Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 212208

Area Forecast Discussion
National Weather Service Salt Lake City UT
408 PM MDT Wed Jun 21 2017

.SYNOPSIS...High pressure will start to weaken and shift south
today as a drier northwest flow develops, and continues for the
remainder of the week. A cooler airmass will spread into the north
starting Thursday while the south stays hot.


.SHORT TERM...High pressure continues to dominate the Desert
Southwest with well above normal temperatures across the region,
and excessively hot temperatures across the southwest corner of
Utah. Afternoon temperatures in the southwest area of Utah are
surpassing 105F for some locations, while up north along the
Wasatch Front, temperatures are climbing into the mid-upper 90s.
Isolated thunderstorms and rain showers across the northern
Wasatch Front and the Unita Basin this afternoon should persist
several more hours until the peak heating of the day subsides.
Coincidentally, the best instability axis remains across the

A cold front will move into northern Utah late this evening and
push south through the day Thursday, eventually making it into
southern Utah tomorrow evening. Gusty winds ahead of the front
this evening across the southwest are already seeing 25 - 30 mph
winds. Behind the front tomorrow, expecting areas across central
and southern Utah to remain gusty as the winds shift from the west
to the northwest. Critical fire weather conditions will persist
across the south through tomorrow, and the going red flag warnings
are continuing.

With the high pressure remaining over the Desert Southwest, the
models are pretty consistent in keeping temperatures aloft very
warm. With such a dry airmass, the excessive heat headlines were
extended for the lower elevations of Utah`s Dixie area through the
weekend. Some mid-level moisture does sneak into southern Utah by
Friday, but under a northwest flow aloft and strong rising
heights, it does not look like there will be much relief for
temperatures going into the weekend.

.LONG TERM (After 12z Saturday)...Early summer pattern continues
through the long term forecast period. Ridging will remain in place
across the Desert Southwest through at least early next week. A weak
shortwave riding the top of the ridge may bring enough
lift/sufficient moisture for high based convection Monday afternoon.
Otherwise, anticipate mainly hot and dry conditions across Utah over
the weekend.

As the upper level ridge breaks down early next week, several global
models attempt to dig a trough down the Pacific Coast/western Great
Basin Tuesday into Wednesday. Given dry, southwesterly flow across
Utah ahead of this system, the main impact to any sensible weather
will likely hold off until the trough crosses the Great Basin. Model
to model consistency on this timing varies, with midweek the
consensus. Current pop grids are fairly close to climo to account
for the low confidence at this time.

Main impact for the long term forecast period is the extension of
the excessive heat warning for the St. George/Utahs Dixie/Zion NP
area through Sunday evening given the very warm overnight lows for
some portions of the previously mentioned area.


.AVIATION...There is a 20 percent chance of thunderstorms at the
KSLC terminal between 22-04Z this evening. Winds will remain
primarily northerly through the evening, but may become
gusty/erratic with passing outflow.


.FIRE WEATHER...Strong high pressure over the region will continue
 the excessive heat along with very low humidity values, Haines
index of 6 across southern and eastern Utah and well above normal
temperatures across northern Utah. Critical fire weather
conditions of gusty winds with low RH will continue the going red
flag conditions and warnings for those areas listed through
Thursday evening. Rapid growth potential of ongoing fires is in

A cold front will move south through Utah late this evening and
through the day Thursday, reaching southern Utah tomorrow evening.
Gusty pre-frontal winds as well as post-frontal winds will be a
concern for critical fire weather thresholds. Isolated to
scattered showers and thunderstorms across the mountain spine
areas of south-central and the eastern mountains will be possible
through this evening. The surface front will move from north to
south late this evening through the afternoon Thursday, as winds
trend from westerly to northwesterly by Thursday evening. Critical
fire weather conditions will remain possible across the south and
east, with winds approaching 25 mph gusts across the south and

With the front on Thursday, a more stable airmass behind this
boundary will create less favorable clearing indicies across the
far northwest areas.


UT...Excessive Heat Warning until 10 PM MDT Thursday for UTZ021.

     Red Flag Warning from noon to 10 PM MDT Thursday for UTZ482-484-

     Red Flag Warning until 10 PM MDT this evening for UTZ495-496.

     Heat Advisory until 10 PM MDT Thursday for UTZ013-020.

     Excessive Heat Warning until 10 PM MDT Sunday for UTZ019.




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