Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 152227
Area Forecast Discussion
National Weather Service Salt Lake City UT
327 PM MST Wed Feb 15 2017
.SYNOPSIS...High pressure aloft will maintain dry and mild
conditions across the region through this evening. Southwesterly
flow will develop Thursday, followed by an active pattern late in
the week into early next week.
.SHORT TERM (THROUGH 00Z SUNDAY)...
Water Vapor Satellite shows a ridge from southern California
across the Great Basin. Several storm systems are approaching the
West Coast. 400-200mb MDCARS wind observations place a 100-130kt
cyclonic jet into the Pacific Northwest. GOES/SLC 12Z RAOB/HRRR
indicate that precipitable water values vary from 0.05"-0.10"
mountains to 0.20"-0.30" valleys. Blended Precipitable Water
product shows an atmospheric river into the West Coast with
origins from near Hawaii.
Storm system currently over northern California is expected to
weaken as it pivots over southern Idaho tomorrow night. An
associated cold front drags across northern Utah tomorrow night.
Ahead of this feature southern winds will begin to gust (hopefully
scouring out some of the building haze). Cold advection showers
are expected to focus across the north into central portions of
the state. Bumped up PoPs north and decreased them further south
further away from the cold advection. Snow levels fall from 6500
feet tomorrow evening to 5500 feet Friday morning. Advection turns
neutral then warm Friday morning putting an end to the showers
across the north.
Next system begins to split over the eastern Pacific early
Thursday night. By Friday, the southern cutoff displaces the
weakening atmospheric river further south nosing into southwest
Utah. Bumped up PoPs beginning Friday morning across the south.
This wave of moisture spreads northward Friday night. Saturday the
nose of the upper level jet affects southern Utah, so expecting
another round of precipitation. Snow levels Friday and Saturday
are between 6500 feet and 7000 feet.
Southerly gusty winds pick back up late Friday and Saturday ahead
of the cutoff storm system.
.LONG TERM (AFTER 00Z SUNDAY)...
In the extended, the closed the low that dives south through the
Desert Southwest late in the weekend also has a splitting wave
ejecting north and east of Utah. Southerly flow turns to the west
as the low digs farther east and south. A weak, yet almost
isothermal, gradient brushes by to the north on Monday breaking
down the weak ridging over the Pacific Northwest. This does little
to our temperatures aloft (speaking of snow levels) so the late
weekend precip event should see snow levels remain above 6500
feet. Speaking of precip, Sunday looks to see a break in precip
across the southern portions of Utah, with another round starting
late Sunday into early Monday, likely due to this splitting trough
feature. Amounts are on the low side, as the moisture tap has
weakened and shifted farther north along the Pacific Coast.
After this weak feature on Monday, warm advection takes
over under weak high pressure ridging. Models are in decent
agreement with the overall pattern through late Wednesday. The GFS
is advertising a more progressive, colder airmass dropping south
through the Great Basin by Wednesday night, some 3-4C degrees cooler
than the ECMWF and about 6-12 hours earlier than the EC. The EC also
is trending as the wetter solution by the end of the week. The
models diverge quite a bit after Thursday, so confidence is low.
Bottom line is the week ahead should continue to be active regarding
several weather features moving through the region.
Surface winds at the SLC terminal will switch back to the
southeast around 02-04Z. Clouds will increase tonight and
Thursday, but ceilings will remain well above 7000 feet through
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