Scientific Forecaster Discussion
fxus65 kslc 191030
Area forecast discussion
National Weather Service Salt Lake City Utah
430 am MDT Fri Jul 19 2019
Synopsis...dry and seasonally warm conditions will continue
across the state through Saturday. High pressure aloft will
strengthen across the region during the latter half of the
weekend into early next week, with moisture expected to spread
northward into the region by midweek.
Short term (through 00z tuesday)...a broad upper trough
encompasses the Pacific northwest/northern rockies this morning.
A potent 140kt jet is located along the downshear side over the
northern High Plains as this trough continues to progress
eastward. Meanwhile an elongated subtropical mid level ridge
extends from the Desert Southwest eastward across the Southern
Plains. This is maintaining a dry southwesterly flow across the
forecast area. As a result another warm, dry, and breezy to
locally windy day is in store for much of central and southern
Utah which will result in continued fire weather concerns.
Meanwhile, as the upper trough passes through the northern rockies
today, an associated dry surface front will push into northern
Utah this afternoon dropping temperatures just a bit.
This evening through tonight a weak shortwave trough currently
located along the California/Arizona border will lift
northeastward across southern and central Utah. Enough mid level
moisture accompanying this feature will allow for a small threat
of showers across the terrain from Boulder Mountain this evening
northward into the Wasatch Plateau region overnight. It would seem
the boundary layer is too dry for precipitation to reach the
lower elevations so have left any mention of showers confined to
The subtropical mid level ridge is forecast to retrograde
Saturday, before quickly amplifying across the region Sunday into
Monday. This will result in a warming trend particularly across
northern Utah. May see a couple of isolated showers and
thunderstorms Monday afternoon across the terrain of southern
Utah. Meanwhile temperatures along the Wasatch front are expected
to exceed the 100f mark by Monday with the lower elevations of
southern Utah generally in the 100-105f range.
Long term (after 00z tuesday)...orientation of an intermountain
ridge is expected to begin overhead, prior to a slight downstream
jog east midweek, and slight retrogression south and west from
there late week (into the lower Colorado valley). These subtle
shifts play an important role in sensible weather locally,
especially regarding sub-trop moisture transport/pooling into our
area (and resultant shower/storm potential). Initially the core of
deep layer moisture is most likely to bulls-eye largely
South/West of the forecast area Tuesday (with ridge axis placement
overhead), but trends thereafter continue to look favorable for
rapid moistening mid/late week as trajectories veer a bit more
westerly as the aforementioned ridge jog/retrogression evolution
Continue to see 1"+ precipitable water values in operationals, and near 2
Standard deviations above the norm in the naefs Wednesday on.
With this, diurnally driven convective development that will
originally be focused over the terrain early in the period should
expand areally to most all of the area during the mid/latter
periods (as moistening occurs from the top down). Continue to
carry elevated pops for convection in the long term, with Lower
Valley potential greatest during the late day/evening hours.
Aviation...southerly surface winds currently in place at the
kslc terminal are expected to become a prevailing northwesterly
between 18-19z. A weak boundary that is expected to cross the
terminal this evening is anticipated to reinforce these
northwesterly winds maintaining them through the overnight hours,
though speeds are expected to gradually fall below 7kts after 07-
08z. VFR conditions will remain under largely cloud free skies.
Fire weather...another day of gusty southwest winds and very low
relative humidity is expected across central and southern Utah
today, and as a result a red flag warning has been issued for
zones where fuels are dry and which are expected to experience
critical fire weather conditions. Meanwhile further north a
dry cold front will drop into northern Utah this afternoon
bringing slightly cooler temperatures along with west to
northwest winds this afternoon.
High pressure will quickly strengthen overhead this weekend
allowing for a warming trend, with temperatures expected to run
a few degrees above normal Sunday into Monday. With this building
high winds are expected to drop off and become primarily terrain
driven. With this high in place, moisture will begin to be drawn
up into the region beginning late Monday or Tuesday, and will
likely remain in place through the remainder of the week. This
will result in an increasing chance for showers and thunderstorms
capable of producing wetting rains.
Utah...red flag warning from noon today to 9 PM MDT this evening for
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