FXUS65 KPUB 131728

Area Forecast Discussion
National Weather Service Pueblo CO
1128 AM MDT Thu May 13 2021

Issued at 658 AM MDT Thu May 13 2021

Updated the forecast to include patchy dense fog over Pueblo and
El Paso Counties this morning. Area observations, satellite
imagery and looking out the window, show areas of dense fog.
Reduced visibility is expected, mainly on Highway 50 and I-25.
Reduce speeds and use low beams.  Mozley


.SHORT TERM...(Today and tonight)
Issued at 345 AM MDT Thu May 13 2021

Currently...satellite imagery this morning shows valley fog and low
stratus over the upper Arkansas River basin and Wet Mountain Valley
along with portions of El Paso County.  Otherwise, generally clear
conditions are prevailing across southern Colorado.  Winds are
relatively light across the region.  Current temperatures are
running in the lower to mid 40s across the Plains, while the San
Luis Valley is seeing lower to mid 30s.

Today and tonight...flat upper ridging over Utah into the Desert
Southwest and troughing across the Central Plains will keep
northwesterly flow across southern Colorado for the next 24 hours.
Weak energy embedded in the flow may spark a few thunderstorms this
afternoon over the southern Sangre de Cristo Mountains, east into
the Raton Mesa region.  Thunderstorms that do form, will quickly
move southeast into New Mexico by late afternoon to early evening.
Lightning and gusty outflow winds will be the main concerns with

There will be near critical fire weather conditions this afternoon,
mainly over the La Garita range, mainly over Saguache County, into
northwest portions of the San Luis Valley.  Winds will be gusty this
afternoon and humidity values low.

Temperatures this afternoon will warm nicely across the region.
Highs for today will reach into the lower to mid 70s for most of
southern Colorado.

Expect any thunderstorms that develop to shift southeast of the area
or dissipate by this evening.  Once this occurs, dry conditions are
expected to prevail across the region.  Across the Plains, a weak
surface low will develop, with southerly winds advecting moisture
northward near the Kansas border.  Lows tonight will remain mild,
with mid 40s across the Plains, and mid 30s across the San Luis
Valley.  Mozley

.LONG TERM...(Friday through Wednesday)
Issued at 345 AM MDT Thu May 13 2021

...Active Severe Weather Pattern for Friday and Saturday and
potentially into Sunday...

...Pattern shifts to a mix of more widespread stratiform/convective
precipitation for Monday and Tuesday with potential for strong
thunderstorms and burn scar flash flooding...

Relatively flat upper ridging translates across CO for Friday with
weak perturbations moving through the flow aloft evident in PV
fields. Appears one wave moves through during the morning with
another during the evening and overnight which won`t particularly jive
with peak heating. However, east to southeasterly low level flow
will advect higher dew points into the southeast plains along and
east of a surface trough axis/dry line and a frontal boundary of
sorts across El Paso county and points eastward. High res CAMs
models show convective development occuring over the mountains in
the afternoon in relatively high based moisture with storms
intensifying as they move eastward into a more moist/unstable
atmosphere. With deep layer shears running around 40 kts and CAPE
values around 1000-1500 J/kg, conditions will be favorable for one
or two severe storms across the southeast plains. The best axis
for instability will be east of a line from La Junta to Kim which
jives well with SPC day 2 outlook. Gusty winds and large hail look
to be the primary risks as LCLs still look a little high this
day. But any right movers could ingest sufficient helicity for
supercell structures with a brief weak tornado potential if
everything comes together just right. This risk looks to be on the
lower side of the spectrum this day. Thunderstorm activity moves
eastward into KS during mid to late evening hours which helps
drive moisture back westward into the southeast plains aided by
westward moving convective outflows.

Saturday look to be a more active day for severe thunderstorms
across most of the southeast plains as moisture axis and higher CAPE
gets driven back into the I-25 corridor.  CAPE in the 1500-2000 J/kg
range will be in place across the southeast plains with deep layer
shears in the 30-40 kt range which will be supportive of a few
severe thunderstorms.  Once again, large hail and damaging winds
will be the primary threats.  But given the stout CAPE and lower
LCLs the potential for a tornado does increase, especially with any
initial rapid development along boundaries. Where low level winds
pull more easterly some enhanced low level helicity may be in place
as well.

While the southeast mountains and plains will see increasing chances
for thunderstorms for Friday and Saturday, the San Luis Valley may
see another period of critical to near critical fire weather
conditions both days. Winds through the mixed layer look a little on
the light side though do tap 20 kts at the top of the mixed layer
during the late afternoon.  Wild card will be high based convection
which may help generate gusty outflow winds and increase afternoon
gusts sufficiently for a brief period of critical fire weather
conditions. Given the low end probability, have refrained from any
fire weather highlights at this time as conditions look too
localized and brief at this point. At last check with land
management agencies, green up was starting to occur so this will
give later shifts time to check on the status.

Operational runs are in good agreement on the next closed low moving
into southern CA/southern NV on Sunday.  Northern stream trough
moves across the northern U.S. Rockies Saturday night which will
send a cold front through the plains with easterly low level flow
advecting 40s to mid 50 dew points back westward towards the
southeast mountains. High CAPE but perhaps weaker shear will be
present this day as both GFS and EC show a distinct shortwave
propagating through the upper ridge aloft. Although CAPE looks
sufficiently high, deep layer shear may be on the weaker side as
upper ridging ahead of western U.S. upper low may weaken the flow
aloft this day. Burn scar flash flooding may be a primary concern as
CAPE over the southeast mountains will increase, with perhaps a more
isolated severe threat across the plains with multicell structures.
Still some uncertainty here on the details.

As the upper low moves across AZ and NM Monday and Tuesday, easterly
low level flow will keep higher dew points and sufficiently high
CAPE values across the southeast mountains and plains each day. As
forcing increases as area comes under difluence aloft we should see
more stratiform precipitation develop with embedded convection each
afternoon and evening dependent on surface heating.  Deep layer
shears will be weaker both days as flow aloft weakens, which will
decrease the severe risk (though perhaps not entirely eliminate it)
but enhance the flash flood threat for burn scars across the
southeast mountains both days. This system will not be as cold as
the last with snow levels likely to remain above 10kft. Cells that
do develop in higher CAPE may still be capable of some pulse severe
type hail but details this far out are still murky. The interior
mountains and valleys will see a good chance for showers and
thunderstorms both days as well as mid level southerly flow
advects moisture into the region ahead of the upper low.
Temperatures will be cooler these days as well with highs topping
out in the lower 70s across the plains...60s mountain valleys and
40s and 50s for the mountains.

Still some residual moisture for showers and thunderstorms behind
the system on Wednesday and Thursday, though with less instability
and weaker flow aloft, severe threat appears lower. Will still be
monitoring burn scar flash flood potential both days, but perhaps
more so on Wednesday before drier air spreads in from the west. -KT


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1125 AM MDT Thu May 13 2021

VFR conditions are expected during the next 24 hours at all 3 taf
sites; KCOS, KPUB, and KALS. Winds will generally be light and





NWS PUB Office Area Forecast Discussion