Historic Unseasonable Flood Begins on Mississippi River; 928 mb Low Hits Iceland

By: Jeff Masters , 5:13PM,GMT on December 30,2015



 

A historic and unseasonable flood has begun on the Mississippi River and its tributaries, thanks to heavy rains that fell from Oklahoma to the Ohio Valley during Christmas week. Never before has water this high been observed in winter along the levee system of the river. The Father of Waters began over-topping its levees just north of West Alton, Missouri (population 500) on Tuesday, forcing evacuations. West Alton lies at the confluence of the Missouri and Mississippi Rivers, about 7 miles upriver from St. Louis. The river is still rising at West Alton, and is expected to crest on Thursday morning at the second highest level ever recorded, about 5' below the disastrous flood of 1993. On Friday, the massive Mississippi River flood crest will reach St. Louis, bringing the second highest waters levels ever recorded there (flood records extend way back to 1785 in St. Louis.) The three river gauges downstream from St. Louis--at Chester, Cape Girardeau, and Thebes--are expected to see their highest water highest levels ever recorded on Friday and Saturday. The latest flood forecasts for the Mississippi River issued Tuesday evening by NWS River Forecast Center predicted that Thebes would be the last location to see an all-time record crest in this flood; below Thebes, flood crests between the 2nd and 4th highest on record are expected along most of the Mississippi and the lower portions of two main tributaries, the Ohio and Arkansas Rivers. As with weather forecasts, the margin of uncertainty in river-crest predictions increases over longer time periods. According to a Wednesday morning summary by TWC's Jon Erdman, the following flooding and flood impacts can be expected farther down river:

• Memphis: Crest late next week higher than 1997 and 1973 floods, but well below 2011 and 1937 floods.
• Vicksburg, Mississippi: Crest in mid-January expected to exceed 1973 flood, but well below 2011 and 1927 floods. Some flooding of city streets and businesses possible.
• Natchez, Mississippi: Crest around MLK holiday may top 1937 flood, but should remain below 2011 record flood. Flooding of Ft. Adams likely.
• Baton Rouge, Louisiana: Crest during MLK week comparable or just below May 2011 flood possible. Areas outside of levee protection may flood. Shipping and industrial activities may be significantly impacted.


Figure 1. The Mississippi River downstream of St. Louis at Thebes was at major flood stage on Wednesday morning, and was forecast to crest on Friday at the highest level ever observed. Flood records at this location extend back to 1844. Image credit: NOAA/AHPS.

On January 20, the flood crest is expected to arrive in New Orleans, bringing the Mississippi River to its 17-foot flood stage in the city, just 3 feet below the tops of the levees. In past years, though, when the river has been forecast to rise to 17 feet in the city, the Army Corps of Engineers has opened up the Bonnet Carré Spillway in St. Charles Parish, which diverts water into Lake Pontchartrain and keeps the river from reaching flood stage in New Orleans. The Corps may also be forced to open the Morganza Floodway in Pointe Coupee Parish, which would divert water down the Atchafalaya River. Opening this spillway has a considerably higher cost than opening the Bonnet Carré Spillway, due to the large amount of agricultural lands that would be flooded below the Morganza Floodway. The Corps also has the option of increasing the flow of Mississippi River water into the Atchafalaya at the Old River Control Structure in Concordia Parish. Operating the Old River Control Structure in this way, though, puts stress on the structure, as I explained in my 2011 blog post, America's Achilles' heel: the Mississippi River's Old River Control Structure. The Tuesday evening forecast from the NWS River Forecast Center predicted that the Mississippi River would crest at Red River Landing, where the Old River Control Structure is located, on January 19. The predicted crest of 62.5' is just 0.9' below the all-time record crest of 63.39' set on May 18, 2011. A water level this high has a good chance of forcing the Army Corps to open the Morganza Floodway in order to relieve pressure on the Old River Control Structure. Both the Bonnet Carré Spillway and Morganza Floodway were opened in May 2011, when the highest flood crests ever observed on the Lower Mississippi arrived. This flood cost approximately $3 billion; $1 billion was required just to repair the damage done to the levee system and various other components of the flood control system damaged by the flood, according to Charles Camillo's book, Divine Providence: The 2011 Flood in the Mississippi River and Tributaries Project. I expect the damage from the December 2015 - January 2016 Mississippi River flood will run into the hundreds of millions. According to a Wednesday news story in The Advocate, the Army Corps will make a decision by January 9 on whether or not to open the Bonnet Carré Spillway. The last time the spillway was opened in January was back in 1937, its first year of operation. In a Wednesday morning Press Release, the Army Corps of Engineers indicated that they are mobilizing people, barges and operational equipment to open a third floodway on the Mississippi River near its confluence with the Ohio River--the Birds Point - New Madrid floodway. Opening up this floodway would help relieve pressure on the levees near Cairo, Illinois, something the Corps was forced to do in May 2011. However, the Corps said that they do not anticipate operating the floodway during the current flood, if current flood height predictions hold.


Figure 2. Existing flood stage on December 28, 2015 (inner colored square) and predicted maximum flood stage (outer colored square region around the inner colored square) for the Lower Mississippi River and two tributaries (the Arkansas and Ohio Rivers) near where they join the Mississippi. I've added numerical ranking on the right side of the squares to indicate where a top-ten flood crest in recorded history is expected. Two gauges are expecting their highest floods on record (Cape Girardeau and Thebes), and most of the Lower Mississippi is expecting a top-five highest flood crest on record. Where the Ohio River joins the Mississippi at Cairo, Illinois, the Ohio River is forecast to crest on January 5 at the third highest level on record; downstream from Little Rock, Arkansas, the Arkansas River is predicted to crest on Friday at the third highest level on record near its confluence with the Mississippi. Image credit: NWS River Forecast Center.

Massive 928 mb storm pummels Iceland and the UK
A massive North Atlantic low pressure system dubbed "Frank" bombed to a central pressure of 928 mb on Wednesday morning and moved over Iceland, bringing heavy rains to Iceland and the UK and hurricane-force winds to the ocean waters between. According to Weather Underground's weather historian Christopher C. Burt's 2011 post, World and U.S. Lowest Barometric Pressure Records, the storm missed setting a lowest pressure for Iceland; the lowest pressure measured on the island is probably the 923.6 mb reading on December 2, 1929. Chris also notes that there are two storms in the North Atlantic that likely had a minimum pressure below 920 mb:

1) Storm of January 10, 1993 deepened to a central pressure of 912-915 mb (26.93”-27.02”) between Iceland and Scotland near 62°N, 15°W

2) Storm of December 15-16, 1986 deepened to at least 916 mb southeast of Greenland near 62°N, 32°W. A ship in the vicinity actually made a measurement of 920.2 mb on December 15th while still some distance from the center of the storm. The British Meteorological Office assessed the central pressure of the storm at this time as being 916 mb (27.05”), but the West German meteorological service proposed a pressure possibly as low as 912-913 mb (see Stephen Burt article in Weather magazine Vol. 42 pp. 53-56, February 1987).

Some links to more info on Frank, courtesy of wunderground member barbamz:

Extreme Weather Causes Damage in East Fjords
Iceland Review, By Vala Hafstad Nature & Travel about 2 hours ago
The severe weather in the East Fjords is among the worst residents have ever experienced, RUV reports. The situation is the worst in Eskifjordur, where a high sea level land hurricane-force winds have threatened the marina. Part of the dock came loose, but rescue workers managed to fasten it. The surf has inundated all docks and the whole harbor area. Roof sheets have blown off several houses. There was high tide at 5:30 am, but since then, water levels have subsided somewhat. Boats that came loose in the marina were successfully tied down. Basements have flooded and tidal waves have reached cabins, never before affected by sea water. Some homes are without power...

VIDEO: "Absolutely crazy" storm in East Iceland
Iceland Monitor | Wed 30 Dec 2015 | 9.56 GMT

BBC Live: Storm Frank hits UK

Guardian: Storm Frank: further floods expected as gales and rain batter British Isles - live

BBC live report especially for Cumbria.

Near the southern coast of Ireland yesterday:





Figure 3. Surface analysis from 06 UTC December 30, 2015 showing intense Winter Storm Frank with a central pressure of 928 mb over Iceland. mage credit: NOAA Ocean Prediction Center.

Incredibly warm air flowing to the North Pole
The counter-clockwise flow of air in advance of Wednesday's Icelandic low is following an unusually contorted kink in the jet stream and pumping relatively warm air all the way to the North Pole, where temperatures near freezing may be occurring. According to Rick Thoman of the National Weather Service in Fairbanks, Alaska, a buoy (64760) just 180 miles from the Pole, at 87.4°N, 154.4°E, reported a 1200 UTC December 30, 2015 temperature of -0.1°C with a -1.6°C dewpoint. Looking at the obs available for the past few days, there is nothing obviously bogus: the buoy was reporting -25°C two days ago. Bob Henson tweeted this fact on Tuesday: reanalysis maps dating back to 1948 (courtesy Steven Cavallo, University of Oklahoma) show only three cases where the North Pole Temperature reached the freezing mark or above in December (and no cases in January - March.) Andrew Freedman of Mashable has more on this freak Arctic warm wave in a Tuesday post.


Figure 4. Temperature analysis from the 00 UTC December 30, 2015 run of the GFS model, showing temperatures near freezing (aqua colors) penetrating very close to the North Pole. These temperatures are about 20°C (36°F) above average. Image credit: University of Maine Climate Reanalyzer.

Jeff Masters