Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 222221

Area Forecast Discussion
National Weather Service Salt Lake City UT
421 PM MDT Thu Oct 22 2020

.SYNOPSIS...A dry cold front will continue to cross Utah today
bringing much colder temperatures to the state. Another strong
cold front will cross the state later Saturday into Sunday,
bringing even colder temperatures and the potential for
precipitation to central and southern Utah.


.SHORT TERM (Through 12Z Monday)...Much colder this afternoon
across much of Utah in the wake of a dry cold front.

As has been predicted well by the global models, a longwave trough
is currently located across central Canada into the central US. A
strong upper ridge is located across the eastern Pacific into the
Gulf of Alaska. A series of shortwaves will continue to dig on
the western side of the longwave trough into early next week.

A particularly strong shortwave will dig southward from
continental Alaska Friday into Saturday. The associated cold
front will bring a much colder airmass into parts of the western
and central US. 700mb temperatures in the wake of the front fall
to near -22C near the US/Canada border in central Montana by
Saturday night. Thankfully, these extremely cold 700mb
temperatures will remain east of the CWA. However, expect strong
cold air advection to allow for 700mb temperatures near -15C or so
across northern Utah by Monday morning.

Light precipitation is expected late Saturday evening into Sunday
across portions of northern Utah, though any amounts will be
light. The best shot for snow accumulations appear to be the
western Uintas.

As far as critical fire weather conditions, additional red flag
warnings have been issued for the Uinta Mountains above 9500 feet
(Friday afternoon/evening) and southeastern Utah (Saturday


LONG TERM (After 12Z Monday)...A deep cold trough has been progged
to push over forecast area through the second half of the weekend,
however, uncertainty has been considerably high as model guidance
can not seem to get a grip on how this system is going to evolve.
Today, ensemble guidance, and even some deterministic runs, have
started to lean toward a more favorable solution. Most guidance is
suggesting a more progressive system, but still fairly sluggish,
that looks to favor the southern half of Utah for precipitation
impacts. There are some outlier ensemble members that support a
cutoff, quasi-stationary, system over southern Utah that would
complicate precipitation and temperature forecasts toward the end of
the forecast period.

At this point, the one thing that remains the most certain is that
temperatures are going to see a significant drop statewide as the
system moves through, with widespread hard freeze conditions
expected Sunday night through at least Wednesday morning. Well below
average daytime high temperatures are anticipated through at least
Tuesday across much of Utah and Uinta County Wyoming. Precipitation
types and specific amounts remain the highest source of uncertainty
in the forecast, however, various guidance sources are beginning to
favor precipitation impacts across the southern half of Utah Sunday
night through Monday morning. With the bulk of the cold air pushing
across Utah Sunday night, snow levels are expected to crash and may
bring measurable snowfall to some southern Utah valleys. Mountain
snow is expected mainly south of Nephi, however, specific amounts
are yet to be determined.

Depending on how quickly this system departs the region,
precipitation may linger across the southern and central mountains
through early Tuesday morning. Leaning toward the somewhat more
progressive system, should see precipitation end by Monday evening,
with temperatures beginning to rise by Tuesday, but remaining below
average through Wednesday. As mentioned before, models are beginning
to come to some sort of an agreement, so confidence should, in
theory, increase over the next day or two.


.AVIATION...VFR conditions are expected at KSLC through the valid
TAF period. A few clouds around 9kft AGL will continue to dissipate
through 00z. Winds will remain northwest 10-15 knots before shifting
to a southerly flow around 06z.


.FIRE WEATHER...A more progressive pattern will continue across the
Interior West through early next week. Gusty winds and low
humidities will continue to bring critical fire weather conditions
to portions of southern and eastern Utah through this evening.
While winds will be less Friday in most locations, winds will
remain elevated across the Uinta Mountains, especially at 9500
feet and above. This will bring another round of critical fire
weather conditions to these areas Friday afternoon and evening. A
strong cold front will cross the state later Saturday into Sunday.
Gusty winds and low humidities will again bring critical fire
weather conditions to portions of eastern Utah Saturday afternoon
and evening. Widespread precipitation is possible with this front,
mainly south of Nephi and especially south of I-70 and east of
I-15 Sunday night through Monday morning.


UT...Red Flag Warning until 9 PM MDT this evening for UTZ480>484-488-

     Red Flag Warning from noon to 9 PM MDT Saturday for UTZ489-494-

     Red Flag Warning from noon to 9 PM MDT Friday for UTZ480-481.




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