Climate and Average Weather Year Round in Wa‘lān Yemen

In Wa‘lān, the summers are short, warm, arid, and mostly cloudy and the winters are cold, dry, and mostly clear. Over the course of the year, the temperature typically varies from 38°F to 80°F and is rarely below 32°F or above 83°F.

Based on the tourism score, the best times of year to visit Wa‘lān for warm-weather activities are from early March to early June and from mid August to mid October.

The warm season lasts for 2.2 months, from May 21 to July 29, with an average daily high temperature above 78°F. The hottest month of the year in Wa‘lān is June, with an average high of 80°F and low of 55°F.

The cool season lasts for 3.4 months, from October 25 to February 8, with an average daily high temperature below 71°F. The coldest month of the year in Wa‘lān is December, with an average low of 38°F and high of 69°F.

In Wa‘lān, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in Wa‘lān begins around September 8 and lasts for 7.6 months, ending around April 26.

The clearest month of the year in Wa‘lān is November, during which on average the sky is clear, mostly clear, or partly cloudy 79% of the time.

The cloudier part of the year begins around April 26 and lasts for 4.4 months, ending around September 8.

The cloudiest month of the year in Wa‘lān is July, during which on average the sky is overcast or mostly cloudy 64% of the time.

Wa‘lān does not experience significant seasonal variation in the frequency of wet days (i.e., those with greater than 0.04 inches of liquid or liquid-equivalent precipitation). The frequency ranges from 1% to 5%, with an average value of 2%.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Wa‘lān is August, with an average of 1.2 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 5% on August 10.

Rainfall

The sliding 31-day quantity of rainfall in Wa‘lān does not vary significantly over the course of the year, staying within 0.1 inches of 0.1 inches throughout.

The length of the day in Wa‘lān varies over the course of the year. In 2024, the shortest day is December 21, with 11 hours, 14 minutes of daylight; the longest day is June 20, with 13 hours, 1 minute of daylight.

The earliest sunrise is at 5:31 AM on June 2, and the latest sunrise is 1 hour, 1 minute later at 6:32 AM on January 23. The earliest sunset is at 5:29 PM on November 21, and the latest sunset is 1 hour, 7 minutes later at 6:37 PM on July 7.

Daylight saving time (DST) is not observed in Wa‘lān during 2024.

The figure below presents a compact representation of key lunar data for 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The perceived humidity level in Wa‘lān, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Wa‘lān experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 5.6 months, from May 18 to November 7, with average wind speeds of more than 6.1 miles per hour. The windiest month of the year in Wa‘lān is October, with an average hourly wind speed of 6.8 miles per hour.

The calmer time of year lasts for 6.4 months, from November 7 to May 18. The calmest month of the year in Wa‘lān is December, with an average hourly wind speed of 5.4 miles per hour.

The predominant average hourly wind direction in Wa‘lān varies throughout the year.

The wind is most often from the west for 3.1 weeks, from March 7 to March 29, with a peak percentage of 41% on March 12. The wind is most often from the east for 2.4 months, from March 29 to June 11 and for 6.0 months, from September 7 to March 7, with a peak percentage of 64% on May 20. The wind is most often from the north for 2.9 months, from June 11 to September 7, with a peak percentage of 54% on August 20.

To characterize how pleasant the weather is in Wa‘lān throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best times of year to visit Wa‘lān for general outdoor tourist activities are from early March to early June and from mid August to mid October, with a peak score in the third week of September.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best times of year to visit Wa‘lān for hot-weather activities are from mid May to mid July and from late August to mid September, with a peak score in the second week of June.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Wa‘lān typically lasts for 11 months (347 days), from around January 10 to around December 22, rarely starting after February 20, or ending before November 24.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms in Wa‘lān should appear around January 14, only rarely appearing before January 12 or after January 17.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences some seasonal variation over the course of the year.

The brighter period of the year lasts for 1.6 months, from May 4 to June 23, with an average daily incident shortwave energy per square meter above 7.2 kWh. The brightest month of the year in Wa‘lān is May, with an average of 7.3 kWh.

The darker period of the year lasts for 2.0 months, from November 20 to January 21, with an average daily incident shortwave energy per square meter below 6.3 kWh. The darkest month of the year in Wa‘lān is December, with an average of 6.1 kWh.

For the purposes of this report, the geographical coordinates of Wa‘lān are 15.070 deg latitude, 44.276 deg longitude, and 8,035 ft elevation.

The topography within 2 miles of Wa‘lān contains very significant variations in elevation, with a maximum elevation change of 1,430 feet and an average elevation above sea level of 8,417 feet. Within 10 miles contains very significant variations in elevation (5,617 feet). Within 50 miles also contains extreme variations in elevation (10,525 feet).

The area within 2 miles of Wa‘lān is covered by bare soil (56%) and sparse vegetation (37%), within 10 miles by bare soil (57%) and grassland (22%), and within 50 miles by bare soil (65%) and sparse vegetation (20%).