Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 221048

Area Forecast Discussion
National Weather Service Salt Lake City UT
348 AM MST Wed Feb 22 2017

.SYNOPSIS...A cold upper trough will cross the region today and
tonight. A cold moist and unstable northwest flow will follow the
trough Thursday into Friday.


.SHORT TERM (Thru 00z Sunday)...An upper trough remains
primarily off the west coast early this morning with a well
defined short wave ahead of the main trof axis moving into nrn CA.
A stalled cold front sits across central UT with a narrowing
swath of precip north of it. Rain has changed over to snow down to
about 4500 ft but there has been little if any accumulation on
pavement below about 5000 ft or so. Above that level roads have
become locally snowy in the mtn valleys and snow packed over the
mtns and across swrn WY.

The flow aloft over UT starts backing this morning as the leading
short wave moves inland and expect the precip associated with the
cold front to become less organized. Also, the lighter precip
combined with a little solar radiation through the clouds should
allow roads to become mostly wet below about 6500-7000 ft.
Expanded the existing Winter Weather Advisory around midnight to
include our WY zone until 10AM. The Advisory for the remaining
areas will stay in effect.

Convergence along the cold front increases this aftn as the
leading short wave approaches and expect precip to increase
accordingly thru this eve and eventually become concentrated
along the wrn slopes of the mtns and in the upstream valleys.

A closed low forms by 12z Thu over nrn UT as the main upper trof
translates inland and this should bring fairly widespread snow to
most of the nrn CWA under the cold pool aloft. The cold front will
have moved out of the CWA by this time with lingering orographic
precip along the central mtns. The airmass is cold enough by this
time that any precip will be falling as snow and there is a good
chance this will impact the morning commute along the Wasatch
Front and into the mtn valleys. It is possible we will need to
expand the Winter Weather highlight to include these valleys thru
at least midday Thu.

Cold unstable nw flow keeps snow showers going into Fri before
ending Fri aftn as a short wave ridge moves into the CWA. Expect
the break to last thru Fri night with warm advection bringing a
chance of precip back to the nrn CWA on Sat.

.LONG TERM (After 00z Sunday)...By 12z Sunday global models really
begin to show variance in detail regarding long wave evolution of
a trough dropping south along the coast, and it`s coupling with a
remnant closed low in the eastern pacific. Globals do agree in
phasing these two systems to some regard, with eventual inland
translation early next week. Timing of details remains to be seen.

Upper diffluence and modest moisture advection during the phasing
stage beginning later Sunday will aid to kick off precip, largely
snow, from SW-NE during the day per GFS. ECMWF, however, depicts
subtle height rises due to a variant evolution of the upstream
trough during the day. For now have leaned towards the more
pessimistic GFS and broad brushed high chance/likely PoPs across
the area.

Thereafter through midweek models converge slightly better
regarding inland translation of the trough, widespread precip
through Tuesday with snow levels reaching most all valleys above
4000ft. Will have to continue to monitor potential significance of
this, but at this time it doesn`t appear to be abnormal for this
time of year.


.AVIATION...Expect VFR conditions at the KSLC terminal through
mid morning with CIGS below 6000 ft. CIGS will gradually rise
above that level after about 17-18z. Expect rain and snow to
expand back over the airfield after about 22z with MVFR
conditions becoming prevalent. Rain will change over to snow by
this eve with IFR conditions likely through the night. Southerly
winds will prevail through this afternoon then switch to NW around


UT...Winter Weather Advisory until 4 AM MST Friday for UTZ007>010-517.

WY...Winter Weather Advisory until 10 AM MST this morning for WYZ021.



LONG TERM...Merrill

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