This report describes the historical weather record at the Francisco Sá Carneiro Airport (Porto, Portugal) during 1990. This station has records back to January 1948.
Porto has a mediterranean climate with dry warm summers and mild winters. The area within 25 mi of this station is covered by oceans and seas (46%), grasslands (32%), croplands (18%), and shrublands (3%)
Daylight saving time (DST) was observed at Porto during 1990. There were two time changes during 1990:
1990 was not a leap year, so it has 365 days and no February 29th. The first leap year before 1990 was 1988 and the first after was 1992.
The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 1990 they occurred on:
|Spring Equinox||Tuesday, 20 March 1990.|
|Summer Solstice||Thursday, 21 June 1990.|
|Fall Equinox||Sunday, 23 September 1990.|
|Winter Solstice||Saturday, 22 December 1990.|
The hottest day of 1990 was July 22, with a high temperature of 95°F. For reference, on that day the average high temperature is 75°F and the high temperature exceeds 85°F only one day in ten. The hottest month of 1990 was July with an average daily high temperature of 78°F.
Relative to the average, the hottest day was July 22. The high temperature that day was 95°F, compared to the average of 75°F, a difference of 20°F. In relative terms the warmest month was May, with an average high temperature of 71°F, compared to an typical value of 66°F.
The longest warm spell was from April 25 to May 19, constituting 25 consecutive days with warmer than average high temperatures. The month of May had the largest fraction of warmer than average days with 84% days with higher than average high temperatures.
The coldest day of 1990 was December 1, with a low temperature of 32°F. For reference, on that day the average low temperature is 46°F and the low temperature drops below 38°F only one day in ten. The coldest month of 1990 was January with an average daily low temperature of 43°F.
Relative to the average, the coldest day was December 1. The low temperature that day was 32°F, compared to the average of 46°F, a difference of 14°F. In relative terms the coldest month was December, with an average low temperature of 43°F, compared to an typical value of 45°F.
The longest cold spell was from January 6 to January 23, constituting 18 consecutive days with cooler than average low temperatures. The month of January had the largest fraction of cooler than average days with 65% days with lower than average low temperatures.
The clearest month of 1990 was March, with 61% of days being more clear than cloudy. The longest spell of clear weather was from April 16 to April 28, constituting 13 consecutive days that were clearer than they were cloudy.
The cloudiest month of 1990 was February, with 14% of days being more cloudy than clear.
This station provides hourly reports of significant weather events at and around the station, but does not report the quantity of precipitation at the station itself. This is common for weather stations located outside of the United States, and for a small subset of stations in the United States that are located at lesser used and smaller airports.
This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.
The day in 1990 with the most precipitation observations was February 8. There were 21 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was October, with 193 hourly present weather reports involving some form of precipitation.
As determined by the present weather reports, the longest dry spell was from July 28 to August 20, constituting 24 consecutive days with no observed precipitation. The month with the largest fraction of days without observed precipitation was August, with 87% of days reporting no observed precipitation at all.
The month with the largest fraction of days with at least some observed precipitation was October, with 68% of days reporting some observed precipitation.
Either snow is exceptionally rare at this location or this station did not reliably report it during 1990.
Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.
When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of 1990 was March with an average daily low humidity of 48%, and the most humid month was February with an average daily low humidity of 68%.
But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.
Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.
Generally speaking, dew points below 50°F will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 50°F to 68°F are fairly comfortable to most people, and dew points above 68°F are increasingly uncomfortable, becoming oppressive around 77°F.
To take some examples, and basing our categorization on the daily high dew point in 1990, January had 18 dry days, 13 comfortable days, and no humid days; April had 14 dry days, 16 comfortable days, and no humid days; July had no dry days, 27 comfortable days, and 4 humid days; and October had 1 dry day, 30 comfortable days, and no humid days.
The highest sustained wind speed was 29 mph, occurring on October 16; the highest daily mean wind speed was 19 mph (October 16); and the highest wind gust speed was 46 mph (October 16).
The windiest month was April, with an average wind speed of 8 mph. The least windy month was November, with an average wind speed of 4 mph.
Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.
The day of 1990 with the lowest average visibility was December 27, with an average visibility of 0.9 mi. The month with the lowest average visibility was August, with an average visibility of 5.0 mi. With an average visibility of 7.1 mi, the month of April had the highest average visibility.
The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.
The day of 1990 with the lowest average cloud ceiling was March 14, with an average cloud ceiling of 49'. The month with the lowest average cloud ceiling was August, with an average cloud ceiling of 2538'. The month of March has the highest average cloud ceiling, with an average cloud ceiling of 11287'.