Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
704 PM MDT sun Aug 31 2014
Synopsis...high pressure will build over the region for the early
part of the week. A Pacific northwest trough is expected to bring
a mostly dry cold front into northern Utah for the latter part of
Discussion...water vapor loop shows northwest flow aloft is
prevailing with weak embedded disturbances over the Pacific
northwest. Amdar 400-250mb wind observations reveal a 75-125kt
northwesterly jet from the Pacific northeast into the central
rockies. GOES/GPS/rap/00z radiosonde observation indicate the precipitable water
value ranges between 0.2" northeast mountains to 0.7" northwest
Dry stable airmass in control with no convective threat tonight. In
fact visible satellite shows last of diurnal cumulus decaying over
the northern mountains. Have lowered sky grids to indicate a clear
night for most.
Rap indicates pressure gradient easing overnight as the storm system
continues to drift into the central Continental U.S.. this will allow winds to
slacken at many locations though will hold a northerly gradient
overnight. With the combination of a dry airmass with clear skies
and decreasing winds...seemed prudent to undercut MOS guidance for
the normally cooler valleys.
Previous discussion...weakening cold front is draped over southern
Utah this afternoon as the associated storm system centered over
Wyoming moves quickly out of the region. A dry and stable airmass
has moved over the forecast area...resulting in just some scattered
clouds. Temperatures over northern Utah are significantly cooler
than yesterday...around 10f below seasonal norms.
However...temperatures over southern Utah are similar to values
High pressure will build over the region for the early part of the
week...allowing dry and stable conditions to continue. The building
ridge will also allow for a warming trend...with maxes expected to
be at or a few degrees above climatology by Tuesday across the entire
By Wednesday...global models all move a trough onshore along the
Pacific northwest coast. They have come into better agreement with
the timing and track of this system...slowing pushing it into the
north central United States by Friday as it splits. The system is
prognosticated only to get as far southern as southern Idaho. However...it
will shift the ridge over the area east...allowing southwest flow to
develop. This will allow just a bit of moisture and instability to
return for the middle and latter part of the week...resulting in
some convection primarily focused over the higher terrain of Utah.
The system is also expected to bring another cold front into
northern Utah...dropping temperatures back below seasonal normals.
Aviation...winds are expected to switch to the southeast between
03z and 05z at the slc terminal...though periods of light and
variable winds could continue through 07z.
Fire weather...the upper level trough currently over the northern
rockies will shift east into the northern plains states overnight.
The associated surface cold front has progressed south into southern
Utah this afternoon...with cooler...dry and stable air following the
front. Below normal temperatures will persist across much of the state
A warming trend will begin Tuesday as high pressure aloft
strengthens to the south of Utah. Temperatures will return to near or
slightly above seasonal norms midweek. The next Pacific trough
entering the Pacific northwest late Tuesday will generate increasing
southerly winds across northern and western Utah. This storm system
could also draw some moisture north into southern Utah for late
Tuesday/Wednesday. Could see isolated convection form over the
higher terrain by late Tuesday afternoon...with a better chance of
additional showers and thunderstorms on Wednesday. Temperatures will cool
again late in the week as the cold front associated with this next
trough sweeps south across mainly northern and central Utah.
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