Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 181627

Area Forecast Discussion
National Weather Service Salt Lake City UT
1027 AM MDT Sun Jun 18 2017

.SYNOPSIS...High pressure will build over the eastern Great Basin
today and remain in place Monday into Wednesday, bringing very hot
temperatures to the region.


.DISCUSSION...The ridge axis has moved onshore along the
California coast this morning, putting the forecast area under a
stable northwest flow out ahead of it. The airmass is already
beginning to dry, with satellite derived PWs predominately in the
0.5 to 0.7 inch range and drier over the mountains. A more moist
airmass lingers over southeast Utah, with PWs still in the 0.8 to
1.0 inch range. With the stable airmass in place, skies are clear
with the exception of a few high clouds.

The airmass over northern Utah and southwest Wyoming will warm
slightly compared to yesterday as southern Utah stays a little
cooler in the wake of yesterday`s cold front, but temperature
differences compared to yesterday will only be in the range of a
few degrees. Northern Utah maxes will be near seasonal normals
while southern Utah will be around 10F above climo.

High pressure will continue to build over the West through the
middle of the week, with the ridge axis moving overhead by Monday
afternoon. This will result in a significant warming trend in
temperatures, with maxes by Tuesday running 15F above seasonal
normals over northern Utah and southwest Wyoming, and in excess of
20F above climo over southern Utah. These temperatures over
southern Utah will be dangerously hot, and going Heat Advisories
and Excessive Heat Warnings cover this threat well.

Conditions will remain dry and stable through Monday but a bit of
moisture and instability from weak shortwaves moving through the
ridge will combine with the hot temperatures to produce a few
showers and thunderstorms over the higher terrain. The ridge is
then expected to flatten beginning Wednesday as a trough drops
south into the Pacific Northwest that will eventually drop a
mostly dry front into the forecast area on Thursday. Differences
among the global models exist regarding the timing and strength of
the front, but regardless of solution, this will will put a dent
in the heat wave by the end of the work week.

No updates expected to the forecast this morning.


.AVIATION...The SLC terminal will see VFR conditions throughout
the day with mostly clear skies. Light winds are expected to
become prevailing northwesterly by 18Z.


.FIRE WEATHER...High pressure will build over the West today with
the ridge axis moving overhead by tomorrow afternoon. This will
result in a period of dry and stable conditions with light winds
and hot temperatures. With this strong heating, a Haines Index of
six is forecast for the southern half of the district tomorrow
through much of the week. A small amount of moisture and
instability will move under the ridge beginning Tuesday that will
result in a few high based thunderstorms over the higher terrain.


UT...Heat Advisory from noon Monday to 10 PM MDT Thursday for UTZ013-

     Excessive Heat Warning from noon Monday to 10 PM MDT Thursday
     for UTZ019-021.




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