Glossary

The bureau's vocabulary.

The terms the desk uses daily, with the local meanings attached. Written for visitors, school groups and new co-op observers.

AAdiabatic: The cooling of rising air and the warming of sinking air, with no heat added or lost. Why hilltops are cooler than the valley floor at the same latitude and hour.
AAnemometer: The spinning cups that measure wind speed. Ashgrove Hill's has turned since 1958 and only stopped once, for a rebuild and a wedge of ice.
AAnticyclone: A high-pressure system, drawn on our charts as a ring of 'H'. Brings the settled spells the almanac calls 'the quiet weeks'.
BBarometer: An instrument reading pressure. The HQ's keeps a 92-year trace in ink; the nib was replaced twice and the ink is always the same blue.
BBeaufort scale: A wind scale from 0 (calm) to 12 (hurricane), judged by what the wind does rather than what it measures. Point Brace still grades its entries by hand.
CCold front: The leading edge of a cooler air mass, drawn with triangles. Crosses the vale quickly and usually loudly.
DDew point: The temperature at which air becomes saturated. When it meets the morning minimum, the fog diary gets an entry.
FFrost hollow: A dip where cold air pools overnight. The vale's hollows are mapped in the 1964 survey and the map has not needed changing.
GGale: Wind of Beaufort 8 or more. A gale watch goes out before it, not after; that ordering is the bureau's oldest rule.
HHumidity, relative: How full of water the air is, as a percentage of what it could hold at that temperature. High in the vale mornings, low on the ridge afternoons.
IIsobar: A line of equal pressure, the grammar of the synoptic chart. Close together means wind; far apart means the quiet weeks.
IIsotach: A line of equal wind speed. The bureau plots them in pencil, lightly, because they move fast.
KKatabatic wind: Night air draining down a slope. On Ashgrove Hill it is a reliable 4 km/h whisper, and observers set their coffee by it.
LLow pressure: A weather system drawn as a ring of 'L', usually with fronts hanging off it. The point-brace keepers call its approach 'the visitor'.
MMean: The average, as in monthly mean temperature. The climate ledger keeps both means and extremes because averages hide the interesting days.
OOccluded front: Where a cold front catches its own warm front. Drawn in purple by everyone, and by the bureau in pencil.
PPsychrometer: Two thermometers, one dry, one damp, spun together to read humidity. The HQ's is brass and older than the dam.
RRadiosonde: The instrument package on a weather balloon. Vale Observatory releases two a day, logged as FW-1### in the ledger.
RRain gauge: The brass cylinder every station and co-op observer keeps. Straight-sided, sharp-lipped, and cleaned weekly; a dirty gauge is a lying gauge.
SStevenson screen: The white louvred box that shelters thermometers from sun and rain while letting air through. Painted white every spring since 1934.
SSynoptic chart: The map of pressure systems and fronts for a whole region, drawn four times a day. The bureau's wall chart is the original artwork of every almanac cover.
TThermograph: A recording thermometer that draws its own line on a rotating paper drum. Forty-one summers of rolls in the HQ cellar.
TTrough: An elongated area of low pressure, drawn as a dashed line. Often announces itself at Point Brace as a wind shift first and a chart line second.
VVisibility: How far you can see. Measured in metres in the log and in adjectives in the fog diaries.
WWarm front: The leading edge of warmer air, drawn with semicircles. Brings long grey rain and, in the vale, the famous October fog.
WWind vane: The arrow that shows where wind comes from. Always named, never named the same thing twice; the HQ's is called Agnes after the first observer.
WWind chill: What cold feels like once wind starts taking heat off skin. The bulletin prints it from November because the dam path asks for it every year.

Definitions are written for this fictional bureau and simplified on purpose.