Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
305 PM MDT Wednesday Mar 12 2014
Synopsis...a developing low pressure system over southern Nevada
will bring clouds and some shower activity to the extreme
southern portion of Utah Thursday. A second storm system will move
southeast and graze northern and eastern Utah on Saturday. High
pressure will return late in the upcoming weekend.
Short term (through 00z sunday)...
water vapor loop shows a closed low developing over the southwest
Continental U.S.. amdar 400-250mb wind observations reveal a westerly
80-120kt jet over Arizona undercutting an expansive ridge over the
northwest Continental U.S.. GOES/GPS/rap/12z radiosonde observation indicate the precipitable
water value ranges between 0.04" and 0.24".
Much drier airmass in place with anticyclonic flow dominating the
northern forecast area. 09z short range ensembles indicate building
instability heading into tomorrow through tomorrow evening across
the southern Utah higher terrain. This will account for a low
probability for showers as the aforementioned upper low traverses
over northern Arizona.
Primary focus during the short term is with the cold frontal passage
Friday night into Saturday. Both the GFS and European indicate the
approaching system will have a nice tropical tap as it enters the
Pacific northwest Friday morning. While the building West Coast
ridge will ensure the system will be a slider over the northern
forecast area...enough cold air associated with the system should
advect in to promote building instability and precipitation. Boosted
probability of precipitation across the north. Also boosted winds with this system as 700mb
flow increases to 35-45kts along with a fairly tight pressure
gradient behind the cold front.
Long term (after 00z sunday)...
temperatures will zoom to above seasonal norms Sunday and Monday
as high pressure builds into the state. Global models diverge
after Monday regarding the timing and evolution of an upper low
moving into the region...though both agree that the state will
stay dry through at least Tuesday evening. The GFS brings the
trough axis and precipitation into Utah by early Wednesday...while
the ec initiates precipitation Wednesday night well ahead of its trough
axis. Have thus removed probability of precipitation for Monday into Tuesday and made
little change elsewhere for day 6 and 7.
Aviation...north winds at the slc terminal will prevail until the
southeast switch around 04z. VFR conditions will persist throughout
the taf period.
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http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)