Tukuk-OSStart With the Two Big Letters
Every surface weather map is a picture of pressure. H marks a high — a region where air is sinking. Sinking air warms as it descends, which suppresses cloud: highs mean fair, calm weather, and in winter they can trap haze and fog. L marks a low — air converging and rising; rising air cools, its water vapour condenses, and clouds and rain follow. Almost all dramatic weather lives around the Ls.
In the northern hemisphere, wind circulates clockwise around a high and counter-clockwise around a low (reversed south of the equator — the Coriolis effect's signature). So the letter alone already tells you which way the surface wind blows nearby.
Isobars: The Wind Speed Knob
The curving lines on the map are isobars — lines of equal pressure, drawn a few hectopascals apart. They are the wind-speed control: packed close together, the pressure changes fast over distance, and the wind blows hard; spread wide apart, the air is gentle. A big L with tightly bunched isobars on one side is a storm; the same L with lazy spacing is a damp calm day. This one rule — tight lines, strong wind — is the single most useful thing on this page.
The Four Front Symbols
Around a mid-latitude low, air masses of different temperature meet along fronts, and the map draws them with unmistakable geometry:
- Cold front — a blue line with triangles. Cold, dense air undercuts warm air, forcing it up fast: a narrow band of showery rain, sometimes thunderstorms, then clearing with a windier, cooler behind it. Passes quickly.
- Warm front — a red line with semicircles. Warm air glides gently over cold: widespread, steady, longer rain over a broad zone ahead of the front, then milder, damper air after.
- Occluded front — a purple line with alternating triangles and semicircles. The cold front has overtaken the warm one and lifted the warm air completely off the ground — the mature stage of a classic low, with a long messy rain episode.
- Stationary front — blue triangles and red semicircles on opposite sides. The boundary stalls, and whatever weather it carries parks over the same towns for days.
The textbook wave of it all: a low spins, its cold front slowly catches the warm front, occludes, and dissipates — one life cycle lasting a few days, which is exactly the rhythm your local weather swings through each week.
The Clouds Tell You the Arrival Order
Before the symbols reach you, the sky sends its own advance party:
- Cirrus — high, hair-fine ice-crystal streaks. If they thicken and spread over hours, a warm front is approaching; rain is often 12–24 hours out.
- Altostratus — the sky turns to a milky sheet; the Sun dims to a watery disc. The warm front's rain shield has arrived.
- Nimbostratus — continuous steady rain or snow, low featureless grey. You are inside the warm-front zone.
- Cumulus towers and a gust front — if instead the afternoon builds cauliflower clouds with dark flat bases, showers and thunder are the local future.
- The clear break after a cold front — that sudden scrubbed-blue sky and cold, clean wind with scattered fast cumulus is the front's passage; the worst is momentarily behind you.
Putting It Together on a Real Map
Open a surface analysis, find the nearest L, note where you sit relative to its warm and cold fronts, read the isobar spacing for wind, then look up and check whether the clouds match the sequence. Within a day or two you will be calling the next twelve hours yourself — and you will understand why the app said what it said, which is the difference between watching a forecast and reading one.
Practise against live data: Tukuk's wind and pressure heat map is at tukuk.org/cuaca/peta, cloud cover for your location at tukuk.org/cuaca/awan, and current conditions anywhere on Earth at tukuk.org/cuaca.