Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 201115 AAA
AFDSLC

Area Forecast Discussion...UPDATED
National Weather Service Salt Lake City UT
515 AM MDT Fri Apr 20 2018

.UPDATE...

&&

.SYNOPSIS...An upper level low pressure system will slowly make
its way across the southern and central portion of the region
today. High pressure will bring a warming and drying trend for the
upcoming weekend.

&&

.SHORT TERM (Through 00Z Monday)...A wind advisory remains in
effect for Great Salt Lake Desert until 9am this morning due to a
strong surface gradient and favorable northerly winds. These winds
will weaken some this afternoon as the gradient relaxes. Most
mesonet sites are reporting wind in the 30-40 mph currently but
should lower by this afternoon. Local strong downslope winds are
occurring along the Northern Wasatch Front where gusts are over 30
mph with isolated gusts in excess of 50 mph. These winds should
decrease rapidly by mid morning if not earlier.

Areas of precipitation are becoming more widespread in the past
hour or two across Utah and Juab counties as the warm advection
becomes more favorable there. The GFS 500-700mb winds are normal
to the equivalent potential temperature contours at this time
across Utah County. However, the latest 06Z GFS guidance shows
that this area vanishes by about 12Z with a new area developing
across southwest Wyoming west southwestward into Salt Lake and
Tooele counties then southward into central Millard County and
Iron County by mid to late morning. Have based PoPs on this idea
which resulted in boosting the PoPs at Tooele, Salt Lake City,
Delta and Cedar City for the morning time frame.

The 700mb temperatures are just cold enough that when the
precipitation intensity increases the rain changes over to snow.
UDOT cameras showing that snow is occurring along the I-15
corridor between Beaver and the I-70 interchange. This is expected
to continue into the morning hours before the 700mb temps warm
enough to have a change over back to rain. Another area where snow
is possible this morning is in the Price area where dew points
are so low that any precipitation that falls will cool the air
mass and have snow occur. By afternoon the 700mb temps warm enough
that a slight chance of rain showers will occur.

The 700mb temperatures lower to -2 to -4 C Degrees over southwest
Wyoming midday which will also be cold enough for snow there. As
the the flow becomes more Nine good upsloping precip is expected
on the north slopes and ridge tops of the Uintas today into
tonight.

Instability is best across the southeast corner of the CWA this
afternoon with LI`s forecast to be below 0 there. However, already
having a thunderstorm popup in northern Carbon County moving NW.
Will update forecast to include isolated thunderstorms for the
north central mountains for today.

Lowered temps under the swath of most likely precip today by a
couple to 3 degrees which seems to better fit the 850 temp
forecast and the 700-850mb thickness.

This closed low moves east of the CWA by midnight so have trimmed
PoPs for this evening and removed all but a band over the high
Uintas. Ridging builds in Saturday through Sunday with a warming
trend.

.LONG TERM (After 00Z Monday)...The ridge shifts further east of the
area Sunday night, as a weak shortwave trough moves across the
Pacific Northwest. This continues to look like a brush by storm for
Utah, with the shallow associated cold front pushing into northern
Utah and southwest Wyoming early Monday morning. Have maintained
some 20-40 percent POPs across the northern third of the CWA Sunday
night through Monday, but in general the best moisture and forcing
will likely remain north of the Utah/Idaho border. Cooling across
the north is expected to be modest as well, with little if any
impact for central and southern Utah.

Any showers should mostly dissipate by Monday evening, as the trough
slides into the Great Plains. Heading into Tuesday through Thursday,
models have finally come into better agreement, with 00Z runs
building a high amplitude ridge over much of the western CONUS for
the middle of the week. This means above average temperatures for
the area and generally dry conditions. Have kept some low end POPs
for some mountain locations through this period, in part because the
GFS keeps a little lingering moisture over the Rockies, and in part
because this is the first time models have really come into
agreement for this time frame. If this ridge remains consistent,
even these low POPs will probably be able to be removed.

Looking beyond Thursday, models move a closed low from the Pacific
into the west coast late Thursday into Friday, though details
differ. Will keep an eye on this feature as it moves closer in time
from its current day 7-10 position, but current model solutions do
not have this low greatly impacting Utah, with the idea that it may
push north of the area as it moves further inland.


&&

.AVIATION...Winds at the SLC terminal may continue to be erratic
through the morning hours, with both northeasterly winds and
southwesterly winds possible at times. These winds should settle
into a more consistent northwesterly direction around 15-18Z. There
is a 70 percent chance of ceilings dropping below 7000 feet between
13Z and 17Z, but only a 20 percent chance of MVFR conditions due to
passing rain showers.


&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Wind Advisory until 10 AM MDT this morning for UTZ005.

WY...None.
&&

$$

SHORT TERM...Struthwolf
LONG TERM...Schoening
AVIATION...Scheoning

For more information from NOAA`s National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php



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