Monday afternoon desk. Water still owns the Southwest. A small Marginal is now on the northern Plains. Not an NWS warning.
This is a live Monday afternoon snapshot of U.S. local-storm activity as of Monday, September 28, 2026. The morning desk opened with a blank severe map. The Storm Prediction Center 2000 UTC Day 1 Convective Outlook, issued 0258 PM CDT, now carries a Marginal Risk of severe thunderstorms across parts of western and northern South Dakota and vicinity. No convective watches are valid. The last issued watch remains number 0674.
The Weather Prediction Center still holds a Moderate Risk of excessive rainfall over portions of the Southwest and Four Corners. The 16Z update expanded that Moderate southwest down the Colorado River to include the California–Arizona–Nevada tripoint. Restoration exposure this afternoon is water first on already wet Southwest ground, then isolated hail and gusty wind on the Dakotas Marginal, plus a short radar-indicated severe thunderstorm warning that fired over San Bernardino County, California. Conditions change fast. Verify with the National Weather Service for the specific county or ZIP before you roll.
What is live this afternoon
SPC summary language at 0258 PM CDT: isolated strong to severe thunderstorms may occur this afternoon and evening across parts of western and northern South Dakota and vicinity. The 20Z update notes stronger surface heating and less cloud cover near northwestern South Dakota, with temperatures into the low and mid 70s F downstream of developing convection near the Wyoming–South Dakota border. Storms were expected to form near the Black Hills around 20–22Z and spread east-northeast along a weak surface front. Stronger cells may produce isolated hail and gusty winds before becoming elevated across northern South Dakota and southern North Dakota later tonight.
Mesoscale Discussion 2330, issued 0240 PM CDT and valid through 2145 UTC, covers the western South Dakota vicinity. Concerning: severe potential, watch unlikely. Watch-issuance probability is 5 percent. SPC language: isolated strong to severe storms may produce sporadic hail through evening. Most probable peak hail size up to 1.25 inches. Most probable peak wind gust up to 60 mph. That is a local pulse, not a watch day.
WPC Day 1 excessive rainfall, updated 1537 UTC Monday and valid 16Z Monday through 12Z Tuesday, remains the national water headline. A Moderate Risk covers portions of the Southwest. The 16Z update expanded the Moderate to the CA/AZ/NV tripoint after coordination with NWS Las Vegas. Marginal and Slight areas were expanded north along the Nevada–Utah border. A separate Slight Risk remains over parts of North Dakota and northwestern Minnesota from training showers on the low-level jet. WPC notes much of the ongoing Arizona rain has been stratiform, but soils are already wet and the terrain is flashy.
National Hurricane Center as of the 2:00 PM MST Monday Polo advisory: Hurricane Polo is still a major hurricane near 25.0°N, 113.0°W, moving northeast at 12 mph, 115 mph maximum sustained winds, 963 mb. Life-threatening winds and flash flooding are beginning over portions of Baja California Sur. That is a Mexico land desk plus a U.S. flood-moisture feed. It is not a California or Arizona hurricane landfall. Hurricane Nolo remains a Central Pacific / Papahanaumokuakea desk. Tropical Storm Rachel is paralleling the southwest Mexico coast. Atlantic Tropical Depression Fay and Tropical Storm Hanna are not a CONUS land-threat desk this afternoon.
Hotspot 1 — Southwest and Four Corners flood Moderate
This is still today’s organized desk. Predecessor moisture from Polo and remnants of Odalys continues to lift north ahead of a mid-level shortwave moving from the California Valleys toward the lower Colorado River Valley. WPC guidance still supports a widespread 1 to 3 inches across the Four Corners region on soils already near saturation. South- and west-facing slopes along the Mogollon Rim and the San Juans remain favored. Burn scars, slot canyons, and rocky fans fail first.
Counties and terrain to watch this afternoon: Mogollon Rim and higher terrain in Arizona; western and southwestern New Mexico including burn-scar drainages near Lordsburg; the San Juan Mountains and adjacent southwest Colorado; southern Nevada valleys; and the newly expanded Moderate near the CA/AZ/NV tripoint and the lower Colorado River. WPC also flagged slow-moving lines along the Nevada–Utah border.
Restoration read: water first. Stage pumps, extractors, and sandbags on known flood ZIPs and burn-scar alluvial fans. Photograph crawlspaces and finished basements as soon as it is safe. Do not treat this as a wind event unless a local warning says otherwise.
Hotspot 2 — Western and northern South Dakota Marginal
This is the only categorical severe area on the current Day 1 map. SPC expects storms to form near the Black Hills and move east-northeast along a weak surface trough and front. MD 2330 keeps a watch off the table. Isolated quarter-to-golf-ball hail and 60 mph gusts are the staffed threats, not a derecho and not a tornado outbreak. Aberdeen and Rapid City county warning areas own the pulse. Northern South Dakota into southern North Dakota trends more elevated after dark.
Restoration read: isolated hail and tree work if a cell verifies. Do not pre-position a regional CAT team on a 5-percent watch probability.
Hotspot 3 — Lower Colorado / San Bernardino isolated SVR
SPC still withholds unconditional severe probabilities for southeast California, southern Nevada, and western Arizona, but NWS Las Vegas issued a Severe Thunderstorm Warning at 129 PM PDT Monday for San Bernardino County until 215 PM PDT. Radar-indicated hazards: 60 mph gusts and quarter-size hail near Amboy and Interstate 40 between mile markers 68 and 98, storm moving northeast at 20 mph. That warning is a short local pulse inside the WPC flood overlay, not an SPC watch.
Restoration read: check I-40 desert ZIPs and any hail-struck vehicles after the cell passes. The bigger ticket in that same corridor remains flash-flood water, not wind.
Just hit
SPC local storm reports for the current 1200 UTC Monday to 1159 UTC Tuesday window showed no tornado, hail, or wind reports as of this afternoon desk. That board resets at 12Z. Last night’s preliminary reports from the 27/1200–28/1159 UTC window remain the open tickets:
- 2216 UTC Sunday — 1.00-inch hail 20 miles south of Merriman, Cherry County, Nebraska. Vehicle damage reported. (NWS North Platte)
- 2330 UTC Sunday — 1.00-inch hail 2 miles north-northwest of Willow Park, Parker County, Texas. (NWS Fort Worth)
- 0032 UTC Monday — 1.00-inch hail 24 miles north of Whitman, Cherry County, Nebraska. (NWS North Platte)
- 1440 UTC Sunday — 66 mph gust 10 miles northwest of Okobojo Creek Recreation Area, Sully County, South Dakota. Mesonet. (NWS Aberdeen)
- 2300 UTC Sunday — 60 mph gust 22 miles west-southwest of Roosevelt, Sutton County, Texas. West Texas Mesonet Sonora 23SE. (NWS San Angelo)
- 2320 UTC Sunday — Unknown-speed wind 4 miles north-northwest of Willow Park, Parker County, Texas. Large tree limbs down on FM 730. (NWS Fort Worth)
No tornado reports were received in that window. Sunday evening Severe Thunderstorm Warnings over southwestern Cherry County, Nebraska, and northeastern Parker County, Texas, have expired. Today’s San Bernardino warning is a live local product, not yet an LSR.
Pulse table
| Region | Main threats | SPC / NWS / WPC level | Status this afternoon |
|---|---|---|---|
| Southwest / Four Corners | Flash flood, training rain, burn-scar runoff | WPC Moderate excessive rainfall | Live through Tuesday 12Z; outline expanded to CA/AZ/NV tripoint |
| Western / northern South Dakota | Isolated hail, gusty wind | SPC Marginal; MD 2330 watch unlikely | This afternoon into evening |
| Eastern Dakotas / NW Minnesota | Training showers, localized flood | WPC Slight excessive rainfall | Ongoing |
| SE CA / southern NV / western AZ | Numerous storms, isolated wet downburst or SVR | General thunder; local SVR San Bernardino | Today into evening |
| Cherry County, NE / Parker County, TX | Quarter hail, tree limbs | Expired SVR / Sunday LSRs | Just-hit cleanup |
| Polo | Baja wind and flood; U.S. moisture feed | NHC major hurricane near Baja Sur | Not a CONUS landfall |
What this means for restoration teams
The national severe map is no longer blank, but it is still a small Marginal. The work that actually fills trucks today is WPC Moderate water on the Southwest and Four Corners. Saturated soils plus burn-scar fans do not need a supercell. Stage extraction before the next training core, not after the first flash-flood warning.
South Dakota is isolated hail and outflow if the Black Hills cells organize. MD 2330 says watch unlikely. Staff it as a local pulse. Cherry County and Willow Park remain yesterday’s hail and limb tickets. Photograph vehicles and roofs in daylight if it is still safe.
Polo is a Baja and Sonora hurricane desk plus a U.S. flood-moisture feed. Do not staff it as a California or Arizona landfalling hurricane. Nolo is a Central Pacific desk.
What this is not
This is not a Slight or Enhanced severe day, not a derecho, and not a U.S. mainland hurricane landfall. Work today, if it verifies, is flash flooding on the Four Corners Moderate, a narrow Dakotas Marginal, and one desert SVR in San Bernardino County. That is the local-storm pattern this desk should staff.
Looking ahead
SPC Day 2, issued 1215 PM CDT Monday and valid 12Z Tuesday through 12Z Wednesday, is a Marginal Risk from southern and eastern New Mexico into west Texas. Isolated severe gusts and a couple of tornadoes are possible Tuesday afternoon through early Wednesday as Polo remnants eject toward far west Texas and southeast New Mexico. Day 3 is already a Slight. WPC keeps Moderate flood language into Tuesday over parts of the Southwest, central and southern Rockies, and southern High Plains. Watch Tuesday morning Storm Tracker rather than assuming today’s small map is the week.
Sources and how to verify
Primary sources: NOAA Storm Prediction Center Sep 28, 2026 2000 UTC Day 1 Convective Outlook; SPC Mesoscale Discussion 2330; SPC Current Watches page (no watches valid as of 1414 UTC Monday); SPC local storm reports for 28/1200 UTC–present and 27/1200–28/1159 UTC; Weather Prediction Center Day 1 Excessive Rainfall Outlook updated 1537 UTC Mon Sep 28; National Hurricane Center Hurricane Polo Advisory 33 at 2:00 PM MST Mon Sep 28; NWS Las Vegas Severe Thunderstorm Warning for San Bernardino County issued 129 PM PDT; National Weather Service warning text compiled at weather.gov.
Check weather.gov for the county warning, spc.noaa.gov for the outlook, watches, MDs, and LSRs, and WPC excessive rainfall for the flood overlay. Morning desk for this calendar day: Storm Updates: Southwest Flood Moderate, Quiet Severe Pulse — Monday, September 28, 2026 (Morning).
Informational only — not an official weather warning. Follow local authorities and the National Weather Service. Turn around, don’t drown.