Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 220248

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

.SYNOPSIS...High pressure will weaken and shift south tonight 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.


.DISCUSSION...Isolated showers continue across parts of Utah and
southwest Wyoming this evening, as a low level cold front slowly
sags southward through the area; that said, the only area that
has been able to sustain long-lived thunderstorms has been the
higher terrain just west of Wendover. Storms continue there as of
02Z, with a few of these storms able to drift off into the lower

North winds across the west desert have been peaking at gusts of
30-40 mph as the surface boundary pushes southward. Temperatures
north of this boundary have still remained fairly warm today,
generally only 1-4 degrees cooler than yesterday`s record or
near-record highs. Across the southern half of Utah, temperatures
remained hot, with a couple high temperature records tied earlier
today at Kanab and Kodachrome Basin State Park.

Cold advection northwesterly flow will increase through tonight
and tomorrow, as the associated shortwave trough continues to dig
south. This will cool temperatures even more across the northern
half of the CWA, with some forecast highs tomorrow as much as 10
degrees cooler than today. This closer-to-seasonal northwest flow
will continue through the end of the week, though temperatures
will still be quite warm across the far south.

The forecast was updated in the afternoon to increase POPs across
the CWA for the afternoon/evening. Will keep an eye on the radar
to see if more POPs need to be added to the 06-12Z period, but
suspect that almost all of the storms will dissipate as forecast.
The previous long term discussion follows.

.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...Northerly winds are expected to persist at the SLC
terminal overnight, though periods of light and variable winds
are possible. There is also a 10 percent chance that the winds
could become erratic due to a stray outflow from dying
thunderstorms between 03Z and 06Z.


.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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