Holiday Weather Event Dill is affecting travel over much of the US. In the Pacific Ocean, El Niño-like conditions already exist and an official El Niño is imminent, while Sea Surface Temperatures (SST) in the Gulf of Alaska have moderated, leading to uncertainty for winter weather over the US.
Elsewhere, the Arctic continues to warm at an alarming rate, lightning injures football fans, Chicago is experiencing its cloudiest December, and days are getting longer in the northern hemisphere. Let’s go Around The World.
Sea Surface Temperatures Influence The Atmospheric Flow
The jet stream pattern is connected to the temperature of the air between the jet stream and the ground. If the air below the jet stream is warm, that air is less dense than cold air. Dense air takes up less space, and allows the pressure at jet stream level to be low. The opposite is true for warm air below the jet stream.
Sea Surface Temperatures (SSTs) affect the air at the surface. Last year the SST in the Gulf of Alaska was extremely warm relative to normal, and this helped keep in place a ridge in the jet stream over the eastern Pacific. Downstream, a trough in the middle of the US brought snow and cold to the eastern half of the country.
El Niño Conditions Are Apparent Now
Though NOAA has not declared an official El Niño, the water in the equatorial Pacific is warm enough to produce El Niño-like effects, such as Extended Weather Event Cucumber which brought rain to southern California in the last few weeks. The Australian record warm weather and drought are also thought to be connected to El Niño.
El Niño is defined as three consecutive three-month periods in which the SST in a certain location in the Pacific Ocean exceeds normal by 0.5 degrees Centigrade. This condition will probably be met next month, but the effects of El Niño have begun.
SSTs in the Gulf of Alaska are still elevated, resulting in a tug of war between the effect of the warm Gulf of Alaska water and the El Niño. Recently, El Niño caused the Weather Event Dill, which brought rain to California. Now the high pressure has re-built over the eastern Pacific, so California will be dry, while the eastern US could have a stormy period.
Holiday Weather Event Dill Is In Its Prime
The disturbed weather event of this big-travel week, which Decoded Science has named Dill, is now heading towards peak activity. Major effects will be as follows:
- Today: Heavy rain on the Gulf Coast and snow in the northern plains and upper midwest.
- Wednesday: Heavy rain along the east coast and some snow in the midwest and Upper Great Lakes.
- Thursday: A new storm crosses the Rockies.
- Weekend: A possible strong coastal storm late this week or early next week.
- Ongoing: Avalanche advisories are in effect for backcountry areas of the Rockies as new snow falls on old pack weakened by warm weather.
Temperatures In The Arctic Continue To Rise Twice As Fast As Elsewhere
Temperatures near the north pole have been rising rapidly for some time.
The anomalies show that most of the warming comes in the winter, when temperatures routinely are ten or more degrees above normal. Statistically, the temperature has risen twice as fast as the overall global increase in the last 40 years.
The likely explanation is that ice is a good reflector of solar radiation and water is not, so the melting of Arctic ice has a feedback effect: Less radiation is reflected and more is absorbed by the surface of the earth.
Still, the fact that this affects winter temperatures more than summer seems backwards, and more research needs to be done on the physical cause of the rapid Arctic warming.
The result of the arctic warming has been to raise pressures near the pole and thus push the jet stream equatorward. Last winter’s frigid temperatures over Siberia and the eastern United States are manifestations of the changing jet stream.
Lightning Strike At Tampa Bay Football Game
A bolt of lightning struck the parking lot minutes after the end of the Tampa Bay-Green Bay football game Sunday, injuring seven people. None suffered life-threatening injuries, but the lesson is clear: Lightning is dangerous. It can strike more than ten miles from its source
Cloudiest December In Chicago
Chicago is on pace to break its December record for cloudiness. The sun has so far been visible only 16% of the potential time, as opposed to an average of 41% and a record of 19%. There have already been 15 days with no sunshine at all.
Solstice Ushers In Longer Days In The Northern Hemisphere
The sun did an unheralded about-face on Sunday as it reached the tropic of Capricorn and turned around as it does every year. The days will get longer in the northern hemisphere, but the coldest weather is yet to come, because of a lag between the amount of sunshine and the temperature in the lower atmosphere.
Weather In The Dead Of Winter
The weather over North America this winter is caught in a tug of war between competing SST anomalies. Which side do you see winning?