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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
1121 am MST Wednesday Nov 25 2015

issued at 1057 am MST Wednesday Nov 25 2015

The cold front is through all but the southern half of Lincoln
County at present. There is some stratus trying to move into the
County Warning Area from the northern Colorado border right now. Latest models
point to a prolonged light snow over much of the County Warning Area until at
least Friday morning. Soundings and cross sections continue to
show the potential for freezing drizzle this evening...especially
over the eastern half or two-thirds of the plains. We went with
advisories for the foothills and all the plains from this evening
into Friday morning. The minor ice accumulation could be
problematic. Temperatures will be steady of slightly falling the
rest of the afternoon.


Short term...(today and tonight)
issued at 440 am MST Wednesday Nov 25 2015

Forecast area is still under a relatively warm and dry southwest flow
aloft at the present advance of a deep closed low centered
over Nevada. Best deep layer qg ascent upstream over Utah...but in
past few hours large scale lift has begun over northwest Colorado as
evident by the expanding middle/upper-level cloud Leaf over the area.
However main attention is on the Arctic front advancing southward
through east central Wyoming atom. Front already appears to have
moved past Torrington and was probably no more than hour or two away
from reaching Cheyenne. Model surface/850mb temperature and wind fields show
the front reaching the southeastern Wyoming/northestern Colorado border by 12z...earlier than
previously fcsted. With pressure falls associated with a surface trough
along the Front Range...there's really nothing to slow its progress.
Mesoscale models show the front blowing through feet Collins and
Greeley between 13z-14z and into the Denver area by 15z...about an
hour or two ahead of schedule. Its arrival will be marked by a shift
to gusty north-northwesterly winds...but not much in the way of cloud development
initially as the local boundary layer is quite dry. Then...with
middle/upper level lift increasing and surface-700 mb winds turning
northeasterly this afternoon...should see fairly quick development in low/mid-
level clouds over/along the Front Range beginning up near the
Wyoming border. Would expect to see isolated snow showers forming
over the northern Front Range after 21z.

Furthermore should see maximum temperatures reached before noon on the plains..
if not by middle-morning with the earlier arrival of the front...with
temperatures falling at a rate of 2-3 degrees per hour during the afternoon.

Tonight is when things come together including a cold and relatively
moist northeasterly upslope flow below 700 mbs will be overlaid by a
relatively dry and warmer southwesterly flow aloft. With surface temperatures on the
plains hoovering around -10c this evening...there's a reasonable
chance that light snowfall developing early this evening will become
mixed with light freezing drizzle. As the cold air deepens
overnight...should see the mix change over to all snow along the
Front Range/I-25 urban corridor around midnight...but continue
overnight farther out across the plains. Accumulation rates for both
snow and ice on the plains will be slow due to the lack of strong
forcing or orographics. But could see anywhere from 1-3 inches of
fluffy snow along the Front Range by morning. Farther out across the
plains...snow accums by morning probably no more than an
inch..together with a thin glaze of ice in some areas. The high
country should see a steady increase in snowfall through the
evening...but east facing slopes of the Front Range likely to see
the best snow accumulation overnight...due mainly to orographic
forcing. Could see anywhere from 2 to 4 inches of snow by
morning...with the heavier amts roughly north of I-70. The park and
Gore ranges in western Jackson County could also see similar
amounts. See lows tonight dipping into the upper teens everywhere.
Keep in mind areas west of the Continental Divide should not feel
much impact from the surge of Arctic air on the plains.
winter weather highlights at this time. But should the freezing
drizzle become heavier and/or more widespread highlights may be

Long term...(thursday through tuesday)
issued at 440 am MST Wednesday Nov 25 2015

It will be a wintry Thanksgiving day across Colorado with the
closed low across western Utah and a strong southwest flow aloft.
Arctic airmass will be well entrenched over the northeast plains
with readings only in the upper teens and lower 20s across lower
elevations. Moisture depth appears deep enough for all snow over
the Front Range but still shallow enough for still a mix of
freezing drizzle and light snow on the far northeast plains. By
Thanksgiving afternoon precipitation type should be all snow over the NE
plains as moisture depth increases. Given only weak ascent and
high stability only expecting light amounts up to 2
inches...highest amounts in and near the foothills during the day. Will
continue to nudge probability of precipitation upwards on Thursday and drop temperatures a
few more degrees.

The close low begins to weak and somewhat shear apart during the
Thursday night and Friday time period. The NAM appears the most
extreme in this shearing while the GFS/European solutions keep the
low a bit more together but with some retrogression in the low on
Friday. This will take more of the energy and moisture away from
Colorado leaving cloudy skies...diminishing snow and mainly
flurries. Additional accumulations will be an inch or less on
Friday. Total accumulations for this 2 day event look to be around
1-2 inches on the far NE plains...2-5 inches across the Front
Range corridor...5-10 inches over the foothills and higher east
slopes. West of The Divide...amounts will be lower and in the 2-7
inch range.

There is still a lot of discrepancy in the models for the weekend
in how the system moves across the region. Confidence in any one
solution remains low. Generally most of the energy is taken into
Wyoming except for the Canadian solution which takes a substantial
piece of energy across Colorado on late Sunday and Monday. Will
still keep low probability of precipitation for the weekend with a very slow warming
trend. Have dropped temperatures a bit more feeling that it will be hard
to scour out the cold air. Temperatures will slowly climb back
into the 30s on Monday and possibly 40s by Tuesday. Will follow
the colder European guidance closer to the forecast.


Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1057 am MST Wednesday Nov 25 2015

Winds are due northeasterly at dia right now with models putting
them due easterly later this afternoon and much of tonight. No
normal drainage patterns for sure. The low ceilings are over the
northern Colorado border right now and the ceiling issues expected
at dia will likely develop in situ sometime late this afternoon
/early evening. Ceilings should be under ovc010 by 00-02z this
evening with visibilities under 1sm with -sn br and maybe -fzdz for a few
hours. This will continue (minus the -fzdz) overnight and much of
the Thursday.


Bou watches/warnings/advisories...
Winter Weather Advisory from 6 PM this evening to 8 am MST
Friday for coz035-036-038>051.



short term...Baker
long term...entrekin

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