Scientific Forecaster Discussion
fxus65 kslc 251050
Area forecast discussion
National Weather Service Salt Lake City Utah
450 am MDT sun Jun 25 2017
Synopsis...high pressure will settle across Utah today. Moisture
will start to increase from the southwest today through Monday. A
cooling trend will begin on Tuesday and continue into Thursday
before high pressure returns for the end of the week.
Short term (through 12z tuesday)....a strong ridge of high pressure
is centered over the Desert Southwest this morning, and the axis
will slowly shift eastward over Utah and southwest Wyoming through
today and tonight. This will lead to another warm and dry day across
most of the forecast area, with anomalous heat continuing in far
Increased mid-level moisture is pushing into southern Utah this
morning, and although instability will remain hard to come by today,
isolated showers/thunderstorms will be possible initiating off the
higher terrain of southern Utah. Have added some 20 percent pops to
account for this possibility; that said, any storms that do form are
much more likely to produce gusty winds than decent precipitation,
as the lower levels remain quite dry.
This mid-level moisture pushes northward overnight, so the isolated
thunderstorm threat will spread to the higher terrain of the entire
County Warning Area on Monday. Monday also has the added benefit of a shortwave
trough pushing inland across northern California and Nevada, and
eventually northern Utah on Monday evening. Have maintained a
mention of showers/thunderstorms across the north Monday afternoon
through Monday night as this wave pushes across the area.
Other impacts from this approaching shortwave Monday include
increased southwesterly flow through the day, and warmer
temperatures across most of the area, excluding Dixie. Dixie is the
one area that actually cools a bit Monday, which looks to push
heatrisk values below warning levels, so ending the excessive heat
warning after Sunday currently looks to be the right call. For the
rest of the cwa, Monday will probably be the warmest day of the
week, with slc possibly reaching 100 degrees.
Southwest winds will be strongest Monday in west central and
southwest Utah. While these winds do not appear strong enough for
wind advisories, they should be strong enough for the previously
issued red flag warning. Winds will likely remain elevated into
Monday evening, as a surface cold front begins to push into northern
Long term (after 12z tuesday)...the shallow cold front will
cross northern Utah Monday night, then weaken across central Utah on
Tuesday. Temperatures on Tuesday will see a noticeable cooling trend
with a drop of between 5-10 degrees compared to Monday. However, a
couple of degrees of cooling can be expected across southern Utah as
well, owing to a small drop in 700mb temperatures as heights lower.
Meanwhile, a drier airmass will start to spread back into the area
from the northwest behind the cold front, although a few convective
cells could initiate along the higher terrain of northeastern Utah.
The near zonal flow pattern that develops on Tuesday will continue
Wednesday into Thursday with weak waves embedded within the flow.
This will maintain cooler temperatures across the area during this
time. Kept some low pops across the mountains of northeastern Utah
for Wednesday as another shallow cold front may act on what's left
of the moisture.
The flow is then expected to trend more anticyclonic late in the
week which should prompt a slight warmup. Model spread increases for
the weekend, as the GFS indicates a stronger trough crossing the
area Saturday afternoon/evening, while the ec maintains a near zonal
Aviation...VFR conditions will remain in place across the slc
terminal through the valid taf period. Light southerly winds will
yield to northwest winds after 17-18z.
Fire weather...strong high pressure remains in place today, which
will allow warm and dry conditions to continue for the area. Mid-
level moisture will increase across southern Utah today, with
isolated showers and thunderstorms potentially forming over the
southern mountains. This threat of thunderstorms initiating over the
higher terrain will spread to both northern and southern Utah on
Monday. On both days, gusty and erratic winds are much more likely
with these storms than any wetting rain.
Southwesterly winds will also increase across the area on Monday,
particularly in southwest Utah. Combined with low relative humidity
values, this will produce critical fire weather conditions. Winds
will likely remain elevated into Monday evening, as a cold front
sweeps across the area. The eastern portions of the state will
remain warm with gusty west-southwest winds on tuesday; will have to
keep an eye on Tuesday to see if red flag warnings are necessary
across the east.
Utah...red flag warning from noon to 10 PM MDT Monday for utz492-493-
Excessive heat warning until 10 PM MDT this evening for utz019.
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