SE.ACMF Meteorological observations — Lowest cloud base, 15 minutes minimum, hourly values

Purpose: Describes current weather and over time the climate. Basis for forecast verification Unit: Eighths for cloud amount and meters for cloud base. Characteristics: In the official network of observations in Sweden there are several stations that report the amount of cloud and cloud base at an hour’s intervals. These stations are equipped with cloud altimeters which measure the height to the underside of the clouds. The cloud amount is determined by an advanced algorithm in the measuring instrument. Most of the measuring stations send fully automatically produced reports and, in the case of clouds, all cloud layers detected by the instrument are reported. Up to 4 cloud layers can be reported. For manual stations which then consist mainly of historical observations: The lowest cloud layer, irrespective of its amount of cloud, reported at least 1/8; Next higher cloud layer covering a total of 3/8 or more of the sky. Next higher cloud layer covering a total of 5/8 or more of the sky. Cumulonimbus clouds not reported under points 1, 2 or 3 are always reported in a specific group regardless of the amount of cloud. This is mainly the case for historical manual observations. Today’s measuring instruments cannot distinguish such clouds. The cloud base to the above cloud layers is also reported.For example, a station can report 1/8 with cloud base 300 m, 3/8 with cloud base 500 m and 5/8 with cloud base 1 000 m. Not all cloud layers are reported as the above rules must be complied with. The unit for cloud quantity is eighths where 0/8 is cloud-free, 8/8 is full crumb. 9/8 means that the cloud sky cannot be observed due to fog or high snowlines. In 9/8, the term vertical visibility is used instead, which indicates how far vertical it is possible to see. The device for cloud base and vertical visibility is meters. Amount of clouds Data is available with a value of 0 to 9. Values 10 to 15 are for data received in the form of aerodrome observations (METAR), such data are not included in this dataset. These values will be empty and therefore cannot be used. Value 0 to 8 means 0 to 8 eighths. Value 9 means that the cloud sky cannot be observed due to fog or high snowlines. Instead of cloud base, vertical visibility is given. Cloud base Cloud base refers to the vertical distance from the ground to the underside of the clouds. Unit meters. Parameter 37 Lowest observed cloud base over the last 15 minutes. Design: Date, time, value and quality. Quality codes: Green values (G) mean approved quality. Yellow values (Y) means data that may be suspiciously inaccurate. It can also be an aggregated value based on other metrics. Limits: 0 to 7 500 m (cloud base) For more info see: https://www.smhi.se/kunskapsbanken/molnighet-och-molnmangd-1.1514 Delivery: Data is delivered in two different ways. 1. Via a user interface where measurement series can be downloaded for one station at a time. Data can be downloaded for the last 24 hours, the last four months or the full time series except for the last three full months (historical reviewed). 2. Via a machine-machine solution (Atom flow rate). There, the same measurement series as above can be obtained as well as real-time data. These are the last hour’s readings. They can be retrieved for one measuring station at a time or for all active measuring stations.