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000
FXUS65 KPUB 030606
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1106 PM MST Sat Dec 2 2023

.UPDATE...
Issued at 637 PM MST Sat Dec 2 2023

After a quick look at cross-sections and mountain wave parameters,
have upgraded the existing High Wind Watches to Warnings and
started them around 03z for the mountains and 06z for the adjacent lower
elevations. Latest 00z HiResW FV3 shows best mountain wave
parameters from 06z through 15z before the upper trough passes
and event transitions to a deep mixing mechanism for high wind
transport to the surface. No changes for our Pikes Peak region
where best parameters are in place from from 03z-12z. While not
all locations in the warning will see damaging gusts,
probabilistic HREF data shows 60-100% of members are exceeding 58
mph along the lower eastern slopes from roughly 11 PM to 8 AM.
There is a bullseye of 50-70 percent of members showing gusts 75
mph or greater in the lee of the Sangre De Cristo mountains north
of highway 160. Of course mountain wave high winds can be
notoriously difficult to pin down spatially, so while the risk
will likely be localized to the lower eastern slopes spreading
into the west sides of the adjacent lower elevations, a broad
brush approach is needed with highlights.

Snow is ongoing across the central mountains and will continue to
ramp up overnight. Other change to grids was to include the lower
eastern slopes of the Sawatch range in a Winter Weather Advisory
for this event. While snow totals will be lighter than the peaks
to the west, high res models show gusts nearing 75 mph spreading
down the eastern slopes which will lead to blowing snow and poor
visibility at times on the higher sides of this zone. Therefore
have expanded the advisory southward to include these areas. -KT

&&

.SHORT TERM...(This evening through Sunday)
Issued at 222 PM MST Sat Dec 2 2023

Key messages...

- Becoming very windy mtns and east slope of mtns tonight and
lasting through tomorrow.

- Winds exceeding high wind warning criteria likely east slopes
Ramparts and Pike Peak, with warning also issued for Sangres, Wets,
Wet mtn valley region and Huerfano county.

- Upgraded to winter storm warnings for central mtns.

Currently...

Snow continues to fall across the central mtns per web cams. winds
have ramped up across a good part of the region as many areas of the
mtns are in the 30 to 50 knt range with 30 to 40 knts plains. Given
the downslope component, temps are relatively mild with readings
around 50F parts of the plains with 40s up in El Paso county. Temps
were in the 30s valleys while higher mtns were in the single digits
to negative single digits.

Overview...

An active 24 hours is in store for the forecast area. Main impacts
will be winds nearly all areas and heavy snow over the central mtns.
It appears from web cams that some hefty snowfall amounts have
already occurred in the c mtns and guidance is indicating more heavy
wind driven snow will occur mainly later tonight and tomorrow
morning. The other concern will be strong winds developing over a
good part of the area. Some of these winds will reach high wind
criteria, especially east slopes of Ramparts and Pikes Peak, and all
of the Sangres, Wets, Wet mtn valley and Huerfano county. This is
all do to a strong jet pushing southwest in the NW flow aloft

Tonight...

Main concern tonight will be winds and snow. Although winds are
going to pick up over all of the higher terrain, the main concern
will be over the east slopes of the rampart range/Pikes Peak this
evening and lasting into tomorrow morning. A narrow band of
potentially damaging winds is expected on the east slopes and a high
wind warning has been issued for this area. Late tonight, the
southern mtn region will get into the action as winds are expected
to reach high wind warning criteria, especially on the WEST side of
the Wet mtn valley. As for the rest of the southern mtns,
probabilities are not as high to hit MTN HIGH WIND WARNING
criteria, but the risk is enough to warrant a watch.

Latest guidance has ramped up snowfall for the central mtns and have
upgraded the central mtns to a winter storm waring. 10 to 20 inches
of snow is likely through tomorrow. The higher valleys of Lake
county will likely see an additional 3 to 6 inches of snow.

Tomorrow...

Damaging wind threat for the Pikes Peak region should diminish,
although strong winds will continue and actually become more
widespread during the morning hours.

The damaging wind threat for the s mtns, Wet Mtn valley and Huerfano
county will increase, especially during the morning daylight hours,
as the jet punches through and the best mtns wave parameters are in
place. It should be noted that the west side of the Wet Mtn valley
may see damaging winds while the east side of the valley may not see
all that much strong wind.

Heavy snow will continue over the c mtns into late morning, with
snow then decreasing. it will remain windy over the higher terrain.

A cold front will push down the plains from late morning into the
afternoon hours, with the winds shifting to a more northerly
component, with winds ramping down asa the afternoon progresses over
the lower elevations.

Some snow showers will be possible over the lower elevations of the
Pikes Peak region from mid morning to early afternoon tomorrow.
/Hodanish

.LONG TERM...(Sunday night through Saturday)
Issued at 222 PM MST Sat Dec 2 2023

Key Messages:

 - Dry and warm for much of next week.

 - Medium to high (40-79%) confidence in a storm system impacting
the area during the end of the work week and into the weekend.

Monday - Thursday: For much of the upcoming week, a quiet stretch of
weather is in store for southern Colorado. Synoptically, an
anomalously strong ridge of high pressure will build and expand over
the region. This feature will bring an increase in descent to the
area, and given that, dry conditions are expected for southern
Colorado. Looking at temperatures, given the strong ridge, and at
least modest downsloping winds at times, there is very high (80-
100%) confidence that much of the area will be 10-20°F above
seasonal values, which both deterministic and ensemble model
guidance strongly support.

Friday - Saturday: For the end of the week and into the weekend, the
start of a pattern change is expected to take place. A troughing
pattern will begin to develop across the western US and start to
push over the region throughout this period. There is still some
timing differences in the ensemble model guidance, but overall, the
model guidance begins to push the troughing eastward during the
Friday period. As this system pushes towards and over the area,
forcing and support will increase in response, and precipitation
chances will become heightened from west to east, particularly along
the mountains. With that all said though, timing is not the only
detail that still needs to be ironed out. Uncertainty exits in the
location, strength, and overall structure (think open wave vs cut-
off low) of the system, all of which will play big roles in how
precipitation, and ultimately any impacts, will materialize. Despite
some uncertainties, general consensus from ensemble model guidance
is leading to at least medium to high (40-79%) confidence in this
overall troughing pattern evolution. As for temperatures, Friday
will be the warmest day as downsloping westerly to southwesterly
winds materialize, leading to another day where temperatures will be
around 10°F above seasonal values. Then Saturday will be much
different, as the system shoves a cold front southward, dropping
temperatures across southern Colorado.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1052 PM MST Sat Dec 2 2023

VFR conditions are expected to prevail for all TAF sites (KALS,
KCOS, and KPUB) throughout the forecast period. Winds will be
synoptically driven at all terminals. There will be strong and gusty
winds out of the northwest for both KCOS and KPUB through the
morning hours, with a lull later tonight and then an increase again
towards the morning hours. There will be some WSCONDS at both
terminals through around 12Z due to elevated speed shear between
FL010 and FL020. At KALS, winds will be strong and gusty during the
daytime hours from the SW initially, and then come around to the
northeast and weaken by later in the evening tomorrow, towards the
end of the forecast period.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 PM MST Sunday for COZ058-060.

Winter Weather Advisory until 5 PM MST Sunday for COZ059-061.

High Wind Warning until 5 PM MST Sunday for COZ072>075-079-080.

High Wind Warning until 5 PM MST Sunday for COZ077-078-087.

High Wind Warning until 8 AM MST Sunday for COZ081-082-084.

&&

$$

UPDATE...KT
SHORT TERM...HODANISH
LONG TERM...SIMCOE
AVIATION...STEWARD