Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 182230
Area Forecast Discussion
National Weather Service Salt Lake City UT
430 PM MDT Sat Mar 18 2017
.SYNOPSIS...A very mild southwest flow will continue into early
next week but a more active pattern is expected to develop by
.SHORT TERM (Through 00Z Wednesday)...A storm system moving
across the northern Rockies will flatten the ridge across the
Great Basin tonight as well as push a weak cold front into
northern portions of the CWA. There is just enough moisture
convergence along this boundary that some showers are expected to
breakout over the higher northern Utah elevations, especially
extreme northwest corner. So far the closest radar echoes of
precipitation are across northwest Nevada near Winnemucca. The
HRRR is not supporting showers moving into the CWA anymore but the
GFS, SREF and EC still show some instability through this
evening. PoPs may be overdone but will let it ride for now.
The cool front should die out over northern Utah late tonight and
allow the surface gradient to weaken. Was concerned that temps in
the SLC would remain in the mid to upper 50s, but with the
boundary moving through the winds will subside and temperatures
should cool to near 50, which is a only a few degrees below what
our normal high is at SLC for March 19.
Another disturbance will ride across the flattened ridge through
Idaho Sunday afternoon which could set off a few showers along the
Idaho border late in the day. Temperatures across northern Utah
will be down about 3-6 degrees Sunday compared to today, while
only 1-3 degrees cooler in the south.
The EC and GFS show a weak disturbance associated with a broad
area of warm advection moving across the Great Basin and central
Rockies Monday afternoon. The low levels remain rather dry looking
so once again have kept the main threat of showers and
thunderstorms across the higher elevations.
A stronger system will approach the western CONUS Tuesday and
south winds are expected to increase with more cooling expected in
the south than in the north as this system will be farther south.
.LONG TERM (After 00Z Wednesday)...The longwave trough developing
along the West Coast is expected to move inland midweek, splitting
as it does so. One piece of energy is progged to move through the
Desert Southwest, and another through the Northern Rockies. This
splitting flow, combined with the general southwest flow aloft which
is unfavorable for moisture transport into our area, should somewhat
dampen the chances for widespread precipitation over our area.
Nevertheless, expecting a big cooldown in temperatures to near or
below normal with a chance of light precip at times. The precip
focus will initially be over northern UT Tues/Wed, then central &
southern UT later Wed and Thursday.
A cold front is expected Thursday, with the GFS showing 700MB temps
dipping as low as -8C over northern UT. This could support graupel
or snow showers to valley floors, with accumulating snow possible in
the mountains. Timing will play a key role in whether frozen precip
is an impact. Currently, the model consensus has the cold air
arriving during the day Thursday, which would result in limited
Global models are in great agreement with a continued active pattern
for the remainder of the week and into the weekend. Brief ridging is
expected Friday, following by a strong closed low moving into the
Great Basin by late Friday into Saturday. This would bring a
continued period of near to below normal temperatures and a threat
of widespread precipitation across the forecast area.
.AVIATION...VFR conditions will continue at the SLC airport today
and tonight. Southwest winds will be gusty at times, though
slackening around 22z-02z due to lake breeze interference. There is
a 20% chance of a temporary westerly wind shift in this period. A
weak boundary tonight will bring a 60% chance of a shift to light
northwest winds about 6-9z, with southerly winds likely returning a
few hours later.
LONG TERM...Van Cleave
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