient for widespread heavy
precip, but should be capable of generate an increase area of
light to moderate precip across northwest Utah late this through
around mid-evening.

Looking at relative lull in precip late Friday night through early
Saturday afternoon as the upper low center drifts south towards
southern Nevada/southwest Utah. Precip should once again increase
in areal coverage and intensity Saturday night/Sunday as mid-level
wrap around warm advection develops on top of the cool/moist low-
level air mass across western/northern Utah and southwest Wyoming.
By Sunday evening the heaviest precip will concentrate across
northeast Utah/southwest Wyoming before finally lifting northeast
across Wyoming with the exiting upper low.

Made earlier updates to end the winter weather advisory and to
adjust Pops and cloud cover across western and northern Utah.
Remainder of the morning forecast looks fine for now.


.AVIATION...Periodic ceilings below 3000 feet will be possible at
the SLC terminal between 15Z and 18Z. Conditions should generally
improve after 18Z, but showers across the area will likely keep
ceilings below 7000 feet through much of the afternoon. Winds may be
light and variable at times through 17Z, before increasing from the
northwest 17-19Z.





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