588
FXUS65 KPUB 040543
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1143 PM MDT Fri May 3 2024

.KEY MESSAGES...

- Severe thunderstorms will be possible later this afternoon and
  through the evening over the eastern plains. Wind gusts in
  excess of 60 mph, hail of up to 2 inches in diameter possible.
  A brief landspout or weak tornado cannot be ruled out.

- A cold front will move through later this evening over the
  plains, with colder temperatures and gusty winds out of the
  northeast behind it.

- General thunderstorms are possible elsewhere over the plains
  and over the eastern mountains, which will continue throughout
  the night for some areas, mainly over the far southeastern
  plains and Raton Mesa area.

- Frost conditions will be possible tonight over El Paso County.

- Increasing winds and fire danger early next week with a
  trend towards cooler and wetter conditions for late week.

&&

.UPDATE...
Issued at 815 PM MDT Fri May 3 2024

Have allowed the Red Flag Warning to expire this past hour, as
winds continue to diminish and RH values improve.

Have kept the Severe Thunderstorm Watch in effect this evening,
as additional strong to severe storms remain possible.
Southward moving strong cold front will encounter stronger south
southeast winds along with dewpoint air still in the 40s to low
50s. This should allow at least isolated thunderstorm
development, some of which will still be capable of producing
hail to the size of quarters and wind gusts to 60 mph. Highest
chances for this to occur late this evening, is along and
southeast of a Kim to Lamar line. Any remaining development
should be southeast of the CWA by around the midnight time
frame.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 224 PM MDT Fri May 3 2024

Currently and through tonight...

A major shortwave trough is continuing to approach the region, with
the development of a lee-side low by later in the afternoon as the
trough axis moves overhead. As this pushes out over the plains a
slightly deepens, it will force a cold frontal boundary to move down
from the north over the plains.  A dryline is going to establish
itself, where there are currently 50+ dewpoints over northeastern
New Mexico that will make their way up over far southeastern
Colorado later this afternoon, this will act as a triggering
mechanism for pre-frontal convective development once the cap
completely erodes and the convective temp is achieved, which may
turn severe given the higher dewpoints and thus increased low-level
instability. An increasing low-level jet out out of the southwest
will also increase shear necessary for further updraft enhancement
and may allow for severe thunderstorm development for the next
couple of hours, mainly over Las Animas County and east. A consensus
of the latest high res guidance has the front beginning to move over
northern El Paso County by as early as 7 to 8 PM, and then push
through the CWA by around midnight. The timing of the front could be
sooner, depending on whether or not if it is accelerated by outflow
from convection that develops along and behind the boundary.

Currently, there have already been multiple cells that have
initiated over this area, which will likely continue to develop as
the lower levels further destabilize by early evening as the low-
level jet increases with effective shear of a magnitude around 30
kts or greater. MLCAPE is also going to increase to 1000 J/kg or
greater, especially over Prowers and Baca counties, mainly after
4pm. With this, the potential for thunderstorms becoming severe will
increase going into the later afternoon/early evening hours,
especially anywhere from La Junta to Kim, and eastward. There are
also going to be general thunderstorms possible over the eastern
mountains and along portions of the I-25 corridor, mainly south of
Pueblo County, that will continue to move off to the east-northeast
after development. Dry conditions, with low relative humidity values
and gusty southwesterly winds will continue to keep fire weather
conditions going until around 9 PM in the San Luis Valley, although
RH values should recover enough to allow the Red Flag Warning to
come down by this time.

The latest CAM guidance and HREF helicity tracks favor development
of stronger, and possibly severe, cells over Prowers and Baca
counties between 6 to 8 PM. In addition, the latest HRRR model also
puts the development of a cell over Baca, with easterly winds
turning into it at 00Z (7 PM), suggesting that there could be
increased SRH values right around this time and possible supercell
development, with the capabilities of producing a brief landspout
and/or weak tornado. It also has something similar right around the
same time over Prowers County, as well as the development of a
strong cell right on the edge of northeastern Kiowa County. The
NAM4km Nest has also been persistent with the past couple of runs of
having a pre-frontal cell develop with over the northwestern Baca
County/Bent County and then move into Prowers County right around
the same time.

Colder air advection moving in behind the frontal passage that will
occur later this evening will allow for temperatures to continue to
drop, especially as skies further clear. This will allow for
temperatures over El Paso County to drop to near, or below, the
freezing mark. Due to this, there will likely be some areas of
frost. Stratus will also develop, mainly along the I-25 corridor
from Pueblo County and northward to Monument. There could still be
some showers, and possibly a thunderstorm, continuing into the early
morning hours of tomorrow. As the lower levels continue to
stabilize, showers will also continue to diminish and move
southeastward and out of the CWA towards daybreak. Lows will bottom
out into the 30s to low 40s over most of the plains, and generally
in the upper teens and 20s for high country.

Tomorrow...

With colder air already in place, it will be more stable over the
plains, and notably cooler. Highs will likely remain in the 60s over
a majority of the plains and San Luis Valley, and only 40s to 50s
for the higher terrain. With residual moisture, and increasing mid-
level flow out of the southwest coupled with orographic lifting,
there will be showers and thunderstorms developing in the afternoon
hours over the higher terrain. This will get pushed out over the
plains by later in the day. These should be more of your "garden
variety" type thunderstorms, although there could be an isolated
storm or two that is on the stronger side. With more of an inverted-
v profile, some of these storms may result in some gusty outflow
winds to 50 mph or greater, and there could be hail up to 1/2 inch
with the stronger storms. The plains will likely remain dry with
more stable air in place, although a few of the showers/storms could
move out over the adjacent plains and portions of the I-25 corridor.
-Stewey

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 224 PM MDT Fri May 3 2024

Weak wave in southwest flow ejects across CO Saturday evening with
cool stable upslope flow maintaining across the plains.  A few
showers may drift off into the adjacent plains but they should
diminish as the move off the mountains into the more stable airmass.
Have trimmed eastward extent of pops into the I-25 corridor during
the evening. Showers and thunderstorms will diminish across the
mountains behind this feature in the evening but could regenerate
across the far eastern plains late Saturday night as the low level
jet increases. Any isolated nocturnal convection will have limited
CAPE resulting in some weak elevated showers/thunderstorms into
Sunday morning.

Temperatures then rebound for Sunday as southerly flow increases
across the region ahead of the next upper low moving into the Great
Basin. Will need to watch the San Luis Valley for potential Critical
Fire Weather conditions until green up occurs. For now, coverage and
magnitude looks too limited with RH the most limiting factor for
Sunday. Showers and thunderstorms will redevelop across the
Continental Divide as moisture increases ahead of the upper low. Out
east it remains largely dry.  Will need to monitor the position of
the dry line but for now dew point return and CAPE looks limited
with little to no initiation along the boundary in the afternoon.

Upper low lifts out across northern CO Sunday night and Monday. With
the more northern storm track, this puts southern CO under the dry
and windy region of the storm. Latest NBM shows potential for wind
gusts greater than 50 mph in the 70-90+ percentile, especially along
and south of highway 50 Monday morning. We could be looking at brief
near high wind potential Sunday morning if we can mix 50-60 kts down
to the surface Sunday morning as the cold front moves through. In
spite of the cool down, it will be very dry and likely a critical
fire weather day for the San Luis Valley and southern portions of
the southeast plains where fuels are still critical. The Continental
Divide will pick up some snow Sunday night through Monday morning
with a diminishing trend in the afternoon as the storm ejects to the
northeast.

The windy and mostly dry pattern continues for Tues and Wednesday
with temperatures rebounding. Then we trend towards a cooler and
potentially wetter pattern as low pressure stalls out over the
western U.S. and a cold front moves through the plains bringing post
frontal upslope flow Thurs into next weekend.  Thursday could
potentially be the coolest and wettest day with snow levels dropping
to around 7000 feet across the southeast mountains.  Still some
details to resolve on the track and strength of the low which will
drive the degree of upslope and precipitation amounts.  EC is weaker
with the upper low and magnitude of upslope, and therefore has less
QPF/snow. Probabilities of greater than 3" of snow accumulation is
less than 30 across all but the central mountains from the National
Blend of Models.  Central mountains fair a little better with
probabilities for up to 6 inches up to 40%. This will bear watching
as details become more certain. -KT

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1134 PM MDT Fri May 3 2024

VFR conditions with mainly dry weather is expected across the
TAF sites this forecast period. While conditions remain clear at
ALS this morning, low stratus will likely build back towards PUB
and COS early this morning. Ceilings are currently VFR and
expect them to remain that way as they move across the
terminals. If ceilings were to fall to MVFR, think COS would
have the higher chance of observing these lower ceilings. Once
again, think this is a low chance though. Any lower ceilings
clear out by early to mid morning, with clearer skies expected
for much of the day. Will see the lighter winds in place this
morning increase during the day, with southeast winds at COS
and PUB and south southwest winds at ALS. Highest gusts at all
sites look to be in the mid 20 kt range. Scattered showers with
isolated thunderstorms will develop over the higher terrain this
afternoon, and think conditions will remain dry at all sites.
With a slightly higher chance for a shower at ALS, have included
a VCSH during the afternoon time frame.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 9 AM MDT Saturday for COZ084-085.

&&

$$

UPDATE...RODRIGUEZ
SHORT TERM...STEWARD
LONG TERM...KT
AVIATION...RODRIGUEZ