Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 130959

Area Forecast Discussion
National Weather Service Denver/Boulder CO
259 AM MST Tue Feb 13 2018

.SHORT TERM...(Today and tonight)
Issued at 230 AM MST Tue Feb 13 2018

The closed upper low over central CA will track southwestward
off the southern CA coast by 00Z. As it does, increasing
subsidence will occur as an upper level ridge develops over
northwest CO. Snowfall will decrease over the northern mountains
as mid level warm air advection occurs. Snowfall later today will
be light and confined generally to the higher west facing slopes.
Will either cancel or allow the Winter Weather Advisory for zone
31 by 6 am. Across the I25 Corridor and Northeast Plains, latest
GOES satellite imagery this morning shows the edges of the
stratus deck gradually eroding away. Low clouds and patchy fog may
linger a bit, but around 12z window, skies should clear, then
mostly sunny and warmer for the rest of the day. For tonight,
NAM12 spatial cross-sections show a good mountain wave developing
after 06z. Sangster models output for from the NAM/GFS runs
suggests watch category regarding the wind gusts. No highlights at
this time but will make sure gusts at or above 60 mph will be
included in the grids.

.LONG TERM...(Wednesday through Monday)
Issued at 230 AM MST Tue Feb 13 2018

Active weather pattern will prevail Wednesday through the early
part of next week with a system affecting the area roughly every
other day. On Wednesday, a west-southwest flow aloft will prevail
over Colorado ahead of a pair of systems along the Pacific coast.
Main thing to watch will be windy conditions Wednesday. During the
morning hours, a mountain wave may be present and help accelerate
winds. Models showing warm air advection at ridge top level which
will help produce a stable airmass. The west-southwest flow aloft
isn`t the best direction for strong winds, but appears gusts to
50 to 70 mph will be possible in the foothills and mountains. It
will be warm Wednesday and with good mixing gusty winds will
spread onto the near by plains during the day.

Moisture will be shallow over the mountains Wednesday. A few
light snow showers can`t be ruled out, but no accumulation is
expected. Moisture will increase Wednesday night and Thursday.
Cold air advection will help to steepen lapse rates, leading to
better orographic lift. In addition to this, lift from the jet is
expected to enhance lift. Should see a good period of snow for the
mountains Wednesday night and Thursday. Light rain/snow will be
possible over the plains Thursday/Thursday night due to the jet
and upslope lift behind a cold front. Any precipitation across the
lower elevations is expected to be light.

Friday and Saturday look to be quiet weather days as the state
will be between systems. Saturday should be a warm and windy day
ahead of an upper level trough diving south across the Pacific

From Sunday on, forecast is highly uncertain. Models show a cold
front dropping south across the area Sunday ahead a Pacific
system. If the front pushes through early highs will only be in
the 30s, if not 50s will be possible prior to the frontal passage.
Models are even more divergent Monday. The ECMWF digs the Pacific
system south over Grand Canyon area, allowing arctic air to spill
into the area. Meanwhile the GFS keeps the trough north of the
state and shows a warm downslope flow. If the ECMWF is correct,
temperatures will struggle to get out of the teens, but if the GFS
is right highs in the 50s would prevail. Will split the
difference and go with highs in the 30s for Monday with a chance
for snow.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 230 AM MST Tue Feb 13 2018

IFR cigs with MVFR visibilities still an issue this morning. The
GOES imagery this morning shows the stratus deck over Denver
eroding on the edges and this trend should continue. May not see
the cigs/vsbys improve completely at the terminals by 12z. After
that, VFR conditions with no restrictions. Surface winds generally
light, but should start to increase from the west near the
foothills after 00z. This may result in some gusty westerly winds
at KBJC to around 20-25 kts this evening.





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