Scientific Forecaster Discussion
fxus65 kslc 262121
Area forecast discussion
National Weather Service Salt Lake City Utah
321 PM MDT Fri may 26 2017
Synopsis...an upper trough will move across the area today. A
cool northerly flow will follow for Saturday. A warming trend
starts Sunday and continues into mid week.
Short term (through 00z monday)...afternoon water vapor loop and 500 mb
analysis depict a tightly wound upper low over eastern Idaho, with
cyclonic flow extending south well into Utah. A notable dry slot
intrusion exists at the mid levels across northern Utah, and has
been providing a delineation in convective initiation between the
upper cold pool nosing into extreme northern Utah and the baroclinic
zone draped across central Utah where isolated to widely scattered
showers exist. The attendant cold front remains nearly stationary
attm, but will push south of the forecast area by tomorrow morning
as the upper trough elongates and begins moving downstream. The
frontal boundary location is currently near I-70.
South of the cold front dry and breezy conditions exist across
southern Utah. With frontal passage either tonight or early tomorrow
morning these winds will die down as a light northerly flow sets up
across the area. Likely to see decoupling later this evening for
many areas prior to that passage however.
The aforementioned northerly flow will remain in place into Sunday,
this driven by the anticyclonic eastern periphery of an amplifying
western Continental U.S. Ridge. Guidance continues to suggest diurnal
convection will occur over the terrain each afternoon, so have left
slight chance/chance mention, but expect little if any rainfall and
more buildups than deep convection.
Long term (after 00z monday)...a high amplitude ridge continues
to build over the western Continental U.S. Heading into Memorial Day, with a
significant warming trend through at least Tuesday. Enough
moisture remains under the ridge to allow for continued afternoon
build-ups/convection over the higher terrain, but otherwise the
beginning of the week should be categorized by mostly clear/sunny
Models have started to converge on a solution for late Tuesday
through Thursday, with an elongated trough moving inland from the
Pacific on Tuesday night. This storm system is currently forecast
to move into the Great Basin on Wednesday, but then begins to
split as it pushes eastward, with a small piece sliding through
the Pacific northwest, and a larger piece potentially cutting off
There is still a fair amount of uncertainty with this solution,
especially considering that the 12z run was the first time the
European model (ecmwf) and GFS were on the same Page with this trough/cut-off low.
That said, have increased pops to put a broad-brush 20% chance of
precip across the County Warning Area late Wednesday through Friday, as the low
potentially slides across the Desert Southwest. Will have to wait
for another run or three to really start to figure out the
details with this storm system, but a somewhat cooler and wetter
pattern is at least possible for the latter half of the week.
Aviation...VFR conditions are expected at the kslc terminal through
the taf period. Northwesterly winds will prevail through about 08z,
before winds shift to the southeast; however, there is a 30-40%
chance of northwest winds continuing through the overnight hours
into Saturday morning.
Fire weather...dry and breezy conditions remain in place south of
a cold front across southern Utah this afternoon, namely south of
the I-70 Corridor. North of the front cooler and slightly more moist
conditions exist, with isolated to widely scattered showers across
east-central and extreme northern portions of the district.
The cold front will push south of the border by tomorrow maintaining
a chance for showers and isolated storms with passage, but as a
whole not expecting any wetting rains. Temps will cool and some
moistening will occur across the south Saturday in the Post frontal
environment, and winds will trend more northerly and much lighter.
Can not rule out buildups and namely isolated showers over the
mountains tomorrow, but once again do not see much if any wetting
rain potential. Similar conditions expected for Sunday, though temps
will be trending to warm slightly, and relative humidity will trend a bit lower.
Thereafter high pressure will dominate the district through at least
midweek. Warming trend temps and drying conditions are expected,
though afternoon buildups can't be ruled out over the prone
Short term/fire weather...Merrill
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