Area forecast discussion
National Weather Service Salt Lake City Utah
339 am MDT Wednesday may 22 2013
Synopsis...a low pressure system will remain over the Pacific
northwest through this week...keeping most of Utah and southwest
Wyoming in a dry southwest flow. A couple of weak cold fronts will
enter northwest Utah through the end of the week but will tend to
dissipate before reaching central Utah.
&&
Discussion...the challenge of the day is the timing of the
shallow cold front making its way to the Wasatch front today.
There are significant differences between computer models in
placement and timing of the cold front as it tries to undercut the
moderate southwest flow aloft. Have little confidence in any one local
model as surface wind fields are all over the place and are
currently either too strong or have directions incorrect already.
By blending the general local models ideas along with the nam12
850 mb winds which currently is showing reasonable accuracy in
location and speed of winds...it looks like the front should reach
the slc area about noon today. There is not much push to this
front so the forecast by both the arw4g and hiresw-arw-west
showing the front stalling at the south end of the Salt Lake
Valley this afternoon looks reasonable. The front should move into
Utah valley this evening but could just dissipate completely
before this occurs.
As one would expect...timing of this front will play an important
role in temperatures today. Due to the breezy south winds
overnight along the Wasatch front we will start off the day with
very mild temperatures in the 60s. Therefore reaching the upper 70s in
the northern Wasatch front areas and near 80 at the slc Airport
should not be hard to do. The southern end of the Salt Lake
Valley as well as points in Utah valley could take a run at the
middle 80s. Model guidance ranges from 73 to 87 for slc today.
Temperature forecast do not get any easier for Thursday across the
north as the winds aloft should erode whatever boundary remains
and bump temperatures back up into the middle 70s. If the south winds
do not surface then a weak northerly flow at the surface could
keep the temperatures somewhat cooler. Another issue is whether
high based convection can develop over extreme northwest Utah over
the Great Salt Lake Desert and/or northeast Nevada this evening
and again Thursday afternoon which if it does occur could help
reinforce the cool pocket via outflows. South of about Juab County
to Uinta Basin line breezy southwest winds are expected today
through the weekend with temperatures near or slightly above normal.
The NAM and GFS indicate some weak instability over the northwest
corner this afternoon and evening due to another lobe of energy
rotating northeast across northeast Nevada. In addition...some
instability is also possible over Tavaputs and uintas.
The strong upper level low over the Pacific northwest will weaken after
Friday and lift northward into Canada. However some troughiness
will remain over the western Great Basin over the weekend keeping
a dry southwest flow in place. Additional energy and moisture is
expected to filter into this trough as it moves into the eastern
Great Basin early next week.
&&
Aviation...the slc terminal will see VFR conditions throughout the
day with some high and middle level clouds. Southerly winds will be
occasionally gusty through the morning before shifting to the
northwest with the passage of a cold front between 17z and 19z.
During this period there is a 40 percent chance that low level
wind shear could occur and persist for a couple of hours.
However...there is a 30 percent chance the frontal passage will
occur later than expected...perhaps during the late afternoon...if
the front stalls over the Great Salt Lake. It is for this reason
that wind shear is not currently included in the actual taf.
&&
Fire weather...a Pacific northwest storm system will make its way
toward Utah...pushing a cold front into northern Utah today and
tonight. Ahead of the front...much of the district will see breezy
southerly winds. The system will graze northwest Utah over the
next couple of days before moving northward into Canada Friday.
Winds will continue to be enhanced for most of the week over Utah
ahead of the system. The system will result in some cooler
temperatures for northern Utah...but should produce little in the
way of precipitation. A second Pacific system will push into the
Great Basin over the weekend...keeping breezy southwest winds
along with low relative humidity values over at least southern Utah through the
weekend.
&&
Slc watches/warnings/advisories...
Utah...none.
Wyoming...none.
&&
$$
Public...struthwolf
fire weather...traphagan
aviation...traphagan
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
visit...
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)
