Winter Storm and High Wind in Colorado, September 8 to 10, 2020

Area Forecast Discussion
National Weather Service Pueblo CO
505 AM MDT Tue Sep 8 2020

.SHORT TERM...(Today and tonight)
Issued at 504 AM MDT Tue Sep 8 2020

The advertised winter storm has finally arrived to southern
Colorado, but the biggest impacts are going to be delayed to the
afternoon and evening. The cold front passed at around 11pm on
Monday, delivering gusty winds, but not wind gusts strong enough to
reach the High Wind Warning criteria. Wind gusts across the plains
are around 30 to 40 knots, therefore we have cancelled the High Wind
Warning for southern El Paso, Pueblo, Otero, and Crowely Counties.
Light rain has been observed across the I-25 corridor this morning,
which aligns well with the previous forecast. The upper level low
pressure center is on track to propagate over eastern Utah and
western Colorado as the day progresses. Once it reaches that point,
the low stalls during the afternoon, which is when the best
isentropic upglide and orographics will be in place. The stalled
position of the low will be an efficient orientation for orographic
lift over the Continental Divide.  The surface to 700 hPa flow east
of the eastern San Juan mountains will be almost due northeast to
east across the forecast area, which brings another element of
orographic lift for all of the mountains. During the early
afternoon, banded precipitation is expected to develop over the
mountains, spreading over the lower elevations, which is where snow
levels will be critical for who will see rain and who sees snow.
During the afternoon, places like the San Luis Valley and the I-25
corridor (south of northern El Paso County) are going to have rain
falling, but by sunset, the rain will transition to snow. During the
overnight, some sleet seems likely over the eastern plains, east of
Pueblo, Huerfano, and eastern Las Animas Counties. Over the lower
elevations, snow is expected to melt on contact on the roads. The
best accumulations will be on grass. The heavy snow will accumulate
on the trees, which could cause broken limbs and power outages.

A hard freeze is expected over northern El Paso County by the
afternoon and will stay below freezing until tomorrow. By night
fall, the San Luis Valley and the rest of the I-25 corridor will be
below freezing for multiple hours, creating a hard freeze.

.LONG TERM...(Wednesday through Monday)
Issued at 504 AM MDT Tue Sep 8 2020

Expect active weather to continue at the start of the period, as
the large upper level low will remain just to the west of the area.
Decent chances for more widespread precip development are also
expected given the southerly flow and stream of energy out ahead of
this system, strong asentropic ascent still focused into southern
Colorado, as well as an abundance of moisture in place. With this
setup in place, anticipate snow to really be focused over the
southern mountains on Wednesday morning, with mainly lighter snow
continuing for the lower elevations especially along and west of the
I-25 corridor. A mix of snow, sleet, or rain may remain possible
further east over the plains, especially along a Kim to Lamar line.
Ptypes do remain tricky in this location given some variability to
the extent of the isentropic ascent and placement of mid level
baroclinic zone. Nonetheless, various guidance is hinting at this
possibility, with forecast soundings showing a distinct warm nose
aloft. Closer to the CO/KS border, have high confidence that rain
will be the main precip type. While only lighter snow amounts are
expected over the lower terrain in the morning, some snow covered
roads will remain possible. However, throughout the morning, drier
air begins to move in with most locations losing crystals by midday.
Additionally, warming anticipated throughout the day into the
evening will all help wintry precip to be less likely over the
plains later in the day on Wednesday.

Have not really adjusted snow amounts for the southern mountains on
Wednesday and into Wednesday night, but will need to continue to
monitor later trends. Some guidance still showing much higher
amounts over the eastern San Juans, as the upper low to the west
slowly begins to lift northeast Wednesday night. Also have not made
any changes to the winter headlines on Wednesday, though do have
similar concerns for higher amounts and a longer duration for
heavier snow across the Mosquito Range and Sawatch mountains. Don't
have confidence at this time, but could see the winter storm warning
in effect for these locations needing to be extended possibly into
Wednesday night. Over the plains during this time, some light precip
development is possible but with lacking deeper moisture in this
location, expect mainly liquid precip. Though another cold night is
expected Wednesday night, conditions should remain warm enough to
limit any ice potential. Will continue to closely monitor this
though.

This system finally begins to lift north/northeast Thursday into
Thursday night, with precip chances lowering for all locations. With
cyclonic flow aloft and upper low/trough axis swinging through on
Friday, surface trough developing over the eastern plains could
support some showers and maybe some thunderstorm development.
However, at this time, the higher focus looks to be to the east.
Drier weather with a warming trend then expected into the weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 504 AM MDT Tue Sep 8 2020

KALS:

VFR conditions are expected over KALS throughout the morning and
part of the afternoon, but by mid afternoon, showers will begin over
the forecast point, transitioning to snow by around 00Z. When the
low clouds form MVFR conditions will form, decaying to IFR in the
evening. Those conditions will continue throughout the rest of the
forecast period.

KCOS:

Gusty northerly to northeasterly winds throughout much of the
forecast period, decreasing in strength during the overnight. MVFR
caliber CIGS have already developed over the terminal and will only
decrease throughout the day. Rain is expected to form during the
late morning and will transition to snow during the afternoon,
around 2300Z. IFR conditions are expected to begin this evening and
last through the overnight, with the potential for LIFR conditions.

KPUB:

Gusty northeasterly winds are expected throwout the forecast
period, beginning to lighten during the early morning on Wednesday.
Low clouds have already formed over KPUB, which will only continue
to lower throughout the forecast period. MVFR conditions are
expected throughout the morning and afternoon, but by the evening
IFR conditions are expected with the onset of rain showers. Light
snow is possible during the overnight over KPUB, as well as spotty
LIFR conditions.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Freeze Warning from midnight tonight to noon MDT Wednesday for
COZ083-086-089-093.

Winter Storm Warning until noon MDT Wednesday for COZ058>063-076-
081-082-084.

Winter Storm Warning from noon today to midnight MDT Wednesday
night for COZ072>075-077>080.

Freeze Warning from 9 PM this evening to noon MDT Wednesday for
COZ069>071-085-087-088-094.

Winter Storm Warning from 6 PM this evening to noon MDT
Wednesday for COZ069>071-087-088.

Winter Weather Advisory from 6 PM this evening to noon MDT
Wednesday for COZ083-086-094.

Winter Weather Advisory from 9 AM this morning to noon MDT
Wednesday for COZ085.

Winter Storm Warning from noon today to 6 AM MDT Thursday for
COZ067-068.

Winter Storm Warning from noon today to noon MDT Wednesday for
COZ064>066.

Freeze Warning from noon today to noon MDT Wednesday for COZ084.

&&

SHORT TERM...SKELLY
LONG TERM...RODRIGUEZ
AVIATION...SKELLY

Hazardous Weather Outlook
National Weather Service Pueblo CO
558 AM MDT Tue Sep 8 2020

COZ058>089-093>099-091200-
Western Mosquito Range/East Lake County Above 11000 Feet-
Leadville Vicinity/Lake County Below 11000 Feet-
Eastern Sawatch Mountains Above 11000 Feet-
Western Chaffee County Between 9000 and 11000 Feet-
Central Chaffee County Below 9000 Feet-
Western Mosquito Range/East Chaffee County Above 9000 Feet-
Saguache County West of Continental Divide Below 10000 Feet-
Saguache County East of Continental Divide Below 10000 Feet-
La Garita Mountains Above 10000 Feet-
Upper Rio Grande Valley/Eastern San Juan Mountains Below
10000 Feet-Eastern San Juan Mountains Above 10000 Feet-
Del Norte Vicinity/Northern San Luis Valley Below 8500 Feet-
Alamosa  Vicinity/Central San Luis Valley Below 8500 Feet-
Southern San Luis Valley-
Northern Sangre de Cristo Mountains Between 8500 And 11000 Feet-
Northern Sangre de Cristo Mountains Above 11000 Feet-
Southern Sangre de Cristo Mountains Between 7500 and 11000 Feet-
Southern Sangre de Cristo Mountains Above 11000 Feet-
Northwestern Fremont County Above 8500 Feet-
Western/Central Fremont County Below 8500 Feet-
Wet Mountain Valley Below 8500 Feet-
Wet Mountains between 6300 and 10000 Feet-
Wet Mountains Above 10000 Feet-
Teller County/Rampart Range Above 7500 Feet/Pikes Peak Between
7500 And 11000 Feet-Pikes Peak Above 11000 Feet-
Canon City Vicinity/Eastern Fremont County-
Northern El Paso County/Monument Ridge/Rampart Range Below
7500 Feet-
Colorado Springs Vicinity/Southern El Paso County/Rampart Range
Below 7400 Feet-Pueblo Vicinity/Pueblo County Below 6300 Feet-
Walsenburg Vicinity/Upper Huerfano River Basin Below 7500 Feet-
Trinidad Vicinity/Western Las Animas County Below 7500 Feet-
Crowley County-La Junta Vicinity/Otero County-
Eastern Las Animas County-Western Kiowa County-
Eastern Kiowa County-Las Animas Vicinity/Bent County-
Lamar Vicinity/Prowers County-Springfield Vicinity/Baca County-
558 AM MDT Tue Sep 8 2020

This hazardous weather outlook is for portions of central...east
central...south central and southeast Colorado.

.DAY ONE...Today and Tonight

An early season winter-like storm will bring heavy snowfall
accumulations to mountains, some heavy accumulations to the
mountain valleys, and lighter accumulations to the plains.
Accumulations over the lower elevations will be highly variable
due to snow melting on contact. During the overnight, mixed
precipitation is possible over the far eastern plains

A hard freeze is expected over the San Luis Valley and along and
just to the east of the I-25 corridor on Wednesday morning.
Freezing temperatures will also be possible across the southeast
plains Wednesday morning as temperatures briefly dip to around
freezing. A hard freeze across the San Luis Valley and along the I-
25 corridor could cause crop damage especially for the warmer season
crops. Exposed irrigation and water pipes could freeze or be
damaged.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Heavy snow is expected to continue over the mountains, and some of
the high valley locations Wednesday and Wednesday night.
Additionally, light snow is still expected over the lower elevations
Wednesday morning, along and west of the I-25 corridor. To the east,
especially along a Kim to lamar line, a mix of snow, sleet, and rain
is possible.

.SPOTTER INFORMATION STATEMENT...

Weather conditions that meet reporting criteria for spotters will be
possible today and tonight across the entire region.

SKELLY/RODRIGUEZ