SPC Sep 29, 2026 1630 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1120 AM CDT Tue Sep 29 2026

Valid 291630Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN
ARIZONA ACROSS SOUTHERN/EASTERN NEW MEXICO INTO WEST TEXAS...

...SUMMARY...
Isolated severe thunderstorm wind gusts and possibly a tornado or
two could occur this afternoon into tonight from southeast Arizona
across southern and eastern New Mexico into west Texas.

...Synopsis...
Fairly complex synoptic evolution is anticipated today through
tonight as a remnants of what is currently Hurricane Polo become
absorbed within the circulation of the deepening mid-latitude
cyclone currently centered over the Lower CO River Valley. In
general, the Lower CO River Valley cyclone is forecast to deepen as
it gradually shifts eastward. In response, Hurricane Polo is
forecast to move quickly northeastward across Sonora and into New
Mexico. Polo is forecast to weaken over the mountainous terrain of
northern Mexico, but will likely maintain some of its warm-core
characteristics through at least tomorrow morning. Additionally,
mass response across the southern High Plains will result in
increasing low-level moisture advection across the southern Plains
while also aiding in surface cyclogenesis across central and eastern
NM late tonight/early tomorrow.

...Southern Arizona...
Recent surface analysis reveals a very moist airmass over southern
AZ, with a corridor of mid to upper 60s dewpoints extending from the
central southern border into the Phoenix vicinity. Surface analysis
also places a weak low over south-central AZ. VAD profiles from IWA
and EMX both show fairly long hodographs, supported by 30 to 40 kt
of low/mid-level southwesterly flow. Widespread showers and
thunderstorms will likely continue throughout the day, with limited
diurnal heating and weak tropical lapse rates keeping buoyancy
modest. Even so, the strong nature of the wind profiles could
support a few at least weak/transient supercells, and potentially
more organized convective bands later today, with at least some
potential for strong thunderstorm wind gusts.

...Southern High Plains...
Thunderstorm coverage is expected to increase notably this
afternoon/evening as the core of Polo progresses into the region.
Tropical character of the airmass will keep lapse rates poor while
cloud cover also limits heating, limiting the overall buoyancy.
Nonetheless, buoyant thermodynamic profiles are still expected to
result in updrafts deep enough for lightning production.
Additionally, low-level wind profiles are expected to lengthen
significantly after 00Z as the remnants of Polo interact with a
dynamically strengthening low-level jet. The widespread storm
coverage will result in a tendency toward complex or linear storm
modes with time, though a few/episodic supercells will also be
possible. A brief tornado and/or strong wind gusts could accompany
any organized, more persistent storm structures.

..Mosier/Chalmers.. 09/29/2026


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SPC Sep 29, 2026 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0751 AM CDT Tue Sep 29 2026

Valid 291300Z - 301200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
ARIZONA/NEW MEXICO TO WEST TEXAS...

...SUMMARY...
Isolated severe thunderstorm wind gusts and possibly a tornado or
two could occur this afternoon into tonight from southern and
eastern New Mexico into west Texas, and across southeast Arizona.

...Synopsis...
A mid/upper-level low and attendant trough will move across the
Desert Southwest through the period. In response to the approaching
deep trough, Hurricane Polo is forecast to move from the Gulf of
California into Sonora this morning. While the tropical cyclone is
forecast to weaken over the mountainous terrain of northern Mexico
later today, a phasing of the mid-level remnants of Polo with the
approaching deep mid/upper-level trough will result in a
consolidating surface low that is forecast to deepen and move across
eastern New Mexico and west Texas tonight.

...Southern/eastern New Mexico to west Texas...
Widespread convection is ongoing and expected to generally continue
into this afternoon and tonight from southern/eastern New Mexico to
west Texas, as increasing large-scale ascent overspreads a very
moist environment. The influence of the remnant tropical system will
result in poor mid-level lapse rates, but increasing deep-layer
flow/shear and enlarging low-level hodographs will favor some storm
organization, especially later this afternoon and evening. The
widespread storm coverage will result in a tendency toward complex
or linear storm modes with time, though a few/episodic supercells
will also be possible. The weak lapse rates and modest buoyancy are
expected to limit the overall magnitude of severe potential, but a
localized tornado and severe-gust threat could accompany any
organized storm structures, particularly this afternoon and evening,
influenced by a nocturnally strengthening low-level jet.

...Southern Arizona...
A moist environment resides in close proximity to the Southwest
Deserts mid/upper-level low, with a belt of very strong deep-layer
winds sampled in available 12z upper-air data and regional WSR-88D
VWPs. Scattered thunderstorms are common this morning, and while
this convection/related cloud cover will generally hinder overall
destabilization, modest diurnal heating will probably lead to some
convective intensification during the day. The strong nature of the
wind profiles could support a few at least weak/transient
supercells, and potentially more organized convective bands later
today, with at least some potential for strong thunderstorm winds
and mostly sub-severe hail.

..Guyer/Bentley.. 09/29/2026


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SPC Sep 29, 2026 0100 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 0100Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 PM CDT Mon Sep 28 2026

Valid 290100Z - 291200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
WESTERN/CENTRAL DAKOTAS AND CENTRAL HIGH PLAINS...

...SUMMARY...
Isolated strong to locally severe storms remain possible this
evening across parts of the western/central Dakotas and also the
central High Plains.

...Parts of the Dakotas into the central High Plains...
Widely scattered strong thunderstorms are ongoing this evening from
eastern ND into western SD. While low/midlevel lapse rates are
generally weak, relatively rich low-level moisture is supporting
MLCAPE of near/above 1000 J/kg, with 25-35 kt of effective shear
sufficient for occasional storm organization. Isolated hail and
strong to severe gusts cannot be ruled out this evening, though a
weakening trend is expected later tonight as convection becomes
increasingly elevated with time.

Farther south, isolated strong storms are ongoing this evening
across parts of northwest NE, and also near the CO/KS border.
Occasional supercell structures will be possible through dusk,
though modest lapse rates and buoyancy may tend to limit the
magnitude of the severe threat. See MCD 2332 for more information
regarding the short-term threat in this area.

..Dean.. 09/29/2026


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SPC Sep 28, 2026 2000 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 2000Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Mon Sep 28 2026

Valid 282000Z - 291200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN PLAINS...

...SUMMARY...
Isolated strong to severe thunderstorms may occur this afternoon and
evening across parts of western/northern South Dakota and vicinity.

...20z Update...
Latest observations depict a corridor of stronger surface heating
and less prevalent cloud cover in the vicinity of northwestern South
Dakota, with surface temperatures noted to have warmed into the
low/mid 70s F downstream of developing convection near the WY/SD
border. Thus, the existing Level 1/Marginal risk was expanded
slightly to the northwest with this outlook update. See recently
issued MCD #2330 and the text below for additional information.

Elsewhere, the forecast remains generally on track, with only minor
adjustments made to the general thunder area based on latest
observational trends.

..Chalmers/Lyons.. 09/28/2026

.PREV DISCUSSION... /ISSUED 1128 AM CDT Mon Sep 28 2026/

...Northern Plains...
Clouds and elevated thunderstorms remain prevalent late this morning
across parts of the Dakotas. A narrow window for strong to locally
severe thunderstorms may exist this afternoon/evening across parts
of western/northern SD and vicinity as convection develops
along/east of a weak surface trough. While lapse rates aloft should
remain modest, filtered daytime heating with surface temperatures
reaching the mid/upper 70s will probably be sufficient for robust
thunderstorm development. A belt of modestly enhanced southwesterly
mid-level flow will extend across the northern Rockies/Plains today,
and 30-40 kt of deep-layer shear should support updraft
organization. Current expectations are for thunderstorms to
initially form near the Black Hills by 20-22Z, and then spread
east-northeastward along/near a surface front through the evening.
The stronger cells may be capable of producing isolated hail and
gusty winds, before convection tends to become elevated with
eastward extent across northern SD/southern ND by late evening.

...Lower Colorado River Valley...
Showers and thunderstorms should develop this afternoon as an
anomalously moist low-level airmass spreads northward ahead of a
mid-level shortwave trough forecast to move from CA/NV to the lower
CO River Valley through the period. Cloudiness and weak mid-level
lapse rates should limit instability through early afternoon, before
cloud cover gradually diminishes through early evening. A stronger
thunderstorm or two may occur parts of interior southern
CA/northwest AZ/southern NV, but the overall risk for severe
hail/wind appears too limited to include any probabilities for this
region at this time.


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