Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
350 am MDT Monday Aug 3 2015
Synopsis...a low pressure system will slowly through northern
Utah today. A drier southwesterly flow will follow for
midweek...though a weak upper level disturbance will scrape across
the northern sections of the forecast area. Moisture may return
late in the week.
Short term (through 06z thursday)...early morning water vapor
imagery and objective analysis depict an upper low spinning across
central Utah. Moisture wrapping around the north side of this
circulation is resulting in fairly widespread rainfall across the
southern Wasatch front southward into the Sevier Valley and Castle
country along with the adjacent higher terrain. Radar and
satellite trends show a slow northward drift of this rainband with
The short range models offer a variety of opinions with respect
to the evolution of this rainband through the morning
hours...however given the slow northward movement of the parent
low coupled with ample boundary layer moisture in place...have
included likely probability of precipitation during the morning across much of northern
Utah...shifting to the Wasatch crest eastward for the afternoon with
scattered convection further south and west along the Wasatch
front into central Utah. The southwest should remain void of
convection today as drier air aloft and subsidence has overspread
this region. With extensive cloud cover and precipitation have also
lowered maximum temperatures considerably across the north this
In the wake of this upper low...mid-level ridging is forecast to
amplify across the eastern Great Basin during the day Tuesday
allowing for a drying trend area-wide. Any lingering convection
should remain confined to the raft rivers and perhaps the high
uintas. A weak shortwave is forecast to eject through the
northern Great Basin during the day Wednesday. Increasing
southwesterly flow may result in locally breezy conditions across
western Utah Wednesday afternoon. With a relatively dry air mass in
place across the area any convective threat with this wave should
remain confined to far northwest Utah Wednesday afternoon and
Long term (after 06z thursday)...ridge of high pressure will
build over the region on Thursday with a dry air mass in place.
GFS and European model (ecmwf) in general agreement with ridge axis shifting east
of forecast area on Friday as a low pressure system over
California open up and lifts northeast...though European model (ecmwf) still about
six hours slower with solution. Ahead of this system...flow
should turn southerly enough to transport moisture into forecast
area...with precipitable water values prognosticated to increase to
around three quarters of an inch by late Friday afternoon.
Thus...current chances for precipitation across primarily southern
half of Utah for Friday afternoon looks good.
Moisture will spread across remainder of forecast area Friday
night. With upper support from trough of low pressure and jet maximum
working across region...chance for showers and thunderstorms
across forecast area justified.
Drier air will spread across forecast area Saturday...but still
enough moisture left to support chance wording for primarily
eastern half of forecast area.
Ridge aloft will build back over region late in the weekend...with
dry weather expected.
Aviation...periods of rain are expected at kslc through the
morning hours...and although ceilings will remain well into the VFR
range...there is a 40 percent chance they will fall below 7 kft
at times through 18z. There is a 40 percent chance for showers and
thunderstorms developing in the vicinity of the terminal after
18z. Winds are expected to remain southerly through early
afternoon before switching to the west...however gusty and erratic
winds can be expected near any thunderstorms this afternoon.
Fire weather...a low pressure system will slowly cross northern
Utah today bringing fairly widespread wetting rains. Drier air in
the wake of this system will spread into southwestern Utah
throughout the day...before spreading northward across the
remainder of the area overnight into Tuesday. This drying trend
will continue through much of the week with only a small threat
for afternoon and evening thunderstorms over the north.
Southwesterly flow is forecast to strengthen Wednesday into
Thursday which could result in locally breezy conditions across
western Utah. Moisture within this flow is expected to temporarily
return northward across the area Friday into Saturday...before
conditions once again dry out for the latter portion of the
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)