Cold air damming is a winter pattern in which a shallow layer of cold air is trapped against the eastern side of a mountain range and refuses to mix out, sometimes for three or four days. Along the Appalachians, forecasters call it the wedge. For weather-sensitive people it is the most misleading pattern of the year, because the surface barometer stays high and nearly flat while the weather steadily deteriorates — grey overcast, drizzle or freezing drizzle, temperatures fifteen degrees below forecast, and no obvious atmospheric event to explain why the week has been so hard.

If you keep a pressure log and have ever had a stretch of bad days that the log completely fails to account for, a wedge is one of the more likely explanations.

If you live downwind of one of the Great Lakes, the single most important thing to know about lake effect weather health is that the heaviest snow arrives on a rising barometer. Lake-effect snow develops behind a departed low, under cold northwest flow, while surface pressure climbs steadily. Someone who has learned to associate falling pressure with symptom days will find that relationship inverted for months at a time — and will conclude, wrongly, that their pressure sensitivity has stopped working.

It has not stopped working. Something else is going on, and it is worth taking apart carefully.

Standard storm preparedness advice assumes someone who can carry water upstairs, sleep on a camp bed, drive to a shelter and stay functional on four hours of sleep. If you live with chronic pain, migraine, fatigue or a condition affected by weather, the useful plan looks different in three specific ways: the preparation has to be finished before the barometric fall begins rather than during it, the supply list has to include the medical items nobody's checklist mentions, and the plan has to assume you may be having a bad day at exactly the worst moment.

That last assumption is the one most people skip, and it is the one that matters most.

A surface weather map is the chart showing highs, lows, fronts and isobars across a region. For someone planning around weather sensitivity, it answers three questions that a single pressure reading cannot: how deep the approaching system is, how fast the change will arrive, and whether it will come as a short sharp jolt or a long slow ramp. Reading one takes about ninety seconds once you know what you are looking at, and it turns "pressure is falling" into "pressure will fall eighteen hPa, most of it between four and ten tomorrow evening."

That difference is the whole point. Planning requires timing, and timing lives on the map.

A front is the boundary between two air masses of different temperature and humidity. There are four types — cold, warm, stationary and occluded — and each produces a distinct barometric signature. A cold front gives a sharp fall followed by an abrupt rise over a few hours. A warm front gives a slow fall over a day or more, then a levelling off. A stationary front gives days of little change with persistent cloud and rain. An occluded front gives the deepest reading of the sequence and the longest recovery.

If you track pressure for health reasons, knowing which front is on the way tells you the shape and duration of the change ahead — information a single pressure number cannot give you.

An Alberta clipper is a fast, compact low-pressure system that forms in the lee of the Canadian Rockies in Alberta or Saskatchewan and races southeast across the northern United States, often covering a thousand miles in twenty-four hours. It is moisture-starved, because it has crossed a continent and a mountain range rather than an ocean, so it usually produces only one to four inches of snow. Its barometric signature is modest in depth — typically 8 to 15 hPa — but remarkable in speed, with the whole fall and much of the recovery compressed into twelve to eighteen hours. For anyone whose symptoms respond to the rate of pressure change rather than the absolute amount, clippers are disproportionately important relative to how little snow they deliver.

The season runs roughly from November through March and peaks in January, and in an active winter the northern tier of states can see one every three or four days.

An atmospheric river is a narrow corridor of concentrated water vapour in the lower atmosphere, typically 250 to 375 miles wide and thousands of miles long, that transports moisture from the subtropical Pacific toward the West Coast of North America. The strong ones carry more water than the Mississippi River at its mouth. They matter for weather-sensitive people because they arrive attached to deep Pacific low-pressure systems, and those systems produce almost all of the barometric pressure movement the West Coast sees in a year. A typical event drops the reading 10 to 20 hPa over roughly a day, with stronger storms going considerably deeper, and then rebuilds it sharply behind the trailing cold front. Between roughly November and March a given coastal location might see fifteen to twenty-five of these, and outside that window the barometer is often nearly flat for months.

That concentration is what makes the West Coast pattern different from anywhere else in the country, and it has a practical consequence: if you are pressure-sensitive and you live on the Pacific slope, your symptom calendar is probably far more seasonal than a sufferer's in Illinois or Georgia.

A bomb cyclone is a mid-latitude low-pressure system whose central pressure falls by at least 24 hPa in 24 hours. That is the entire definition. The process is called bombogenesis or, in the technical literature, explosive cyclogenesis, and it happens when a developing storm sits over a sharp temperature contrast — most often where cold continental air meets a warm ocean current. For weather-sensitive people the significance is not the wind or the snow but the slope: a bomb cyclone produces the fastest sustained barometric decline that mid-latitude weather is capable of, sometimes 2 hPa per hour maintained for most of a day. If your trigger is the rate at which pressure changes rather than how low it goes, this is the extreme case.

The term entered popular use relatively recently, and it is worth being precise about what it does and does not mean.

A squall line is a long, organised band of thunderstorms, often hundreds of miles from end to end, that moves as a single unit ahead of or along a cold front. When one passes overhead, the barometer does something it does at no other time: it jumps. A rise of three to six hPa inside ten to fifteen minutes is typical, sometimes more, produced by a dome of cold air spreading out beneath the storms. A derecho is the extreme version — a squall line that travels at least 400 miles producing widespread damaging wind, and whose pressure jump can exceed ten hPa. These are the fastest barometric changes in ordinary weather, and they are almost entirely invisible in a daily record.

If you have ever had a headache arrive with a summer storm and found nothing in your pressure log to explain it, this is the most likely reason.

The North American monsoon is a seasonal wind shift that brings moisture from the Gulf of California and the eastern Pacific into Arizona, New Mexico and adjacent states from roughly late June through September. It transforms a region that spends three quarters of the year with an almost motionless barometer into one that produces some of the fastest short-term pressure changes anywhere — not from large storm systems, but from outflow boundaries racing off collapsing thunderstorms, which can jump the reading three to six hPa in under fifteen minutes. For weather-sensitive people in the Southwest, the practical consequence is that the symptom year is sharply divided, and almost everything worth tracking happens in about ten weeks.

Understanding the mechanism explains both why the rest of the year feels so stable and why the monsoon feels so unlike it.

A hurricane's pressure field extends far beyond its wind field. The measurable pressure deficit of a large tropical system typically reaches 400 to 600 kilometres from the centre, and the outer edge of that field can be detected further still. That means a city 300 kilometres inland will record a genuine barometric fall from a coastal hurricane — commonly 8 to 20 hPa rather than the 40 or more seen at landfall, and spread over a longer period. Because tropical systems weaken but also broaden after landfall, the inland pressure signature is a long shallow trough rather than a sharp V, and it can last several days.

This is why people well away from any coast sometimes notice something during hurricane season and assume they must be imagining it.

Tropical systems produce the deepest barometric pressure falls in the ordinary weather calendar. A strong hurricane's centre can sit 60 to 80 hPa below normal sea level pressure, and even a modest tropical storm passing nearby will move the barometer more in twelve hours than a winter cold front does in three days. For weather-sensitive people this is worth preparing for rather than reacting to, because unlike most triggers, a hurricane announces itself three to five days ahead. The preparation that matters is unglamorous: refill prescriptions early, protect sleep, plan for the power going out, and decide in advance what you will do if you get an attack during an evacuation.

Atlantic hurricane season runs from 1 June to 30 November, with activity concentrated heavily in August, September and early October. The eastern Pacific season starts slightly earlier, on 15 May.

A nor'easter is a coastal low that develops off the southeastern United States and intensifies as it tracks northeast along the seaboard, drawing its energy from the temperature contrast between cold continental air and the warm Gulf Stream. For anyone living between the Chesapeake and Maine, these storms produce the deepest and longest barometric pressure falls of the year — commonly 25 to 40 hPa, occasionally more, developing over eighteen to thirty-six hours. The season runs roughly from October through April and peaks in January and February. Because the fall is both large and sustained, nor'easters are the single most identifiable weather trigger in the Northeast's calendar.

They are also, from a tracking point of view, the easiest events to study, because they are unambiguous on a chart.

Your weather app almost certainly shows sea level pressure, not the actual pressure where you are standing. The two differ by roughly 1 hectopascal for every 8 metres of elevation, which means a barometer in Denver genuinely reads around 840 hPa while the app reports something close to 1015. The adjustment exists so that a weather map can show where the highs and lows actually are, rather than a picture of the terrain. For anyone tracking symptoms against pressure, the adjustment is harmless and arguably helpful, because what the body responds to is change over time, and the adjustment is a near-constant offset that does not affect change.

The confusion this causes is common enough that it is worth walking through properly, especially if you own a home barometer or a weather station that reports something different from your phone.

The hours before severe weather have a characteristic feel that many people describe the same way: heavy, close, still, with a headache building. Meteorologically there is something real to point at. The warm sector ahead of a spring storm system combines falling pressure, a sharp rise in humidity, unusually warm air for the season, and often a mesoscale low that deepens locally over a few hours. Several of those factors are independently associated with headache. What cannot be said is that the atmosphere gives warning of a tornado specifically — the pre-storm environment is identical whether or not a tornado eventually forms, and no symptom should ever be used in place of a warning.

That last point matters enough to lead with. Taking shelter is a decision made on official warnings, not on how your head feels.

Altitude acclimatization is governed almost entirely by one variable: how fast you ascend. Above roughly 3,000 metres, increase your sleeping altitude by no more than 300 to 500 metres per night, and take a full rest day every third day or every 1,000 metres gained. Climb high and sleep low if the terrain allows. Everything else — hydration, food, avoiding alcohol, and in some cases acetazolamide — helps at the margins, but none of it substitutes for going up slowly.

The reason this advice is so specific is that acclimatization is a set of physiological changes that take a fixed amount of time. You cannot will them to happen faster.

Several large population studies have found that people living above roughly 2,000 metres report migraine more often than people at sea level, with the effect strengthening above 3,000 metres. The most-cited work, a Nepalese population survey, found migraine prevalence rising with residential altitude in a stepwise fashion, and studies in Peru, Turkey and Colorado point the same way. The effect is modest — this is a shift in the odds, not a transformation — and it appears to be driven by sustained mild hypoxia rather than by pressure as such.

That distinction matters, because it explains why living high feels different from sitting through a storm.

A car can take you from valley floor to 3,000 metres in under an hour. That is a pressure drop of roughly 150 to 200 hectopascals in forty minutes — about ten times faster than the sharpest weather system you will ever sit through. The headache that follows is usually a combination of mild hypoxia, sinus and middle-ear pressure that has not equalised, and in migraine-prone people a genuine attack triggered by the rate of change. Slowing the ascent where you can, stopping at the top before descending, and actively equalising your ears on the way up are the three things that make the most difference.

The key point is that speed of change matters independently of how high you actually go.

No study has followed migraine sufferers who relocated from high to low elevation, so there is no direct evidence either way. The population research linking altitude to migraine prevalence is cross-sectional — it compares different people in different places, not the same person before and after a move. Anecdotally, some people improve substantially and others notice nothing. Given that moving house is expensive and irreversible, the sensible approach is to test it with an extended stay and a symptom log before making any decision.

The gap between what the population data shows and what it can tell an individual is the whole story here.

A diving headache almost always has one of four causes: carbon dioxide build-up from skip-breathing or over-exertion, sinus or middle-ear squeeze from failed equalisation, jaw and neck strain from gripping the regulator, or a mask strapped too tightly. Decompression illness is far down the list and usually comes with other symptoms. The pressure changes involved are enormous — descending ten metres doubles the absolute pressure on your body, a change roughly fifty times larger than a severe storm — but the body handles them well as long as the air spaces equalise.

Working out which of those four you have is straightforward once you know what to look for, and it changes what you should do about it.