Thursday, November 16, 2017

Sea Fog over the Lake

Last December, many Chicagoans woke up to see wispy layers of fog rolling off of Lake Michigan. This is a fairly common weather event that happens when a mass of very cold air blows over warmer water, often called arctic sea smoke or sea fog. On this particular day, the air above the lake was 3 degrees and the water was 35 degrees.

When the cold air blows over the warm water, the water near the surface evaporates into the colder air above and increases the humidity in the air. When the air reaches its dewpoint, the vapor condenses into fog.

This phenomenon really only happens when there are strong winds driving the colder wind out over the lake. This weird effect can happen even if Lake Michigan is covered in ice .

Arctic sea fog

Tuesday, November 14, 2017

Will it Snow on Thanksgiving?

All throughout the nation, cities have been reporting early snowfall and extreme cold.  Many people are wondering, will it snow for Thanksgiving? According to meteorologist Tom Kines, "It's not out of the question that if the precipitation came in early enough Thursday, you might have to worry about ice or maybe snow at the start [of the day]".  While this is not a very forward answer, it does give us a hint that there will be some ice on the roads.  It is better to be cautious then sorry.  The temperature is said to dip into the low thirties, giving us the strong guess for snow, but Kines says this ice will not last too long. 

Thanksgiving weather forecast

Extreme Winter Weather

For some parts of the US like the great plains and the midwest, the winter has already come and settled in.  Starting as early as the end of october, regions all across the United States have felt the icy breath of winter.  Examples of this are the rockies, mississippi valley and Northwest.  Joining these areas in mid november are "much of the midwest and east".

According to the Accumulated Winter Season Severity Index, twelve cities have already been hit by what is classified as extreme weather.  In Duluth, the city has already had a quarter of their average snowfall come through the region.  In the Northwest, Seattle saw their earlier snowfall in over 120 years.  These reports file in from all over the country and tell us that Winter will not be over as soon as we hope. 

Image result for weather severity index 2017 snow

Shelf Clouds

Shelf clouds, also called arc clouds, are typically seen at the leading edge of a squall line of thunderstorms. Although they might look similar, shelf clouds are nothing like tornadoes; what you see in a shelf cloud is the boundary between the downdraft and the updraft of a thunderstorm. Rain-cooled air descends in the downdraft then spreads when it reaches the earth's surface, then warmer, moist air is lifted at the gust front of the rain-cooled air. When the warmer air condenses, a shelf cloud forms.

Shelf clouds, after they have passed, can cause strong wind gusts and heavy rain or hail. These wind gusts can be so strong that they are able to knock over trees and power lines.

Shelf cloud, Bozeman, Montana

La Niña Conditions Have Arrived and Are Likely to Remain Through Early 2018, NOAA Says

La Niña conditions have officially developed and may continue through early 2018, potentially influencing the weather conditions we see in the United States this winter, according to an update issued by NOAA on Thursday.
La Niña is the periodic cooling of the equatorial eastern and central Pacific Ocean. When sea-surface temperatures are cooler than average by at least 0.5 degrees Celsius, along with consistent atmospheric indications, a La Niña is considered to be in place.
NOAA said oceanic and atmospheric signals in October and early November are consistent with a weak La Niña. You can see the strip of cooler-than-average sea-surface temperatures near the equator as of early November in the graphic below.
The black box highlights the cooler-than-average sea-surface temperatures near the equator indicating La Niña conditions on Nov. 9, 2017.

There is a 65- to 75-percent chance of weak La Niña conditions continuing through the winter months ahead based on the latest forecast guidance, NOAA said. This would mark the second consecutive winter with weak La Niña conditions as a potential weather influence.
We may already be observing some influence from La Niña on weather conditions in the U.S. this fall with early low-elevation snow and below-average temperatures in the Northwest during October and early November. This is consistent with what is typically observed in that region of the country during La Niña events.

La Niña Is Here – What Does That Mean For Me?

First off, no single La Niña produces the exact same outcome.
La Niña, El Niño or the lack of either, known as the neutral phase, is only one large-scale forcing on the atmosphere. It is not the sole factor in determining whether a season is wet, dry, cold or warm. Other atmospheric influences are in play, including atmospheric blocking.
Nevertheless, there are some general themes to expect in a La Niña winter, according to NOAA:
  • Southern U.S.: Above-average temperatures and below-average precipitation.
  • Northern U.S.: Below-average temperatures (particularly northern Plains and Northwest) and above-average precipitation.
Winter outlooks issued in October by The Weather Company, an IBM Business, and NOAA both had a strong La Niña flavor in terms of the temperature and precipitation expectations.
Below-average temperatures are most likely in the Northwest and Upper Midwest, while the South is forecast to be warmer than average.

Winter Temperature Outlook

The red contour in the South corresponds to higher probabilities of above-average temperatures. The darker blue areas in the Northwest and Upper Midwest have the highest odds of below-average temperatures. The light blue and orange contours show where temperatures may be slightly below or slightly above average, respectively. (The Weather Company, an IBM Business)

Portions of the Ohio Valley, Great Lakes and northern Rockies have the highest odds of above-average precipitation this winter. Depending on temperatures at any given time this winter, we could see increased odds of snow in those regions.
Meanwhile, the South could be in for a dry winter, which is typical during La Niña. If this pans out as forecast, there is the possibility of growing drought conditions in parts of the Southeast, and it may also give a boost to wildfire danger in this region next spring.

Winter Precipitation Outlook

Dark green shaded areas in the Great Lakes, Ohio Valley and the northern Rockies have the greatest odds for above-average precipitation this winter. Locations highlighted in dark brown across the South have the highest probability of drier-than-average conditions. Areas not shaded have an equal chance of seeing precipitation below, above or near average. (NOAA)

During last winter's weak La Niña, the West and Upper Midwest had one of the wettest winters on record, while a large swath of the East, South and Midwest had one of the warmest winters since record-keeping began.

What Does Lack of El Niño, La Niña Mean For Winter?

Neither El Niño nor La Niña is expected through winter. The so-called neutral conditions still offer clues on what winter could bring.
This neutral phase means there is no push in the atmosphere in either direction from the equatorial Pacific water. This lack of forcing can make it more difficult to predict the weather pattern in the months ahead, and there are many other elements to consider.
NOAA indicates that the polar jet stream may be shifted farther south and have more of a tendency to allow colder-than-average air into portions of the Midwest and Northeast during a neutral winter.
Meanwhile, much of the southern tier of the U.S. may end up with a warmer-than-average winter overall.
In addition, the subtropical jet stream may shift the track of storms to bring an overall wet winter to much of the South. The Pacific storm track may also result in low-pressure systems moving more into the Northwest versus California compared to a typical El Niño winter. 
However, it is important to note that this is just an overall trend of the season from December through February as a whole. Individual cold fronts and low-pressure systems will deviate from this at times.
Sea surface temperature differences compared to average in degrees Celsius. Area in red box highlights where sea surface temperatures are monitored for possible El Niño or La Niña conditions.
When sea-surface temperatures are warmer than average in the eastern and central equatorial Pacific by at least 0.5 degrees Celsius for at least three months along with consistent atmospheric indications, an El Niño is considered to be in place. When sea-surface temperatures are colder than average by at least 0.5 degrees over that same period, a La Niña is in effect.
The latest NOAA update indicates a 55 percent chance of neutral conditions continuing through this winter.

Impacts on Hurricane Season, Fall From a Neutral Phase

Potential winter weather pattern when El Niño and La Niña are absent.
Neutral conditions have been factored into this fall's temperature forecast, with most of the contiguous U.S. likely to see near-to-above-average temperatures. The exception is the Pacific Northwest where near-to-slightly-below-average conditions are currently anticipated through fall.
A lack of El Niño conditions has already played a role in the Atlantic hurricane season forecast.
El Niño can result in widespread and hostile upper-level winds in the Atlantic Basin, which inhibits the formation of tropical cyclones. Without the unfavorable winds that El Niño was expected to bring, there is a higher chance for a more active Atlantic hurricane season than previously forecasted.
El Niño and La Niña are different phases of the El Niño-Southern Oscillation (ENSO) pattern. ENSO refers to the fluctuations in temperature between the ocean and atmosphere in the eastern and central equatorial Pacific that can shift back and forth irregularly every two to seven years. 
Each phase of ENSO can trigger some notable changes in temperature, precipitation and winds in the equatorial Pacific. These changes can then disrupt large-scale air movement in the tropics and consequently weather across the globe.
ENSO conditions are just one piece of a large puzzle in determining the weather in a given season or month. 

Monday, November 13, 2017

Some strange sort of "fire rainbow" appeared in the sky iin Arizona on the 7th of November, 2017. Water droplets in the clouds, mixed with refracting light makes this phenomenon possible.