Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 211740

Area Forecast Discussion
National Weather Service Salt Lake City UT
1140 AM 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.


.DISCUSSION...Temperatures across the area this morning are
already quite warm, approaching the mid to upper 80s in many
locations across the central and southern areas of the state and
upper 70s elsewhere. Precipitable water from the 12z SLC RAOB
sounding is near 0.80 inches which is in line with short term
forecast models; also showing values 0.6 to 0.7 inches across most
of Utah. Temperatures aloft this morning show a slight warming
trend compared with yesterday, as 700mb readings at at 16C this
morning. Light westerly flow aloft this morning and minimal sky
cover should lead to another warm day across the state.

The high pressure that has dominated the region the past several
days looks to continue to do so today. The heat headlines in place
today will remain through tomorrow, as temperatures continue to
remain hot across the south reaching near 112F and hot in the
north with SLC forecasting 101F.

A front is progged to drop into northern Utah this afternoon and
early evening with an axis of instability from northeast Nevada
through northeast Utah, likely pointing to another round of
convection later this afternoon into evening. The previous
forecast is in good shape, so no updates planned at this time.

.Previous discussion (Through 12z Friday)...SPC SREF ensemble
continues to indicate sufficient instability this afternoon/eve
driven by diurnal thermal input within this zone, and NCAR
simulated reflectivity points toward another round of convective
initiation over both the eastern Nevada mtns and along/downstream
of the Uinta/Wasatch Plateau spine. Timing of the NV convective
evolution into the west/north looks to hold off until after 00z in
large, so opted to trim PoPs slightly across the west this
afternoon, but left isolated potential along the UT mtn spines and
downstream. Areal extent of isolated convection does look to
increase this evening across northern/central portions aided by
more focused convergence from the aforementioned northern branch,
and downstream maintenance of some of the cells out of Nevada
along and ahead of a shallow surface boundary moving into the
north. With sufficient DCAPE, gusty wind threats remain a
potential through about the middle of the night.

The aforementioned boundary will surge south into central Utah come
Thursday, cooling the north some 10 degrees, but shallow nature and
loss of upper support will limit any notable sensible weather
changes across the south. Convective potential is expected to wane
as well Thursday, as mid level moisture/instability will dissipate
in wake of passage to the north, and ahead of it in the south.
Rolling with a dry forecast with only some buildups over the
southern UT mtns Thu afternoon.


.AVIATION...Northwest winds will persist at the SLC terminal today.
Gusty erratic outflow winds from nearby thunderstorms could
impact the airfield between about 23z-07z. Northwest winds are
expected to remain through Thursday morning.


.FIRE WEATHER...Strong high pressure will maintain excessive heat,
bone dry RH, and a Haines index of 6 across the south, with temps
across the north hovering near 15 degrees above climo. Isolated
critical winds remain forecast for portions of the SW this
afternoon, and though speeds are borderline, an RFW remains in
place for gusts over 30mph and low RH coupled with the high
Haines. Rapid growth potential remains high for ongoing fires and

UT...Excessive Heat Warning until 10 PM MDT Thursday for UTZ019-021.

     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.




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