Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
1021 am MDT Wednesday Aug 20 2014
Synopsis...the airmass over the forecast area will slowly dry
today...though conditions will remain unsettled over the next few
days. A cold trough will move across northern Utah over the
Discussion...shortwave which brought precipitation to the Wasatch
front overnight and early this morning is now moving through
northeast Utah. With a period of subsidence in its wake anticipate
a bit of a break for northwest Utah through maybe 1800 UTC.
However...a reasonably moist airmass remains in place across most
of Utah. Although we have seen some middle level drying low level
moisture still entrenched with surface dewpoints generally in the
middle 50s to the lower 60s statewide.
Airmass will destabilize quickly this afternoon and expect scattered
thunderstorms to develop once again. Instability is greatestacross
east central Utah this morning with SBCAPE in excess of 1500 j/kg.
This area also has deep layer shear greater than 30 kts...so
storms that develop in this area could show some organization and
also produce locally heavy rain. Rap and NAM models indicate that
best instability this afternoon will be over the western valleys
and...with the GOES total precipitable water imagery indicating
values of .75" to 1" remaining in place across western
Utah...anticipate scattered convection to develop this afternoon.
Given current trends have increased probability of precipitation a bit in eastern valleys
as well as the uintas and central mountains for this afternoon.
NAM model indicates that another middle level shortwave will move
into northwest Utah tonight. This feature could be the focus for
additional convection to develop and move into the northern
portion of the state. The hrrr model certainly supports this as it
moves an area of of precipitation into northwest Utah after 0000 UTC.
Aviation...elevated southeast winds will prevail at the slc
terminal through the day...though there is a 20 percent chance of
winds shifting to the northwest after 21z. Gusty and erratic outflow
winds are possible with vicinity showers after 20z. Typical southeast
drainage flow should resume between 03-05z.
Fire weather...some of the moisture from the monsoonal surge will
remain across the region through the next several days as a trough
develops over the Pacific northwest and then swings through Utah
Saturday. Minor disturbances between now and Saturday will kick off
convection both day and night through Friday producing isolated
wetting rains across the south and widely scattered wetting rains
across the north. Relative humidity levels will be elevated during
the next few days as well. The trough developing over the Pacific
northwest will interact with the moisture thats remains over the
northern half of the region on Saturday likely producing widespread
rain. Temperatures will be cooler during the next several days...
especially Saturday due to the cold front and precipitation. Drying
will return Sunday into Monday but another trough may increase
chances of showers Tuesday.
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