Scientific Forecaster Discussion
fxus65 kslc 170247
Area forecast discussion
National Weather Service Salt Lake City Utah
847 PM MDT Mon Oct 16 2017
Synopsis...a warming trend will continue through the middle portion
of the week as high pressure remains in place. The next storm system
is forecast to cross the area Friday into Saturday morning.
water vapor satellite shows a ridge building in from the
southwest. 400-200mb mdcars wind observations place a 60-90kt
anticyclonic jet from the Pacific northwest into the central
rockies. GOES/slc 00z radiosonde observation/hrrr indicate that precipitable water
values vary from 0.05"-0.10" southern Utah and mountains to
0.15"-0.25" northern valleys.
The ridge axis is expected to shift east from Nevada overnight,
with an increase of cirrus. Amount of cirrus should not diminish
radiational cooling significantly, and with a very dry airmass in
place temperatures should dip overnight. Lowered overnight lows
especially in locations with inverted conditions. The temperature
trend however is warmer than last night as the 850-700mb thickness
continues to increase.
Going forecast in great shape. Updated diurnal T/relative humidity curve based on
latest observations and guidance.
high pressure remains centered just to the west of the forecast
area this afternoon, resulting in a dry and stable west to
northwest flow. The airmass at 700mb is in the +6c to +8c range,
resulting in continued mild conditions over the higher terrain.
Though noticeably warmer than yesterday in the valleys, limited
mixing is inhibiting these temperatures from being fully realized
in the valleys. As a result, maxes are running just a few degrees
below seasonal normals.
The ridge is expected to track east tonight and tomorrow as it
flattens, with the axis moving east of the forecast area by
tomorrow afternoon. The resultant west to southwest flow will
allow for improved mixing, resulting in further warming in the
valleys and allowing those maxes to warm to values a little above
Models have been consistent in indicating that a rather weak
shortwave will impact southern Utah late Tuesday into Wednesday,
though they continue to disagree with regard to the precise track
of this wave. The main impact of this wave will be to increase
cloud cover somewhat, with little if any associated precipitation
anticipated. Behind this wave, the flow aloft is expected to
become more southerly beginning Thursday ahead of the next
approaching storm system, allowing for more mixing and warming
valley temps just a bit. These winds could become breezy for many
locations across the forecast area on Friday as the system and
associated cold front approach.
The late week trough continues to trend less amplified and more
progressive in guidance, with the 500 mb cold pool remaining north of
the Utah/Idaho border with passage late Friday/Friday night. With this,
both any connection to deeper moisture from the south, or strong
deep layer cold air advection from the north are lost. Guidance continues to
portray a decent mid level baroclinic zone with passage of the
cold front, but with upper level support just a bit too far north
the frontal push should be fairly shallow, with any precip
confined to this zone Friday evening through mid level axis
passage early Sat morning. Model quantitative precipitation forecast has decreased as such (both
in areal coverage and significance). Have continued a trend of
lowering pops this package.
Warm advection in slightly anticyclonic W-NW flow will punch into
northern portions of the area rapidly Saturday into the overnight
hours. Outside of a net increase/maintenance of clouds over the
north, do not foresee much precip threat in this pattern as the
better forcing remains tied north closer to the jet.
Thereafter through the end of the period mid level ridging is
expected to build into the Great Basin region yielding another
period of tranquil and near seasonal conditions early next week.
operational weather concerns will remain minimal at the kslc
terminal through the valid taf period. Winds are calm, and
southeast drainage flow is expected to develop during the next
hour or two.
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