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fxus65 kbou 230927 

Area forecast discussion
National Weather Service Denver/Boulder Colorado
327 am MDT Wed Oct 23 2019

Short term...(today and tonight)
issued at 319 am MDT Wed Oct 23 2019

An upper level trough, in northwest flow aloft, will affect the
area later this aftn thru tonight. At the sfc, one surge of cooler
air will move into nern Colorado this morning, while a stronger surge
moves in late this aftn into the evening hours.

Cross-sections show moisture affecting the mtns thru this aftn,
with improving lapse rates, so will see areas of generally light
snow. At lower elevations, can't rule out a chc of showers this
morning near the Wyoming border, and again by aftn, as the secondary
surge of cooler air moves across. As for highs over nern Colorado will
keep readings in the 50s.

For tonight, the upper level trough will move south southeast
across the region. Most of the models, show favorable northeast
upslope component along and east of The Divide, along with
deepening moisture and favorable lapse rates. In addition, an
area of mid level qg ascent, will affect the area as well. Thus
one would expect precip to increase over the higher terrain and
across the I-25 urban corridor this evening with rain quickly
changing to snow at lower elevations. The only model which doesn't
support this scenario is the hrrr, which has more of a downslope
component and drier air in the lower levels. Thus it generates
much less precip across most of the area. Since the CMC, ECMWF,
NAM and GFS are in relative good agreement have decided to ignore
the drier hrrr.

As for snow amounts, the heaviest looks to be along and south of
I- 70 over the higher terrain and across the Palmer Divide. Over
the I-25 corridor most of the accumulating snow will be over
southern areas ("2-4") while further north towards Fort Collins
amounts may end up under an inch. By late tonight, the snow
should gradually end from north to south.

Long term...(thursday through tuesday)
issued at 319 am MDT Wed Oct 23 2019

The weather event that will bring snow to the region starting
Wednesday will wrap up Thursday morning, but not without impacting
your morning commute.

Model consistency is good through 72 hours with the upper trough
over the southwest portion of the state by 12z Thursday. A surface
high to the north will help to keep cyclonic north to northeast
flow at the surface aiding in prolonged upslope conditions into
the early hours on Thursday. By 9 am on Thursday the trough will
shift south and increasing northerly flow with qg subsidence will
help to dissipate snow from the north to the south. Some areas
across the southern Front Range foothills and Palmer Divide could
see light snow continue into the early afternoon hours given
northerly flow helping with orographic influence and some
lingering moisture. Clouds will dissipate by the afternoon hours
with temperatures getting into the lower 40s.

For Friday, upper level north to northwesterly flow will return
with dry conditions lasting through Saturday. Strong warm advection
Friday will help to bring temperatures back into the 60s with
some mid-level moisture bring partly cloudy conditions.

The next system to impact the region will arrive Sunday morning in
the form of a cold front that will pull cooler northerly flow and
moisture southward. At the synoptic level a low over northern
Canada will have a large trailing trough extending back into Idaho
that is currently projected to push south-southeast through the day Sunday.
There isn't much consensus within models or ensembles with regards
to the path of the trough. Some models will bring colder temps and
precipitation early Sunday with a dry pattern following into the
start of next week while others prolong the trough impacts with a
slower progression keeping a cooler and wetter pattern in place.
Will maintain a blend of model solutions for now with temps
trending cooler and pops slightly higher behind the trough on
Sunday and extending into the start of next week.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 319 am MDT Wed Oct 23 2019

First cold front was already moving thru cys early this morning.
This front will probably reach dia at 12z with gusty north winds
for a few hours. Another surge will moves across by mid to late
aftn with another round of gusty north to northeast winds. As this
front moves across there could be a chc of rain showers. By this
evening, should see an increasing chc of showers which will change
to all snow by 7 PM or so. Periods of snow will continue thru
midnight or so and then taper off late tonight. Accumulations at
dia will be up to 2" with higher amounts at apa and bjc. Should
see a gradual decrease in ceilings and visibilities by early


Bou watches/warnings/advisories...
Winter Weather Advisory from 6 PM this evening to 8 am MDT
Thursday for coz034-035-037-039-040.

Winter Storm Warning from 6 PM this evening to 8 am MDT Thursday
for coz036-041.


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