Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 290938
Area Forecast Discussion
National Weather Service Salt Lake City UT
338 AM MDT Wed Mar 29 2017
.SYNOPSIS...High pressure will build into the region today. The
high will give way to the next Pacific storm system that crosses
the area late Thursday through Friday night. High pressure returns
for the weekend.
.SHORT TERM (THROUGH 12Z SATURDAY)...
A ridge is building in aloft behind the last storm, as a series of
shortwaves ride across the northern Pacific in what will become
our next storm.
Global models have been in good agreement for some time now that a
closed low would affect the region late in the week. However, the
storm track and where the deepening occurs has been waffling a
bit, and these factors are a big deal in precipitation and wind
Models have trended a little faster with a little later deepening,
bringing the cold front through the area late tomorrow and
tomorrow evening. Thus have sped up the initiation of PoPs to the
area in the grids along with increasing PoPs due to the latest
projection of the cold pool.
This storm has a nice height fall/rise couplet, moisture tap well
into the Pacific and a colder airmass. Precipitation is first
supported tomorrow across the north with increasing divergence,
PVA and as the exit region of a cyclonically curved jet arrives.
Gusty pre and post frontal winds are expected tomorrow afternoon
and evening, a little below advisory criteria. Post frontal winds
may be enhanced due to convection as the cold front crosses the
The storm then slows as it deepens later tomorrow night and Friday
across southwest Utah. Two important things then occur. First,
warm advection wrap around occurs north of the cyclone potentially
impacting northern and wester Utah. Also, northerly winds become
quite gusty across western Utah as the jet at 700mb increases to
50kts with a tightening pressure gradient as a ridge begins to
nudge into the region. Not expecting strong easterly winds along
the Wasatch, though they are forecast to increase. This is because
there is not really any 700mb cold advection from Wyoming due to a
lack of cold airmass (and very high pressures) to our northeast.
We are just entering the Watch period for this storm. However
decided not to issue any Winter/Wind Watches due to the
sensitivity of these conditions to slight track differences. Also
later shifts will better be able to collaborate with our
.LONG TERM (AFTER 12Z SATURDAY)...
Anticyclonic northerly flow translating overhead will aid to
rapidly squelch precip across the eastern third of the area
Saturday morning, this as the upper low discussed in the short
term continues a downstream track. Yet another break from the wave
train will occur thereafter through Sunday, but this break now
looks to be short lived.
Global models have actually trended similar regarding the track and
evolution of the next open wave poised to descend SE across the
northern/eastern Great Basin late Sunday night through Monday, prior
to this wave closing off near the UT/CO border. Previous runs have
either amplified this wave west (GFS), or progressed it to the
northeast (EC). This said, the latest 00z solutions seem to be
coming towards a more common solution digging it southeast through
the area. This is quite similar to the long wave pattern evolution
as of late, thus feel quite confident in the big picture model
Details will remain challenging with such a system, especially in
the long term, but what is becoming increasingly evident is the
breadth of CAA behind a cold front will be fairly significant (cold
enough for at least a mix of snow across the western valleys
Monday). Have trended PoP grids away and above from climo, and
focused the best chances for widespread precip over the northern
half of the area. If models continue a similar run to run pattern,
will have to significantly up PoPs across the above mentioned areas
Monday into the overnight hours.
Thereafter guidance points towards low amplitude ridging building
across the area midweek. This said, the progressive eastern pacific
pattern will continue as another modest slug of moisture/short wave
energy punches into the NorCal/PacNW Wednesday on.
Operational weather concerns will remain minimal at the
KSLC terminal through the valid TAF period. Light and variable
trending light southeast surface winds will remain in place this
prior to becoming a prevailing northwest between 18-20z.
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