Scientific Forecaster Discussion
fxus65 kslc 240326
Area forecast discussion
National Weather Service Salt Lake City Utah
926 PM MDT Wed Aug 23 2017
Synopsis...a gradual warming and drying trend will take hold
across the region beginning tomorrow as high pressure aloft
returns to the Great Basin.
Discussion...convection blossomed across parts of northern Utah
this afternoon as a weak upper-level impulse slid by and created
an unstable environment with around 1000 j/kg of surface-based
cape. Environmental shear was too weak for rotating updrafts
capable of much more than pea-sized hail. However, terrain forced
winds around the south-end of the oquirrhs combined with a
preexisting northerly lake breeze in the Salt Lake Valley created
enough low-level shear to support a couple stronger updrafts in
the southern Salt Lake Valley this afternoon, one of which dropped
quarter-sized hail in Herriman.
Most of this convective activity has fizzled across the state
this evening with the upper-level disturbance pushing northeast
out of the region and the loss of daytime heating. However,
convective-allowing models hint at a few isolated cells lingering
through midnight or just after, mainly across northern Utah. The
current forecast has a good handle on this possibility, so no
forecast updates planned tonight. Outflow from earlier storms in
far northwest Utah may bring a brief period of breezy northerly
winds across the Great Salt Lake, Salt Flats, and reaching the
northern end of the Wasatch front as far south as Salt Lake Valley
later this evening.
Previous discussion...issued 351 MDT...
Short term (through 12z saturday)...with high pressure building
over the region tonight through early next week, the forecast area
will see a gradual warming and drying trend. Maxes should be
running around 5f above seasonal normals by Saturday. Lingering
moisture will combine with daytime heating to produce a few
showers and thunderstorms over the higher terrain through the
first part of the weekend, but overall coverage will be on the
decline as moisture continues to decrease.
Long term (after 12z saturday)...in the extended period starting
this weekend, an amplifying ridge of high pressure across the Desert
Southwest is the main feature of interest. Rising heights into the
early part of next week, Tuesday, as well as increasing mid-level
temperatures will settle in across the eastern Great Basin area,
Mostly dry and warm conditions will be present under the
aforementioned ridge through the upcoming week. As the high rotates
around the area, nearly centered over Utah and Nevada, the flow
across eastern Utah looks to favor an east- northeast direction.
This may give hope to any precipitation or convection to develop
across the higher terrain elevation areas of southern through
northeastern Utah through mid-week. Moisture looks pretty meager in
the extended. By Tuesday, some increase in low-mid level moisture by
way of mixing ratios will increase slightly, and namely across
southern Utah. All this said, have kept very light pop mention in
the extended, and kept any mention to the mountain and higher
terrain locations of Utah.
Aviation...VFR conditions will continue at the slc terminal
tonight and tomorrow. A period of gusty northwest winds up to 25
kts is possible this evening as outflow from distant thunderstorms
approaches the terminal between 3z and 430z. There is a 30%
chance the outflow will not reach the terminal. Winds will
eventually turn to southeasterly; likely 5-7z if outflow reaches
the terminal, otherwise around 4z.
Fire weather...showers and thunderstorms have developed once again
over the district this afternoon with the best coverage over the
higher terrain and near the Utah/Idaho border in association with
shortwave energy lifting northward. The threat of these storms
will continue through the early evening before diminishing.
High pressure will build over the district beginning tonight,
resulting in a gradual drying and warming trend through early next
week. Enough lingering moisture and instability will exist to
allow for isolated showers and thunderstorms over the higher
terrain during the afternoon and evening hours at least through
the weekend. With areal coverage of this convection being limited,
there will be little chance of wetting rains.
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