EMP risk areas are the places in the United States where an electromagnetic pulse, from a high-altitude nuclear burst or a severe solar storm, would hit the power grid and electronics hardest and keep the lights off longest. We treat risk as a set of factors that change by place, not a single danger zone. Once you know those factors, you can size your preparedness to your own ZIP code.
You may have wondered whether your region would suffer most. That is a fair question. The answer depends on geometry, grid design, geology and the age of the equipment down the road. Whether you are building your first three day kit or planning for a long term outage, the same factors apply, and you can look up each one.
Start by pulling out a recent electric bill. Write down your utility's name and your ZIP code. Those two details unlock every check that follows, and they take two minutes to find.
How Burst Altitude Decides Who Gets Hit
Learn burst geometry and you can place your home relative to any hypothetical high-altitude detonation. Nuclear EMP risk areas depend more on geometry than on how close you live to a likely target. Geometry sets the footprint, and the grid you sit on decides what happens after.
Three Pulses in One Flash
A high-altitude nuclear EMP, or HEMP, arrives as three overlapping waves. Each one threatens different equipment.
- E1, the fast spike. It arrives in billionths of a second and can overload small electronics, circuit boards and control chips.
- E2, the lightning cousin. It lasts from microseconds to about a second and acts like a lightning strike, which grid controls handle well unless E1 has already damaged their protection.
- E3, the slow push. It lasts seconds to minutes and drives current into long transmission lines and the large transformers at their ends.
Altitude Sets the Footprint
A pulse reaches everything within line of sight of the burst. The higher the burst, the farther the horizon.
- Low burst, about 30 km (19 miles) up. The footprint reaches roughly 600 km (370 miles) in every direction, about the size of a single region.
- Medium burst, about 100 km (62 miles) up. The radius grows to roughly 1,100 km (700 miles), enough to cover a large multistate area.
- High burst, about 400 km (250 miles) up. The radius stretches to roughly 2,200 km (1,400 miles), which puts nearly the entire continental United States in view.
Why the Strongest Fields Smile South
Field strength is uneven inside the footprint. Gamma rays from the burst knock electrons loose in the upper atmosphere. Earth's magnetic field bends those electrons, and that bending creates the E1 field. The field peaks where electrons cross magnetic field lines at close to a right angle. In the Northern Hemisphere, field lines dip toward the north, so that peak falls south of the point directly below the burst. The strongest zone curves in an arc shaped like a smile. Directly under the burst, fields run at roughly half the peak, and they drop off quickly to the north.
The EMP Commission, formally the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack, described these effects in its 2004 and 2008 reports. Those reports remain the most cited public sources on HEMP.
Distance Is Not a Shield
It makes sense to feel safer far from big cities. For blast and fallout, distance does protect you. A high-altitude pulse works differently, and a rural county south of a burst point could see stronger E1 fields than a city directly beneath it. Keep your rural location as an asset for space and supplies, and add electronics protection to your plan so geometry is covered too.
The Three US Grids and Why Your Interconnection Matters
Identify your interconnection and you will know how far an outage could spread and where emergency help would come from. Your grid is one of the quieter factors behind EMP risk areas. The US power system is three largely independent grids linked only by a few limited direct current (DC) ties. After the grid comes the ground beneath it, which shapes solar storm exposure.
Meet the Big Three
- Eastern Interconnection. It runs from the Atlantic coast to the Great Plains and into eastern Canada, carrying roughly two-thirds of US electricity demand through a dense web of lines.
- Western Interconnection. It covers the Rocky Mountains to the Pacific, plus western Canada and part of Baja California, and it relies on long lines that cross open country.
- ERCOT. The Electric Reliability Council of Texas runs the grid for most of Texas, serving about 26 million customers with only small links to its neighbors.
Separation Cuts Both Ways
The gaps between grids act like firebreaks. A cascading failure in one interconnection rarely jumps into another. The same gaps limit how much power one region can send another in an emergency. Texas saw this during Winter Storm Uri in February 2021, when ERCOT could not import enough power and millions of people lost electricity for days. If you live on a more isolated grid, plan for a longer self-reliant stretch. That same isolation means your recovery depends less on events hundreds of miles away.
Long Lines Catch More Current
E3 and geomagnetically induced currents (GICs) build voltage along the length of a transmission line. Long, high-voltage lines across sparse country can collect more of that current and push it into transformers. Dense, heavily meshed areas spread the load across many paths, but they also hold many more transformers that need protection. Neither layout is safe or doomed. Each carries a different kind of exposure.
Regulators have responded. In 2013, FERC Order 779 directed NERC to write standards for geomagnetic disturbance (GMD). NERC standard EOP-010 requires operating procedures for GMD events, and TPL-007 requires GMD vulnerability assessments of grid equipment.
Find Your Grid
Search your utility's name with the words balancing authority or RTO to learn which regional transmission organization serves you. Major RTOs include PJM, MISO, SPP, NYISO, ISO New England, CAISO and ERCOT. Many utilities in the Southeast and West operate outside an RTO, so note that if it applies. Write your interconnection and RTO next to your ZIP code, ready to score.
Latitude, Geology and Solar Storm EMP Risk Areas
Check your geomagnetic latitude and your bedrock, and you will know your exposure to a severe solar storm. Solar storm EMP risk areas follow different rules than nuclear ones. After the sun and the soil, local equipment decides how long the lights stay off.
A Slower Kind of Pulse
A geomagnetic storm begins when a coronal mass ejection, a burst of charged particles from the sun, strikes Earth's magnetic field. The shaking field induces slow currents in the ground that act much like E3. A solar storm produces no E1 spike, so your phone, car and laptop stay unharmed. The main threat is to the power grid and its large transformers. During the 1859 Carrington Event, telegraph lines sparked and some operators sent messages with their batteries disconnected.
Geomagnetic Latitude
Geomagnetic latitude measures distance from Earth's magnetic poles rather than its geographic poles. The geomagnetic north pole sits in the Arctic near Greenland, tilted toward North America. As a result, US cities have a higher geomagnetic latitude than European cities at the same geographic latitude. Northern states sit closer to the auroral zone, where storm currents run strongest. In a severe storm, that zone pushes south across more of the country.
Resistive Rock
Ground type decides how strong the induced electric field becomes. Conductive ground, such as thick sediment and wet clay, carries current away gently. Resistive igneous and metamorphic rock, such as granite, blocks that flow. The geoelectric field builds, and current takes the easier path through power lines and transformers. Parts of the upper Midwest, the Northeast and the Appalachian corridor sit on this kind of rock. Coastal areas can see enhanced effects, because conductive seawater meets resistive land at the shoreline and concentrates the field.
Real storms show the pattern. On March 13, 1989, the Hydro-Quebec grid, built on the resistive Canadian Shield, collapsed in about 90 seconds and left 6 million people without power for about nine hours. The same storm damaged a large transformer at a New Jersey nuclear plant. The 2003 Halloween storms caused a blackout in Malmo, Sweden, damaged transformers in South Africa and disrupted satellites.
Check Your Region
Sign up for free alerts from NOAA's Space Weather Prediction Center. Its G1 to G5 scale rates storms from minor to extreme, and a G4 or G5 alert gives you hours to charge batteries and fill water jugs. Next, look up your area in the USGS geoelectric hazard assessments, which rate regions by how strong storm fields can get. If you live in a northern state on resistive rock or near a coast, mark your solar risk as elevated. If you live farther south on deep sediment, mark it lower and put more of your budget toward everyday outage supplies.
Local Grid Fragility: Assessing Your Own Risk
Score your community and you turn every factor above into a plan sized to your family. Two neighboring towns can face very different outcomes from the same event, and local equipment is the reason. Scoring your EMP risk areas leads straight into steps you can start this weekend.
Transformers Set the Clock
Large power transformers are the grid's critical weak point. Each one can weigh 100 to 400 tons and is built to order, with replacement lead times that often run from one year to several. A blackout from tripped breakers can end in hours. A blackout from burned transformers can last months. That is why recovery time matters more than the initial outage. Industry programs such as the Spare Transformer Equipment Program keep some spares ready, which shortens the wait in many areas.
Score Your ZIP Code
Rate each factor as low, moderate or elevated.
- Burst geometry. Mark every continental US location as moderate, since a high burst can reach nearly all of it.
- Interconnection. Mark elevated if your grid has limited outside ties or your power arrives over long, sparse lines.
- Geomagnetic latitude. Mark northern-tier states elevated, middle states moderate and southern states low.
- Geology. Mark elevated for resistive bedrock or a coastal boundary, and low for deep sediment.
- Local infrastructure. Mark elevated if your town relies on one substation, sits far from power plants, or your utility has no published hardening plan, and call to ask about its GMD vulnerability assessment.
- Water and fuel. Mark elevated if your water comes from an electric well pump or your nearest fuel station has no generator.
Mostly low scores point to a solid three day kit. A mix points to one week of supplies. Several elevated scores justify long term planning for water, power and food.
Rural and Urban Outages
If you live rurally, your well pump stops when the power does, and fuel may be miles away. Utilities restore hospitals, water plants and dense lines first, so rural lines often come back last. Your space is the asset, with room for water barrels, a hand pump, a woodstove and a garden. If you live in a city, water plants may run on backup generators for a few days, and fuel lines form fast. Your neighbors are the asset, with more hands and skills within walking distance.
Steps for This Weekend
- Backup power. Set up a generator or a solar panel with a battery bank to keep a fridge, lights and medical devices running, and rotate stored fuel every six months.
- Water storage. Store one gallon per person per day, starting with three days and building toward two weeks.
- Faraday storage. Put a spare radio, flashlight and old phone in a metal can lined with cardboard, then test it by calling the phone inside and adding foil layers if it rings.
- Shelf-stable food. Lay in food that needs no cooking or refrigeration.
- Community planning. Meet your neighbors and agree on a meeting spot and a shared skills list.
Ready.gov offers free checklists for power outages and family plans. For the full household plan, see EMP Preparedness for Your Family on Prepper Life. With each factor scored, you know which EMP risk areas apply to you and where your preparedness effort pays off most.
