Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
435 PM MDT Monday Sep 15 2014
Synopsis...high pressure will strengthen across the interior west
through the first half of the week. Tropical moisture will surge
northward into southern Utah late Wednesday...then continue north
across the entire area by Thursday.
Discussion...a ridge continues to build over the Great Basin
this afternoon...bringing warmer than seasonal temperatures to
Utah and southwest Wyoming. Enough moisture remains under this
ridge to support isolated showers and thunderstorms...primarily
along the higher terrain...as well as in far eastern Nevada and
west-central Utah. With the stable conditions in place...most of
these cells are fairly weak and low topped...with only the storms
coming out of Nevada generally strong enough to produce a fair
amount of lightning.
Tuesday is expected to be fairly similar to today...perhaps even a
couple degrees warmer as the ridge intensifies. On
Wednesday...deep tropical moisture associated with Hurricane Odile
will begin making its way northward...but looks to remain
primarily south of the Utah/Arizona border through 00z
Thursday...with precipitable water values near St. George forecast
to be in the 0.75-1.00 inch range.
The best moisture surge for the forecast area comes Wednesday
night and Thursday...with precipitable water values above an inch over almost all
the County Warning Area by 00z Friday. Have kept probability of precipitation high on Thursday...as
numerous showers and thunderstorms across the area still looks to
be a good bet. It is Worth noting however that precipitable water values are not
expected to be as high over Utah as with Hurricane Norbert...and
the duration/strength of the forcing will also be weaker than the
event last week. All of this said...heavy rainfall and flash
flooding are still possible across the area...but at the moment
this does not look to be a repeat of the Norbert event.
Models push a Pacific trough into the Great Basin late Thursday
through Friday...which dries out the County Warning Area from the northwest.
Both the GFS and European model (ecmwf) have generally been cutting off the trough
into a closed low over Southern California late Friday...and where
this low GOES after that has a large impact on if/when moisture
returns to the County Warning Area. Models have produced about half a dozen
different ideas for this low over the last 24 hours...so
confidence beyond Friday remains low. For now...have kept slight
chance probability of precipitation across southern Utah for the weekend...as some of the
solutions return moisture to the area for days 5-7.
Aviation...VFR conditions will continue at the kslc terminal
through the taf period. Northwest winds this afternoon are expected
to become southeast between 0200 UTC and 0400 UTC.
Fire weather...temperatures will continue to exceed norms by 5 to
10 degrees across the region through Wednesday. Convective activity
will promote isolated thunderstorms each afternoon. Minimum relative
humidity values in the valleys will be in the middle teens tomorrow and
inch upward Wednesday as moisture begins to increase. This moisture
will surge northward into Utah Thursday and Friday. Wetting rains
are likely Thursday with some drying expected to occur from
northwest to south over the weekend.
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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)