KATC StormTeam 3 Weather BLOG

Addendum to this blog entry…surprise shower activity on December 31st brought 0.09″ of rain officially to Lafayette, making 2011 the 2nd driest of all time with year end totals unofficially at 35.88″.

 While the Japanese earthquake and tsunami was the natural disaster story of the year in 2011, in the U.S. droughts, floods, fires, very deadly tornado outbreaks, an East Coast earthquake and Hurricane Irene composed most of the weather/disaster headlines nationally.

Locally in Acadiana, there were some major headlines as well with a couple of weather stories related to climate rather than individual events.

The National Weather Service in Lake Charles summarizes many of the specific weather events in Acadiana with some of the top stories this year involving an ice storm, tornadoes, a river flood “that wasn’t”, a “beneficial” tropical storm and all-time records for the hottest summer and the driest year. 

The first of two deadly events of the year involved an ice storm on February 3 and 4th laying down a glaze of ice 1/4″ or more across portions of Acadiana along and north of the I-10 corridor that left more than 26,000 without power and numerous traffic accidents causing one fatality. 

About a month later a severe weather outbreak produced at least 4 tornadoes in Jeff Davis and Acadia Parishes including an EF2 tornado that struck Rayne. The Rayne tornado produced 111-135mph winds damaging or destroying more than 600 homes and responsible for 12 injuries and one death. The tornadic damage cost were estimated in the tens of millions.

This was the beginning of a very deadly, record breaking tornado season in the U.S. with the Mississippi and Missouri devastating EF4/5 tornadoes responsible for taking hundreds of lives and producing hundreds of millions of dollars in damage-swaths.

While a drought continued in Acadiana from the previous year, this spring we found ourselves dealing with a potential “flood of our generation” as water rose to dangerous levels in the Mississippi and Atchafalaya River Basins.

Spring floods across the Central and Northern U.S. manifested in some of the highest levels recorded in the Lower Mississippi River in April and May. This resulted in the opening of the Morganza Spillway for the first time since 1973 to relieve Mississippi River pressure from Baton Rouge to New Orleans dumping excess water into the Atchafalaya Swamp.

Fortunately the river levees held and predicted flooding inundations by the Army Corps of Engineers never materialized across both river basins.  Thanks to the ongoing drought, the Atchafalaya Basin absorbed and held delivery of more than 50 Superdomes worth of water per day for several weeks as water levels met or exceeded 1973 levels.

Outside of large tracts of farmland and crops being lost fortunately there were very few homes and camps inundated by the flood water, but preparing for the flood was quite costly for many.

The Atchafalaya Flood had some positive effects helping recharge portions of the swamp and build new wetland areas along the immediate Acadiana Coast at the Atchafalaya River outlet, but the effects of additional pollutants in the Basin, if any, from the Mississippi River has yet to be determined.

The threat of flooding from the river basins eased by mid-June as heat increased and drought worsened across Acadiana.

The summer of 2011 went into the record books as the hottest on record in 118 years with June, July and August temperatures collectively averaging roughly 3 degrees above normal. Daytime highs this summer were generally 1-2 degrees above normal with afternoon heat much more expansive with the lack of frequency of typical scattered showers and storms that the area normally enjoys during the hot summer months.

Interestingly enough Acadiana’s overnight lows were even warmer averaging 4-5 degrees above normal which was likely related to less night-time evaporative cooling from less rainfall.

Heat waves and droughts work hand and hand and feed off each other, and this year that was especially true for Louisiana into Texas.

With impending tropical weather threatening Acadiana this weekend I wanted remind everyone to stay apprised of the weather conditions very closely as there will likely be big changes ahead.  Part of that obviously (or hopefully) is watching KATC TV and following us on katc.com.

In addition our weather page, you can find pertinent links to very important web-sites on our Hurricane Center Page.  Our hurricane Center includes a tracking map and links to the local National Weather Service, the National Hurricane Center and Emergency Preparedness information.  These links are all essential to have on hand during a storm.

During the last two plus years I have found Facebook and Twitter as excellent tools for not only disseminating information but gathering it.  They both have strong and weak points, but Facebook in particular I think is important to have on hand, and on your smart-phone, for a hurricane or any emergency situation where traditional lines of communication may be compromised.

Facebook is easy to use and it’s a great way to stay in contact with loved ones and friends…and say what you will about social media, I believe at the very least, it is a great tool in an emergency situation.

During any emergency KATC will be broadcasting live and streaming on the web on katc.com, but you can also follow us on twitter too.  The “tweets” from the Weather Lab meteorologists can be followed right on our weather page so you don’t even have to mess with setting that up if you don’t want to.

On Facebook, I would highly recommend following KATC’s page for the latest news, Dave Baker, Natalie Noah and me (Rob) for the latest weather updates.  If you click on the aforementioned links make sure you “like” the page to get our information streaming to your home page.

Good luck with the storm this weekend and for the rest of hurricane season.  Rob

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

Widespread rain and thunderstorms in the first couple of days in November brought impressive rain totals to Acadiana mainly across the I-10 Parishes southward.  Coastal parishes experienced the heaviest rains with totals generally in the 4-6 inch range. 

Hot spots in Vermilion Parish exceeded 8 inches across from Abbeville southwestward where flooding occured including water in some homes. 

Rain totals in Lafayette were in the 2.5-3.5 inch range while most areas north of I-10 indicated 1-2 inches of the wet stuff.

These rains have certainly eased the severity of the on-going drought, but the area will likely stay in “moderate to severe” drought status as many areas remain more than 10-15 inches below year to date normals.

In addition, due to the recent rains, the burn ban has been lifted.  Dry conditions will stay in Acadiana through the second week of November with the next significant chances of rain arriving about mid-month.

It promises to be a rather wet week for most of Acadiana as we continue to deal with the remnants of TD5 as it drifts westward toward Acadiana  Tuesday and the northward Wednesday.   A FLOOD WATCH has been posted for portions of Acadiana from Tuesday morning through Wednesday in the anticipation of the heavy rain threat.

 As expected over the weekend this remnant system persisted across the interior portions of the Gulf States and then dropped back to the south with the circulation getting back out over open Gulf water late Sunday night.

Hurricane Hunters flew this system Monday afternoon just south of Mobile, Alabama.  The reconnaissance plane found broad low pressure, like last week, but disorganized thunderstorm activity near the center, like last week.  This time around upper level conditions are a little more favorable for development through Tuesday prior to the circulation making landfall over Eastern Louisiana Tuesday afternoon.  If thunderstorms cluster near the center of circulation later tonight it will likely become an “official” tropical system

Based on upper level conditions and broad lower surface pressures this system is very close to being a depression and may become one at any time through tomorrow.  If the system is upgraded, tropical storm warnings would probably be issued for portions of Louisiana through the Alabama coast.

The bottom line with this system is that it will be a major rain-maker with rainfalls of 3-5″ likely around this system and up to 8-10″ possible near where the center of circulation travels through mid-week.  Rainfall totals will likely be directly correlated to the speed, or lack of, this exhibits over the next few days.  Most computer models earlier today indicated the greatest threat of flooding rains will be in the eastern part of the state Tuesday and then the central part of the state Tuesday night into Wednesday. 

More recent computer model runs this evening are much more robust with rainfall totals in Acadiana with  3-5″  possible through Thursday with isolated spots receiving possibly more than double depending ultimately where the center of circulation goes and how quickly it moves.  Stay with KATC and katc.com for the latest information.

Flood Watches are in effect for much of Southern Louisiana through Thursday morning including the I-10 and coastal parishes in Acadiana.  Rainfall totals over the next several days will generally be in the 2-3″ range with isolated areas possibly receiving 5″ or more through Thursday. 

KATC’s FutureCast is actually indicating much more rainfall over the next 72 hours across portions of Louisiana with hot spots over Southeast Louisiana and possibly coastal Acadiana exceeding 10″.  What happens in “real-life” and on the computer are almost always two different things but the model is highlighting the potential for heavy rains….hopefully most of this will remain offshore.

Meanwhile Alex continues to churn and slowly intensify in the Southwestern Gulf of Mexico with landfall expected south of the Texas border Wednesday evening/night.  Alex should become a hurricane later tonight as drier more stable air on the northwestern flank of this system has kept the system a tropical storm today.  That drier air appeared to be getting sealed out of the system late this afternoon so the storm is likely very close to a hurricane as of this evening.

Gusty easterly winds offshore the Louisiana coast will likely ramp up Wednesday while swells from the south make for 4-8 foot seas close to home but deep water areas toward the oil spill will likely push into the 8-12 foot range.   Tides along the coast were running 1 foot above normal today and should continue to near 2 feet above normal Wednesday.  A Coastal Flood Advisory continues as of this evening for elevated tides expected through Thursday.

Busy in the WeatherLab again today…here’s the latest crawl we are running on air…FLASH FLOOD WARNINGS are in effect through 1015pm for LAFAYETTE, VERMILION, ST MARTIN, IBERIA and ST MARY PARISHES…A FLASH FLOOD WATCH remains in effect for all of Acadiana through Tuesday…Locally heavy thunderstorms should continue over southeastern portions of Acadiana this evening and will redevelop overnight through tomorrow in other locations…Activity will be capable of producing 3-5 inches of rain in just a few hours resulting in localized street flooding…Isolated spots may see 4-6 inches or more through tomorrow which may result in more serious flooding…

Upper level forcing will keep showers and storms with us through tomorrow with ample lift behind a cool front (keeping us wet) that will push across the area early Tuesday morning.  Temperatures will drop nicely through the 50s Tuesday and into the low-mid 40s for Wednesday morning.  The clouds will likely stay with us behind the front with yet another low pressure system forming in the Gulf Wednesday/Thursday.  Patchy light rain or drizzle will likely move back into the area for late Wednesday with a round of rain possible through Thursday.  There are hints that the next weather system may stay far enough offshore to warrant lower rain chances mid-week, but recent weather patterns dictate a wetter forecast to be the most prudent at this time.  It should finally clear out and dry out for Friday into the weekend!

Heavy rainfall led to widespread flooding during the early morning hours across portions of Iberia and St Mary Parishes.  Storm total rainfall accumulations ranged up to 6-9″.  Rain totals were in the 6-7″ range in and near New Iberia and Jeanerette into portions of St Mary Parish with over 8.5″ reported in the Centerville area in St Mary Parish.  Fortunately the showers and storms did not reorganize Tuesday afternoon/evening with just on and off showers anticipated through this evening.  Rain chances should end by midnight but fog should follow.  The National Weather Servicehas issued a Dense Fog Advisory for the area as the winds are expected to relax in a nearly saturated lower atmosphere.  The fog should lift quickly around daybreak or shortly thereafter as drier west -northwest winds will freshen and increase from the north-northwest.  Temperatures will stay rather mild this evening in the upper 60s but should drop into the mid-upper 50s tomorrow morning.  In fact, it may chill down several degrees during the day in spite of mostly sunny skies.  So it will likely feel cooler by lunch time so make sure you send the kids and yourself off with a jacket or sweater.  Breezy and cold conditions will move in for our Wednesday night with lows by Thursday morning likely to be in the mid-upper 30s.  While Wednesday and Thursday will be partly to mostly sunny and cool clouds will return Thursday night with rain not far behind on Friday.  Friday’s weather system may produce and inch or two of rain, especially along the coastal parishes, but I am not expected a repeat of what ocurred over the last 24 hours.  A wetter and stormier weather system however is on the docket for early next week.  In between, we’ll characterize this weekend as partly cloudy and seasonably mild.  Slight rain chances on the 8 Day Forecast this weekend are a hedge on the leftover Friday system and for the following system early next week.  It remains rather obvious that an active, hard to time El Nino storm pattern will stay with us through Christmas…no rest for the meteorologists nor our saturated grounds.