Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
417 am MDT Friday Jul 25 2014
Synopsis...a stalled surface front will remain across central
Utah through Friday...maintaining moisture across the south and
drier air across the north. This moisture will slowly work its
way northward during the upcoming weekend...and remain in place
into early next week.
Short term (through 06z tuesday)...a stationary surface front
remains draped across central Utah early this morning. This boundary
is separating a moist airmass to the south...which is rotating
around a middle level ridge centered across the Southern
Plains/southern rockies...from a drier and slightly cooler
airmass to the north...associated with a westerly flow across the
Pacific northwest/northern rockies. This boundary is expected to
lift slightly northward during the day today...with a threat for
showers and thunderstorms spreading northward into central
Utah...and perhaps as far north as Utah County...by early this
Middle level heights are forecast to rise across the forecast area
during the upcoming weekend...as the middle level ridge amplifies
across the region. With the ridge axis forecast to remain just
east of the area...southerly flow will act to pull moisture
northward across the remainder of the forecast area by late
Saturday night/Sunday...with this moisture lingering into early
next week...and have trended precipitation forecast this way. With
deepening moisture...heavy rainfall and flash flood potential
will be on the rise as well.
Long term (after 06z tuesday)...following the moisture surge into
northern Utah on Sunday and Monday...upper level flow over the County Warning Area
looks to turn more westerly for Tuesday and Wednesday...which will
help create a slow drying trend across the area. Have kept the
downward trend in probability of precipitation in the forecast for the middle of the
week...but kept mentionable probability of precipitation in the higher terrain for all days.
Despite this slow drying...models are still indicating a fair amount
of cloud cover over the area for Tuesday and Wednesday...so have
cooled temperatures just a bit for those afternoons.
For Thursday and Friday...the European model (ecmwf) and GFS have slightly different
ideas about where the ridge will re-center itself. As is usual this
time of year...this small difference has a profound effect on how
deep the moisture is over the forecast area. The ec produces
continued drying into the end of the week...while the GFS brings new
moisture up from the south. Due to this uncertainty...have simply
kept probability of precipitation near climatology for days 6 and 7...with temperatures
slightly above seasonal normals.
Aviation...light and variable winds will likely continue at the slc
terminal between 10z and 15z...before increasing steadily out of the
north between 15z and 18z. VFR conditions should prevail under
mostly clear skies...with showers and thunderstorms remaining well
south of the terminal through today.
Fire weather...yesterdays cold front has left a dry airmass over
northern and western Utah...which should help restrict shower and
thunderstorm activity to southern and eastern Utah today and
In southwest Utah...gusty southwest winds will develop yet again
this afternoon...and will likely combine with low relative humidities
to produce critical fire weather conditions in zones 492 and
495...so a red flag warning has been issued for those zones.
Isolated critical conditions may be possible in other parts of
western and central Utah. Winds for Saturday into the beginning of
next week should be considerably lighter...as high pressure builds
over the area.
Moisture will move northward on Sunday and Monday...producing a
chance of showers and thunderstorms across pretty much the entire
Utah...red flag warning from noon today to 9 PM MDT this evening for
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)