FXUS65 KBOU 180405 CCA
Area Forecast Discussion...CORRECTED
National Weather Service Denver/Boulder CO
905 PM MST Sun Dec 17 2017
Issued at 840 PM MST Sun Dec 17 2017
Strong mid-level subsidence and drying presently over the forecast
area and aligned with the 500 mb trough axis is clearly evident
on GOES-16 6.95 um WV imagery. Mid-level warming has also strengthen
the mtn top stable layer producing a mtn wave along the Front
Range. The cross mtn wind component does not appear to be all that
strong attm, and therefore ridge top and upper east slope winds
generally have remained on the light to moderate side (in the
20-40kt range). However, still believe speeds will increase
especially in high wind prone areas such as up around timberline
and along the Peak-to-Peak highway over the next few hours with
a near mean state critical layer passing over the area on the back
side of the exiting trough. Could see peak gusts to 50 kts in the
high exposed area through midnight. After which time, should
see winds gradually weaken with the mean state critical layer
moving east, and the mtn wave relaxing with weakening of the mtn
top inversion. On the plains, a strong sfc based inversion and a
weak pressure gradient will mean light breezes and hazy conditions
for much of the night.
.SHORT TERM...(This evening through Monday)
Issued at 125 PM MST Sun Dec 17 2017
Stratus deck has been dissipating rapidly early this afternoon
with just few patches of low clouds over Weld and Morgan counties.
The upper level trof will sweep across Northern Colorado through
this evening with skies becoming mostly clear. As the upper trof
passes, there will be an uptick in winds over mountains and east
slopes with stronger wind gusts this evening with increased
subsident flow. Dry and warmer day on Monday under a weak west to
northwest flow aloft. Temperatures will rebound back into the 50s
across lower elevations.
.LONG TERM...(Monday night through Sunday)
Issued at 330 PM MST Sun Dec 17 2017
Models have upper ridging moving into the CWA Monday night
...with a weak closed low south and southeast of Colorado. Weak
west-northwesterly flow aloft is progged Tuesday and Tuesday night.
Increasing west-southwesterly flow aloft is expected Wednesday
and Wednesday night as an upper low strengthens and moves
southeasterly into Utah by 12Z Thursday morning. There is benign
synoptic scale energy progged on the QG Omega fields for Monday
night into Wednesday morning. Upward energy moves in ahead of the
upper trough/closed low the rest of Wednesday and Wednesday night.
The low level winds are fairly weak through much of the period
and should adhere to normal diurnal trends. After midnight
Wednesday night, a cold front is progged into northeast Colorado
with pretty strong northeasterly winds behind it. Moisture-wise,
some of the models have a bit of upper and mid level moisture
around Monday night into Wednesday, but nothing significant. There
is no measurable precipitation noted on the QPF fields. No pops.
For temperatures, Tuesday's highs are similar to Monday's.
Wednesday's highs are 2-6 C warmer than Tuesday's. For the later
days, Thursday through Sunday, models have an upper trough/closed
low move across Colorado late Thursday and Thursday night. There
is a tad of short wave ridging behind it early Friday. By Friday
night through the weekend into early next week, a mean long wave
trough is progged to cover much of North America. Thursday and
Friday's highs will be below seasonal normals, with Saturday's and
Sunday's well below normals. I suppose winter had to finally
arrive over the forecast area. Some snow is possible on Thursday,
Saturday and Sunday for the plains, and all four days for the
mountains. Right now, the snowfall does not look significant, but
we are still several days out.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 840 PM MST Sun Dec 17 2017
Light drainage (south-southwest) winds of 4-12 kts will prevail
across the Denver metro area for the remainder of the night.
Although near the base of the foothills, such as at KBJC, westerly
winds may gust to 20kts at times through 08z tonight. Otherwise,
VFR conditions will continue beneath an increasing cover of high
altitude cirrus clouds.
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