The winter of 2017-2018 is now half over, and so far has been dominated by large temperature extremes. The first three weeks of meteorological winter averaged well above normal across a large portion of the country, but extreme cold has dominated since then. The return to warmth is expected for the next two weeks, but current expectations are that colder weather will then return again during February.Topics: Frontier |
The QBO, or Quasi-Biennial Oscillation, is an oscillation in the wind direction in the stratosphere within about 15 degrees of the equator. Over a roughly two-year period, winds tend to oscillate between westward and eastward, with the switch between west and east winds starting high in the stratosphere and then shifting lower in altitude with time. The QBO is the result of waves propagating vertically in the atmosphere that then interact with the mean flow to slowly change wind speeds and direction. These changes influence the overall global circulation patterns, which in turn influence winter weather patterns across North America. The following plot shows the regular cycle in the QBO. Interestingly, the QBO has been positive for the last two winters, a highly unusual event. Since last winter, the QBO has turned sharply negative though, and that negative trend should continue into the upcoming winter.
With the pattern turning cold enough at the end of October to produce widespread frosts and freezes, it is an excellent time to look at when the average first freeze occurs across the country. Once frost begins to show up, the first snowfall will soon follow.
As of early October, the 2017 Atlantic hurricane season has produced 14 named storms, 8 of which have reached hurricane strength, and 5 of those major hurricane status (Category 3 or higher). Regarding storm numbers, this year is still below the average (since 1995) of 16 named storms for both neutral ENSO years and La Niña years (a La Niña is developing this year), but already at the average for hurricanes and one storm ahead of the average for major hurricanes.Topics: Tropical | Frontier | Hurricane |
Summer 2017 was hotter than normal for the U.S., ranking 15th hottest on record out of the last 123 years. However, unlike summer 2016, the heat this year was focused on the western half of the country, with the eastern US much more seasonal overall. The plots below show the monthly temperature anomalies for each month of the summer, along with the summer composite.Topics: Frontier |
After seeing the devastation caused by Hurricane Harvey, you might want to find a safer place to live than the hurricane prone Gulf Coast. While both the Gulf and East Coasts are prone to major hurricane landfalls, many areas of the country have risks. The Plains, Midwest, and Southeast have frequent tornadoes, much of the West has earthquakes, forest fires, and volcanoes, and while some northern areas have fewer natural disasters, they do have more snow and cold.Topics: Tornado | Snow | Hurricane | Wildfire | Flood |
While some extreme heat has been seen this summer across portions of the country, most recently across the Pacific Northwest, the entire June-August summer period is running much cooler than last year for the country on a population weighted basis.Topics: Frontier |
The developing pattern across North America features a strong upper level ridge along the West Coast and a central and eastern US trough. The West Coast ridge is sending temperatures to near all-time record highs across the Pacific Northwest while directing cooler air southward out of Canada into the Plains and Midwest where temperatures are falling to much below normal levels. We thought it would be worthwhile to look at past August patterns and find those that were similar to this year.Topics: Frontier |
While it is July and quite hot across much of the US, HBO is currently advertising the new season of Game of Thrones with a “winter is coming” hashtag, so we might as well talk about US winter temperature trends. Westeros (where the Game of Thrones story takes place) tends to see multiple years pass between winters, but then often sees extremely cold winters when they occur. Winter generally occurs every year across the US, but winter seasons have been growing increasingly variable in recent years.Topics: Frontier |