Cold-wave heating risk and wide-footprint windstorms create different outage problems across winter and summer.
Illinois combines a very high modeled risk score (NRI 90.4) with only seven federal declarations in ten years, suggesting many consequential outages never rise to the federal declaration threshold.
Cold-Wave and Tornado 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 flooding in central and southern Illinois.
Source: FEMA DR-4728Evidence 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.
Central Illinois Flooding DR-4728 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.
The gap between high NRI modeling (90.4) and low declaration count (7) suggests local events that may not reach the federal threshold.
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
IOU
IOU
Municipal
Municipal
Treat winter duration as primary, then validate summer storm flexibility.
Heating-system support, communications, and medical continuity during a winter outage.
Load
1189W
Target
24h
Minimum
46,900 Wh
This scenario assumes your home uses a gas furnace or boiler that still needs blower power. Portable power stations are not a substitute for electric resistance heating.
Size this scenario in calculatorAdd refrigeration to preserve food during a multi-day grid outage while keeping heating-system support online.
Load
1396W
Target
48h
Minimum
110,100 Wh
Consider expandable systems or solar for events beyond 48 hours.
Size this scenario in calculatorCritical Note: No single portable power station in our database covers the full 24-hour baseline at this load (46,900 Wh target vs. 6,144 Wh max in our current database). Use solar recharge, load rotation, or expandable systems for longer events.
Planning for brief outages only when cold-wave events require longer essential coverage.
Forgetting communications and medical-device continuity during winter interruptions.
Not accounting for heating-support blower surge behavior during startup.
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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. The gap between high NRI modeling (90.4) and low declaration count (7) suggests local events that may not reach the federal threshold.
For the primary scenario on this page (24-hour heating-support essential), the estimated minimum is 46,900 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.
Sizing around nameplate watts without translating that into usable runtime under inverter losses. See the common mistakes section above for more state-specific pitfalls.
