Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Salt Lake City Utah
416 PM MDT Thursday Apr 24 2014
Synopsis...a mild southwesterly flow will develop tonight and
increase Friday ahead of the next Pacific storm. This system will
cross the region late Friday through Saturday. A weak trailing
system will cross northern Utah late Sunday.
Short term (thru 00z mon)...the upper ridge axis has shifted
east of the County Warning Area this afternoon and a mild southwesterly flow has developed
across the area.
This flow will increase tonight through Friday and back to more
southerly ahead of a broad trough in the eastern Pacific that is forecast
to eventually swing inland Friday and across the Great Basin on Sat.
The associated frontal boundary gets pushed into northwestern Utah after
midnight tonight then stalls as the main upper trough digs down the
A surface low is forecast to deepen over southern Utah Friday and generates
a tight pressure gradient allowing south winds south of the low
to become strong during the day tomorrow. Speeds could locally
reach marginal warning levels in the higher southwestern valleys but
overall should be in the advisory range and have issued wind
advisories for about the southern 1/3 of the County Warning Area. Winds should begin to
decouple tomorrow evening although local gusty winds could continue through
Sat. Precipitation should begin across the northwest by tomorrow morning north
of the front and slowly increase through the day becoming widespread
during the evening and finally developing across all of western Utah after
Most of the precipitation occurs before the coldest air with this trough
arrives. Expect sufficient snowfall in the mountains to warrant an
advisory but the main impact would be generally above about
7000-8000 feet starting late Friday night or Sat morning. So did not
issue any winter weather highlights today.
The precipitation remains widespread through Sat then winds down Sat night
with gusty northwest winds developing sun as the deep surface low
moves off into the plains. The upstream wave for Sun afternoon appears
weak but could bring light precipitation to most of the northwestern County Warning Area by the
end of the day.
Long term...as the large Pacific trough moves away from the
area...a weak disturbance embedded in the northwesterly flow will
move across the area Sunday evening into Monday morning. Only
light additional precipitation is expected with this disturbance.
The pattern then transitions to a less active period...with a ridge
expected to develop across much of the western United States. The
12z ec and 12z GFS are both similar in the evolution of this ridge
through roughly Tuesday. Rather large differences in position and
amplification of the ridge emerge at this point. One of the biggest
questions is if and where a Pacific low will retrograde off the
British Columbia coast. This has a large impact on the nature and
location of the ridge later next week. There is a large degree of
spread between the ec and the GFS and even the individual members of
the GFS ensemble.
Given the uncertainty...kept much of the forecast similar to the
previous package with a few adjustments.
Aviation...operational weather concerns will remain limited at the
kslc terminal through the valid taf period. Northerly winds will
continue through 02-04z this evening before becoming southerly.
Utah...Wind Advisory from 10 am to 9 PM MDT Friday for utz013>016-
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