22-26 February 2021

Items of Interest:

• Becoming AWARE -- During this coming week (22-26 February 2021), Louisiana has scheduled its Severe Weather Awareness Week. If you live in Louisiana, you should take time to become familiar with the various public affairs announcements issued by your local National Weather Service Office. Other states farther to the north will be observing their Severe Weather Awareness weeks in the next ten weeks.
• Image of bright aurora over Alaska and Canada captured by polar-orbiting satellite -- An image of bright aurora (or northern lights) stretching across Alaska and northwestern Canada during the first week of February was obtained the Visible Infrared Imaging Radiometer Suite (VIIRS) on the NOAA/NASA Suomi NPP satellite. The aurora, which appeared as white-colored waves over the dark and nearly moon-less nighttime sky, were generated by high energy particles and radiation from the Sun arriving and exciting the molecules in the Earth's magnetosphere. [NASA Earth Observatory]
• Early upper-air weather data were obtained from kites and aircraft -- NOAA's National Centers for Environmental Information (NCEI) posted a "Planet Postcard" that featured information about the upper-air observations program operated by the U.S. Weather Bureau (the predecessor to the National Weather Service) from the late 19th century. The weather data collected from tethered kites, aircraft observations and balloons are now achieved at NCEI. [NOAA NCEI News]
• Leap years and calendars -- This year (2021) is considered a "normal" year with 365 days. Last year (2020) was a leap year with 366 days, with one additional day inserted at the end of February. Since the Earth completes one orbit around the Sun in 365.2422 days, calendars based upon integer days must be adjusted every few years so that recognizable events, such as the occurrence of the vernal equinox, do not progress through the year. In the first century BC the Julian calendar was developed by Julius Caesar who decreed a calendrical reform with a 365-day year that involved the inclusion of an extra day to the end of February. However, over several centuries, the timing of the vernal equinox (and the Christian celebration of Easter) crept earlier by roughly 10 days. To correct this inconsistency, an additional reform was instituted by Pope Gregory XIII in 1572 that included the requirement that only those centurial years divisible evenly by 400 (e.g., 1600, 2000) would be leap years, while the other centurial years (e.g., 1800 and 1900) would not.
  The National Centers for Environmental Information recommends that the climate normals for 28 February be used also for 29 February in a leap year.
• A change in meteorological seasons -- Sunday, 28 February 2021, marks the end of meteorological winter in the Northern Hemisphere, which by convention, is the three-month interval of December, January and February. The following day (1 March 2021) represents the beginning of boreal meteorological spring, the three-month interval of March, April and May. At the same time, meteorological summer in the Southern Hemisphere ends and autumn begins.

Weather and Climate News Items:

• Eye on the tropics ---Two organized tropical cyclones (atmospheric low pressure systems such as tropical storms or hurricanes that form over tropical oceans) were found last week traversing the waters of the Southern and Northern Hemispheres:
  • In South Indian Ocean
  • During the week before last, a weather disturbance developed along the eastern coast of the southern African nation of Mozambique. This system became a subtropical depression made landfall near Inhambane, Mozambique without significant development; however, torrential rains associated with depression fell across southern Mozambique. By late that week, this depression began intensifying as it took a clockwise loop over Mozambique, before emerging over the warm waters of the Mozambique Channel. During the beginning of last week, this system passed to within 160 miles to the west of Europa Island. The tropical depression where it became Tropical Storm Guambe late last Wednesday when maximum sustained winds were determined to be 50 mph. Over the next day, Guambe continued rapid intensification as it traveled southward over the Mozambique Channel. Guambe became a category 1 tropical cyclones on Friday afternoon when sustained winds reached 80 mph. By late Friday, Cyclone Guambe reached its peak intensity as a category 2 tropical cyclones when maximum sustained surface winds peaked at 100 mph. On Saturday, Guambe weakened and by Sunday morning, wind speeds had dropped to 50 mph, resulting in reclassification down to tropical storm status. Further weakening occurred on Sunday. On early Monday, Tropical Storm Guambe was tracking toward the east-southeast as it was approximately 860 miles to the south-southeast of Europa Island. This tropical system was about to merge with a mid-latitude trough of low pressure and become extratropical as it loses its tropical characteristics.
  • In the western North Pacific Ocean
  • A tropical depression formed early last week over the waters of the western North Pacific more than 500 miles to the east of the Philippine Islands. This system briefly passed over Palau archipelago in the Micronesia region, accompanied by torrential rains. Traveling toward the west and west-northwest, this tropical depression strengthened, becoming Tropical Storm Dujuan, the basin's first named tropical cyclone of 2020, late Thursday as maximum sustained surface winds reached 40 mph. Over the following day, Dujuan continued to strengthen as it headed for the southern Philippine island of Mindanao, with sustained winds peaking at 50 mph. However, Tropical Storm Dujuan weakened to become a tropical depression late Saturday as it entered an unfavorable environment before reaching the islands. On Sunday, maximum sustained surface winds surrounding Dujuan had increased to 40 mph, as it became a tropical storm for a second time, before making landfall on some of the Philippine Islands. By late in the day, Dujuan weakened to a tropical depression. On Monday, Tropical Depression Dujuan was heading northwestward and was located approximately 430 miles southeast of Manila, Philippines. Maximum sustained winds were 30 mph. This tropical depression was expected to dissipate by late Monday or early Tuesday.
• Increases in hurricane intensity around Bermuda appear linked with elevated ocean temperatures -- Researchers from the United Kingdom's University of Southampton and the National Oceanography Centre along with the Bermuda Weather Service claim that the mean hurricane intensity near Bermuda in the subtropical North Atlantic Ocean has increased since 1955, along with increased ocean water temperatures. Using the maximum wind speed as a measure of hurricane intensity, they found the winds doubled from 35 to 73 mph over the 65-year period, while sea surface and sub surface temperatures in the region increased by up to 1.1 Celsius degrees. The increased water temperatures appear to provide the additional energy for hurricanes to intensify. [University of Southampton News]
• Climate model projections of sea level rises are confirmed by sea-level observational data -- Scientists from several Australian and Chinese research institutions recently reported on their examination of the global and regional sea level projections of two reports by the Intergovernmental Panel on Climate Change (IPCC). These two reports were the Fifth Assessment Report (AR5) and the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC). The researchers claim that the projections of rising sea levels this century made in these reports are in good agreement with observed global and coastal sea level data gathered from satellites and a network of 177 tide-gauges from the start of the projections in 2007 up to 2018. Furthermore, the projections were as accurate at the regional and local level as they were at the global level. [Phys.org News]
• Review of global weather and climate for January 2021 -- Using preliminary data collected from the global network of surface weather stations, scientists at NOAA's National Centers for Environmental Information have determined that the combined global land and ocean surface temperature for January 2021 was 1.44 Fahrenheit degrees (or 0.80 Celsius degrees) above the 20th-century (1901-2000) average, which is the seventh highest global temperature anomaly (difference between the observed month and the long-term average) for any January since global climate records began in 1880. When considering land and ocean separately, the global land surface temperature anomaly for January 2021 was eighth highest in the 142-year record, while the January 2021 ocean surface temperature anomaly also was the eighth highest, despite a large region of below-average sea surface temperatures across the equatorial Pacific Ocean associated with the ongoing La Niña episode. [NOAA/NCEI State of the Climate]
  According to the National Snow and Ice Data Center, the extent of Arctic sea ice for January 2021 was the sixth smallest monthly extent for any January since satellite surveillance began in 1979. Antarctic sea ice extent in January tied January 2007 for the thirteenth smallest January ice extent on record in the Southern Hemisphere.
  The extent of the Northern Hemisphere snow cover during January 2021 was 24th smallest for the 55-year period of record that started in 1967. [NOAA/NCEI Global Snow & Ice]
  NCEI also provides a map showing the "Global Significant Weather and Climate Events map for January 2021."
• Preparation of NOAA's Monthly Global Climate Report is highlighted -- A member of the Climate Monitoring Branch of NOAA's National Centers for Environmental Information posted a blog on the ClimateWatch Magazine in November 2018 that describes how colleagues have been preparing NOAA's Monthly Global Climate Reports from the NOAA Merged Land Ocean Global Surface Temperature Analysis Dataset (NOAA GlobalTemp) that are released by around the 18th day of the following month. These climatologists compile and analyze observed temperature and precipitation data that have been collected by land-based stations, ships and buoys from around the globe during the previous month, producing their report in timely fashion. In addition to producing tabulated data sets, they create a variety of global anomalies and percentiles maps showing the departure of the observed monthly temperatures from a long-term average or the temperatures ranked in terms of percentiles. Attention was also given to the early portion of the global records that extend back to 1880, while the continental record only goes back to 1910. NOTE: Since this original blog was written, NOAAGlobalTemp has been updated to the new versions comprised of the Global Historical Climatology Network-Monthly version 4 (GHCNM v4) and Extended Reconstructed Sea Surface Temperature version 5 (ERSST v5) in 2019. [NOAA NCEI News]
• Satellites view extent of power outages across southeastern Texas-- The winter storm that traveled across Texas early last week brought rain northward across Texas at the same time record cold air was being spread southward, resulting in freezing rain and widespread icing conditions. The icing was responsible for slippery roads along with downed trees and power lines in southeast Texas. Day/Night Band imagery obtained from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument onboard the NOAA-30 polar-orbiting satellite shows the San Antonio, Austin and Houston metropolitan areas before and after the storm, revealing the diminution of nighttime illumination from city lights caused by the widespread loss of electric power. [NOAA NESDIS News]
  Images of the Houston metropolitan area from the VIIRS instrument on the NOAA/NASA Suomi NPP satellite and from the Operational Land Imager (OLI) instrument on NASA's Landsat 8 satellite also show the loss of nightlights due to the ice storm. [NASA Earth Observatory]
• Hawaii's snow-capped volcanic peaks seen from space -- Images obtained in early February from the Operational Land Imager (OLI) instrument onboard NASA's Landsat 8 satellite show snow covering the volcanic peaks of Mauna Kea (13,803 ft elevation) and Mauna Loa (13,448 ft) on Hawaii's Big Island. The snow cover on these peaks was from three Kona-type storms that passed near Hawaii beginning in mid-January. Using visible and infrared data collected from the MODIS sensor onboard NASA's Terra satellite, scientists at NASA Goddard Space Flight Center have determined the amount of snow over the two peaks by calculating the Normalized-Difference Snow Index (NDSI) for the first week of February. Thney extended the NDSI time-series graph for Mauna Kea and Mauna Loa that began in the year 2000. Their combined weekly NDSI value in early February 2021 for the two volcanoes is the second-highest in the 2000-2021 record, falling just below the record set in 2014. [NASA Earth Observatory]
• Why the Southern States experienced "thundersleet" -- Professor Marshall Shepherd, Director of the University of Georgia’s (UGA) Atmospheric Sciences Program and past President of the American Meteorological Society, recently posted a blog describing the occurrence of "thundersleet" across the South at the start of last week. He likened this term to thundersnow, which is the occurrence of lightning and audible thunder while snow is falling; however, in this case, ice pellets, also known as sleet, are falling when lightning and thunder are being detected. In this case, the precipitation that started from the cloud as snow melted to form rain in a layer of warm air with temperatures above the freezing point, but then fell through a sufficiently deep subfreezing layer for the rain to freeze into ice pellets. The air needed to be sufficently unstable to cause convection that resulted in vigorous vertical motion leading to electrostatic charge separation and then lightning and thunder. [Forbes]
• Seasonal (3-month) Seasonal weather outlook released -- Late last week, forecasters at the NOAA Climate Prediction Center released their new national Seasonal Outlook for the next three months that consists of meteorological spring 2021 in the Northern Hemisphere (March-May). Specific details of their outlooks include:
  • Temperature and precipitation outlooks -- According to their temperature outlook, over three-quarters of the land area comprising of the contiguous U.S. should experience a high chance of above average temperatures for Spring 2021. This region runs from the Atlantic Coast to California along the Pacific Coast. The greatest probability of unseasonably warm weather should be found across the Southwest, centered upon the Four Corners States (Arizona, Utah, Colorado and New Mexico) and stretching across Texas. On the other hand, sections of the Northwest could see a good chance for below average spring temperatures, primarily across Washington state, the Idaho Panhandle and northwestern Montana. The outlook indicates that the remainder of the "Lower 48 States" that stretch from Oregon and northern California eastward across the northern Rockies, the northern Plains and upper Mississippi Valley to the western Great Lakes would have nearly equal chances of below, near or above average temperatures (identified by the "EC" label). The northern half of Alaska appears to have a high chance of a warm spring, with the highest confidence running along the regions to the north of the Brooks Range. Conversely, the southern and southeastern sections of the 49th State have the highest probability of below average spring temperatures.
    Their precipitation outlook indicates that the Southwest and sections of the Southeast stand a better than even chance of below average precipitation for Spring 2021. The region with the highest chances of a dry spring would be centered across the Four Corners States and across the Florida Peninsula. Conversely, the most of the Midwest and Northeast, along with the Northwest should expect a wetter than average spring. The area around the western Great Lakes and over Washington state would have the highest chance of above average spring precipitation. The remainder of the "Lower 48 States" are considered to have essentially equal chances of below, near or above average precipitation for meteorological spring. A southeast Alaska, including the Panhandle, could have a dry spring, while western Alaska could have above average precipitation over the next three months.
    A summary of the prognostic discussion of the 3-month outlook for non-technical users is available from CPC. These forecasts were based in part on the continuation of the current La Niña conditions in both the atmospheric and oceanic circulations through most of meteorological spring, before making a transition to ENSO-neutral conditions during late spring and early meteorological summer in the Northern Hemisphere. Other factors considered include temperature and soil moisture trends and the output from numerical weather prediction models influencing both the temperature and precipitation outlooks. The forecasters' confidence on their outlook discussion for individual regions of the nation is given. A description is also provided as how to read these 3-class, 3-month Outlook maps.
  • Seasonal Drought Outlook -- The forecasters at NOAA's Climate Prediction Center also released their US Seasonal Drought Outlook last week that would run from mid-February through May 2021. Their CPC outlook shows that the current drought conditions found across most of the western half of the 48 contiguous United States should continue to experience drought conditions; last week's U.S. Drought Monitor map provides the current extent and intensity of the drought across the nation. Drought was expected to expand across the southern Plains, extending northward from the Texas Gulf Coast to Kansas. Most of the Florida Panhandle also could see drought development. Improvement of current drought conditions could occur across sections of the interior Northwest (Oregon and Washington), the Midwest and Northeast.
    Note: a Seasonal Drought Outlook Discussion is included describing the forecasters' confidence.
• An All-Hazards Monitor -- This Web portal provides the user information from NOAA's National Weather Service, FAA and FEMA on current environmental events that may pose as hazards such as tropical weather, fire weather, marine weather, severe weather, drought and floods. [NOAA/NWS Daily Briefing]
• Earthweek -- Diary of the Planet [earthweek.com]