Scientific Forecaster Discussion
fxus65 kslc 222141
Area forecast discussion
National Weather Service Salt Lake City Utah
341 PM MDT Thu Jun 22 2017
Synopsis...a generally dry and stable west to northwest flow
aloft will exist across Utah through Friday. Strong high pressure
aloft will return to the region over the weekend. A brief surge
of moisture will move through the area Monday, followed by a dry
westerly flow aloft by the middle of the week.
Short term (through 06z monday)...the cold front that pushed south
and east earlier this morning has now progressed through the entire
state with winds remaining gusty behind the front. Visible satellite
imagery this afternoon has cumulus clouds developing across Castle
country and across southwest Utah, and quickly moving south and east
with the mid level steering flow winds of 25 knots. Of greater
interest visibly is the smoke plume of the Brian Head fire between
Parowan and Cedar City. This plume stretches eastward and can be
seen streaming all the way into southwest Colorado to the city of
Durango. Destabilization across the south and east this afternoon may
spawn a few isolated showers, with the best precipitable water
values over central Nevada and southwest Utah.
The surface gradient becomes north-south oriented this evening as
the ridge of high pressure becomes flattened across the Desert
Southwest and the upper level trough moves east through the Dakotas.
With the amplification of the ridge moving up the coast of
California the winds aloft become weaker Friday and cooler
temperatures slide through far northeast Utah. Surface temperatures
across northern Utah will see this cooling reflection over the next
day or so before rebounding as the ridge settles back over the
region. Southern Utah will see very little change in temperatures,
as 700mb temperatures continue at 14-18c.
Moving into the weekend, strong northwest flow remains the
dominating feature as high pressure persists across the region.
Differences between models have 700mb temperatures ranging from 12-
14c, resulting in little day to day change in surface temperatures
through late weekend. Very dry conditions remain in place,
especially across southern Utah. The going excessive heat warning
for Utah's Dixie will remain in through the weekend, as hot
temperatures persist and the heat risk remains elevated.
Long term (after 06z monday)...the strong upper ridge centered
across the interior west Sunday night/Monday will maintain hot
temperatures across much of the forecast area to begin the week.
Moisture working through the mean ridge position could spawn a few
showers or thunderstorms across western/northern Utah late Sunday
night. This moisture will expand across the remainder of the
forecast area Monday. Strong differential heating will kick off
terrain-based convection beginning late morning, with scattered
convection likely during the afternoon. Some potential for
organized convection late afternoon through the evening as the
various models are indicating a weak shortwave lifting northeast
along the back side of the upper ridge.
The late Monday shortwave along with subsequent shortwaves moving
east across the northern rockies will flatten the upper ridge over
the Desert Southwest/southern rockies Tuesday. The cooler air
aloft settling into Utah will lower temps to around late June
norms across the north, while southern Utah will turn a little
cooler during the midweek period.
Fire weather...critical winds and very dry humidity values across
the area are the primary fire weather concerns through the next 24
hours. Where fuels are cured and the Haines indices are projected at
a value of 6, red flag warnings currently remain through this
evening where areas of fire growth and/or maintenance are most prone.
As the cold front pushed south and east through the state today,
winds behind the front remain gusty and will likely persist into the
early evening hours until peak heating has come to an end. As cooler
temperatures settle in across the north the next two days, expecting
the critical wind threat to decrease, although with this said, winds
are expected to be breezy Friday afternoon. As wind trends back off
Friday, very low relative humidity continues but threshold values are not expected
to be met at this time. The prolonged heatwave across the south is
expected to continue through the weekend, even cooling a degree or
Utah...excessive heat warning until 10 PM MDT this evening for utz021.
Red flag warning until 10 PM MDT this evening for utz482-484-488-
Heat advisory until 10 PM MDT this evening for utz013-020.
Excessive heat warning until 10 PM MDT Sunday for utz019.
Short term/fire weather...Dewey
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