133
FXUS65 KPUB 211753
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1153 AM MDT Sat Sep 21 2024

.KEY MESSAGES...

- Widespread showers developing from south to north through the day,
  with a second round spreading north and east across south central
  and southeast Colorado late this afternoon into tonight.

- Isolated to scattered thunderstorms, greatest coverage south of
  Highway 50, with a low confidence for strong storms this afternoon
  for the San Luis Valley and southern mountains.

- Snow levels may drop down to around 9000 feet tonight, though
  accumulations up to 10 inches to stay across the higher peaks
  above 10kft.

- System departs on Sunday with continued higher mtn snow and rain
  across the plains early which diminishes late morning through
  early afternoon.

- Another Frost or Freeze possible for the San Luis Valley Sun
  night/Mon AM.

&&

.SHORT TERM /THROUGH SUNDAY/...
Issued at 357 AM MDT Sat Sep 21 2024

Current water vapor imagery indicates upper low across southwestern
Arizona, with showers and thunderstorms spreading out ahead of the
system across central and into northeastern Arizona early this morning.
Further east, prefrontal trough across the southeast plains has breezy
southerly winds keeping dew pts in the 50s south and east of trough,
while north and west, dew pts have started to come down into the 20s
and 30s. The winds and associated mixing have kept temperatures up
with 3 am readings in the 50s and 60s across the plains, and in the
30s, 40s and 50s across higher terrain.

For today, latest models continue to indicate the Arizona upper low to
lift out into the Four Corners region by 00Z, with moisture and lift
increasing across south central and southeast Colorado within increasingly
diffluent southerly flow aloft. At the surface, a cold front, currently moving
across the Colorado/Wyoming border, will continue to push south across
the Palmer Dvd between 12Z-14Z, with breezy northerly winds of 15 to 30
mph in its wake across the southeast plains through the late morning,
with winds across the plains slowly turning more east to northeast through
the afternoon. With that said, we will see showers and thunderstorms
developing across the southern tier of Colorado this morning, with
precipitation increasing in coverage as its spread north across the
region through late morning and afternoon. Most of the latest high res
models, along with the latest SPC Day 1 outlook, are keeping the potential
for severe storms south of area in New Mexico. However, the HRRR does
continue to indicate a stronger line of storms and helicity swaths across
the San Luis Valley between 22Z Sat and 00Z Sun, which conceptually seems
plausible, with the expected strong shear and diffluence aloft as the upper
low moves across the Four Corners. Will need to monitor latest models
and trends for the potential of strong to severe storms across the southern
tier this afternoon. Southerly flow aloft across the region will keep snow
levels rather high aoa 11,000 feet through the day, though with
strong diabatic cooling, could see some light accumulations
down to 10,000 feet this afternoon.

A second round of precipitation, associated with the deformation band
of the upper low, will develop and spread north and east across south
central and into southeast Colorado later this afternoon and evening
with the low progged to lift out across the Pikes Peak Region early
Sunday morning. Best coverage remains over and near the higher terrain,
where easterly upslope flow will be maximized. Latest qpf have also
trended that way, with 1/2 to 1 inches expected over and near the
eastern mountains. Snow levels come down to around 9K feet this evening,
with the potential for some light accumulations at this level, however,
the most impactful snowfall will remain aoa 10-11K feet, with
5-10 inches of snow possible across the higher peaks of the
central mtns into the Pikes Peak region, where a winter weather
advisory remains in effect through the day Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Issued at 357 AM MDT Sat Sep 21 2024

Upper low lifts into NE CO by mid day Sunday with fairly extensive
showers and higher elevation snows across the southeast
mountains/plains early Sunday morning.  These should gradually
wane as the upper low lifts off to the northeast during the late
morning and afternoon. Pikes Peak region will still be under a
moderate rain/snow band early Sunday morning with snow levels
dropping to around 9000 feet early Sun morning.  There could be some
snow flakes mixing down to 8500 feet if diabatic cooling from heavy
precipitation can produce an isothermal layer. However, most
accumulation should stay above 10000 feet given the warmth of the
ground, with the higher peaks seeing up to 10 inches of
accumulation. The majority of southern CO will see rain which
will diminish through the afternoon, though lingering
instability behind the system will keep at least some isolated
showers through the afternoon across the mountains. Temperatures
will be quite a bit cooler with highs in the 50s to near 60
across the lower elevations, and a mix of mid 20s and 30s across
the mountain peaks and 40s to lower 50s for the lower mountain
communities.

Should be a cool night across southern CO behind the system
Sunday night with lows dropping into the 40s and upper 30s
across the plains. Conceptually this should bring a freeze to
the San Luis Valley with National Model Blends indicating a
50-80% probability of sub freezing temperatures, though
probabilities of a killing freeze (less than 28 degrees)
decreases rapidly to less than 20%. Guidance keeps lows for KALS
in the low to mid 30s. Will hold off on a freeze watch for now
given some discrepancies in guidance as some models keep dew
points up with the possibility of some fog formation. But
suspect some sort of frost or freeze highlight will be needed.

Temperatures rebound for Monday then another trough drops in from
the northwest for late Monday into Tuesday. EC is farther east than
its earlier runs from yesterday, and more in line with the
other long range models, but is still the strongest with
developing a cut off low across eastern CO/western KS by 00z
Wed. Canadian is similar with this scenario, while GFS is faster
and more open with the energy as it moves across CO. Ensemble
means are more open with the system. Moisture will be more
limited with this next wave, with isolated to scattered showers
possible Monday night into Tuesday. Did decrease pops some from
the National Model Blends which likely carries some influence
from earlier runs with the more western cut off low. A
reinforcing cool surge will knock temperatures back a few
degrees for Tuesday keeping readings below normal.

Upper ridge eventually returns for mid to late week with drier
weather and a gradual warming trend expected. -KT

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1133 AM MDT Sat Sep 21 2024

Upper level low across nrn Arizona at midday will move north
and east across south central Colorado through the evening,
then continue into northeastern Colorado on Sunday. This system
will develop widespread precipitation, with showers and
thunderstorms spreading north and east across the central
Rockies through tonight.

At the taf sites, lowering VFR cigs and vcsh 18z-20z, then more
widespread showers and areas of MVFR cigs/vis from 20z until at
least 08z. Risk of tsra this afternoon at KALS and will carry a
20z-24z tempo, while at KPUB and KCOS, tsra threat is later in
the period generally in the 00z to 04z timeframe. After 08z,
precip trends back toward vcsh, though with plentiful moisture
and weakening winds, prevailing MVFR cigs are likely at all
sites, with a risk of IFR 10z-18z, especially at KALS if
significant precip occurs Sat evening.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Sunday for COZ058-060-
082.

&&

$$

SHORT TERM...MW
LONG TERM...KT
AVIATION...PETERSEN