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fxus65 kbou 161052 

Area forecast discussion
National Weather Service Denver/Boulder Colorado
352 am MST Sat Dec 16 2017

Short term...(today and tonight)
issued at 352 am MST Sat Dec 16 2017

Today is starting off quite mild with current temps near 50f in a
few spots along the foothills where light westerly breezes have
held. Meanwhile shallow cold inversions have developed in low
lying areas. Surface analysis shows a cold front pushing south
through Wyoming and this front will push across the plains and
I-25 corridor later this morning. Significant cooling is lacking,
but there will be enough upslope and upper level cloudiness to
take several degrees off high temperatures today. We'll still be
running nearly 10 degrees above normal.

For tonight, low level moisture will continue to increase with
weak upslope behind the front. We expect narrow T/TD spreads with
areas of light drizzle and fog developing. Cross sections shows
warmer temperatures in the moist layer, now approaching only -8c
(no ice nucleation) so if we see light precipitation it will
likely be in the form of freezing drizzle versus light snow. At
this time, don't expect a widespread event but something to watch
is how much low level moisture can advect in. If freezing drizzle
does become more widespread, may see some impacts on elevated
surfaces like bridges and overpasses. Mountain areas will have a
hard time seeing any deeper moisture through tonight so we may be
able to totally remove chance of precipitation there.

Long term...(sunday through friday)
issued at 352 am MST Sat Dec 16 2017

Sunday morning will begin with some lingering fog, stratus and
possibly a little freezing drizzle as the cold airmass will remain
over the area. By midday, conditions will be improving as drier
air aloft mixes to the surface under weak flow and subsidence.
Temperatures will remain chilly through the afternoon. Monday
through Wednesday will see temeratures moderate as forecast models
show the flow aloft returning to northwesterly. During this time
period a flat upper ridge will be in place over the Rocky
Mountains. By Wednesday the models show a decent upper trough
moving over the Pacific northwest, on its way to Colorado. This
digging trough will contain a good shot of cooler Canadian air.
Quasi-geostrophic diagnostics shows a good period of dynamic
forcing over northern Colorado on Thursday as the upper trough
moves over the state. MOS guidance shows the high temperatures on
Thursday in the lower to mid 20s, with cooler temperatures then
continuing into the Holiday weekend. Will mention the chance of
snow on Thursday for now. The GFS and European model (ecmwf) have slightly
different solutions at this time, with trajectory being not quite
northerly enough for a good snow setup over northeast Colorado.
Later model runs still have the chance to improve the forecast
scenario, but the main story for now will be the big change in
temperatures from Thursday Onward.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 352 am MST Sat Dec 16 2017

Main aviation concerns are for low ceilings and potential for
light freezing drizzle after 06z tonight. Cold front will move
across the area switching winds around to the northeast around
16z. VFR conditions will persist today with only broken upper
level cloudiness, but then low level moisture will increase this
evening. Should see a lower IFR deck developing 06z-08z. Enough
low level moisture in weak upslope to warrant a chance of light
freezing drizzle and possible LIFR in fog/low ceilings. A light
ice glaze is possible especially on elevated surfaces if freezing
drizzle becomes more widespread.


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