Scientific Forecaster Discussion
fxus65 kslc 171522
Area forecast discussion
National Weather Service Salt Lake City Utah
922 am MDT Tue Oct 17 2017
Synopsis...a warming trend will continue through the middle portion
of the week. A weak storm system is forecast to cross the area
Friday, bringing cooler temperatures and mountain showers.
Discussion...another quiet weather day is in store as a ridge
axis currently observed over northern Nevada and southern Oregon
per water vapor satellite imagery pushes east into our area today.
Some high-level moisture embedded within the ridge will bring a
few high clouds, but otherwise clear skies and warm temperatures
are expected, with upper 60s to lower 70s for many Utah valleys.
Some haze is possible with subsidence under the ridge and perhaps
lingering smoke aloft from recent norcal fires.
No changes needed to the going forecast.
Previous discussion...issued 3:37am MDT...
an upper ridge remains in place this morning, with some thin high
clouds drifting across the area. The ridge will weaken this
afternoon as a weak shortwave disturbance approaches the area.
Southwesterly flow aloft will increase a bit, allowing for warmer
temperatures, particularly in valley areas, as mixing will improve
slightly. Otherwise, dry and stable conditions will persist today
The southern end of the shortwave disturbance is now more
consistently forecast by the models to strengthen across southern
Nevada and northwest Arizona tomorrow. It is then forecast to lift
northeast across Utah tomorrow night into Thursday. Although
moisture will increase with this disturbance, given the dry lower
levels currently in place, valleys will be hard pressed to receive
much in the way of precipitation. However, have increased pops to
allow for slight chance wording of pops across the higher terrain.
Although this system will be accompanied by increased cloud cover
and a slightly cooler airmass on Thursday, better mixing as
southwesterly flow strengthens again should keep temperatures on the
warmer side and above normal for most areas.
Long term (after 12z friday)...the Pacific northwest trough
continues to evolve with the latest model guidance for late in the
week. The overall trend continues to be a warmer and drier
(relatively) weather system to impact Utah and southwest Wyoming.
As the cold front moves through Utah and southwest Wyoming Friday
afternoon (with both the surface gradient and the 700mb baroclinic
zone), the best window for precipitation looks to be Friday
afternoon and early evening. With this forecast package the pop
forecast was aimed to display this time period better for
precipitation chances. As latest model guidance has come available,
both extended global models are trending more north with the trough
and thus the best dynamics are trending more north of Utah, as well
as a downward trend in precipitation amounts. The cold pool aloft
remains farther north in the core of the trough while the 700mb
baroclinc zone becomes a bit less organized as it progresses through
Utah late Friday. With the best timing for precipitation Friday
evening, snow levels cool to near 6300 feet or so. While the axis of
moisture quickly rotates eastward, the cold air aloft continues to
settle in across northern Utah.
Models have agreed fairly well on the exit of this trough Saturday
as warm advection and significant rising heights build in behind the
departure of the upper level trough. Some mid-high level moisture is
still evident in the guidance, though very little dynamics support
any chance of precip for the weekend and going into early next week.
Temperatures warm again to near seasonal normal going into the
extended period as high pressure builds across the region.
Aviation...VFR conditions will prevail with minimal operational
weather concerns at the kslc terminal through the valid taf period.
Southeasterly winds currently in place are expected to shift to the
northwest between 18z-19z today, with a return to the southeast
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