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Area Forecast Discussion (AFD)

Issued by Salt Lake City, UT (SLC)

                            
000
FXUS65 KSLC 190357
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
957 PM MDT Tue Jun 18 2019

.SYNOPSIS...High pressure aloft will bring drier and warmer 
weather to the area through early Thursday. A cold front will then
move through Thursday, bringing substantially lower temperatures 
for Friday and through the weekend.

&&

.SHORT TERM (Until 00z Saturday)...Lingering convection from this
afternoon has ended with the loss of daytime heating and the
arrival of a drier/stable air mass in the wake of the exiting
mid-level trough. Anticipating little more than terrain-based
convective cloud cover and maybe a shower or two developing again 
at peak heating Wednesday. 

The cold core upper low moving south through western Canada
Wednesday will settle into the northern Rockies along the 
Montana/Canada border Wednesday night. Slightly lowering heights 
ahead of this advancing feature will hold temps in check across 
much of the state Wednesday. A rather substantial vorticity lobe 
rotating south along the western periphery of the upper low will 
carve out a trough across the northern/central Great Basin 
Thursday night. The associated surface cold front supported by 
strong low-level cold advection will strengthen as it surges south
across northern and central Utah overnight. Limited moisture 
along with much of the dynamic support lagging back to the north 
will initially limit convective precip to mostly isolated showers 
through late Thursday night.

Convection may gain more organization across central through
northeast Utah early Friday along the near 700mb baroclinic zone 
which is forecast to stall Friday morning. Precip through early
afternoon will focus on the boundary, though looks to remain
light. A trailing, and somewhat stronger vorticity lobe late
Friday will further deepen the trough over the Great Basin and
lead to improving baroclinic structure for deep lift as the mid-
level cold air and dynamic support for lift interacts with the
low-level baroclinic zone. 

Temperatures Thursday night/Friday will come in much colder with
many areas seeing temps Friday down about 10 to 15 degrees from
Thursday's highs. The unseasonably cold temps will continue into 
the long term forecast period this weekend. 

.LONG TERM (After 00Z Saturday)...The upper trough is forecast to 
linger over Utah Friday night into Saturday, bringing cool and 
showery weather, especially over the southern and eastern portions 
of the state. In western Utah, drier air begins pushing into the 
area Saturday, as WNW flow develops behind the slowly-but-surely 
eastward migrating system. 

After a transition day Sunday, a ridge is forecast to build over the 
Rockies through Monday, with a closed upper low setting up off the 
PacNW coast. Ensemble guidance has been fairly consistent about the 
setting up of this pattern, which will lead to a warming and drying 
trend for Utah and southwest Wyoming for the beginning of the week.
 
The devil is in the details however, namely how far inland that 
upper low shifts for Tuesday through Thursday. Placement of this low 
is where the biggest deviations currently are in the extended 
ensemble guidance (with concurrent discrepancies in the 
placement/magnitude of the forecast ridge somewhere over the Great 
Plains). If this pattern sets up right, the first 90 degree day of 
2019 in Salt Lake City is not out of the question sometime in the 
middle of next week. For now, the forecast remains in the mid-80s, 
but this warmer weather (with breezy southwest winds) will be worth 
keeping an eye on.

&&

.AVIATION...A dry and stable west-northwest flow aloft will 
maintain VFR conditions under mostly clear skies through the 
current TAF period. Southeast winds will switch back to the 
northwest around 18z Wednesday.

&&

.FIRE WEATHER...A drier air mass will move into the area tonight
as a weak ridge builds into the Central Rockies. This will bring 
an end to the recent days of showers/thunderstorms, with generally
clear skies expected. This will also bring warmer and drier 
conditions tomorrow. A trough will then approach the area Thursday
and push a cold front across the northern districts Thursday 
evening and through the southern districts by Friday morning. 
Breezy southwest winds can be expected ahead of this front, 
especially for southern districts. The far southwest corner of 
Utah in particular will be windy and dry Thursday afternoon. 
Lastly, a few showers and thunderstorms will likely accompany
the front from the southwest deserts to the Uintas, with very
low chances elsewhere due to the drier continental air mass 
associated with the trough. Some snowflakes are possible
above 8,000 feet.

Quiet and much cooler weather is in store for the area for the 
remainder of the workweek and into the weekend. Temperatures 
Friday and Saturday will run 10-20 degrees below normal. 

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...None.
WY...None.
&&

$$

Conger/Schoening

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visit...
http://weather.gov/saltlakecity/general/afd_faqs.php