2018-04-13 (IPMA)
At the end of the afternoon of April 10, 2018, snow was reported in some places in the Lisbon region, and it was discussed whether this occurrence was actually snow or hail, considering that both types of precipitation may be sometimes confused.
In the Automatic Weather Stations maintained by IPMA in Lisbon (Gago Coutinho, Geofísico / Jardim Botânico, Amoreiras and Oriente) the air temperature during the afternoon reached values of the order of 10 to 12 ° C, having occasionally and temporarily decreased to minimum values of the order of 8 ° C, associated with precipitation situations.
According to a study carried out in 2011 with data from meteorological stations in mainland Portugal in the period between 1941 and 2009, it was found that 99.3% of the snow cases occurred with air temperature values between -7 ° C and +5 ° C, with half of the episodes occurring between -1 ° C and +1 ° C. On the other hand, a study in the UK suggests a 10% probability for air temperature values of 4 °C.
Thus, the occurrence of snow in Lisbon in the described situation would represent a very improbable phenomenon, having in addition to assume the existence of temperatures lower than those registered in IPMA´s weather stations. In these circumstances, it is most likely that the phenomenon may correspond to a precipitation process with melting of ice crystals.
Thus, in order to better characterize the present situation and thus contribute to a better understanding, all users of IPMA meteorological information are invited to share reports related to this event through the IPMA community area at www.ipma.pt, directly through of the address http://meteoglobal.ipma.pt/ or through IPMA´s APP in "SEND OBSERVATION". The shared information should include the location, the instant, the type of precipitation observed and, if available, the air temperature, in as much detail as possible. If there are movies of the occurrence they should be sent to the address info@ipma.pt.