Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
1001 am MDT sun Jul 5 2015
Synopsis...high pressure will remain centered over the southern
rockies into early next week. Abundant moisture along with weak
weather disturbances moving through the region will generate
showers and thunderstorms early this week.
Discussion...morning water vapor and 500 mb analysis depict a
shearing short wave stretching from northern Utah to northwestern
Nevada...with a noted deformation axis stretching across southern
Idaho/northern Utah. Scattered to numerous showers and isolated
thunder exist within this zone with copious cloud cover across the
north and east...largely clear skies across the southwest. Have
upped morning probability of precipitation roughly 20 percent across the north as many
areas will see at least some precipitation into the early afternoon.
A well defined back edge exists both in precipitation and cloud cover
from roughly Delta northwest to Wendover within both a drying and
subsident environment in the Lee of this wave. Have maintained
scattered afternoon precipitation wording in forecast but expect all but
the far north will be largely precipitation free by 20-21z...with the
south transitioning into a more typical isolated to widely
scattered terrain based convective environment.
Although the morning will remain significantly cooler in the north
do anticipate a net thinning of cloud cover this afternoon/evening
allowing temperatures to bump into the middle 80s Wasatch front. Regardless
temperatures will remain significantly cooler than experienced over the
last few weeks.
Primary updates were a net boosting of probability of precipitation/clouds in the north
through early afternoon...previous discussion follows.
With heights building back in behind the disturbance tonight believe
convection will decay by Monday morning. However diurnal convection
is expected to redevelop across the region both Monday and Tuesday
afternoon and evening given the amount of instability in place
under the ridge.
Temperatures continue to run at or above normal...though much cooler
than prior week with the ridge breaking down.
Drier air is expected to start to move in from the southwest
during the day Wednesday as a Pacific storm system approaches the
California coast. This system is prognosticated to move onshore and
toward the forecast area...though global models disagree on the
timing. GFS moves the system onshore during the day Thursday and
then pivots it over Utah Thursday night/Friday bringing moisture
and instability back to at least the northern two-thirds of the
forecast area. Ec is noticeably slower with the system...not
bringing it onshore until Friday. After that...the system weakens
considerably as it moves into the Pacific northwest...keeping a
dry southwesterly flow over the forecast area into the upcoming
weekend. Given the significant differences in the guidance and
lack of run-to- run consistency...have chosen to basically split
the difference with regard to probability of precipitation from about Thursday on.
Aviation...scattered showers will continue to impact the kslc
terminal into the early afternoon...but impacts will remain
largely minimal to the terminal. Ceilings will remain at or above 8000
feet above ground level and precipitation rates generally light. North winds will
transition to a prevailing northwest and remain in place into this
Fire weather...isolated to scattered showers and thunderstorms will
be the rule through the middle of next week. New lightning starts
are the primary concern...with some storms providing an opportunity
for a wetting rain. The increase in convection will trend
temperatures down a notch and humidity up a bit.
An abrupt pattern shift is currently advertised during the middle of
next week. A dry and very gusty southwesterly flow develops trending
humidity lower. Convection will still be around...though wetting
rain becomes less of a possibility as activity becomes higher
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