Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 201033

Area Forecast Discussion
National Weather Service Pueblo CO
433 AM MDT Sat Apr 20 2019

.SHORT TERM...(Today and tonight)
Issued at 433 AM MDT Sat Apr 20 2019

Upper trough across southern CA will fill as it lifts northeastward
ahead of the west coast upper trough moving onshore this afternoon.
Incoming mid/high based moisture will cause an increase in clouds
today with some isolated to low end scattered showers and
thunderstorms developing over the mountains during the afternoon.  A
few of these will spread into the adjacent plains this afternoon,
however very dry subcloud airmass will limit their ability to
produce any rainfall at the surface east of the mountains.  However
some virga and locally gusty winds will be possible.

Otherwise today should be a warm and breezy day across the area. The
plains will warm well into the 80s with some readings just touching
90 degrees across the plains.  This will put relative humidity below
10 percent.  Combined with afternoon breezes, weather conditions
will be meeting critical fire weather conditions.  However, given
the fuels are entering green up and considered not critical for fire
spread, no fire weather highlights will be issued.  Might be good to
exercise caution if dealing with spark producing equipment in drier
areas, as finer dead fuels may still be receptive to fire spread.
Temperatures will also be above normal across the mountains and
valleys today. Winds and pops will decrease tonight as we await for
the next round on Sunday. -KT

.LONG TERM...(Sunday through Friday)
Issued at 433 AM MDT Sat Apr 20 2019

Sunday and Sunday Night:

A slow moving upper level low pressure system will be located over
northern Nevada at the beginning of the long term forecast period
(Sunday at 6AM MDT). A shortwave trough will propagate off of the
primary low, which will develop over southern Colorado on Sunday
afternoon. The shortwave trough will create a surface lee cyclone
over the eastern plains, which will enhance advection of Gulf of
Mexico moisture over the high plains. The surface low will wrap the
moisture around itself and will produce a moisture boundary that
will propagate over the eastern Plains during the evening hours,
traveling from the northeast to southwest. Analyzing forecast
sounding over the eastern plains during the evening hours reveals
areas of 500 to 1000 J/kg over Kiowa, Bent, and Prowers Counties.
The hodograph during this time period is fairly linear, meaning the
potential for a left moving supercell exists during the evening
hours. The LCLs are around 3000 meters, so tornado chances are very
low, but some severe criteria hail, and severe criteria wind gusts
(which seems most likely) are possible. The Palmer Divide will see
showers do to upslope flow from the North and the potential for weak
thunderstorms. The previously mentioned outcome is dependent on
where the surface cyclone develops. If the surface cyclone is
further north, the severe thunderstorm risk will remain further
north, and the same comparison can be said if the surface cyclone is
further south.

The Continental Divide will see upslope flow and waves of cyclonic
vorticity advection during the afternoon, which will result in snow
(over the highest peaks), rain, and some weak thunderstorms. Once
the moisture boundary reaches the mountains on the eastern plains,
upslope flow will form snow and rain showers over the eastern
mountains.  The showers will continue through the overnight hours in
to Monday.

High temperatures during the afternoon will be dependent on how
quickly the surface low develops and how quickly the moisture
boundary propagates over the region. At this point in time, peak
heating shouldn`t be hindered, so the Plains should be in the 70s to
low 80s, the San Luis Valley will be in the 60s, the upper Arkansas
River Valley will be in the 60s, and the mountains will be in the
30s to 40s.

The added moisture over the Plains during the overnight hours will
keep low temperatures in the 40s, the San Luis Valley and upper
Arkansas River Valley will still be able to reach the upper 20s to
lower 30s, and the mountains will be in the 20s.

Monday and Tuesday:

The upper level low will now be over Arizona on Monday. Analyzing
MSLP fields on Monday reveals a pressure deficit over New Mexico
with increasing pressure to the north. The surface flow will follow
that pressure gradient creating north to northeasterly winds moving
towards the eastern mountains and the Raton Mesa. The upslope
forcing will create snow over the highest topography and showers and
weak thunderstorms. QPF values are all over the place in regards to
model data, so a model blend using the ECMWF and the NAM were used
to create a more balanced value during the period. The talk in the
office is about the flooding potential for the Spring Burn Scar with
all of the rainfall in the forecast. At this point in time, the
general consensus is that the rain will not fall at rate to cause
any flooding concerns. The streams may see some swollen flows do to
Spring runoff and added runoff from the precipitation, but there
shouldn`t be any negative impacts.

The pressure gradient will relax on Tuesday, implying that upslope
precipitation will cease. Overcast conditions are expected to
continue on Sunday though. As the upper level low continues to
slowly propagate easterly, the deformation zone north of the cyclone
center will bring rain and snow over the mountains and San Luis
Valley. These showers will have mountain top instability available,
so heavier rain and snow bands will form over them.

High temperatures on Monday and Tuesday will be right around average
for this time of year.

Wednesday and Thursday:

An upper level ridge will develop over the Great Basin providing
Colorado with a drier and warmer air mass. There may be some ongoing
mountain showers during the afternoon due to ripples in the upper
level flow, but the general outlook is dry conditions for both
Wednesday and most of Thursday. Temperatures will warm back up on
Wednesday, with high temperatures around 5-10F above average, and
even warmer on Thursday, with high temperatures around 15-20F above


Diurnally driven thunderstorms are being resolved over the mountain
tops and are resolved to advect over the plains. Storms that form
will be weak and likely not severe. Temperatures are expected to
continue to rise on Friday, as well.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 433 AM MDT Sat Apr 20 2019

VFR conditions expected at the terminals with increasing high
cloudiness expected this afternoon.  Winds will increase from the
southwest to west in the 15 to 25 kt range at all three terminals
during the afternoon. Isolated high based showers and thunderstorms
will develop over the mountains this afternoon and move off into the
adjacent plains during the evening.  KALS will have the best chance
of VCTS. Local wind gusts up to 40 kts will be possible with high
based showers through the early evening hours, though odds are low
of these impacting the terminals directly given localized nature.
Winds will decrease by 02z with enhanced westerly winds continuing
overnight at KCOS and KPUB.  Lowering CIGS with showers will spread
into the Continental Divide towards morning. -KT




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