Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/04/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 428 PM MST Fri Sep 3 2021

.UPDATE...Updated Aviation Discussion...

&&

.SYNOPSIS...
Mostly dry conditions will prevail heading through the weekend with
just a slight chance for storms over mountains of eastern Arizona.
Towards the middle of next week, modest rain chances return for most
locations. Temperatures will warm to near and slightly above
normal levels for much of the next week.

&&

.DISCUSSION...
A ridge axis was elongated across far SE Arizona this afternoon
resulting in dry SW flow situated over the entire forecast area. 12Z
regional sounding data sampled lingering amounts of ample low level
moisture (~12 g/kg), albeit topped by a resounding amount of dry air
above the boundary layer. In situ ACARS soundings depict this
evolution with lower level moisture profiles being eroded with
mechanical mixing, and 9-10 g/kg well mixed profiles likely to
materialize by late afternoon. With the ridge axis south of the area
and subsidence predominating, deep convection is unlikely in all
but the most preferred upslope, terrain areas (and outside the
forecast area) through tomorrow. Even getting organized outflow
boundaries from distant storms may be difficult; and likely only
periodic increases in mid/high clouds from storm complexes in
northern Mexico should be expected for most communities.

Ensemble output continues to exhibit excellent agreement that high
pressure will migrate westward across the CWA over the weekend and
H5 heights intensifying close to 595 dm over cntrl CA/NV early next
week. During this transition, there may be some periodic high
elevation storms but the tendency among the ensemble majority is
towards a continuation of dry, warm weather. NAEFS 500 mb height
mean shows values peaking near the 99th percentile over western NV
early next week, though barely clipping above the 90th percentile
within the local CWA (500 mb heights 591dm-594dm). Correspondingly,
NAEFS mean temperature forecasts within the forecast area in the sfc-
H7 layer depict only minimal positive anomalies. For lower
elevations, the chance of hitting 110F next week remains around 10-
40% for SE CA/SW AZ, and less than 10% for south-central Arizona.

During the middle and and of next week, the aforementioned anti-
cyclone will progress back eastward towards the four corners as
Pacific energy nudges the entire Conus pattern. Uncertainty among
ensemble solutions grows markedly owing to (sometimes subtle)
forecast differences in high pressure expanse, strength, and
positioning. Some NAFES members shrink the high pressure influence
and peel off a PV anomaly from the northern stream jet into an
easterly wave directed at the forecast area. Other members expand
and strengthen the anti-cyclone sequestering moisture and any
shortwaves well into northern Mexico. There are even other solutions
that recycle moisture and energy around the western periphery of the
anti-cyclone (impacting SE California) as it moves into the central
high plains. With this wide range of possible outcomes, the mandated
NBM forecast output essentially mirrors a climatological forecast
for the latter half of next week.

&&

.AVIATION...Updated at 2325Z
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Expect light diurnal winds with gradually increasing mid/high clouds
from the south tonight and lasting through Saturday morning.
High terrain isolated to scattered convection is expected Saturday
afternoon, but well outside of Phoenix`s area. The chances for any
outflows into the lower deserts on Saturday is generally less than
a 10% chance.

Southeast California/Southwest Arizona including KIPL and KBLH:

There are no aviation concerns with light winds and few if any
clouds through the next 24 hours.

&&

.FIRE WEATHER...
Sunday through Thursday:
Rain chances will be very low for all but the far eastern mountains
of Arizona Sunday, with the rain chances increasing a bit by midweek
and spreading to most locations. Humidity trends will show a very
slight upward trend while temperatures remain persistently near
normal. Winds will generally follow diurnal trends aside from
stronger gusts in thunderstorm outflows.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...18/Iniguez
AVIATION...Kuhlman
FIRE WEATHER...Iniguez



Area Forecast Discussion

National Weather Service Pueblo CO

 600 PM MDT Fri Sep 3 2021

.MESOSCALE DISCUSSION...
Issued at 559 PM MDT Fri Sep 3 2021

Main Forecast Concerns/Challenges:

1) We continue to monitor thunderstorm trends across El Paso
County/I-25 corridor hear in the near term as well as over the
eastern plains along the Highway 50 corridor later this evening
into the overnight hours.

2) A quick summary: Thunderstorm development across El Paso
county has stayed somewhat on the weaker side late this afternoon
and this looks to continue to be the case over the next couple of
hours. However, can`t completely rule out an isolated stronger
storm across El Paso county over the next 1-2 hours.

3) Concerns are increasing for more organized development around
Pueblo and to the east across the Highway 50 corridor later this
evening into the overnight hours. In this location and during that
time, all hazards are possible including an increasing risk for
heavy rainfall and flash flooding.

Latest radar imagery continues to show persistent thunderstorm
development across the Palmer Divide, where low level convergence
and deep moist upslope flow are in place. An MLCAPE axis of 500
j/kg in this location along with steeper low and mid level lapse
rates are supporting these thunderstorms. While instability,
focus, and shear are in place, these storms have struggled to
strengthen and maintain themselves though. Looking at RAP analysis
and even more recent AMDAR soundings out of COS, there are some
warmer temperatures aloft that are likely playing a big part in
storm intensity at this time. Short term guidance/soundings have
initialized fairly well with current conditions, and the forecast
soundings over the next couple of hours show these warmer temps
aloft maintaining themselves. So, think thunderstorm development
will likely continue across the Pikes Peak region, Palmer Divide
and into other areas of El Paso county over the next couple of
hours but this development should stay subsevere. However, can`t
rule out a stronger storm producing small hail up to one half inch
and wind gusts up to around 50 mph.

Once again, concerns are increasing for more organized
development around Pueblo and to the east over the plains later
this evening and tonight. While conditions aren`t appearing to
come together right at this moment, latest trends and guidance are
indicating this will change by mid evening. The mid level energy
noted on latest WV imagery ejecting out ahead of a low amplitude
mid/upper trough is expected to arrive over the next couple of
hours. The arrival of this mid/upper forcing will help support lee
troughing and a developing 700mb low across the eastern plains,
with increases in 700mb and 850mb WAA as well as even some FGEN.
The arrival of all of this increasing large scale ascent will of
course support quickly developing thunderstorms but also support
the erosion of the warm temps aloft. Instability develops across
the plains as well as advects overhead this evening, while the
resultant easterly flow supports strong and deep moist advection.

So, expect additional thunderstorms to develop in the 8-10 pm
time frame over the Pueblo county area and quite possibly southern
El Paso county. During this time, developing MCS to the north is
expected to dive south/southeast into the better instability with
latest trends suggesting all of this merging into a larger complex
of storms over the eastern plains/Highway 50 corridor late this
evening into the overnight hours. Large hail to one inch is
possible, though the previously mentioned warmer temps aloft may
continue to help limit the extent of any hail tonight. A higher
threat may be be damaging wind gusts possibly in the 60-70 mph
range. However, even with this threat, there is still some
uncertainty based on factors such as how long the overlap of
forcing and instability will be and the time of night - likely
increasing CIN. Additionally, surface trough axis and possible
upstream outflow boundary could serve to increase the tornado
threat later this evening, and will continue to closely monitor
trends for this possibility. Lastly, the previously mentioned
moist advection will likely bring mid to upper 60s surface
dewpoints into eastern Colorado with short term guidance showing
850mb dewpoints of around 20c approaching the CO/KS border
tonight. This increased moisture along with storm mode (east to
west multicell and possibly training) will support an increased
risk for heavy rainfall and flash flooding. One last item to note,
is that this threat of severe storms and flash flooding could
extend well into the overnight hours for areas over far eastern
CO.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 240 PM MDT Fri Sep 3 2021

Main Points:

1) Showers and thunderstorms are expected to increase in coverage
later this afternoon and well into the overnight hours.

2) The Palmer Divide area will be seeing storms pass through, with
gusty winds, locally heavy rainfall and small hail as potential
threats. These storms should pop up in the next few hours and last
until around midnight.

3) Strong to severe storms will be possible later this evening and
tonight over the eastern plains, with the main threats being gusty
winds, hail of 1-2 inches, and perhaps even an isolated tornado.

Currently...

Cloud cover over the CWA has broken up slightly compared to this
morning, allowing for increased heating at the surface. A few
showers have already popped up over both the Continental Divide and
the far southeast plains, with no impactful weather reported as of
yet. Just north of our area, past the Palmer Divide, several strong
thunderstorms have already formed near the Denver Convergence Zone,
with storm motion vaguely heading northeast.

Today-Tomorrow...

The tip of an upper-level trough is currently making its way
eastward across Colorado, carrying with it enhanced lift and the
majority of the forcing for enhanced precipitation. Showers have
largely dwindled over the mountains and activity has steadily moved
east throughout the day, although coverage is expected to increase
overall as we progress later into the afternoon-evening hours,
thanks to a healthy influx of mid-level moisture expected to
circulate in around the upper-level high to our southeast. A weak
surface boundary is also set up far to the southeast, intersecting
portions of our southeast plains, which is assisting in giving us
some easterly upslope flow over the plains. The slowly recovering,
semi-stable air present in that area will also delay the onset of
significant convection for a few hours yet at least, but once
heating is able to overcome it and increase instability it may
result in stronger storms this evening.

Several short-term models have been consistently overmixing the
boundary layer over our area, mixing out dewpoints by several
degrees and limiting the extent of convection expected in our area.
Given current moisture profiles over the plains, these models
(including the HRRR) will have a bit less weight in the forecast for
today and tonight, while the NAM seems to be handling things much
better. Current analysis shows 500-1000 J/kg of CAPE over the Palmer
Divide area, and between 1000-1500 over the far southeast plains.
Around 30 knots of effective bulk shear are also present over the
Palmer, with a considerable 45+ knots over the plains. Current
dewpoints over the southeast plains are also currently sitting
around the mid-60s.

As of now, the main factor inhibiting thunderstorm development over
the plains is the semi-stable air (and related CIN) sitting in that
area. As daytime heating works to overcome it and continuously
destabilize the environment, the main forcing will come later this
evening as the axis of the upper trough passes overhead. As it does,
that forcing is expected to spark thunderstorms along and near the
boundary, assisted by easterly upslope flow increasing low-level
convergence. With the CAPE and shear in place, as well as the ample
moisture available in that area, we can expect a drastic increase in
precipitation over the next 12 hours.

To start, mostly moist, westerly flow aloft will assist in
increasing shower coverage over the mountains later this afternoon,
mainly over the San Juans, Sangres, and Continental Divide. As the
trough axis moves more to the east, the main forcing will expand to
cover the I-25 corridor, where upslope into our eastern mountains
and the Palmer Divide will assist in sparking scattered to
widespread showers and thunderstorms. As better forcing moves east
and the plains become further destabilized, strong to severe
thunderstorms will become possible later this evening into tonight.
Given the available surface vorticity traveling along with the upper-
level features, as well as the notable amounts of CAPE and shear
available, gusty 60 mph winds and 1-2 inch hail will be well within
the realms of possibility. Additionally, should an updraft manage to
latch itself to the existing surface vorticity and maintain itself,
cannot rule out the threat of an isolated tornado. Given the
strength of the easterly winds expected over the plains, this threat
could extend back to near the I-25 corridor, but is mainly confined
to the southeast plains near the CO-KS border.

Later tonight, storms are expected to continue, and as the upper
trough moves east, storms are expected to move off of the Palmer and
head southeast, where several short term models are actually
resolving a larger system with potential QLCS properties moving
across parts of the eastern plains before moving into Kansas by
tomorrow morning.

Showers are expected to persist into Saturday morning, although they
should be more stratiform in nature. A cold front is expected to
push south across the plains by late morning. Recent model trends
have been consistent in keeping the front more robust, meaning that
it will likely keep precipitation widespread over parts of the
southeast plains and our southeast mountains. However, given the
cooler, more stable air behind the front, thunderstorms, should any
manage to form, will likely be much weaker than the storms we expect
to see this evening. With post-frontal upslope flow expected to set
in by early afternoon, main concerns for Saturday`s weather will be
storms firing over and near the Spring Burn Scar, with flash-
flooding concerns on the table should a more convective storm manage
to drop consistent rain. Otherwise, things tomorrow will be more
stratiform, with overcast skies over much of the plains and cooler

.LONG TERM...(Saturday night through Friday)
Issued at 240 PM MDT Fri Sep 3 2021

Overall, there is great agreement through the extended between the
operational solutions and ensembles. This leads to higher
confidence in the extended period.

Saturday night...an upper level trough is forecast to slowly move
east into the Missouri Valley Saturday night, with trailing energy
shifting south across Eastern Colorado. Moist, easterly upslope
flow will be ongoing, with widespread precipitation from the
Eastern Mountains, east along the New Mexico border. Weak
instability may lead to a few thunderstorms over southern Sangre
de Cristo and Raton Mesa areas. Locally heavy rainfall may be
possible with stronger cores, which could produce a low risk of
flash flooding on the Spring burn scar. This activity will shift
south and east overnight, clearing to the southeast Sunday
morning.

Sunday through Thursday...high pressure will build over the Great
Basin and slowly shift eastward during this period. This will keep
dry conditions across southern Colorado for the Sunday afternoon,
through Thursday time frame. A dry cold front will bring a
continued cooler air mass to the area, with upper 80s to lower
90s across the Plains. Temperatures will gradually warm up by
Thursday, with mid to upper 90s expected across the Plains.

Friday...the upper level high will shift east into the Central
Plains by Friday, with southwesterly flow returning to souther
Colorado. Embedded energy could bring back showers and
thunderstorms to the forecast along the Mountains.  Mozley

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 240 PM MDT Fri Sep 3 2021

KALS: VFR conditions expected over the next 24 hours. Winds will
become gusty later this afternoon to about 20 mph before weakening
again this evening.

KCOS: VFR conditions generally expected through the next 24 hours.
Isolated to scattered showers and thunderstorms are expected in the
area, beginning after about 01Z and lasting through about 06Z
tonight. Given the nature of the expected precipitation, it is still
unclear whether anything will move directly over the terminal. If it
does, expect brief periods of moderate to heavy rainfall and gusty
erratic outflow winds. Will continue to closely monitor the area
this afternoon and evening. Precipitation should move away from the
area after midnight. After about 08Z tonight, there is a chance of
some lower clouds developing over the terminal, but left with VFR
conditions for now.

KPUB: VFR conditions are expected over the next 24 hours. Isolated
to scattered showers and thunderstorms will begin in the area around
23Z and increase in coverage throughout the evening and into the
overnight hours. Direct impacts to the terminal are still expected
to be low at this time, so left as VCSH. If a shower does manage to
move over the terminal, brief periods of moderate to heavy rainfall
and gusty erratic winds could be expected along with brief vis drops
to MVFR. Rain is expected to clear out after about 09Z, where clouds
will disperse and winds will weaken into tomorrow morning.


&&

.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

MESOSCALE...RODRIGUEZ
SHORT TERM...GARBEROGLIO
LONG TERM...MOZLEY
AVIATION...GARBEROGLIO