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fxus65 kbou 220920 

Area forecast discussion
National Weather Service Denver/Boulder Colorado
320 am MDT Tue Oct 22 2019

Short term...(today and tonight)
issued at 314 am MDT Tue Oct 22 2019

Northwest flow aloft will remain over the area today and tonight.
Moisture embedded in the flow has combined with favorable
orographic component, to produce areas of light snow early this
morning, in the mtns. There may be a lull in activity later this
morning thru mid aftn, however, another surge of moisture is fcst
by late aftn into the evening hours. Thus should areas of light
snow increase by late afternoon and continue. Eslewhere it will
be dry thru the aftn with warmer temperatures across nern Colorado.

For tonight, there is some potential for high winds, in the
normal windy areas, across the foothills. Cross-sections show
some amplification of mtn wave between 03z and 09z with component
along winds around 50 kts. Thus may see a few gusts up to 75 mph
overnight. Meanwhile late tonight a cold front will be near the
Wyoming-NE border with stratus possibly developing by 12z.

Long term...(wednesday through monday)
issued at 314 am MDT Tue Oct 22 2019

The big story in the extended is the system that will bring snow
and colder temperatures to the region starting Wednesday and lasting
into Thursday.

The synoptic set-up has an upper low pushing northeast out of the
Great Lakes and into southern Ontario with a trailing shortwave
moving southeast through the northern plains Wednesday. Models are
in general consensus on the path of the shortwave, with the
Canadian and ec with a stronger westerly pull for the trough. The
ec keeps upslope flow along the foothills longer with this outcome
and a strong closed low at 700 mb. We will have to watch the
progression of the trough as it makes its way southward to see
where the pattern will shift. Overall however, models are
indicating accumulating snow for the mountains and adjacent plains
for Wednesday evening into Thursday afternoon. Models have
trended slightly earlier with the evening commute on Wednesday
possibly impacted. The bulk of the forcing arrives Wednesday
evening with increased qg and an upper level jet. Moisture
increases with the help of the jet and surface front that drops
out of the north late afternoon on Wednesday. This will help to
dissipate the strong downslope winds from earlier in the day and
usher in cooler air along with the increased mid and upper level
moisture. Model cross-sections indicate areas of csi between 00
and 06z Thursday that will increase the potential of banded
precipitation overnight Wednesday. As mentioned before colder
temperatures will accompany the front with -12c at 700 mb possible
by early Thursday morning. This will help to support snow
production for the region. One of the biggest questions is if/when
the moisture and colder air lines up with the best lift to create
the biggest impact for area travelers Wednesday night. Current
model projections show increased probability for this scenario to
occur with model upper air soundings showing column saturation by
22z (16l) with good dendrite growth potential. For the higher
terrain orographic light snow will be ongoing Wednesday with
intensity increasing with the onset of better synoptic lift
Wednesday afternoon and early evening. I'm going to go ahead and
issue a Winter Storm Watch for the southern foothills and Palmer
Divide given the potential for more snow due to banded
precipitation and prolonged upslope. Other areas such as the
northern foothills to include the higher elevations of Boulder
County, the central mountains, and Park County could reach
advisory criteria.

The shortwave trough will continue to push south as the main
piece of energy slips into northern nm by noontime on Thursday.
This is when most models end precipitation for the region as qg
subsidence increases and northwest flow dominates once again.
This will return flow to more downslope for areas along the base
of the foothills helping to warm temperatures into the upper 30s
to lower 40s by the late afternoon hours.

For Friday and into the weekend northwest flow will switch more
zonal with the onset of an upper ridge as an east-west oriented
trough makes its way slowly southward out of the northern plains.
This will keep the region dry Friday and Saturday and help
temperatures to rebound back into the upper 60s to lower 70s by
Saturday. By Sunday, models start to diverge on the placement of
the trough which in turn impacts the overall synoptic pattern.
However, there could be another chance for some colder
temperatures and precipitation for the region with the passage of
a surface cold front Saturday into Sunday. Stay tuned for more


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 314 am MDT Tue Oct 22 2019

VFR today and tonight. Drainage winds early this morning will
gradually become more westerly by 16z. By 19z exepct a more
northwest component with a few gusts up to 25 mph thru 00z. By
early evening winds will become more westerly and then shift to
drainage before 06z.


Bou watches/warnings/advisories...
Winter Storm Watch from Wednesday evening through Thursday
morning for coz036-041.



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