Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
416 PM MST Thursday Feb 11 2016
Synopsis...high pressure will remain over the intermountain west
through Friday. A couple of weak weather disturbances will cross
northern Utah this weekend.
Short term (through 12z monday)...a strong ridge remains in place
over the Great Basin this afternoon...keeping a stable airmass in
place. Temperatures at 700mb remain quite mild...generally between 2
to 5c across the forecast area. As a result...most higher elevation
sites continue to see dry and mild conditions. However...lower
valleys of mainly northern and central Utah remain mired in
inversions with fog and low stratus. Satellite trends do indicate
the stratus eroding a bit along the edges this afternoon...but not
enough to significantly affect temperatures.
Expect the stratus to continue overnight with fog increasing in
coverage after sunset despite increasing high clouds helping to
limit radiative cooling somewhat. Not issuing any fog highlights
with this package even though some dense fog is expected.
Rather...will allow later shifts to monitor trends as the high
clouds may affect the coverage of dense fog. Not looking at any
significant changes in the weather for tomorrow.
For the weekend...a couple of weak storm systems are still expected
to graze northern Utah. Because these storms are not very
strong...they are not expected to sweep away the inversions.
Rather...cooler air aloft will gradually erode the inversions from
above. The Saturday storm is only expected to put a small Dent in
the inversion and not expected to produce much if any in the way of
precipitation. The storm on Sunday will be a bit cooler...usher in
stronger winds aloft and some light precipitation for the north. The
winds are not expected to mix down to the valley bottoms so as a
result the inversions may not completely erode away.
Nevertheless...with the latest ec coming in stronger with the storm
than the 00z run...the potential for a significant improvement to
air quality seems more likely.
Long term (after 12z monday)...low amplitude ridging centered over
the norcal coast will maintain a somewhat progressive northwesterly
flow aloft early next week. Remnant moisture from the previous short
wave and weak jet support aloft may maintain isolated mountain snow
showers across the far north Monday into the overnight hours...but
largely looking at a somewhat improved and partially mixed
environment...with dry conditions dominating. Axis of aforementioned
ridge will trend to shift inland and overhead through the midweek
period allowing another round of rising heights and subsident
warming...this likely strengthening inversions across the valleys
and basins once again. This said...net strength and amplitude of
this ridge will be weaker than the current situation...and residence
time quite a bit shorter.
Global models do pick up on a net pattern change across the western
Continental U.S. Late next week as mean flow across the eastern Pacific
transitions more zonal driving at least the remnant energy of an
adequate trough inland into the eastern Great Basin.
Evolution...timing and amplitude of this remains low confidence at
this time due to substantial spread in guidance...but the likelihood
of having some semblance of a trough move through in the Thursday or Friday
timeframe looks like a decent bet. The combination of increased flow
aloft and cloud cover ahead of this combined with modest cold air advection at the
low/middle levels during passage may have a notable affect on the
persistent inversions at that time.
Aviation...prevailing IFR conditions in haze/fog and low stratus
are expected to remain in place at the kslc terminal through the
valid taf period. Surface visibilities have improved to MVFR levels
for the time being but aforementioned stratus is unlikely to thin at
this point this afternoon. Dense fog is expected to once again creep
into the northwestern portion of the airfield tonight...and a 60
percent chance exists that this fog will spread across the airfield
sometime within the 09-14z window.
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)