Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
358 PM MST Tuesday Nov 25 2014
Synopsis...a disturbance will continue to move through the area
through tonight. High pressure will build over the area
Wednesday and remain in place through the upcoming weekend.
Short term (through 00z saturday)...light to moderate snow
continues over the mountains of northern Utah...with little to no
precipitation being observed across valley locations outside of a
few sprinkles/flurries. The 12z slc radiosonde observation indicated a significant
dry layer at the low levels and 12z NAM bufr soundings indicated
even the Cache Valley had a significant low level dry layer.
The dewpoint in Logan has increased to near 30f currently. NAM
bufr soundings indicated a sufficient increase in low level
moisture would occur for at least the Cache Valley to realize
precipitation at the surface. Given the current dewpoint
depressions...expect the 12z NAM bufr soundings were overly
ambitious with the moistening of the low levels for the Wasatch
front. Observations support this assertion. Kept low end probability of precipitation for
the Wasatch front tonight...but these may even be too high.
Most model guidance indicates a period of enhanced precipitation
will occur later this afternoon into this evening across the far
northern mountains of Utah. 700mb winds in excess of 50kts
continue in this area. Decided given the combination of snow and
strong winds to continue the Winter Weather Advisory for the
northern Wasatch mountains north of Interstate 80. Additional
accumulations outside this area will be light.
As previously mentioned...700mb winds are quite strong this
afternoon...with nearly 70kts forecast by multiple models across
Uinta County Wyoming. Observations along Interstate 80 have
indicated wind gusts near 52 miles per hour so far...but expect some areas of
Uinta County are exceeding 58 miles per hour at times. These strong winds
will cause travel impacts to area roads including Interstate 80
from the Utah/Wyoming border to the Uinta County line...especially
high profile vehicles and lightweight vehicles such as trailers.
700mb winds remain strong into the overnight hours and the surface
gradient remains fairly strong as well. Depending on the evolution
of the winds over the next few hours...the High Wind Warning may
need to be extended.
High pressure then builds into the area for the remainder of the
week...with increasing temperatures. The ridge will begin to
flatten Friday. Disturbances embedded in the flow around the top
of the ridge may bring the slight chance of a shower or two to
mountains right along the border of Utah and Idaho Friday
afternoon...but the biggest noticeable change will be an increase
in cloud cover...particularly across northern Utah.
Long term (after 00z saturday)...heights lower slightly Saturday in
response to short wave energy rotating through the northern rockies
region. Global models in good agreement with this feature and
response...presence of modest moisture within confluent and near
westerly flow may kick off a few showers along the Utah/Idaho border.
That said...with jet north of the area and any energy remaining very
weak locally an all dry forecast may come to fruition. This more
likely Sunday when heights build once again in response to a reload
of a West Coast trough.
Primary forecast challenge focuses on said trough and its evolution
as it moves into the eastern Great Basin early next week. Both European model (ecmwf)
and GFS show a splitting nature to the system either just west or
overhead...fair middle level baroclinicity/cold air advection with
passage and modest moisture. Extent of southern split an important
detail lacking at this time and has a direct impact on quantitative precipitation forecast
amounts...but fairly confident in at least light amounts Monday
night/Tuesday and probability of precipitation reflect that. Did lower probability of precipitation Monday some 10
percent due to GFS hedging more towards the European model (ecmwf) in a slower
nature with more split.
Aviation...ceilings at or below 6000ft above ground level are expected to be the
primary operational concern at the kslc terminal through this
evening. Southerly surface winds are expected to continue with
moderate gusts up to 20 knots at times through 01-02z.
Utah...Winter Weather Advisory until 8 PM MST this evening for utz007.
Wyoming...High Wind Warning until 9 PM MST this evening for wyz021.
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)