Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 062128

Area Forecast Discussion
National Weather Service Pueblo CO
328 PM MDT Thu May 6 2021

.SHORT TERM...(Today and tonight)
Issued at 350 AM MDT Thu May 6 2021

Upper ridge migrates eastward through the Rockies overnight and
Friday, with axis over the High Plains by late Friday evening. After
a clear and seasonably cool overnight, flow aloft on the backside of
the ridge turns swly and slowly increases on Fri, with lee surface
trough/dryline pushing eastward across the plains late in the day.
Low level moisture return on the plains is rather modest, with some
dewpoints in the low 40s along the KS border ahead of the dryline
toward 00z, which yields CAPE in the 500-800 J/KG range.  Mid level
lapse rates are fairly steep, and with some weak convergence near
the surface trough/dryline, we`ll likely have a few higher based
storms develop 21z-00z, with perhaps a few severe wind gusts
possible. SWODY2 has strip of marginal over the plains from KLHX
eastward, which looks reasonable for now. Farther west, steep lapse
rates but very dry low levels will lead to some isolated storms over
the mountains and I-25 corridor, though suspect precip will limited,
with virga and gusty outflow winds the main features. Winds will be
strong enough to warrant a Red Flag Warning for the San Luis Valley,
where green-up is still rather slow, but will hold off on fire
weather highlights elsewhere, as fuels are greening up and duration
of lower humidity may end up less than 3 hrs. Max temps Fri will
soar with ridge and deep mixing, and expect some low 90s to reappear
on the plains.

.LONG TERM...(Friday through Wednesday)
Issued at 350 AM MDT Thu May 6 2021

...Critical Fire Weather Conditions possible for the San Luis Valley
during the afternoon and into the early evening on Friday. Then
again these conditions will be possible in the Upper Arkansas River
Valley, San Luis Valley, and over the most of the plains east of the
I-25 corridor, ahead of the approaching cold front during the
afternoon on Saturday...

...Chance of thunderstorms Friday evening over the mountains and
plains later in the evening, some of these thunderstorms could be
severe, especially over the eastern plains...

...Next major system to impact the region this weekend and going
into early next week with much cooler and unsettled weather
returning to the region. Snow showers over the mountains and evening
thunderstorms will begin later on the day on Saturday at the first
initial cold front moves in from the north. With relatively high
CAPE values in place, there is a chance of severe weather over the
plains along this frontal boundary. A secondary wave will produce a
low to the south of the CWA on Sunday and Monday with a decent
amount of precipitation expected for all areas for both days. There
will still be a chance of snow showers over the higher elevations
and thunderstorms on Tuesday as well...

Friday evening...

With the mid to higher level moisture being advected in from the
southwest ahead of the trough upstream, and with decent CAPE and
SI/LI values, scattered thunderstorms that have developed during the
afternoon over the mountains will continue to progress ENE with some
of them possibly being severe, especially over Baca County where
CAPE values look to be the greatest. These storms will continue to
move into the eastern plains and eventually cross over into Kansas
by 03Z, with subsequent clearing taking place throughout Friday
night. Strong and gusty over the San Luis Valley will continue to
diminish throughout the evening, and RH recoveries should be
favorable, along with virga possibly wetting the lower levels and
keeping lower RH values at bay, therefore critical fire weather
criteria conditions in this area should end by 01Z. With downsloping
winds into the later part of the evening, this should help to
moderate the minimum temperatures for the plains a bit, while all
other areas are right around the seasonal average.

Saturday through Tuesday...

The ridge is going to break down as longwave troughing begins to
take over and dominate the region going into the early part of next
week. The next major shortwave will start to impact the area,
beginning with snow showers over the northern central mountains by
early Saturday morning. There will be more developing showers and/or
thunderstorms later in the day on Saturday over the mountains and
some of these could move out into the plains later in the afternoon,
although with the lower levels remaining much drier, most of these
will likely evaporate out in the form of virga over much of the
region on Saturday. The models are still having a difficult time
agreeing on the exact timing and placement of the low pressure
system associated with this trough, especially past Sunday. The
timing of the front differs slightly as well with the models,
although it is an apparent that as an average between all of the
ensembles, that FROPA should begin over El Paso County right around
00Z on Saturday, and then progress southward and eventually over
the entire CWA by around 06Z. There is a decent amount of shear
and CAPE associated with this frontal boundary, especially over
the eastern plains, with some of the models such as the NAM12
displaying values at nearly 3000 J/Kg over the eastern plains as
the front dips further southward. This could potentially produce
some severe thunderstorms that have the possibility of rotating,
with an isolated tornado not being ruled out. After the front
moves through, the low will become positioned to the south and
there will be cooler air advected in behind so the snow levels
will begin to drop throughout the night on Saturday, from about
10,000 ft to 10,500 ft over most of the CWA, down to around 7,000
ft over the northern areas and 7,500 to 8,000 ft over the southern
areas of the CWA. The positioning of the low will determine which
areas receive the most precipitation, although most of the plains
and especially along the I-25 corridor will get a fair amount of
rain due to overrunning in the lower levels for both Sunday and
Monday as the low begins to stall out over the region. Cooler air
behind the front will help to stabilize the low to mid levels with
much lower CAPE values, therefore thunderstorms could be embedded
in the rain bands developing in the deformation zone, but
widespread convection is not expected. For Tuesday, the European
(ECMWF) model still has the eastward progression of this system be
slightly quicker than the GFS model. It is likely that there will
be higher amounts of precipitation expected over the southeastern
plains for Tuesday afternoon as the deformation zone begins to
shift further east at this time.

Wednesday and Thursday...

The longwave trough is finally going to begin to shift more
eastward, allowing for some weak ridging to take place over the area
and clearing out with high pressure moving building back in.
Temperatures will also begin to moderate back to more seasonal
values, especially by Thursday. Only a slight chance of a few
afternoon thunderstorms will be possible over the central mountains
due to some mid level moisture advecting into the ridge from
upstream, otherwise mostly clear skies will dominate the entire CWA
for both days.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1129 AM MDT Thu May 6 2021

VFR conditions at all terminals overnight, with generally light
diurnal winds. On Fri, s-sw winds will increase at all terminals,
with some gusts to 25 kts at KALS after 18z. Low risk of a tsra at
all terminals after 20z, though coverage looks too isolated to
include in any taf for now. Do expect gusty/erratic outflow winds at
KPUB and KCOS after 21z, as virga and high based storms will be in
the area.


Red Flag Warning from noon to 8 PM MDT Friday for COZ224.



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