Wide-footprint windstorms, flooding, and cold snaps create different outage problems across summer and winter.
Illinois combines a very high modeled risk score with a NOAA record dominated by Thunderstorm Wind, Flood, Flash Flood, Winter Storm, and Tornado events, so the practical outage case is broader than a winter-only description.
Mixed Windstorm, Flood, and Winter Reliability
Illinois faces its most severe grid disruptions not from hurricanes or ice but from derechos, fast-moving windstorms that can match hurricane-force intensity with almost no advance warning. Commonwealth Edison, the dominant utility in northern Illinois, serves more than four million customers across the region, covering roughly 70 percent of the state's population.
In August 2020, a derecho tore across the Midwest with wind gusts exceeding 80 miles per hour. At its peak, more than 800,000 ComEd customers lost power. The storm damaged substations and transmission towers in addition to the typical overhead line and pole failures. ComEd described portions of the restoration as a grid rebuild rather than a simple repair job, and full restoration took six days. The south suburbs of Chicago were hit hardest, with communities like Harvey seeing more than 90 percent of customers without service for days.
For backup sizing, the derecho pattern matters because it combines the destructive force of a hurricane with the footprint of a regional thunderstorm. Damage spreads across a wide corridor, stretching mutual aid resources thin and extending restoration timelines beyond what a typical summer storm would require. Despite that scale, the August 2020 derecho does not appear in the federal declaration count shown above, which is exactly the point: some of Illinois's most consequential outages never cross the federal declaration threshold.
Federal disaster declaration for severe storms and flooding in Illinois in September 2023, reflecting a broader statewide outage pattern than a flood-only label would suggest.
Source: FEMA DR-4749Evidence trail
These notes trace the editorial claims above back to FEMA, DOE, utility, or other cited records.
FEMA declaration count (7) from OpenFEMA API, deduplicated by disaster number, DR/EM/FM types, 2014-2023.
NRI composite score (90.4) from FEMA NRI county layer, population-weighted to state level; top modeled hazards are Cold Wave, Tornado, and Heat Wave.
NOAA outage-relevant event mix is led by Thunderstorm Wind (12,437), Flood (2,222), Flash Flood (2,219), Winter Storm (1,550), Tornado (1,423), and Strong Wind (1,347), with Cook, Du Page, Will, Kane, and Champaign leading county counts.
Illinois Severe Storms and Flooding DR-4749 from FEMA disaster declaration records.
Aug 2020 derecho wind gusts (80+ mph, northern IL): National Weather Service Chicago, August 10 2020 Corn Belt Derecho event summary (2020-08).
ComEd outages (800K customers, 4M total served, 70% of state, 6-day restoration, Harvey 90%+ outage): ABC7 Chicago citing ComEd figures (2020-08).
Structured FEMA NRI, HHS emPOWER, NOAA Storm Events, and EIA methodology is documented separately on the methodology page.
NRI's top modeled hazards are Cold Wave, Tornado, and Heat Wave, while NOAA's outage-relevant record is led by Thunderstorm Wind, Flood, Flash Flood, Winter Storm, Tornado, and Strong Wind events..
NOAA storm-event records filtered to outage-relevant event types for Illinois. Counts reflect historical storm-event assignments, not confirmed utility outages.
Analysis window
2005-01 to 2024-12
Included storm-event records
23,093
Source as of
2026-03
Included exact NOAA event types for Illinois: Thunderstorm Wind, Tornado, High Wind, Strong Wind, Flash Flood, Flood, Winter Storm, Ice Storm, Freezing Rain, Heavy Snow, Blizzard.
In this filtered NOAA record set for Illinois, Jun has the highest monthly count (4,622 records) , and Thunderstorm Wind is the leading event type. This chart shows frequency in NOAA records, not how severe a specific outage may be.
5 events were not mapped to a county ranking.
45 events were not mapped to a county ranking.
14 events were not mapped to a county ranking.
96.4% of listed records were matched directly to this county.
86.2% of listed records were matched directly to this county.
96.5% of listed records were matched directly to this county.
83.0% of listed records were matched directly to this county.
85.2% of listed records were matched directly to this county.
90.4% of listed records were matched directly to this county.
With the current Illinois NWS county crosswalk, mapped forecast zones are effectively 1:1 with counties; a small number of unresolved forecast zones remain excluded from county rankings.
Direct county match
79.0%
Mapped from forecast zone
20.4%
Not assigned to county ranking
0.7%
Unresolved forecast zones
2
County-level HHS emPOWER counts for electricity-dependent Medicare beneficiaries in Illinois.
94,354 Medicare beneficiaries in Illinois have claims associated with electricity-dependent medical equipment. (HHS emPOWER, 2026-03)
County-level HHS emPOWER records for this state. Medicare enrollment data only. 102 counties are included in this state snapshot.
Smaller Medicare base; interpret this percentage with extra caution.
Smaller Medicare base; interpret this percentage with extra caution.
Smaller Medicare base; interpret this percentage with extra caution.
Counties with higher concentrations may face elevated community-level demand for backup power during outages. This does not indicate individual medical necessity.
Limitations: Reflects Medicare beneficiaries with claims associated with electricity-dependent medical equipment. Does not capture non-Medicare or uninsured populations. HHS masks cells from 1 to 10 as 11.
The GeneratorChecker Backup Priority Index is a county shortlist for backup planning, combining historically frequent outage-relevant storm activity with larger county counts of electricity-dependent Medicare beneficiaries. It is planning context, not a forecast or an outage guarantee.
BPI version
v1.0
Analysis window
2005-01 to 2024-12
Matched counties
102
Counties qualify for the public BPI only when both signals land at or above the 80th percentile within the state. The shortlist excludes low-base medical counties and counties with less than 30% direct NOAA county matching.
Qualifying counties shown on the page: 5.
Percentiles are computed within Illinois only and are not comparable across states.
1. COOK
County FIPS 17031
At-risk Medicare count
27,767
Storm-event records
1,351
Direct NOAA county match
96.4%
2. DU PAGE
County FIPS 17043
At-risk Medicare count
4,907
Storm-event records
567
Direct NOAA county match
86.2%
3. WILL
County FIPS 17197
At-risk Medicare count
4,074
Storm-event records
564
Direct NOAA county match
96.5%
4. KANE
County FIPS 17089
At-risk Medicare count
2,660
Storm-event records
477
Direct NOAA county match
83.0%
5. LAKE
County FIPS 17097
At-risk Medicare count
4,331
Storm-event records
370
Direct NOAA county match
77.8%
State-level utility structure from official EIA Form 861 data, shown as planning context alongside the weather and medical layers.
Data year
2024
Utilities in scope
25
Residential customers represented
5,233,221
97.5% of in-scope residential customers in Illinois are served by utilities that report complete annual SAIDI and SAIFI pairs to EIA for 2024, excluding major event days.
GeneratorChecker does not blend statewide SAIDI or SAIFI values across IEEE and Other Standard reporters in this public layer.
This block identifies the utility structure behind the state, but it does not score your local grid reliability.
IOU • IEEE reporter
IOU • IEEE reporter
IOU • IEEE reporter
Municipal • Other Standard reporter
Municipal • IEEE reporter
Start with a 24-hour storm-continuity bundle, then add winter heating support if your household needs to bridge a colder second day.
Primary Illinois scenario: derecho, flood, or severe-storm outage interrupts refrigeration, communications, medical support, and basic work continuity.
Load
698W
Target
24h
Minimum
27,600 Wh
This is the broader Illinois baseline for storm-driven outages that do not fit a winter-only template.
Size this scenario in calculatorExtended Illinois scenario: colder multi-day outage where food preservation, communications, medical support, and a gas-heating blower all need to stay online.
Load
1396W
Target
48h
Minimum
110,100 Wh
This scenario adds heating-system support and does not model electric resistance heating.
Size this scenario in calculatorCritical Note: No single portable power station in our database covers the full 24-hour baseline at this load (27,600 Wh target vs. 6,144 Wh max in our current database). Use solar recharge, load rotation, or expandable systems for longer events.
Sizing for winter only when Illinois also sees wide-footprint summer windstorms and flood-driven outages.
Forgetting communications and medical-device continuity during regional storm recovery.
Not accounting for heating-support blower loads when a colder outage stretches beyond the first day.
A 1,500W space heater drains a power station in 1-2 hours. Here's the honest math on battery-powered heating, plus smarter alternatives that actually work.
From CPAP to oxygen concentrators, here is a practical checklist for keeping medical equipment running during power outages. Includes sizing math and emergency contacts.
For home backup, you need surge capacity for fridge compressors and enough Wh for multi-day outages. Here are the best options from our database of 33 stations.
Composite score: 90.4 / 100
Rating: Very High
Top modeled hazards: Cold Wave, Tornado, Heat Wave
Hurricane score: 35.4
Winter Weather score: 84.3
Wildfire score: 37.4
Total (2014-2023): 7
Most recent: 2023-11-20 Flood
| Type | Count |
|---|---|
| Flood | 3 |
| Biological | 2 |
| Severe Storm | 1 |
| Tornado | 1 |
Required Wh = (Total Load W × Target Hours / Inverter Derate) × Safety Factor
Inverter derate: 0.70 (30% real-world loss)
Safety factor: 1.15
Rounding: Up to nearest 100 Wh
Illinois has an NRI composite risk score of 90.4 (Very High), with 7 federal declarations from 2014 to 2023. NRI's top modeled hazards are Cold Wave, Tornado, and Heat Wave, while NOAA's outage-relevant record is led by Thunderstorm Wind, Flood, Flash Flood, Winter Storm, Tornado, and Strong Wind events..
For the primary scenario on this page (24-hour storm continuity), the estimated minimum is 27,600 Wh for a 24-hour target. Refine this in the calculator with your actual devices.
NRI is a modeled risk index based on hazard exposure, vulnerability, and expected loss. FEMA declarations reflect federally declared incidents. They answer different questions — use both signals together for planning.
Buying for one season only and missing that Illinois households may need both storm continuity and winter heating support. See the common mistakes section above for more state-specific pitfalls.
The main difference is scale. A derecho can damage lines, poles, and substations across a much wider region at the same time, creating multi-county restoration stress and a longer outage pattern than a more localized thunderstorm usually causes.
