Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 280848
Area Forecast Discussion
National Weather Service Salt Lake City UT
248 AM MDT SUN AUG 28 2016
.SYNOPSIS...An upper low over Arizona will move east to the four
corners tonight. High pressure will move in tomorrow behind this
system, allowing for a drying and warming trend for the first part
of the upcoming week.
.SHORT TERM (THROUGH 06Z WEDNESDAY)...
Water vapor loop shows a closed low over north central Arizona,
with a trough extending to the northeast. MDCARS wind
observations show a 50-75kt cyclonic jets from Arizona into the
central Rockies, and over the Pacific Northwest. GOES/HRRR/00Z
KSLC RAOB indicate the precipitable water value ranges from
0.20"-0.30" northern mountains to 0.75"-1.00" southern valleys.
Starting out this morning with copious cloud cover in proximity to
the aforementioned upper low and trough across south central and
southeast Utah. While proximity to the dynamical forcing should
aid in general ascent, questions remain about instability in this
region during the afternoon. Further to the northwest, deep
convection is more likely to occur this afternoon with better mid
level lapse rates. Locally heavy rainfall may occur in these
areas from Zion into the central mountains.
Supporting heavy rainfall in areas with better instability include
a deeper warm cloud layer than yesterday, dewpoints in the 50-60F
range along the Arizona border with precipitable water values near
an inch, and a northerly storm motion.
Narrow margin for error today for flash flooding, meaning areal
coverage is limited due to stable airmass moving in from the
west, and across the east by convective debris. Thus not issuing a
flash flood watch though possibility exists in local areas this
afternoon and evening.
During the next several days convection should become more
isolated, diurnal in nature and tied to the higher terrain as
anticyclonic flow develops aloft. This will support a warming and
drying trend across the region.
.LONG TERM (AFTER 06Z WEDNESDAY)...
Global models have backed off on the midweek moisture surge
significantly with the 00Z model runs. Model to model consistency
issues increase significantly toward the end of the week, with
large implications on the sensible weather.
An upper level trough is expected to approach the coast Tuesday into
Wednesday. At least one global model indicated jet dynamics
supportive of nocturnal convection early Wednesday. As the jet
transitions overhead Thursday, expect the convective threat to
As mentioned earlier, the differences in the global models increase
significantly after this point (from Friday onward). Given poor
model to model and run to run consistency across the global model
suite, kept pops below climatological averages from Friday onward as
an attempt at a blend between the very dry GFS and the wetter EC.
Southerly winds at the SLC terminal are expected to shift to the
northwest between 19-20Z.
Yesterday`s ERC values were at or above the 97th percentile
across portions of northern Utah, while stations across southern
Utah remain below the 50th percentile.
A warming and drying trend will prevail into mid week. Convection
will become more isolated, diurnal in nature, and tied to the
terrain especially by tomorrow. Still a good chance for wetting
rain under showers today.
Southerly winds look to increase across the western valleys
Tuesday though critical fire weather conditions expected to be
isolated, limited by sub-critical gusts most locations. Dry
microburst winds may be supported due to high-based showers during
the late afternoon and evening hours in this area as well. Similar
conditions need to be monitored for the same area during the
second half of the work week.
A monsoon push will increase the coverage of thunderstorms during
the second half of the work week, supporting a gradual cooling
and moistening trend and another round of lightning.
SHORT TERM/FIRE WEATHER...Rogowski
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