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Area forecast discussion 
National Weather Service Salt Lake City Utah
550 am MST Sat Dec 27 2014

Synopsis...high pressure aloft will slide southeast across Utah
today. The next cold Pacific storm system will reach the area late
in the weekend... and remain through the middle of next week.


Short term (through 00z wednesday)...skies are clearing across the
area this morning in response to high pressure building into western
Utah...with the exception of a few patches of stratus. Fog may
develop in a few spots this morning...and reduction in visibilities
have already been noted in Logan and Brigham City metars. Warm
advection develops at 700mb this afternoon...but stable airmass and
cold start to the morning will prevent much warming in valleys
today. Most areas except far southern Utah likely to remain near to
below freezing.

Next storm system noted on water vapor imagery over the central
British Columbia coast. Clouds will spread into the area later today
as 700mb warm advection strengthens...with light snow developing
this evening near the Idaho border. Models not developing
significant amounts into Utah in the overrunning airmass.
Rather...precipitation intensifies and becomes more widespread over
northern zones Sunday morning owing to destabilization of the
airmass as cooler air spreads in at 500 and 700mb while the surface
boundary remains upstream. Models indicate the surface boundary
finally arriving into northern Utah late Sunday afternoon through
Sunday evening. Heaviest snow north of I-80 likely to occur during
the day Sunday...while Salt Lake valleys...Utah County...and
adjacent mountains should see greatest intensity behind the front
late Sunday afternoon through Sunday night. Although the front will
end up through southern Utah by Monday morning...the upper support
starts lagging by snow will be quite a bit less south of
around I-70.

Snow will linger into Monday but an overall decrease in coverage and
intensity is expected. However...another reinforcing trough will
carve into the area...eventually closing off over the central Sierra
Nevada by Tuesday evening. This system will allow an Arctic airmass
to spill into the area from across The Divide. This cold airmass
will be associated with enhanced easterly winds across northern Utah
and southwest Wyoming...and particularly near Wasatch front canyons.
However...the positioning of the low looks to be a bit too far west
to produce a strong downslope event.

Typical of Arctic airmasses...this boundary will not be associated
with a lot of moisture. However...good low-level convergence along
this boundary may still lead to accumulating snow northern and
central portions Monday and Monday night and spreading into southern
Utah on Tuesday. Needless to say...temperatures will trend
significantly colder behind the front late Monday through midweek.

Regarding highlights. Because the storm looks to develop a bit
slower than previous thinking...with significant precipitation
mostly holding off until tomorrow morning...have left watches in
place. However...have expanded the watch farther south to include
the southern Wasatch front and the Wasatch Plateau since these areas
seem like they would see similar impacts even with slightly less
snow than the zones to their north.


Long term (after 00z wednesday)...upper trough continues its dive
southward Tuesday night/Wednesday morning as it closes off. The
system is prognosticated to slowly move across Arizona through
Friday...keeping moisture and instability over primarily southern
Utah. Because of this...have maintained scattered probability of precipitation over the
south through Thursday night. Upper flow should keep an east/NE
direction through Thursday before becoming more northerly Friday as
the low exits. Pressure gradient remains fairly tight over much of
the area through Wednesday some possibility of canyon
winds exists in prone areas through then.

Behind the exiting models maintain a slowly warming
northwest flow over the forecast area through next weekend. Waves
moving over the ridge are expected to keep the flow dirty for
northern have kept some probability of precipitation in for the higher terrain of
that area.


Aviation...the slc terminal will see VFR conditions through the
morning. Clouds are scattering out this morning...but occasional
ceilings near 7000ft are still possible through 15z. Southeast winds are
expected to shift to the northwest between 19z and 21z...but there
is a 20 percent chance this will occur later than expected or not at


Slc watches/warnings/advisories...
Utah...Winter Storm Watch from late tonight through Monday morning for

Winter Storm Watch from late tonight through Monday morning for




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http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)

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