Weather map

Weather map of the southeastern United States on October 9, 1843 by James Pollard Espy .

A weather map in the general sense is a map that makes the weather conditions over a geographic area at a specific point in time visually detectable. The point in time can be current, in the past or in the future ( weather forecast ).

From a meteorological point of view, it is understood to mean the momentary state of the air pressure conditions over a larger area. Such a weather map provides information about the wind speed and wind direction or allows possible weather hazards to be identified at an early stage. It also enables a forecast of the coming weather. It can also be used sensibly in everyday life.

history

James Pollard Espy created the first series of weather maps of the United States for the US Army in 1843. The French scientist Urbain Le Verrier , who first created one for France on February 19, 1855, is considered to be the inventor of the map with weather forecast .

Ground weather maps

A weather map (ground weather map) for Europe and the North Atlantic with station data

Creation of a weather map

The traditional and well-known form of the weather map is the ground weather map , sometimes also called the ground map for short . For such a map can be created, must first air pressure readings of all the weather stations , that is all on the ground monitoring stations located, are present in the catchment area of the map. The data are entered in the map, which is still empty, according to the geographic position of the respective weather station.

In the next step on the map of the highest and the lowest air pressure value to be searched and with a H for high pressure area or with a T for depression (international also L for engl. Low highlighted). The isobars , i.e. the lines along which the same air pressure prevailed at the time of measurement, are then drawn around the high and low pressure centers . The isobars, like other isolines , each have discrete values. On German weather maps, these are usually values that can be easily divided by five. The real measured values of the weather stations, however, are distributed within a continuum . Therefore, many measuring stations are not exactly on one isobar: If an air pressure of 1002 hectopascals (hPa) was measured at weather station A and a value of 1008 hPa at weather station B, then the isobar for 1005 hPa runs roughly in the middle between A and B.

Simple weather map features at a glance

In addition to the isobars, there are further details on a weather map, here the most important:

Fronts
symbol	description
	Warm fronts are drawn in with a line made up of red semicircles. They canmeanprolonged rain and lead to an increase in cloud cover and a slow rise in temperature.
	Cold fronts are drawn in with a line of blue triangles. The weather remains inconsistent when a cold front passes through, and showers and thunderstorms occur frequently. The air temperature drops.
	Occlusions are drawn as a purple semicircle next to a triangle. It arises when the faster cold front reaches the slower warm front and it combines with it. The weather remains fickle and rainy within an occlusion.
	stationary fronts are drawn in with a line of alternating blue triangles and red semicircles.
	Wedges of the relative topography are drawn with an orange line with alternating lines.
	Trough lines are drawn in with a blue dashed line
	Convergences are drawn in with a blue line with alternating lines

Pressure areas
Art	Letter
High pressure area	German : H och	English : H igh	French : A nticyclone (old: h aute pression)	Russian : W erchnij
Low pressure area	German : T ief	English : L ow, C yclone	French : D épression (old: b asse pression)	Russian : N ischnij
High altitude core	German : HTK	English : Low Pressure Center	french :	Russian :

Precipitation
Art	presentation
rain	Area light green hatched or dotted.
snow	Dark green hatched area or with asterisks.
fog	Area hatched or dashed in yellow.

More accurate weather maps and weather map symbols

Arrangement of the weather data

More detailed weather maps have further information on current weather events. They contain data on temperature , wind strength , wind direction , air pressure change, precipitation , cloud type , cloud cover , cloud base , dew point ( humidity ) and the current weather.

For this purpose, this data is inserted into the weather map in a special pattern. The position of the data on the weather map marks the geographic position of the weather station. Only the most important stations are inserted with their data. Otherwise the map would be too overloaded with weather data and no details would be recognizable.

Wind speed, cloud cover and air pressure tendency

Cloud cover
symbol	code	description
	0/8	No clouds
	1/8	Sunny
	2/8	Bright
	3/8	Slightly cloudy
	4/8	Cloudy
	5/8	Cloudy
	6/8	Heavily cloudy
	7/8	Almost covered
	8/8	Covered
	9/8	Sky not recognizable

Air pressure trend (3 hours)
symbol	description
	Increasing
	Rising, then falling
	Rising, then stable
	Rising or stable, then falling
	Falling or stable, then rising
	Stable
	Falling
	Falling then rising
	Falling then stable

Wind speed
symbol	Knots, km / h
	0 kn, 0 km / h
	5 kn, 9 km / h
	10 kn, 19 km / h
	15 kn, 28 km / h
	20 kn, 37 km / h
	25 kn, 46 km / h
	30 kn, 56 km / h
	35 kn, 65 km / h
	40 kn, 74 km / h
	45 kn, 83 km / h
	50 kn, 93 km / h
	55 kn, 102 km / h
	60 kn, 111 km / h
	65 kn, 120 km / h
	100 kn, 185 km / h
	105 kn, 194 km / h
Wind direction of the symbols above: ${\ displaystyle \ rightarrow}$

Weather

symbol	number	description
	00	Cloud development in the last hour not observed or not observable
	01	Cloud dissolution or regression during the last hour
	02	Consistent cloud cover for the last hour
	03	Increasing cloud cover for the last hour
	04	Reduced visibility due to smoke
	05	Dry haze
	06	Dust vapor (dust particles partially visible)
	07	Sweeping or drifting dust or sand , but not well-developed dust devils or sandstorms
	08	Small bombs (dust devils) in the last hour or currently observable, but no sandstorm
	09	Dust or sand storm in sight at the time of observation or during the last hour at the weather station
	10	Moist haze
	11	Flat fog with a height of less than two meters in individual swaths or banks at the weather station
	12	Coherent, flat layer of fog with an elevation of less than two meters at the weather station
	13	Weather lights , but no thunder audible
	14th	Virga (fall strip) in sight
	15th	Precipitation or praecipitatio in sight, but more than 5 km away
	16	Precipitation or praecipitatio in sight, less than 5 km away but not directly at the weather station
	17th	Thunderstorm or distant thunderstorm at the station with audible thunder , but no precipitation
	18th	Gust collars visible in the last hour or striking gusts at the station
	19th	Funnel clouds or tornadoes during the last hour on or near the weather station
	20th	Snow drizzle or drizzle (not freezing and not as a shower ) stopped in the last hour
	21st	Rain (not freezing and not as a shower ) stopped in the last hour
	22nd	Snowfall (not as a shower) stopped in the last hour
	23	Sleet or ice grains (not as showers) stopped in the last hour
	24	Freezing rain or drizzle stopped in the last hour
	25th	The rain shower stopped in the last hour
	26th	Snow or snow showers stopped in the last hour
	27	Hail or sleet has stopped in the last hour
	28	Fog has cleared in the last hour
	29	Thunderstorm stopped in the last hour
	30th	Light or moderate sand or dust storm, weaker in the last hour
	31	Light or moderate sand or dust storm , unchanged during the last hour
	32	Light or moderate sand or dust storm , got stronger during the last hour
	33	Strong sand or dust storm , weaker during the last hour
	34	Strong or moderate sand or dust storm , unchanged during the last hour
	35	Strong or moderate sand or dust storm , got stronger during the last hour
	36	Light or moderate snow sweeping (below eye level)
	37	Heavy snow sweeping (below eye level)
	38	Light or moderate snow drift (above eye level)
	39	Heavy snow drift (above eye level)
	40	Fog or ice fog at some distance, but has not reached the observer in the last hour. The visibility is over a kilometer and the fog itself extends vertically up to the height of the observer.
	41	Fog or ice fog in swaths, therefore strongly fluctuating visibility.
	42	Sky visible in spite of fog or ice fog , although it got thinner in the last hour.
	43	The sky is obscured by fog or ice fog , which has become thinner in the last hour.
	44	Sky visible despite fog or ice fog , with no changes in the last hour.
	45	Sky obscured by fog or ice fog , with no changes in the last hour.
	46	Sky visible in spite of fog or ice fog , which became thicker in the last hour.
	47	Sky obscured by fog or ice fog , which has become thicker in the last hour.
	48	Fog or ice fog with frost or clear ice formation with a visible sky
	49	Fog or ice fog with frost or clear ice formation when the sky is overcast
	50	Light, intermittent , non-freezing drizzle
	51	Light, non-freezing drizzle without interruptions
	52	Moderate, not freezing drizzle intermittently
	53	Moderate non-freezing drizzle without interruptions
	54	Strong, not freezing drizzle intermittently
	55	Heavy, non-freezing drizzle without interruptions
	56	Light freezing drizzle
	57	Moderate or heavy freezing drizzle
	58	Light rain mixed with drizzle
	59	Moderate or heavy rain mixed with drizzle
	60	Light, non-freezing rain intermittently
	61	Light, non-freezing rain without interruptions
	62	Moderate, non-freezing rain intermittently
	63	Moderate, non-freezing rain without interruptions
	64	Heavy, non-freezing rain intermittently
	65	Heavy, non-freezing rain without interruptions
	66	Light freezing rain
	67	Moderate or heavy freezing rain
	68	Light rain or drizzle mixed with snow
	69	Moderate or heavy rain or drizzle mixed with snow
	70	Light snowfall with interruptions
	71	Light snowfall without interruptions
	72	Moderate snowfall with interruptions
	73	Moderate snowfall without interruptions
	74	Heavy snowfall with interruptions
	75	Heavy snowfall without interruptions
	76	Ice needles , with or without fog
	77	Snow pebbles , with or without fog
	78	Single snowflakes , with or without fog
	79	Ice grains
	80	Light rain shower
	81	Moderate or heavy rain shower
	82	Very heavy rain shower
	83	Light snow shower
	84	Moderate or heavy snow showers
	85	Light snow shower
	86	Moderate or heavy snow showers
	87	Slight sleet showers , with or without rain or sleet
	88	Moderate or heavy sleet showers with or without rain or sleet
	89	Light hailstorm with or without rain or sleet , but without thunder
	90	Moderate or heavy hailstorm with or without rain or sleet , but without thunder
	91	Thunderstorms during the last hour, but now only light rain at the time of observation
	92	Thunderstorm during the last hour, but now only moderate or heavy rain at the time of observation
	93	Thunderstorms during the last hour, but now only light precipitation as snowfall , sleet or hail at the time of observation
	94	Thunderstorms during the last hour, but now only moderate or heavy precipitation as snowfall , sleet or hail at the time of observation
	95	Light or moderate thunderstorm without hail but with rain , snowfall or sleet at the time of observation
	96	Light or moderate thunderstorm with sleet or hail at the time of observation
	97	Strong thunderstorm without hail but with rain or snowfall at the time of observation
	98	Thunderstorm with dust or sand storm at the time of observation
	99	Strong thunderstorm with sleet or hail at the time of observation

Wind and pressure field

The wind is the movement of air and thus a mass flow . It results from the imbalance of two air masses of different pressure and temperature.

The gradient force controls the air flow from high pressure to low pressure. Due to the Coriolis force, their direction is subject to a deviation in the direction of movement to the right in the northern hemisphere and to the left in the southern hemisphere . The geostrophic winds run almost parallel to the isobars, but the ground wind (10 m wind) deviates by 25 to 40 degrees in the direction of the low due to the ground friction. This also enables the approximate wind direction to be determined.

The wind speed depends on the distance between the isobars. If the isobars are very close to one another, a storm or even a hurricane can occur. One speaks of a convergence when the lines run close together. If the isobars are far apart, as is the case with some high pressure weather conditions, then there will be weak winds or even no wind. Here one speaks of a divergence .

The following table gives an approximate information about the wind speeds depending on the distance between the isobars, but there is a significant dependence on the geographical latitude:

100 years of meteorological cooperation: The stamp from 1973 shows a weather map of the German weather service

Distance between the 5 hPa isobars	Wind force
600 km	Light breeze ( Beaufort scale 2)
500 km	Moderate breeze (Beaufort scale 4)
400 km	Fresh breeze (Beaufort scale 5)
300 km	Strong wind (Beaufort scale 6)
200 km	Stiff wind (Beaufort scale 7)
100 km	Storm (Beaufort scale 9)

Altitude weather maps

All previous sections dealt with ground weather maps , which are based on the air pressure from measurements on the ground. In contrast, altitude weather maps are determined with the help of data from radiosondes . Altitude weather maps provide the indispensable supplement with regard to what is happening in the free atmosphere , especially with regard to the pressure and flow fields at these altitudes. Disturbing influences from mountains, cities and other obstacles are absent here, and so the isohypses (contour lines of a certain air pressure surface ) usually have a smoother course than the isobars on the ground weather map.

The weather on the ground affects higher altitudes and vice versa.

The image of the altitude weather map can be very different from that of the ground weather map. The development of low pressure areas on the ground shows that the development at altitude only gradually reacts to the weather on the ground.

When assessing altitude weather maps, altitude lows with often extreme cold air inclusions ( cold air drops ) play a major role. Low temperatures at high altitudes trigger unstable weather conditions (showers, heavy rain ) , especially in summer with warm air close to the ground .

The following altitude weather maps are most commonly used:

Altitude weather maps for main printing areas :
Pressure level	height
850 hPa	1457 meters
700 hPa	3013 meters
500 hPa	5574 meters
300 hPa	9164 meters
200 hPa	12000 meters

literature

Wolfgang Weischet: General climate geography . 3. Edition. de Gruyter, Berlin / New York 1980.
Rolf F. Nohr: Maps on TV: the production of positioning . LIT, Münster 2002, p. 196–208 ( ruhr-uni-bochum.de [PDF]).

Web links

Commons : Weather map - album with pictures, videos and audio files

Weather and climate. German weather service - weather maps
Ground weather map symbols (offers PDF)
Entry scheme for altitude weather reports (PDF)
Current ground weather map (DWD) Europe, with isobars and fronts, updated every six hours

Individual evidence

^ ^A ^b First Report on Meteorology, to the Surgeon General of the United States Army. October 9, 1843.

[espy-1] A ^b First Report on Meteorology, to the Surgeon General of the United States Army. October 9, 1843.