Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
848 am MST Wednesday Feb 10 2016
Synopsis...high pressure aloft will remain the dominant weather
feature over the intermountain west through the end of the week.
A couple of weak weather disturbances will cross northern Utah
Discussion...water vapor loop shows a ridge dominating the
west. Amdar 400-250mb wind observations place a 125-160kt
anticyclonic jet from central Canada into the eastern Gulf Coast.
GOES/hrrr/GPS/12z slc radiosonde observation indicate the precipitable water value
ranges between 0.05"-0.10" mountains...to 0.20"-0.30"
northern/west central valleys.
With an inversion in place...main concern is haze/fog/stratus and
The inversion has lowered to 846mb with a strength of 11.5c. Have
become more aggressive with fog/stratus depiction. Through the
morning went with areas of dense fog for many valleys...backing of
to patchy fog during the afternoon. Stratus may erode at edges such
as along Wasatch front and Cedar City this afternoon.
Temperatures are nearly persistent in strongly inverted
valleys...with a blend of guidance in the mountains and far
the strong upper ridge centered across the intermountain region
will remain in place as the dominant weather feature through the
end of the week. Stratus that expanded rather quickly across the
northwest desert yesterday now encompasses much of the northern
and western valleys early this morning. Looking at some erosion of
the stratus around the perimeter this afternoon...though suspect
most of this will return again tonight.
The areal extent of fog continues to increase underneath the
valley inversions across western and northern Utah. Pockets of
dense fog have been observed...with the most notable increase
near the Great Salt Lake. Suspect that fog will remain an issue in
many of the same areas the next couple of nights as long as the
upper ridge remains locked in on the Great Basin.
A series of weakening shortwaves will at least temporarily knock
down the ridge this weekend. Enough lift could be generated by
these passing features to bring light precipitation to the far northern
zones Saturday. More importantly sufficient cooling aloft could
weaken over even mix out entirely the valley inversions in place
across northern Utah Saturday afternoon.
The ridge will be flattened by a trough that right now appears to
have enough cold air to eradicate the inversion according to the
GFS. However...the once colder solution (the ec) is not as cold as
previous forecast from more than 12 hours ago. The fact that the GFS
went away from the colder solution for the 12z run but now has
come back to nearly where it was 24 hours ago with -7 to -10 degrees
c my confidence is increasing that our inversion will be broken
here over the weekend. Due to the cold air erasing the
inversion...valley temperatures along the Wasatch front and other valley
will benefit for at least one day with better air. Temperatures
are expected to rise moderately due to the increased instability.
Have boosted probability of precipitation over northern Utah and southwest Wyoming Saturday
night through Monday as a series of weak ripples move through. The
temperature difference between 700 mb and 500 mb is right at the threshold
to allow for some instability showers.
Tuesday the ridge rebuilds ahead of a stronger looking trough
scheduled for the end of the work week. Winds are expected to pick
up ahead of this latter storm system which will aid in dispersing
the stagnant air in the valleys and keep temperatures relatively
Aviation...the slc terminal will continue to see periods of LIFR
conditions in fog through this morning. These conditions are
expected to improve to IFR/MVFR around 17-19z...though a slight
chance exists that visibilities of 1sm or worse will linger past
19z. Dense fog is likely again tonight. The most likely period for
dense fog to return to the runways is 06z-10z...though there is a
chance fog could return from the Great Salt Lake as early as 00-03z.
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