Drought

Superfog is the current buzzword in the weather world, so why has it caused so many issues in Louisiana?

One-sentence summary

Superfog, or near-zero visibility caused by the combination of fog and wildfire smoke has wreaked havoc on Louisiana recently, so we take a deep dive into how the term came about and why this is such a problem there this year.

Superfog: A super serious problem in Louisiana

If you’ve been paying attention to the news lately, particularly as it relates to weather, you’ve likely heard about “superfog” leading to a couple deadly traffic incidents in Louisiana. If you missed that news, here are a couple articles to catch you up.

The first incident was a major pile up on I-55 a couple weeks ago that killed at least 7 and injured over 60 people.

More recently, another superfog event led to an 11-car pileup on I-10 east of New Orleans that killed one and injured eight.

So what’s the difference between regular fog and superfog? And why is it so problematic?

What is superfog?

The technical definition of “superfog” is a combination of smoke and water vapor that produces zero visibility over roadways. What sets it apart from regular dense fog? The smoke. “Water vapor that produces zero visibility” is usually just plain old fog. When you combine fog and smoke and get zero visibility, you get “superfog.”

You may say to yourself, “Self, I thought smoke and fog was known as ‘smog?'” You are correct. The difference is that smog typically results from manmade pollutants, whereas superfog is produced from “smoldering organic material” and has extremely low visibility.

Is superfog some new clickbait term?

“Superfog” is not clickbait, a new term, nor is it a new problem. In fact, the South has been a notorious hot spot for superfog incidents for many, many years. This front page headline from the May 8, 2000 Biloxi Sun Herald reported on a similar incident on I-10 due to smoke from a prescribed burn mixing with fog.

The Biloxi Sun Herald after a May 2000 superfog event in southern Mississippi. (newspapers.com)

In that article a Mississippi Highway Patrol officer was even quoted as saying “We’ve had two or three multi-car accidents because of smoke and fog mix.” A 1989 study by Hugh Mobley found that from 1979 through 1988, visibility reduction caused by smoke or a combination of smoke and fog caused 28 fatalities, over 60 serious injuries, numerous minor injuries, and litigation expenses into the millions. That study, as cited in a more recent 2003 USDA Forest Service paper by Gary L. Achtemeier started to quantify the impacts of what had (presumably) yet to be coined as “superfog.”

The origin of the term “superfog” itself seems to come from Achtemeier. As best as I can tell, he first formally coined the term in a 2001 abstract that I believe was intended for an American Meteorological Society meeting. So, I think Achtemeier is the Father of the term Superfog, and Hugh Mobley may be the originator of understanding its impact. Whatever the case, in this 2003 USDA Forest Service paper by Achtemeier, he does a good job explaining why the South is a hotbed for superfog events. And it appears that recent issues in Louisiana broadly fit the mold.

In his paper, Achtemeier notes a high number of prescribed burns that are done in the South. To my knowledge, the recent fires in Louisiana were not prescribed burns. But his other points stand. It’s a relatively humid period in the cool season right now, making fog more likely on the Gulf Coast. And this most recent marsh fire occurred very much at the wildland/urban interface in New Orleans East. So you have a number of people traveling in a smokey area, with conditions ripe for fog. From the paper, you can see imagery that shows the difference and uniqueness of superfog. Unlike regular dense fog with, say, visibility under a quarter-mile, superfog is literally zero visibility, often 10 to 20 feet or less. It’s easy to understand why that would lead to such severe outcomes on roadways. Anyway, if you want to better understand some of the initial hypothesis behind specific superfog development, that paper makes for an interesting read.

Why all of a sudden in Louisiana?

Louisiana is currently experiencing one of their worst droughts in recent memory.

While a new drought monitor update will be released later this morning, Louisiana is in just an exceptional and widespread drought. (US Drought Monitor)

Almost 70 percent of the state is covered in level 4 of 4 (exceptional) drought. It’s bad. And marsh fires have been happening for weeks from Cameron Parish in the southwest corner of the state east into the New Orleans area. Now, as fog season begins to ramp up on the Gulf Coast, we are seeing additional consequences of these fires.

If you want to look more specifically at Tuesday’s incident, you can at least pick out the fog easily on modeling. A forecast sounding, or vertical profile of the atmosphere from the NAM model averaged for the area just east of New Orleans at 7 AM on Tuesday shows what we call an inversion in the atmosphere about 500 to 1,000 feet off the ground.

A model forecast atmospheric sounding (vertical profile) from Tuesday morning east of New Orleans showed conditions ripe for the development of fog. (Tropical Tidbits)

What is an inversion? Normally, as you go up in altitude temperatures decrease. Inversions are places in the atmosphere where temperatures actually rise as you go up in altitude. In other words, you see warming in a slice of the atmosphere before temperatures begin to cool again. Inversions tend to suppress thunderstorms. During the storm season, we refer to these as “caps” or “capping” in the atmosphere. That inversion acts as a barrier to cloud-top growth, or vertical development. It also tends to act as a “lid” on the atmosphere, trapping any gunk underneath it near the surface. This can cause smog in cities and fog in cities and rural locations as well. In most cases, inversions tend to break as surface temperatures warm up during the day. But long-duration inversion events over days or worse with fog and severe smog problems will sometimes occur in Utah’s Wasatch Front in the winter months. There is also Tule fog in California’s Central Valley, which is common in the cool season.

In this case, a sharp, shallow inversion in a humid environment was able to lead to fog development outside New Orleans on Tuesday. The fog in the area of the fire was able to transition to a localized superfog event just east of New Orleans.

A cool front should push through most of Louisiana by early next week hopefully providing a respite from fog. But it does appear that another substantial period of humidity and fog risk may be possible later next week. The NWS in New Orleans has been all over this for awhile now and remains the best source for local information in that area.

October 6, 2023 Outlook: Philippe to bring wind and rain to Maine and Canada and even some snow to Quebec and Ontario

One-sentence summary

Philippe will bring a variety of weather to Maine, Quebec, and Ontario this weekend as it transitions to a non-tropical storm and offers up heavy rain, gusty winds, and even some snow in parts of Canada.

Philippe destined to follow Lee’s footprints

Tropical Storm Philippe is a little stronger today as the center approaches Bermuda. Wind gusts over 50 mph were reported on the island this morning. The forecast remains mostly on track, with Philippe essentially being a smaller, less intense version of last month’s Hurricane Lee.

Philippe is in the initial stages of extratropical transition, where it goes from a tropical entity (a storm that derives energy from warm water) to something akin to a nor’easter (a storm driven by jet stream processes and one that will acquire fronts). Storms are displaced east of Philippe’s center today. (Weathernerds.org)

Philippe will likely become post-tropical by tomorrow and transition to a strong nor’easter-type storm as it moves toward the Gulf of Maine or Bay of Fundy this weekend. It is expected to hook back to the north and west across Quebec and eventually stall out on the south end of James Bay, bringing rain and even some snow to Quebec or portions of interior Ontario.

As Philippe transitions to an extratropical storm it will hook back to the north and west across Quebec and settle near the border with Ontario. (Tomer Burg)

The National Hurricane Center will not be issuing tropical products for Philippe as it moves into Canada and New England, indicating that while it will bring impacts they should be managed at the local level. I think a very plain language translation of this means that, while a notable storm, it is not expected to be an especially damaging one. Marine impacts should primarily be gusty winds and large swells. We’re in a lower phase of the tide cycle right now so that helps mitigate that risk a bit.

Rain totals will peak in interior Maine, portions of the Adirondacks in New York, and interior Quebec, where as much as 5 inches of rain is possible. Click to enlarge. (NOAA WPC)

But the main concern with this will likely be tomorrow night and Sunday with locally heavy rain. Total rainfall may exceed 3 or 4 inches in spots, especially in interior Maine and Quebec (north & west of Quebec City, Montreal, and the National Capital Region). Grounds are still fairly damp, so flash flooding is a distinct possibility in spots. Snowfall would be most likely along the Ontario/Quebec border and north of a Sudbury-North Bay line in Ontario.

Watching the Gulf next week

We are starting to see some vague model agreement on next week’s setup with Pacific moisture and tropical noise tracking across Mexico and potentially into the Gulf of Mexico.

The upper level map suggests that whatever happens in the Pacific may get pulled across Mexico next week and into the Gulf, maybe as a lower-end storm, maybe as just a bunch of added moisture. (Tropical Tidbits)

The pattern in the Pacific is such that we should see a bit of a weird entanglement between Tropical Storm Lidia, Invest 99E (the disturbance off the Mexican coast), and an upper level trough in the atmosphere over the Southern Plains and Southeast. How so? In some way, either Lidia or 99E or both will get “pulled” northeast toward Mexico by the upper trough, which will then allow that cluster to track into the Gulf of Mexico. From there, it should probably track northeast or east-northeast across the Gulf toward Florida or the eastern Gulf Coast. What will it be? I don’t know. Probably not a large storm; probably something lower-end. But it could end up being a rain and/or severe weather producer in the Gulf waters or near the coast (or ultimately in Florida). The timing of all this would be late next week. We have a few days to watch this, and we’ll have an update this weekend and on Monday.

Elsewhere, the NHC continues to outline an area deep in the Atlantic that could develop, but it is unlikely to impact land if it does so.

Winter is coming

In addition to the potential snow from Philippe’s remnants in Canada this weekend, we have freeze warnings now populating across the Plains. Freeze watches and warnings extend from northeast Colorado and central Kansas into the Dakotas and portions of western Minnesota.

NWS watches and warnings as of Friday morning shows freeze warnings for more of the Dakotas, Nebraska, and portions of Kansas, Colorado, Wyoming, and Minnesota. Red flag warnings indicating fire risk due to drier air will be posted in the Deep South. (Pivotal Weather)

Low temperatures this morning are in the 20s in spots in Montana but will expand over a wider area on Saturday morning. A warming trend will follow for a time early next week.

Lower Mississippi River dryness

We continue to see the situation in the Lower Mississippi River basin look worse. For Louisiana salt water intrusion to halt or reverse, we need rain upstream; something that can basically flush the salt out. The forecast upriver from New Orleans does not look great, with Memphis likely to see a declining water level over the next 7 to 10 days and most of the Ohio Valley seeing less than half an inch of rain over the next week.

Water levels at Memphis remain near their all-time record lows set earlier this year. (NOAA)

The water level at Memphis this year preliminarily set a new record of -11 feet, and the level by the end of the forecast above has them down to about -10.6 feet again. Hopefully some more meaningful rain can fall around mid-October in the middle Mississippi and Ohio River Valleys, but much more is needed to alleviate the expanding problems in Louisiana. Thankfully at least, the projections for how far north the saltwater wedge gets have slowed considerably.

To solve Louisiana’s Mississippi River salt water crisis a significant weather pattern change is needed. Is any in sight?

At The Eyewall, we’ve focused on hurricanes and tropical storms since our launch in June. Some of you have asked what we’ll do during the offseason, and the answer is we will probably pull back our posts to every few days unless there’s a major weather event, and we will focus on extreme weather impacts in North America. We don’t want to offer clickbait or drama, but a forecast, an explanation, and context. I’ve decided to roll out something of that nature today with a focus on the Mississippi River salt water intrusion crisis in Louisiana.

One-sentence summary

The situation with salt water creeping up the Mississippi River in Louisiana is a complex one but one that has a basic solution (more rainfall) that does not look likely to be in the cards over the next 2 to 3 weeks in any meaningful capacity.

What is happening?

If you’ve been following the news lately, you may have heard about salt water creeping upriver in the Mississippi River in Louisiana. In the most simple terms, as dry weather has led to low river flows in much of the Mississippi Valley, denser salt water has been able to creep north at the bottom of the river. This isn’t unprecedented, but it isn’t common either. This happened to a much lesser extent last year and more notably back in 1988, when the salt water barrier shifted over 100 miles up the river west of New Orleans. This led to a couple days of salt water intrusion into New Orleans’ water supply which ended quickly.

WWNO, the NPR affiliate in New Orleans has a great rundown of what’s happening.

Tulane’s School of Public Health & Tropical Medicine also published a “5 things to know” that is helpful.

Virtually the entire Mississippi Valley is in drought right now, with a good chunk of the Missouri and Ohio River Valleys that feed the Lower Mississippi also in drought or abnormal dryness. The hot, dry summer in Louisiana in particular has exacerbated the dryness and drought there, with the entire southern two-thirds of the state in either exceptional or extreme drought.

Louisiana is in pretty terrible drought right now, but the situation upstream on the Mississippi is only marginally better, with widespread dry or drought conditions into Minnesota and along the Missouri and Ohio Rivers as well. (US Drought Monitor)

The last 60 days have seen 5 to 50 percent of normal rainfall along the Mississippi south of Memphis. The Ohio Valley and Missouri Valley have both seen 50 to 75 percent of normal rain. All this combined with the extreme drought in Louisiana has led to a confluence of problems and an expanding salt water wedge.

Over the last two months, rainfall has been 25 percent of normal or less in much of southwest Mississippi and Louisiana, and only marginally better than that in most areas along the Mississippi, Ohio, and Missouri Rivers. (NOAA)

What is the rainfall outlook?

To solve this problem, the main thing you need is just simply rain. It needs to rain in the Ohio, Missouri, and Mississippi Valleys sooner than later. Is there anything in sight over the next two weeks? Not really. The Lower Mississippi Valley should see minimal relief. The Ohio Valley looks quite dry. The Missouri Valley and Upper Mississippi are more mixed, but we’re just not seeing signs of any appreciable rainfall over the next two weeks.

Both the European model (shown here) and the GFS model are advertising below average precipitation over the next two weeks over virtually the entire Mississippi River drainage basin. (Weather Bell)

This is why you are seeing so much news about preparations for this in New Orleans and other Louisiana communities. Without meaningful rain over the next two weeks, you will continue to see the salt water migrate north. Current weather forecasts push us out to about mid-October and current projections for the wedge have it getting to New Orleans in later October. Even if 10 inches of rain fell over Memphis on October 15th, it would take some time for that water to flow downstream and get to New Orleans and southeast Louisiana. And isolated rain is not the answer. This problem requires a lot of upstream rain over a broad area. So it seems pretty clear that this problem is going to worsen.

So when can we expect a change? Well, when we look at the Climate Prediction Center’s outlook for weeks 3 and 4 (and granted, this is from last Friday), we can see signs of life in Texas or the Southern Plains, but probably nothing that would help “solve” the problems in Louisiana.

The situation within the Mississippi Basin does not look to improve a whole heck of a lot in mid October either. (NOAA)

The CPC outlook for October is positive with a lean toward above normal rainfall in the mid-Mississippi Valley. I’m not sure if changes over the last week since this map’s release have necessarily lowered chances of this outcome, but I don’t believe they’ve helped much.

The bottom line: The situation with salt water in the Mississippi River is going to worsen in the coming weeks, and there is not necessarily any strong signal for changes in the rain patterns over the key areas required to alleviate the problem. We need to see a change in the rainfall chances in either or all of the Ohio, Mississippi, and Missouri River Valleys before we can be confident that some help will be on the way. And at least into mid-October and possibly late October, that’s not likely to occur.