KATC StormTeam 3 Weather BLOG

As the Mississippi and the Atchafalaya Rivers are slowly cresting, the Army Corps of Engineers has initiated the process of closing gates on the Morganza Spillway.

The Corps in coordination with the U.S. Geological Service also disclosed higher than previously calculated flow rates being released at the Spillway.  At it’s maximum release point when 17 of the 125 gates were opened, the Spillway was releasing 172,000 cubic feet of water per second (cfs) into the Atchafalaya Swamp.

As of Thursday afternoon May 26th, the Corps had closed 5 gates with 12 currently opened releasing 120,000 cfs into the Atchafalaya Basin, or the equivalent of 69 Superdomes of water per day.

As the Mississippi River slowly recedes and turbulent flow rates decrease, more gates at the Morganza Spillway will likely be closed.

One of the key factors mentioned in the last several weeks is the flow rate of the Mississippi River at the Red River Landing.  When the flow rate at the Landing drops below 1.5 million cfs technically all the gates at the Morganza could be closed.   The flow rate as of May 26th had decreased from a peak near 1.7 million cfs to 1.55 million cfs and has been decreasing by roughly 10,000 cfs per day.

But turbulent flow changes along the entire stretch of the Mississippi River southeastward through Baton Rouge and New Orleans, stress factors on all levees and on the Morganza Spillway itself are also factors that are considered in the opening and closing process of the Spillway.

Based on the current data and trends I would expect on average about one gate per day to be closed at the Morganza Spillway with all gates possibly closing within roughly a two week time-frame. 

While there is no “official” time table on when all gates will be closed it will likely be much longer before backwater flooding begins to decrease.

Until then, backwater flood rises of at least another 1-2 feet (from this publishing date) can be expected through the first week or two of June.

Once backwater flooding crests, which may be sometime in mid-June, it will likely take another month before water levels decrease to a “live-able” level for those who have camps and homes in and near unprotected flood areas.

The anticipated Atchafalaya Flood has been tardy and rather unpredictable over the last couple of weeks. 

As of Friday, May 20th the National Weather Service in coordination with the River Forecast Center (RFC) and the Army Corps of Engineers had dropped the FLOOD WARNING for the Atchafalaya River at Butte La Rose northward with the revised crest now expected to be 24.5ft May 27th at Butte La Rose. 

This is 2.5ft lower than earlier forecasts meaning that fewer areas will flood in and around the Butte La Rose area northward through Krotz Springs. 

Backwater flooding will still be likely, but perhaps less severe, especially if your property is at a base flood elevation of 25 feet or higher.  For some, this may translate to a few feet of water or less, rather than the 5-10 feet of water that was originally forecast for low lying unprotected areas.

Meanwhile the Atchafalaya is still expected to crest in Morgan City near 11ft on May 29th.  So the expected flooding in low-lying unprotected areas in Lower St Martin and St Mary Parishes will still be likely into June. 

Why the change?  Apparently the drought over the last couple of years has been underestimated by the computer models that the Corps and RFC have been using.  The Basin soil has absorbed a significant amount of the initial water releases from the Morganza Spillway.  Once saturated however, the water will flow.

In addition, the Corps and the RFC have speculated that some ridging in the Atchafalaya Swamp has diverted the spillway water farther to the east.

Although the news is better, it is too early to tell how this flood will ultimately manifest.

As of this posting, 17 of the 125 bays of the Morganza Spillway have been dumping Mississippi water at a rate near 114,000 cubic feet per second (cfs) into the Atchafalaya Swamp.

This is enough volume to fill up the Louisiana Superdome in less than 24 minutes, or roughly 60 Superdomes full of water per day. 

Given the volume of the water pushing through the Morganza Spillway, areas expected to flood will flood, just later than originally predicted, and hopefully less than the Corps of Engineers originally indicated.

The water rises should be most dramatic during the last week of this month and once the flood arrives, it will likely stay for weeks, perhaps a couple of months.  Past Atchafalaya floods have lasted 5-8 weeks.

Here’s some historical information I tabulated on previous big floods…

The record crest of the Atchafalaya of 27.23 feet at Butte La Rose resulted in water levels of 26 feet or greater for 43 days.

Crests of over 26 feet in 1961 and 1962 resulted in water levels greater than the 26 foot level for 39 to 51 days respectively.

Wind direction, speed and tides will ultimately dictate on how quickly, or slowly, the Atchafalaya drains into the Gulf of Mexico.

It could be as late as July before some residents in portions of the Atchafalaya Basin can return to their property. 

Below are notable crests over 20 feet at Butte La Rose and levels in the last 10 years. 

Date              River Stage at Butte La Rose

3/03/59             23.40
4/24/60             24.20
6/02/61             26.60 39 days over 26 feet
4/10/62             26.40 51 days over 26 feet
4/07/63             24.70
4/03/64             22.92
4/23/65             23.83
5/17/66             22.70
6/04/67             20.67
4/19/68             22.48
2/23/69             22.65
5/19/70             21.72
5/23/73             27.28 43 days over 26 feet

3/11/01             17.90
6/08/02             17.50
3/12/03             17.30
7/01/04             14.90
2/03/05             19.00
3/30/06             11.70
2/01/07             16.10
4/28/08             20.00
5/28/09             18.80
2/17/10             17.20

Thanks to a KATC viewer – Gary Marks for helping tabulate some of the above data.

Morganza Spillway in 1973

There are three kinds of major flooding that can inundate Acadiana with water: flooding from local heavy rains, storm surges from Gulf of Mexico tropical systems, and then flooding from rising waters from our large rivers that are water sheds from somewhere else.  Occasionally we see a combination of at least two.

This time around it will be the “Big Rivers”. 

Although the details of the impending flooding of the Mississippi and the Atchafalaya Rivers remain unclear, it appears that the river flooding in Acadiana’s eastern parishes will be the worst of our generation.  

Thousands of camps, homes and businesses will be flooded from Point Coupee Parish southward through St Landry, St Martin, Iberia, St Mary and Terrebonne Parishes from the Atchafalaya River Basin alone.

Low lying areas unprotected by levees will flood, including 1000′s of acres of farm land that will likely result in at least tens of millions of dollars in losses. 

 This flood will be limited to “river-vulnerable” communities and will not flood locations in New Iberia, Lafayette and westward; the rest of Acadiana will just ironically continue to suffer through a very bad drought. 

As for specific homes, camps and communities it is very nearly impossible to predict who will flood and who won’t.  

The forecast will be a challenging combination of meteorological and hydrological prediction, understanding whether the river forecast models take into account latest river silting and flows properly, and then there are geographical and geopolitical considerations.  

The bottom line is that if it flooded in 1973, it will likely flood this time around, and there are strong indicators that it will likely be worse.   

While river crest dates and levels will likely change in the weeks ahead, it appears that the amount of water coming will exceed anything Southern Louisiana has seen in a very long time. 

The preliminary Army Corps of Engineers Flood Inundation Map looks quite ominous with up to 5-15 feet of water possible in some inhabited areas inside the Henderson Levee.

Given it was been nearly 40 years since the last major flood in this basin, I would venture to guess many areas and communities have been developed into higher flood risk areas, meaning more homes, camps and businesses are exposed to a greater flood risk since 1973.

Knowing your elevation and risk to backwater flooding outside of the levees is critical.  I encourage everyone to check with their  local officials and attend any community meetings that will be held in the weeks ahead. 

At this time, other river basins outside of the Atchafalaya should not be impacted in a major way, however Bayou Courtableau and Bayou Teche may take on some slow, but palatable rises into June…and technically this could affect the Vermilion River in a minor way.   Just about everything with this impending flood remains in question as we are about to enter truly uncharted waters.

I find it quite ironic that in the midst of a severe to extreme drought across much of Acadiana this spring that some communities in the Atchafalaya Basin will likely see 5-6 feet of water for weeks.  Mother Nature has certainly has a nasty sense of humour.

The Process

With the huge amount of water and its volumetric flow heading down the Mississippi, it is enevitable that this water and it’s swift current will challenge many levee systems southeastward through New Orleans. 

While the opening of the Bonnet Carre spillway will relieve some of this pressure downstream, it is likely that the River Control Structures and the Morganza Spillway will be utilized to divert 50-54% of the Mississippi River into the Atchafalaya River Basin.  The normal flow at the River Control Structure diverts 30% of the Mississippi River into the Atchafalaya.

The water release through the Morganza Spillway then floods nearby fields traveling southward through coulees and canals and low lying fields in the plains west of the Atchafalaya.  The process will be complex, as there are main river levee, basin flood levee and plug levee interactions.   After that, there will likely be interactions with private property levees and berms so predictability of this event  and who exactly will flood, will be such a challenge to the professionals. 

Links to Check and Follow

To keep up with this event I have including links to many agencies that will be tracking this flood starting with The National Weather Service who issue the flood warnings based on the hydrology.  The Army Corp of Engineers website is “the” site for the “big picture”. 

In addition there are excellent articles that depict the historical development of the Mississippi & Atchafalaya Rivers and it’s basin control structures.  Check these links out as they better explain the complex process that we are about to witness.  I also found an interesting article on nola.com by Oliver Houck, from a New Orleans and state-wide perspective

Finally stay with KATC for the latest river projections and flood predictions.  In addition to katc.com please follow KATC on Facebook and my Facebook or twitter feed.  

Rob Perillo

April 2011 was the second warmest on record going back to 1893 in Lafayette missing being the warmest all time by 1/10 of a degree.

Mean temperatures (which are the averages of daily highs and lows) near 73.9 degrees this April was nearly 7 degrees above normal.  

This year was also 3-4 degrees warmer than last year so our utility bills will likely be higher for all of us this month.

Although some benefical rains did fall in the last week of the month and recent early May rains have also helped to stall the drought, rainfall deficits area-wide are still near 60% of normal for the year.  Most of the area will likely stay in, or close to severe drought status.

The outlook for May calls for a continuation of above normal temperatures for Acadiana with below normal rainfall.

Respected Colorado State hurricane forecasters Drs. Klotzbach and Gray continue to call for an active hurricane season with 16 named storms, 9 hurricanes and 5 major storms (averages over the last 40 years are 11, 6 and 2 respectively).  

 “We continue to foresee well above-average activity for the 2011 Atlantic hurricane season. Our seasonal forecast has been reduced slightly from early December, since there is a little uncertainty about ENSO and the maintenance of anomalously warm tropical Atlantic SST conditions. We continue to anticipate an above-average probability of United States and Caribbean major hurricane landfall.”

Key factors this year include La Nino slowly fading to a neutral condition through the heart of hurricane season which should be an enhancing factor with less upper tropical shear(with the absence of any El Nino). 

Much above normal Atlantic sea surface temperatures continue, although some cooling has been noticed over the last few months, but will serve as an enhancing factor.

While forecasting total net tropical cyclone activity in the Atlantic has been rather accurate and useful to meteorologists, the bottom line is whether how many of these storms will strike the U.S. and more importantly for us, the northern Gulf Coast. 

Seasonal forecasting of landfalls remains mostly a statistical low skill forecast, but as Dr. Gray is famous for saying, “sooner or later the statistics will right themselves”…meaning continued active season forecast will eventually translate major landfalls a la 2004, 2005 and 2008.

After two very quiet years in the Gulf of Mexico, statistics do favor much more activity threatening the Gulf this year with the hurricane forecast team indicating a 47% chance of a major storm striking from the Florida Panhandle to Brownsville (the 100 year normal is 30% for the same area).  Since 1995 odds of Gulf Coast strikes have been 40% or greater with 2009 & 2010 odds roughly equal to this year’s forecast.

While not statistically significant, Louisiana has been struck by major or near major storms with significant storm surges every three years since 2002; Lili (2002), Katrina & Rita (2005) and Gustav & Ike (2008)…hopefully this year we can break that trend!

I have received a number of phone calls, emails, tweets and Facebook messages this week from concerned viewers about the potential radiation leaks from the earthquake/tsunami crippled nuclear power plants in Northeastern Japan.  Fortunately, I do have a background in forecasting radiation and can tell you there should be absolutely no concerns for anywhere in North America including Hawaii.

The current radition releases by steam and any possible future melt down (or downs) will keep all dangerous radiation levels local to Japan and generally less than 50 miles of the plant.

In the mid-1980s I worked at the James A. FitzPatrick Nuclear Power Plant in upstate New York and consulted with Niagara Mohawk’s 9-mile Point nuclear facilities, both of which are in Lycoming, New York.  I worked as an Emergency Planning Meteorologist which involved computer modeling of potential radiation releases in case of an accident.  This was a period that came shortly after the Three Mile Island accident in the late 1970s that prompted much more stringent procedures for developing accident plans for earthquakes and possible terrorist attacks etc at nuclear power generating facilities.

It was my job to take potential radiation release scenarios and incorporate local meteorological conditions and then forecast where any potential radiation would go and how it would disperse.  At the time, there was no off-site facility at the power plant, so if radiation was released, it was my job to travel to the plant and forecast where the radiation would go…not at a palatable job scenario!

The bottom line with the dire ongoing situation in Japan, and steam or meltdown related radiation releases, while certainly extremely hazardous and potentially deadly, will likely be confined to less than 50 miles within the plant’s radius depending on low level winds and weather.  Radioactive iodine and cesium (which generally released in these scenarios) are relatively heavy when compared to that of the properties of air so they “precipitate” out of the atmosphere rather quickly.

Normally any deadly amount will be confined to within 20-30 miles of the point source but could travel a little farther is there is actually a low-level stable atmospheric layer. 

In all the scenarios I have ever worked rarely would deadly/hazardous radiation be transported beyond 30 miles beyond the point source…this however, does not mean that radiation could travel further than that.

But the thought that this radiation could get to the upper atmosphere and get carried hundreds of miles is nearly impossible, unless a summer-like thunderstorm could co-locate right over the facility at it’s maximum radiation release time…highly unlikely (less than .001% chance).  Therefore any concerns outside of Japan is unfounded. 

Some of us may remember the atomic bomb tests of the 1950s and 1960s in South Pacific.  Those radiation releases did get into the upper atmosphere and got carried by the jet stream as the bomb process itself and the ensuing mushroom clouds certainly brought high radiation levels up to 50,000-60,000 feet.  The process of a nuclear melt down at a power plant is very different process and much more localized and considered a “lower atmospheric level” event. 

In addition, from the literature I studied at the time, any radiation that may be deposited in the ocean nearby Japan, will likely sink as well, but transport in the ocean theoretically could be a slightly greater distance than atmospheric dispersion.

The localized effect (within 30 miles) of high/deadly radiation amounts in Japan nearby these plants however, cannot be understated.

Rob

After a substantially colder than normal December and January, and a very cold first week of February, Acadiana experienced above normal temperatures over the last several weeks of the month.  This pushed February 2011 to  slightly above normal conditions.  Daytime highs for the entire month averaged 1.5 degrees above normal (near 66 degrees) while overnight lows were right on mark (at 44.9 degrees).

Continuing from the 2010 theme, precipitation for February was 43% of normal in Lafayette, with significant drought conditions possibly developing over the next few months.

The long range outlook from the Climate Prediction Center into March calls for above normal temperatures to continue while precipitation should be below normal. 

I would certainly expect more of the same for April and May as this would be consistent with continuing La Nina or Nuetral conditions with the Southern Oscillilation.

The question I’m getting most right now, is if we can start planting our gardens?  In Acadiana, on average, we see our last substantial freeze usually in the last week of February through the first week of March.  However, freezes have been recorded as late as the first couple of weeks in April.

Climatologically speaking, there is a 50% chance of a freeze after March 1st.  Factor in current trends it appears we are looking freeze free through the first 10-11 days of March but there will be arctic air lurking in the high U.S. Plains around the second week of the month, but currently I do not see a storm system that will bring that air to Acadiana.

But if you can wait a few more weeks for planting, you’ll all but guarantee not having to repeat the process later in March or April.  I would however recommend to fertilize our lawns as they’re coming out of winter stasis.

The pattern that consistently dislodged arctic air southward toward the lower 48, called the Arctic Oscillation, has shifted opening up the door for milder conditions across much of the US over the next couple of weeks.

Acadiana’s winter has experienced temperatures roughly 3 degrees below normal overall with 26 days of sub-freezing temperatures recorded this winter in Lafayette which is roughly 2-3 times of normal.

The pattern over the next couple of weeks will support a strong sub-tropical ridge of high pressure over the Gulf which will shunt significant arctic cold fronts away from the area while allowing for spring-like conditions until the last few days of the month.

History tells us that there will be a few more freezes through March, but near-term 60s and 70s will be the mainstay for Acadiana over the next couple of weeks.

KATC Meteorologist Natalie Noah reported on the Arctic Oscillation last week with her story following below….

The Arctic Oscillation is one of many climate patterns that can reach far around the globe to affect the day-to-day weather.

The Arctic Oscillation (AO) has a significant influence on winter weather in the U.S.  The northern U.S., eastern U.S., and as well as Western Europe. The AO refers to a seesaw pattern in atmospheric pressure between the polar regions and the middle latitudes. It fluctuates on the order of weeks and months, though it also shows some tendency to favor one phase or another for years at a time.

The AO features a negative (cold) phase, which brings higher-than-normal pressure over the polar regions and lower-than-normal pressure over the middle latitudes; the positive (warm) phase brings the opposite conditions.

The AO went into negative phase in the Northern Hemisphere winter of 2009-2010. The AO was in negative mode again in the winter of 2010-2011, affecting temperatures across the Northern Hemisphere as early as December 2010.

It is forecast that the U.S. may see a positive mode in the AO during this month (February 2011) which will shift the extremely colder temperatures and winds to the Arctic allowing land temperatures across the U.S. to warm.  

From the National Climate Data Center (NCDC), Climate Data Report For The Month Of January 2011.

After running some of the actual temperatures for Acadiana of December of 2010 through the present our averages have been running significantly below normal.  Average “mean” temperatures for December 2010 (high/low divided by 2) were about 4 degrees below normal.  The mean for January through the third week of the month has been 2.5 degrees below normal.

The forecasts from the Climate Prediction Center this winter was for above normal temperatures…as I blogged about last month, just a subtle shift of the average trajectories of cold Canadian air can make a big difference…and it has across Louisiana. 

Part of the colder than normal temperatures experienced across the Gulf South can also be attributed to an extra stormy pattern along the East Coast with healthy snow storms ushering snow-chilled arctic air farther to the south.

Although the 30 day pattern from the Climate Prediction Center is still insisting on above normal temperatures for the area, I would take that with less than a grain fo salt.  The shorter term “long-range” models through the next two weeks is decidedly colder than normal for Acadiana with a possible major Eastern U.S. arctic outbreak centered around February 1st…we’ll see!

Bottom line for now, expect higher tha normal heating bills this winter.  Rob

Although 2010 finished on the wet side, rainfall deficits for the entire year made 2010 the 7th driest on records.  Were it not for a very wet weather system that produced more than 3 inches of rain on December 29th and 30th, 2010 would have finished in the top five driest on record.  Accurate rainfall records have been kept in Lafayette since 1893, 117 years.

Acadiana-wide rainfall totals ranged anywhere from 15-25 inches below normal.  Average yearly rainfall in Lafayette is near 62 inches while the numbers shade a few inches higher southeastward toward Morgan City and a few inches lower to the northwest.

Drought conditions continue for a good part of Acadiana while the status of the drought worsens farther west toward the Texas border.  Per the last blog entry, not much help is expected over the next few months while a La Nina pattern continues into at least early summer.