2:00 PM | An update on El Nino...signs that a weak one is forming, but a "super" El Nino is very unlikely

[NOAA/NESDIS Sea Surface Temperature Anomaly chart for September 4, 2014]

Discussion

Summary El Nino, which refers to warmer-than-normal waters in the central and eastern tropical Pacific Ocean, can have an important effect on global weather patterns. There were some forecasts earlier this year for a “super strong El Nino” to form, but we argued against that back in April here at "thesiweather.com" providing several reasons as to why that did not appear likely (http://thesiweather.com/2014/04/22/1100-am-el-nino-on-the-way-but-odds-are-against-a-super-one/) and it now appears very unlikely. There are signs, however, that a weak El Nino is starting to form and even a weak El Nino can have important implications on global weather patterns for the upcoming fall and winter seasons.

El Nino signs The first sign that suggests an El Nino is indeed developing in the Pacific Ocean is the noticeable area of warmer-than-normal sea surface temperatures (SST) now seen just off the west coast of South America. The latest SST anomaly map from NOAA shows this area of warmer-than-normal temperatures (circled area above; reds, oranges, yellows) which actually were first in evidence during the spring and, in fact, this fueled El Nino speculation; however, there was then was a temporary reversal earlier this summer in that particular temperature trend. In the last few weeks, however, the warmer-than-normal sea surface temperature trend has become re-established and is likely to persist for awhile.

A second signal that suggests a weak El Nino is forming has to do with the southern oscillation index. The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean. The SOI is calculated using the pressure differences between Tahiti and Darwin. Sustained negative values of the SOI below −8 often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean. The last three full months have seen an increasing “negative” trend in the SOI providing evidence that an El Nino is indeed forming (June: -0.8, July: -4.0, August: -10.1).

Potential Winter Implications One final note, a wintertime weak El Nino can have important implications to winter weather patterns in the Northeast US. For example, a weak El Nino can help to strengthen the southern branch of the jet stream across the southern US during the winter season and this could add to storminess (and snowfall) along the east coast. Not only is the magnitude (weak, moderate or strong) of an El Nino important in determining its potential impact on winter weather here in the Northeast US, but its location in the Pacific Ocean is critical as well. For example, a weak El Nino based in the central part of the Pacific Ocean tends to help generate more snowfall in the Northeast US compared with an El Nino centered in the eastern Pacific. Odds favor a centrally-based weak El Nino as we approach the upcoming winter season, but stayed tuned on that one.

2:45 PM | The Iceland volcano erupts, but a far bigger explosion occurs on the other side of the world

[Ash plume from Rabaul volcano in Papua New Guinea]

Discussion

Summary The Bardarbunga volcano in Iceland that we have been tracking in recent days has finally erupted, but it was not a big explosive event. Meanwhile, there has actually been a far bigger eruption in Papua New Guinea at the Rabaul volcano on Mount Tavurvur and this has the potential to do more damage to nearby population centers. In addition to the direct threat to people in nearby locations, volcano eruptions can produce ash that is extremely hazardous to jet aircraft that inadvertantly fly through it. The ash is composed primarily of silicate particles that melt when ingested into the combustion chamber of a jet engine, causing severe loss of engine performance and perhaps, a complete shutdown of the engine.

Iceland The Iceland volcano which sits beneath a glacier has been receiving most of the attention lately and last night it finally started erupting as lava emerged from a fissure. A fissure eruption is one in which lava essentially flows up through vents in the ground spread out over a larger area. The eruption lasted about four hours and came after weeks of earthquakes in the region. The eruption did not spew ash into the atmosphere and has had minimal effects on flights and it is in a relatively remote area of Iceland. Even though the eruption has stopped for the time being, earthquakes continue to rumble indicating magma is still on the move, and this volcano will continue to be closely monitored. By the way, in an odd twist of fate by Mother Nature, the remains of Hurricane Cristobal raced from off the US east coast into the North Atlantic during the past couple of days and actually dumped some serious snow on Iceland as well as on eastern sections of Greenland.

Papua New Guinea Meanwhile, on the other side of the world, the large Rabaul volcano began erupting earlier today and it has spewed out plenty of ash into the atmosphere. The ash plume has apparently reached about 11 miles into the air and has indeed disrupted air travel in that part of the world. This was the first major eruption of this volcano – one of the most active in Papua New Guinea - in about twenty years. In 1994, an eruption there nearly destroyed Rabaul altogether, forcing residents to flee.

Impact Volcanic eruptions along with oceanic and solar cycles play crucial roles in our global climate. The most substantive climatic effect from volcanoes results from the production of atmospheric haze. Large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere and these clouds can circle the globe within weeks of the volcanic activity. The small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures. The sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space. In fact, the formation of atmospheric sulfur aerosols has a more substantial effect on global temperatures than simply the volume of ash produced during an eruption.

Not only does the type and amount of ash from volcanic eruptions play a critical role in its potential effect on global temperatures, but the location of the eruption is also very important. Volcanic eruptions in the tropics, for example, can be much more important than those in the mid-latitudes for a couple of reasons. First, the sun heats equatorial regions more than in mid-latitude or polar regions; therefore, any disruption to solar radiation in the tropics can have more serious effects on global temperatures. Second, upper level winds - which act to spread and disperse ash plumes – are typically weak over tropical regions as compared with the mid-latitudes, for example, and this could impact the longevity of any ash cloud in a particular region.

The atmospheric effects of volcanic eruptions were confirmed by the 1991 eruption of Mount Pinatubo, in the Philippines. Pinatubo’s eruption cloud reached over 40 kilometers into the atmosphere and ejected about 17 million tons of SO2, just over two times that of the El Chichon, Mexico volcano in 1982. The sulfur-rich aerosols circled the globe within three weeks and produced a global cooling effect approximately twice that of El Chichon. The Northern Hemisphere cooled by up to 0.6 degrees C during 1992 and 1993.

3:00 PM | The first half of September looks quite warm in the Mid-Atlantic region

[Euro computer model forecast at 500 millibars for September 7th]

Discussion

August has brought a continuation of below normal temperatures to the Mid-Atlantic region following a slightly cooler-than-normal month of July, but it looks like at least the first half of September will be on the warmer-than-normal side. The persistent upper air pattern of recent months featuring numerous troughs of low pressure centered over the Midwest and Great Lakes will change over the next several days to one with strong high pressure ridging centered in the Southeast US. Indeed, the 500 millibar forecast map from the latest European computer forecast model run (above) depicts high pressure in the Southeast US about 10 days from now. From this position, high pressure over the Southeast US will pump in warm, humid air from the Gulf of Mexico region to the Mid-Atlantic which until now this summer has not been sustainable by the atmosphere for more than a couple of days at a time. Supporting evidence for this warm outlook during the first half of September comes from NOAA’s Climate Forecast System (CFS version 2) forecast model which shows warmer-than-normal conditions during the first 10 days of September in much of the eastern half of the nation (orange/red areas in two maps below). Looking even farther ahead, I believe it is possible that the warmer-than-normal weather pattern that develops next week may end up continuing into October, but there is likely to be a transition back to colder-than-normal conditions before the winter locks in.

[NOAA/Climate Forecast System forecast maps for temperature departures from normal for the next two weeks]

1:00 PM | Northern lights, an update on the Iceland volcano, and mysterious lights from the Napa earthquake

Discussion

Northern Lights [Northern lights earlier today as seen in Devil's Tower, Wyoming; courtesy spaceweather.com]

A coronal mass ejection (CME) reached the Earth’s upper atmosphere early today sparking bright auroras around the North and South Poles and in high latitudes. In fact, reports of northern lights have poured in today from across the northern US including such states as Maine, Michigan, Wisconsin, Idaho, North Dakota and Washington. The CME that instigated today’s display was launched toward Earth on August 22nd. According to “space.com”, the solar wind speed did not change much when the slow-moving CME arrived. However, the storm cloud was still “effective” because it contained a south-pointing magnetic field that opened a crack in Earth’s magnetosphere. Solar wind is pouring in to fuel the on-going display. High latitude sky watchers should remain on alert tonight for auroras as solar wind conditions continue to favor geomagnetic activity.

[NOAA POES satellite data shows the extent of this morning’s "statistical aurora oval" well down into the mid-latitudes; courtesy NOAA Space Prediction Center].

Iceland Volcano Earthquakes are rocking Iceland’s Bardarbungo volcano, adding to concerns that magna movements may trigger an eruption that could hinder air traffic. Two earthquakes measuring over 5.0 shook the volcano under the vast Vatnajokull glacier earlier today and over 500 quakes have hit the area since midnight. Scientists say that 50 million cubic meters of molten rock has moved in a 24 hour period. If it continues to head north, it could link up with the Askja system and trigger a large eruption. In 2010, Iceland's Eyjafjallajokul volcano erupted and sparked a week of international aviation chaos. Some 100,000 flights were cancelled after aviation officials closed Europe's air space for five days out of fears that volcanic ash could harm jet engines.

[The ash cloud from the Eyjafjallajokull eruption in 2010 created a major disruption for air travel]

Mysterious Lights Mysterious flashes of light in the sky were reported by several people during last Sunday’s magnitude 6.0 earthquake in the Napa region of northern California. Witnesses said the strange phenomenon looked like lightning and similar flashes of light have been reported in earthquakes around the world from Japan to Peru. One scientist called this phenomenon “earthquake lights” and suggested they are a consequence of the stresses building up deep below the earth that cause an electric current to flow to the surface and burst through the earth. This typically happens before or during an earthquake. Most reports said there were one to two seconds between the light flashes. Research continues in this area - many seismologists do not believe such things are real.

12:55 PM | Cooler-than-normal weather pattern to continue through August for much of the nation

Discussion

Our great summer weather pattern continues here in the Mid-Atlantic region with temperatures starting off the month of August at below normal levels (DC: -1.5°, Central Park, NY -1.1°, Philly -2.4°). Yesterday was the first time this month that Philly Airport reached 90 degrees and temperatures over the weekend couldn’t escape the 70’s. In fact, a huge chunk of the nation has started off the month of August with below normal temperatures (see plot above). July turned out to be slightly below normal in temperatures for the big cities along the I-95 corridor (DC, Philly, NYC).

As far as the rest of the month of August is concerned, indications are quite strong that the overall cooler-than-normal weather pattern will continue in much of the country. One longer-range computer forecast model called the Climate Forecast System (CFS version2) predicts cooler-than-normal temperatures in much of the same area in each of the next three weeks (green regions in forecast maps below for weeks 1, 2 and 3). Similar to the first five days of August, much of the nation is predicted to experience below normal temperatures with the exceptions being the western states and extreme Northeast. The CFS computer forecast model has a pretty good track within these type of time scales. Looking even farther ahead, there are a few signs that a change to warmer-than-normal is possible for much of the nation come September.

1:30 PM | Unusual California weather lately including a "chilly" Death Valley

[Nationwide radar; courtesy mesonet.org]

Discussion

The highest temperature ever (reliably) recorded on Earth was 134 degrees and it occurred in the Furnance Creek section of Death Valley, California on July 10, 1913. This past Sunday, however, the high temperature in Death Valley maxed out at a relatively chilly 89 degrees which is nearly 30 degrees below average for this time of year. It set the record there for the coolest high temperature ever recorded for the date (August 3rd) by smashing the old record of 104 degrees set in 1945. In fact, this was only the 8th time that a high temperature in the 80s has occurred in Death Valley in July or August with records going back to 1911 and there hasn’t been a high less than 90 degrees since 1984 (source Capital Weather Gang).

One of the factors that caused the unusual chill in Death Valley was an extensive cloud cover that blocked out the typical intense sunshine. Copious amounts of moisture poured into southern California during the weekend from the Pacific Ocean which resulted in unusual rainfall for this time of the year. In fact, some areas received record amounts of rainfall for the date which led to floods and mudslides in mountainous areas. Rain continues today in California, but this time it is falling across northern parts of the state.

1:25 PM | Tropical activity in the eastern Atlantic

[Latest visible satellite image of the tropical Atlantic Ocean; courtesy Penn State e-wall]

Discussion

All in all, the tropical season so far has been rather quiet in the Atlantic Basin given the frequency of wind shear over the Atlantic Ocean and the steady westward push of dry (Saharan-layer) air off of the west coast of Africa. There is now another tropical wave moving westward in the eastern Atlantic and it should develop into the second named system (Bertha) of the season later this week, but it will face some obstacles in its development in the near term.

[Tuesday analysis of the Saharan Air Layer (SAL) using data from the Meteosat-9 satellite; courtesy University of Wisconsin - CIMSS]

First, this new wave will fight against some rather high wind shear in its vicinity later today and tonight. Varying wind speeds and directions with altitude (i.e., wind shear) is usually an inhibiting factor when it comes to the development of tropical systems. Second, as has been the case quite often this tropical season so far (and last year as well), dry air is pushing westward from western Africa and this wave has to endure more of this Saharan-layer dry air over the next couple of days (yellows, oranges; map courtesy University of Wisconsin - CIMSS). If it should survive the wind shear and dry air - and odds are better than 50/50 - then this tropical wave would likely continue on a west-to-northwest path for the next few days and reach the Antilles Islands region of the eastern Caribbean Sea by the weekend and then the Bahama Islands region by early next week. A second tropical wave follows close behind currently churning westward just off the west coast of Africa, but it is way too early to tell if that system will ever strengthen into a named storm.

2:30 PM | Atlantic Ocean now showing some life

Discussion

The only named tropical system so far this season has been Arthur which formed off the southeast US coastline earlier this month and reached hurricane status (category 2). There is now a pretty healthy-looking tropical wave way out in the Atlantic Ocean and this could eventually become the first “Atlantic-type” tropical storm of the season, but it does have some dry air to penetrate in the near term.

The latest Saharan air layer tracking product (courtesy University of Wisconsin – CIMSS/NOAA-HRD) shows a large expanse of dry air off the west coast of Africa (“oranges and yellows”) that extends well out into the Atlantic Ocean and “in front” of the generally westward-moving new tropical disturbance. This tropical system will encounter some of this African dry air mass in the near term, but it also will be moving into a region with favorable sea surface temperatures of greater 80 degrees. Should the tropical wave survive its encounter with the dry air and develop into a named tropical storm, it would become known as Bertha. We’ll monitor its progress over the next few days here at thesiweather.com.

10:45 AM | The sun has gone quiet...solar cycle 24 continues to rank as one of the weakest cycles more than a century

Discussion

Overview

Ten days ago, the sun was quite active and peppered with several large spots. Now the sun has gone quiet and it is nearly completely blank. The sun goes through a natural solar cycle approximately every 11 years. The cycle is marked by the increase and decrease of sunspots which are visible dark regions on the sun’s surface and cooler than surroundings. The greatest number of sunspots in any given solar cycle is designated as the “solar maximum" and the lowest number is referred to as the “solar minimum” phase.  It appears that the solar maximum phase for solar cycle 24 may have been reached and it is not very impressive. It looks as if this solar cycle is “double-peaked” (see below) which is not all that uncommon; however, it is somewhat rare that the second peak in sunspot number during the solar max phase is larger than the first. In fact, this solar cycle continues to rank among the weakest on record which continues the recent trend for increasingly weaker cycles. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906. Going back to 1755, there have been only a few solar cycles in the previous 23 that have had a lower number of sunspots during its maximum phase. For this reason, many solar researchers are calling this current solar maximum a “mini-max”. Solar cycle 24 began after an unusually deep solar minimum that lasted from 2007 to 2009. In fact, in 2008 and 2009, there were almost no sunspots, a very unusual situation during a solar minimum phase that had not happened for almost a century.

Consequences of a weak solar cycle

First, the weak solar cycle has resulted in rather benign “space weather” in recent times with generally weaker-than-normal geomagnetic storms. By all Earth-based measures of geomagnetic and geoeffective solar activity, this cycle has been extremely quiet. However, there is some evidence that most large events such as strong solar flares and significant geomagnetic storms tend to occur in the declining phase of the solar cycle. In other words, there is still a chance for significant solar activity in the months and years ahead.

Second, it is pretty well understood that solar activity has a direct impact on temperatures at very high altitudes in a part of the Earth’s atmosphere called the thermosphere. This is the biggest layer of the Earth’s atmosphere which lies directly above the mesosphere and below the exosphere. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation and are highly dependent on solar activity.

Finally, if history is a guide, it is safe to say that weak solar activity for a very prolonged period of time (several decades) can have a negative impact on global temperatures in the troposphere which is the bottom-most layer of Earth’s atmosphere - and where we all live. There have been two notable historical periods with decades-long episodes of low solar activity. The first period is known as the “Maunder Minimum”, named after the solar astronomer Edward Maunder, and it lasted from around 1645 to 1715. The second one is referred to as the “Dalton Minimum”, named for the English meteorologist John Dalton, and it lasted from about 1790 to 1830. Both of these historical periods coincided with below-normal global temperatures in an era now referred to by many as the “Little Ice Age”. In addition, research studies in just the past couple of decades have found a complicated relationship between solar activity, cosmic rays, and clouds on Earth. This research suggests that in times of low solar activity where solar winds are typically weak; more cosmic rays reach the Earth’s atmosphere which, in turn, has been found to lead to an increase in certain types of clouds that can act to cool the Earth.

Outlook

The increasingly likely outcome for an historically weak solar cycle continues the recent downward trend in sunspot cycle strength that began over twenty years ago during solar cycle 22. If this trend continues for the next few cycles, then there would likely be more talk of another “grand minimum” for the sun. Some solar scientists are already predicting that the next solar cycle, #25, will be even weaker than this current one. However, it is just too early for high confidence in these predictions since some solar scientists believe that the best predictor of future solar cycle strength involves activity at the sun’s poles during a solar minimum and the next solar minimum is still likely several years away.

Video

httpv://youtu.be/3aRIW4SWkFU

12:15 PM | Kind of a "polar vortex" look to next week's weather maps

[12Z Euro 500 mb height anomaly forecast map for next Tuesday, July 15th; map courtesy Weather Bell Analytics at weatherbell.com]

Discussion

Last summer, the hottest weather in the Mid-Atlantic region took place in the week between July 14th and July 20th with Philadelphia, for example, averaging an impressive 95 degrees for high temperatures over the 7-day period. The same time period this summer - which happens to be next week - looks like it may have a far different result and the upper level weather maps may actually resemble the “polar vortex” pattern made famous this past winter.

Today's European computer forecast model indicates there will be an anomalously strong upper level low situated over the central Great Lakes in much the same manner that occurred frequently during the past winter (see above; 12Z Euro forecast map courtesy Weather Bell Analytics at weatherbell.com). Also, in much the same manner as this past winter, the coldest air relative-to-normal is likely to occur over the Great Lakes and Upper Midwest, but cooler-than-normal air is likely to extend all the way to the Mid-Atlantic coastline. Normal high temperatures have now climbed to 87 degrees in Philly, 89 in DC, and 84 at Central Park, NY and these levels are more than likely not going to be reached for at least a portion of next week. The cold front that will usher in this cool air mass is likely to arrive in the Mid-Atlantic region in the Monday/Monday night time frame - perhaps associated with numerous showers and thunderstorms.