Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 081751
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1151 AM MDT Sat May 8 2021

.SHORT TERM...(Today and tonight)
Issued at 340 AM MDT Sat May 8 2021

Key Messages Today/Tonight...

- Red Flag conditions expected across the SLV floor today, again.
- A few stronger thunderstorms possible across the plains this
afternoon. Maybe a few supercells as well...

Feel like this is a close repeat to yesterday in terms of potential
weather impacts though today we throw a cold front into the mix and
add in some better shear, oh man, talk about exciting!

Unfortunately yet again today, the San Luis Valley will be on the
drier side of the moisture pool with stronger west-northwest winds
expected as mid-level shortwave moves through. Given green-up in the
fuels is still occuring and delayed in some areas and low RH values,
Red Flag conditions will persist today.

The severe thunderstorm potential is higher today than yesterday
with better support at the surface and from aloft. The
aforementioned shortwave trough of low pressure will aid in high
terrain showers that push off towards the east by mid/late
afternoon. At the same time a quick cold front sweeps through from
the north by mid-afternoon bringing with it gusty north winds.

You know here in eastern Colorado we like to do our severe weather
just a little different than most. Ana-frontal supercells and
blowing dust are on the table this afternoon and evening as
surface low pressure develops across southeast Colorado pulling
the cold front through faster. Right behind the front low-level
moisture will be ample with increasing shear values, upwards of
40-45 knots 0-6 KM, and 500-1000 J/kg of surface based CAPE. The
favored corridor of stronger to severe storms is Colorado Springs
southward into Kim, CO though the bulk of the activity is becoming
a bit more clustered from far eastern El Paso County into Prowers
County, north of Hwy-50...where have we heard this before. While
larger hail, 1-2" and damaging winds look to be the main threats,
can`t ever rule out something spinning over this area with storms
ingesting early convective outflows and proximity to a density
boundary.

As activity slides farther east into OK/KS we look to have a pretty
big lull in showery activity through much of the overnight hours.
Need to get the stronger east flow building up Sunday morning
enhancing the upslope potential for stratiform rain and some snow
mixing in.

.LONG TERM...(Sunday through Friday)
Issued at 340 AM MDT Sat May 8 2021

...Cooler and wetter pattern for Sunday through Tuesday though
another round of Critical Fire Weather conditions expected across
the San Luis Valley...

-Long Term Key Messages-

1) Wetter weather for Sunday through Tuesday with potential for
snow levels to drop to around 7000 feet Sunday night and down to
6000 feet Monday night for the central and southeast mountains and
adjacent plains.

2) Critical Fire Weather conditions will plague the San Luis
Valley for yet another day on Sunday.

2) Rounds of heavy wet snow possible across the higher elevations
Sunday through Monday night with winter weather highlights
possible for the central and southeast mountains above 8000 feet.

3) Minor snow accumulations on grassy surfaces possible across
the crest of Monument hill Sunday night and again Monday night.

Not much change in the model biases through the event with EC and
EPS farther north with the upper low/filling trough as it ejects
in a couple pieces across the northern/central Rockies in the
Saturday night through Monday night timeframe. GFS and GEFS still
slower, farther south and more closed off with the secondary
closed low as it moves across Monday night-Tuesday. Canadian
leans towards the EC only slightly faster, and the NAM gives a
nod to the GFS solution. Main impact this has on the system for
southern CO is how low snow levels will get, with the colder runs
(NAM and GFS) bringing snow into Colorado Springs Monday and
Monday night...while EC and Canadian keep snow levels across the
mountains. Followed NBM which is a conservative blend of the two
for now.

As for the details...energy dropping out of Canada carves out the
upper low across ID Sunday and Sunday night with post frontal
upslope flow moistening the low levels across the southeast
mountains and adjacent plains with showers breaking out in the
morning. Lift increases as the upper level flow buckles and
becomes more southwesterly ahead of the advancing system and
showers and embedded afternoon thunderstorms will develop across
central and southeast mountains and spread off into the adjacent
plains where the cooler airmass will limit convective strength.
There will be some elevated instability aloft so do think some
thunderstorms will survive as they move off into the adjacent
plains, but should weaken with mainly rainfall, perhaps some brief
snow pellets or graupel and lightning will be the main risks. The
exception to this may be across the southern Sangres and Raton
Ridge area where higher dew points may advect northward as
pressures fall to the south and along the Raton Ridge. CAPE still
looks on the marginal side in most models though deep layer shear
will certainly be favorable for organized severe storms if the
instability is present. Have a hunch that the stronger storm
development will be south of the area as it is typically quite
difficult to scour out the cooler air given the surface pressure
rises across the plains. But certainly some small hail and locally
heavy rainfall look possible. Snow levels will be around
9000-10000 feet on Saturday so will need to monitor the Spring
burn scar for localized flash flooding, but it still appears this
risk will be on the lower side of the spectrum. Meanwhile, strong
west to southwest winds and low humidity will spread into the
southwest mountains and San Luis Valley and given the receptive
fuels across the valley have hoisted another Fire Weather Watch
for Sunday afternoon and evening.

Best lift with the first round of upglide spreads in Sunday night
with a broad area of precipitation developing across the southeast
plains. Models place the heavier bands in different locations but
there will likely be two focus areas, one farther south along the
southern border nearer the front where upglide is maximized
initially, then another along the Palmer divide where a combination
of upslope and upglide coincide. This band will lift northward
overnight into Monday morning. Snow levels may drop to around
7000-8000 feet Sunday night (lowest across the north) with the
first round of mountain snows...which could bring a wet 1 to 5
inches of snow across the central and southeast mountains,
especially north of highway 50...with the potential for a slushy
inch or two on grassy surfaces across the Palmer Divide.

Precipitation may wane off Monday morning...though models differ
with this, before a second round develops across the mountains
Monday afternoon aided by instability from cooling temperatures
aloft as the upper trof advances eastward. Another round of
stronger upglide sets in Monday night with the focus this time
likely to be farther north as the mid level baroclinic zone
tightens up as cold air with the system sinks southward. Seems
the band of heavier precipitation this time may set up along and
north of highway 50. Degree of cooling and snow levels Monday and
Monday night are very much in question with the colder NAM12
suggesting it could snow in Colorado Springs as early as Monday
afternoon, while models resolving a more northern track to the
system suggest snow levels may wait to drop to around 6000 feet
until Monday night. Have leaned towards a warmer solutions for
now, but it does appear that another round of moderate snow could
fall across the Central and southeast mountains with the heaviest
accums north of highway 50. Northern El Paso county down to near
Colorado Springs could see another 1 to 3 inches of slushy
accumulations. All totaled grids are carrying around 3 to 8
inches of snow for the Sawatch and Mosquito ranges, northern
Sangres, Wets and Pikes Peak with some local amounts of 12 inches
or a little better across the Wets and Pikes Peak above 10-11kft.
The Palmer Divide could see 2 to 5 inches though all of it may not
stick to the ground at one time...and pavement surfaces are
likely to remain wet or slushy at best which should limit impacts.
The remainder of the plains will see rain...with total
accumulations through Monday night in the .50 to 1.00 range, with
the highest values likely to be north of highway 50. The southwest
mountains and San Luis Valley get slighted from this system and
are more likely to pick up 0.10 to 0.40 at best.

Tuesday will still be unsettled depending on the timing of the
upper trough as it exits eastern Colorado. Showers and embedded
thunderstorms will be less widespread this day and likely tied
more to the mountains with higher peaks seeing an additional inch
or so of snow and lower elevations seeing an additional up to .10
of liquid in some locations. Snow levels rise some in the
8000-9000 feet range through the day but again, precipitation
should not be as heavy or persistent.

Drier and warmer weather returns for late week as the system
departs to the east and the next upper ridge translates in. -KT

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1125 AM MDT Sat May 8 2021

At KCOS, VFR conditions today with gusty west winds shifting to
the north after 22z as a cold front moves through. Risk of a vcts
behind the front from 22z-00z, though with limited moisture,
gusty and erratic winds will be the main features of any storms.
Clouds will thicken and lower overnight, with MVFR cigs and a vcsh
by 10z-12z Mon. Prolonged period of MVFR/occasional IFR cigs and
periods of showers then likely through Sunday.

At KPUB, gusty w-nw winds expected through the afternoon, then
shifting to the north behind a cold front 23z-01z. Clouds then
thicken and lower overnight, with some MVFR cigs and showers
likely from Sunday morning onward.

At KALS, strong w-sw winds gusting to 30-40 kts may produce some
blowing dust and brief periods of MVFR visibility this afternoon
and early this evening, with perhaps a vcsh adding to wind speeds
after 22z. Winds diminish with VFR conditions overnight and early
Sunday.


&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening for COZ224.

Fire Weather Watch from Sunday morning through Sunday evening
for COZ224.

&&

$$

SHORT TERM...HEAVENER
LONG TERM...KT
AVIATION...PETERSEN


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