Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 271048
Area Forecast Discussion
National Weather Service Salt Lake City UT
448 AM MDT WED JUL 27 2016
.SYNOPSIS...High pressure will maintain hot and dry conditions
through much of the remainder of the work week. This high will
move east late in the week allowing moisture to slowly increase
from the south Friday through the upcoming weekend.
.SHORT TERM...A ridge will be building over the western Great
Basin today into Thursday creating a dry northwesterly flow across
the CWA. Water Vapor satellite and PW imagery showing this
dramatic drying this evening and overnight. There may be an
isolated buildup over Boulder Mountain late this afternoon but
measurable rain is not likely.
This northwest flow will bring in slightly less hot temperatures
in across northern portions of the CWA today, where the GFS 850mb
temps are 1 to 2 degrees Celsius cooler. Across central and
southern Utah the 850 mb temps are the same or within 1 degree
Celsius warmer than where they were yesterday. The 850 mb
temperatures are expected to warm 1 to 1.5 degrees Celsius more
Thursday and then remain the same or cool a degree Friday. Have
used these 850 mb trends to forecast the max sfc temps across the
CWA during next few days. With current forecast temps and RH the
criteria for an Excessive Heat Warning has been exceeded in Dixie
for Thursday and Friday. Will let day crew evaluate and issue if
they agree with forecast.
The ridge shifts eastward by late Thursday allowing some moisture
to filter into southwest Utah. This moisture is expected to be at
high levels so dry thunderstorms the most likely impact. By
Friday, the moisture will increase some more and spread a little
farther north but still believe most of this convection will be
producing more wind then rain.
.LONG TERM (THROUGH 06Z SATURDAY)...A weak disturbance embedded
within the high pressure across the desert southwest is progged to
lift northeast across Utah on Saturday. This will allow midlevel
moisture to spread north, with showers and thunderstorms increasing
in areal coverage Saturday afternoon. Many of these showers are
expected to be high-based and produce little rainfall, especially
across northern and portions of central Utah along the leading edge
of the moisture plume. Otherwise, temperatures will remain quite
warm across the area.
Saturday night into Sunday, a shortwave trough will track east along
the Canadian border with the northwestern states. This will shift the
ridge axis east which will allow a better chance for moisture to
increase into Utah. That being said, the ridge will also flatten and
its elongated orientation is not the most ideal for a good monsoonal
moisture surge. The best moisture will remain across southern Utah,
although PWATs in the 0.75-0.9 inch range will be enough to produce
a few showers across portions of northern Utah through Tuesday given
enough instability. Temperatures will trend downward during the
early part of next week with the moisture and associated cloud cover.
By late Tuesday, another trough crossing the PacNW and northern
Rockies will flatten the ridge even more and potentially push a weak
cold front into northern Utah. This will spread drier air back
into the area from the west-northwest.
.AVIATION...Southerly winds at the SLC terminal will likely shift
to northwest at 17Z with a 40 percent chance of shifting by 15Z.
VFR conditions will prevail through the TAF period.
.FIRE WEATHER...A ridge will be building over the western Great
Basin today into Thursday resulting in a dry northwesterly flow
across the fire district. Water Vapor satellite and PW imagery
shows this dramatic drying past several hours. Only buildups that
may occur this afternoon will be across the Boulder Mountain area.
Single digit RH values will be common across the region today and
Thursday. By late Thursday some moisture could reach back into
extreme southwest Utah producing isolated high based
thunderstorms. This area of convection will expand Friday as
moisture wraps around the ridge and spreads farther north and
east. Again this convection will most likely be high based so the
potential for scattered dry thunderstorms with gusty micro burst
winds will become a concern over the southwest quarter of Utah.
Moisture is expected to spread across the entire fire district
this weekend with deepest moisture and hence the best threat of
receiving rain will be over the southeast half of Utah while the
western and northern portions of the fire district will be on the
periphery of the moisture and could see repeated dry thunderstorms
into early next week.
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