Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
457 am MST sun Nov 29 2015
Synopsis...a cold upper level low pressure system will remain
over the Great Basin through the remainder of the weekend. High
pressure aloft will settle into the region early next week.
Short term (through 00z thursday)...the upper low which has
resided across the region over the past couple of days continues
to slowly spin in place. A cold moist boundary layer airmass
continues to produce pockets of light snow and with very cold
surface temperatures anything that falls is sticking to all
surfaces. With the low centered on top of northern Utah very weak
forcing will likely limit coverage this morning...however as this
low begins to slide east a light northwesterly flow should allow
for a better chance of snow across northern and central Utah. Have
lowered probability of precipitation this morning into the chance category then maintained
likelies this afternoon and evening. If snowfall does indeed
become organized late this afternoon and evening may need a Winter
Weather Advisory for impact despite only minor accumulation.
As this low slowly slides off to the east rising middle level heights
and warming temperatures aloft should allow valley inversions to
slowly become established through the middle portion of the week.
This will significantly limit warming across the valleys while
the higher terrain should see temperatures rebound Tuesday into
Long term (after 00z thursday)...late Wednesday starts with a ridge
centered over the County Warning Area...with strong low level inversions likely in
place. Even with the ridge shifting east of the area Wednesday
night...another cold and mostly clear night should be on tap.
Southwesterly flow begins to increase significantly on Thursday
ahead of an approaching Pacific trough. This trough gets close
enough by 00z Friday that both mixing and afternoon high
temperatures should increase a fair amount in many valley
locations Thursday afternoon. How quickly this trough progresses
across the Great Basin will determine whether Thursday night is
also warm and well mixed. Have generally trended toward the
slower/warmer solution for Thursday night...as these troughs have
had a tendency to slow down as they approach the area...especially
when they are trying to split on our doorstep.
Yes...this trough late in the week could yet again be another
splitting storm as it moves through Utah. The 00z runs of both the
GFS and European model (ecmwf) came in significantly weaker and less organized with
this storm...as one piece of the storm digs into Arizona late
Friday into Saturday...while another piece remains north over
Montana. Have made relatively few changes to the forecast...as the
previously forecast slight chance probability of precipitation Friday seem adequate to
cover this potentially weak storm.
Whether this storm is fairly consolidated or not...models have
generally been keeping the pattern progressive heading into next
weekend...with a ridge re-building over the region for Saturday
and Sunday. Temperatures those days will be largely dependent on
how strong the late week storm turns out to be...and how cold the
airmass is that accompanies it. Despite inversions...the highs for
next weekend could be warmer in the valleys if a weaker/warmer
storm helps replace the cold low level airmass that is currently
Aviation...ceilings at the slc terminal will likely decrease
through the day...remaining below 7000ft through much of the taf
period. The chance of snow showers will increase through the
day...with shower activity expected to peak between 19z and 23z.
MVFR conditions are likely under any of these showers...and IFR
conditions are possible under the heavier storms. Showers could
cause erratic winds...but in general winds should increase from
the north starting around 15z-18z.
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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)