Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
422 am MDT sun may 3 2015
Synopsis...a mild and increasingly moist west to southwest flow
will remain over Utah through early next week. A slow moving
disturbance will impact the region Wednesday through Saturday.
Short term (through 06z thursday)...a mild and somewhat moist
southwesterly flow extends across the region early this morning.
This moisture is by and large confined to the middle levels with a
deeply mixed boundary layer evident in the 00z kslc sounding.
Regional radar imagery indicates high based showers extending
across southern Utah...however given the aforementioned dry boundary
layer and shallow nature to the convection would not expect any of
this precipitation is reaching the surface although cant rule out
gusty microburst winds from this activity. As the day wears on
anticipate another round of high based convection this afternoon
largely focused on the higher terrain...but possibly drifting into
the adjacent valleys at times. Maintained scattered wording across
the higher terrain but trimmed back probability of precipitation across the valleys into
the slight chance/isolated category.
A weak upper low currently situated off the California coast is forecast
to slowly drift inland Monday...then across the Desert Southwest
on Tuesday. May see a light uptick in moisture Monday into Tuesday
with the approach of this wave...but otherwise would expect little
impact on the forecast area as any dynamic support with this wave
looks to remain weak and confined south of the area.
By Wednesday an upper trough is forecast to drop into the Pacific
northwest...backing and increasing the flow aloft across the
forecast area. Cooling middle level temperatures coupled with
lingering moisture and weak embedded features rotating through the
strengthening flow will bring a better chance for convection
across the northern half of the area. Have maintained an upward
trend in probability of precipitation across the north while decreasing probability of precipitation across the
south Wednesday afternoon/evening. Additionally have maintained a
cooling trend Wednesday with the low encroaching on the region.
Long term (after 06z thursday)...ec and GFS models continue to
be slower in bringing the Pacific trough into the eastern Great
Basin. This potential slowing was advertised more than 24 hours ago
with the GFS ensemble Standard deviation showing the largest
discrepancy between members being on the west side of the trough.
This slowing down trend will allow temperatures to remain warm
through Thursday with the 700 mb temperatures still near plus 4 or higher
except for the extreme western portions of the County Warning Area near the Nevada
border. Have boosted temperatures by several degrees accordingly. Noticed
that the precipitable water trend is reaching its peak Monday through Tuesday
night but then as the trough gets closer and the southerly winds
increase a drier air mass is tapped from Arizona and points
farther south. Have decreased probability of precipitation over the County Warning Area Thursday morning
and across eastern and southern portions of the County Warning Area for Thursday
afternoon through Friday night as cooling aloft and dynamics
associated with trough are expected to remain well west of this
area and also the air mass will be somewhat drier as precipitable waters lower.
Have bumped probability of precipitation for northern and central Utah Saturday as the
models are in agreement that the core of the moist trough will
move northeast across this portion of the County Warning Area for the best chance
of precipitation. 700 mb temperatures lower to minus 4 degrees so have
cooled the maximum temperatures for Saturday from about Delta northward. The
system exits most of the County Warning Area Saturday night leaving a dry
anticyclonic flow across the region Sunday with temperatures
expected to rebound back to normal.
Aviation...southeast winds will prevail at the slc terminal
through 18-19z before shifting to the northwest. There is a 10
percent chance for high based showers and thunderstorms from 19z
until 02z. The main threat will be erratic gusty winds in around
any of these showers or storms.
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