By:
Bob Henson and Jeff Masters
, 3:24AM,GMT on December 28,2015
Figure 1. Damage from the tornado that struck Rowlett, Texas, on Saturday evening, December 26, 2015. The tornado was rated at least EF3.
Deadly tornadoes strike near Dallas on Saturday
Ahead of a strong cold front in west Texas, supercell thunderstorms that ripped across the sprawling eastern part of the Dallas area spawned several tornadoes that killed 11 people. One violent tornado that killed eight people in Garland was rated EF4, while “at least EF3” damage was found in Rowlett, just east of Garland. Two people died in Copeland, about 15 miles to the northeast, where EF2 damage was documented. According to the Dallas Morning News, as many as 1000 structures were damaged across north Texas, many of them severely. The storms were fed by a very strong upper-level jet as well as unusually high instability for December (around 3000 joules per kilogram, which would be concerning in springtime, much less wintertime). Temperatures reached 80°F in Dallas just hours before the tornadic supercell arrived, with a summerlike dew point of 67°F.
The widespread persistence of warm, humid conditions over the last few days has led to a unprecedented U.S. stretch of severe weather for December, including tornadoes from Mississippi to Michigan on Thursday. Sunday was the seventh day in a row with at least one U.S. tornado reported--the first such week-long stretch for any December in Storm Prediction Center records dating back to 1950, as noted by WU contributor Dr. Phil Klotzbach. The previous record string of six days, December 22-27, 1982, occurred during the “super El Niño” of 1982-83. Another tragic milestone: 2015 is the first year in records going back to 1875 that has seen more confirmed tornado-related deaths in December than in the rest of the year combined. The only other year with December having more deaths than any other single month was 1931, according to statistics analyzed by Harold Brooks (National Severe Storms Laboratory).
Figure 2. From Ropesville, TX, about 20 miles southwest of Lubbock, on Sunday, December 27, 2015: “Blizzard conditions hit this area last night with 50 - 60 mph winds and they haven't let up. These mailboxes have taken a nice beating over the last 15 or so hours.” Image credit: wunderphotographer docshovel39.
Blizzard pummels southern High Plains
As severe storms continued to rumble across east Texas on Sunday, the western part of the state was dealing with a crippling blizzard that extended into eastern New Mexico, while freezing rain knocked out power to tens of thousands of western Oklahomans. Exceptionally strong winds--gusting above 70 mph in some areas--have led to near-zero visibilities and drifts of 6 feet or more, paralyzing travel across the region. Roswell, NM, had racked up 15.5” for the day by 8 pm CST Sunday, topping its one-day record of 12.3” and approaching its two-day record of 16.9”. Lubbock, TX, picked up 2.7” between 6 and 7 pm CST Sunday, pushing its storm total to 9.2”. The city’s heaviest-on-record storm total of 16.9” was picked up on January 20-21 during (you guessed it) the super El Niño of 1982-83. As the upper-level storm and associated low head northeastward on Monday, more snow and ice will plaster a swath extending from Kansas to Wisconsin and Michigan.
Massive flooding hits Missouri and Illinois, killing 13
The weekend storm brought incredibly heavy rains to eastern Oklahoma, northwest Arkansas, and Southwest Missouri, with 10.0" falling in a 30-hour period ending Sunday evening on the south side of Springfield, Missouri. On Sunday, Governor Jay Nixon declared a state of emergency in Missouri due to heavy flooding all across the state, and urged Missourians in flood-affected areas to not drive into flooded roadways and avoid travel if possible. Eight people died Saturday night in Missouri in floods; six of the deaths occurred in two separate incidents where cars drove into flooded roadways in Pulaski County and were swept away by water. In southern Illinois, three adults and two children drowned Saturday evening when their car was swept away and sank in a rain-swollen creek. An additional 1 - 2" of rain is expected over most of Missouri and Arkansas by Monday evening, but dry weather is mercifully expected the rest of the week. The 4.87” of rain in St. Louis on Saturday made it the third wettest calendar day in records going back to 1874. More rain on Sunday pushed the city to its wettest year on record, beating 57.96” in 2008.
Figure 3. Observed precipitation amounts for the 48-hour period ending on Sunday, December 27, 2015, at 8 pm EST. Rainfall amount of 6"+ were widespread across eastern Oklahoma, northwest Arkansas, and southwest Missouri, with some areas seeing 10"+. Image credit: NOAA/NWS.
Historic flood imminent on the Mississippi River
The Mississippi River near St. Louis was near flood stage late last week due to excessive rains of 2 - 4" (400 - 600% of average) that fell during the past two weeks farther upstream in Iowa, Wisconsin, and Minnesota. A massive pulse of flood waters from this weekend's epic December rains will pile into the Mississippi River over the next few days, bringing the river to flood levels never recorded this time of year. The Mississippi River at St. Louis was approaching moderate flood state on Sunday evening, and is forecast to crest on Wednesday at the second highest level ever observed, just five feet below the all-time record set during the disastrous flood of 1993. Flood records at this location extend back to 1785. It’s worth noting that, of the top 40 Mississippi River flood crests in St. Louis history, only one has occurred in a winter month (Dec-Feb). That was the #9-ranked crest of 39.27”, recorded (when else?) on December 7 during the super El Niño of 1982-83.
Downstream from St. Louis, the Mississippi River is forecast to crest late this week in Chester and Cape Girardeau, Missouri above the all-time record 1993 flood; NOAA warns that at the flood levels expected, the Degognia and Fountain Bluff Levees will be overtopped. NOAA projects that the massive flood crest will propagate downstream to the Gulf of Mexico next week, bringing flood heights that are expected to be between the 2nd highest and 4th highest on record all the way to Baton Rouge, Louisiana. Extreme rains that caused major flooding across central and northern Alabama late last week will only add to the water moving toward the Mississippi.
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 Carre Spillway in St. Charles Parish, which diverts water into Lake Pontchartrain and keeps the river from reaching flood stage in New Orleans. According to a December 25 article by Mark Schleifstein of NOLA.com, this option will be discussed on Monday at an Army Corps flood "flood fight" meeting, along with the less likely possibility of opening 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 Carre Spillway, due to the large amount of agricultural lands that would be flooded below the Morganza Spillway. 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 always makes me nervous, as I explained in my 2011 blog post, America's Achilles' heel: the Mississippi River's Old River Control Structure. Both the Bonnet Carre Spillway and Morganza Floodway were forced to open in May 2011, due to highest flood crests ever observed on the Lower Mississippi. This flood cost over $2 billion; I expect the damage from the December 2015 - January 2016 Mississippi River flood will run into the hundreds of millions.
Figure 4. The Mississippi River at St. Louis was approaching moderate flood state on Sunday evening, and is forecast to crest on Wednesday at the second highest level ever observed, just five feet below the all-time record set during the disastrous flood of 1993. Flood records at this location extend back to 1785. Image credit: NOAA/AHPS.
The Big Christmas Warm
Hundreds of records were buried by sunshine, warmth, and humidity instead of white-Christmas snowfall all across the eastern U.S. during the holidays, especially on Thursday and Friday. Christmas Day was the apex for the north-south breadth of warmth, with record highs set from Florida (82°F in Jacksonville) to Maine (62°F in Portland). Many records on Thursday and Friday were smashed by margins of 10°F or more. The Christmas Eve readings of 72°F at Albany, NY, and 68°F at Burlington, VT, both set all-time records for December. As noted by WU weather historian Chris Burt, these are truly impressive records given the late date in a month that gets progressively colder, not to mention the long periods of record at both sites (since 1883 in Burlington and 1874 in Albany). Chris adds that Philadelphia has seen eight days this month through Sunday with record daily highs: “Not since records began in Philadelphia back in 1874 has any other month of any single year experienced as many daily record highs as this December!” The capital of Christmas commerce, New York City, basked in record warmth of 72°F on Thursday and 66°F on Friday. As of Sunday, Central Park had yet to get below 32°F this fall or winter; its monthly average (12/1 – 12/26) of 52.0°F was running at an astonishing 13.8°F above normal and 7.9°F above the previous December record, going back to 1871. A cooldown this week will reduce that value, but a warmest-on-record December is all but certain for much of the eastern U.S. It’s no wonder that flowers and shrubs are blossoming from Washington to New York.
At this writing, NOAA’s U.S. Records site had not yet been updated with the many records after Dec. 24, but for the period 12/1 – 12/24, December saw a phenomenal 3164 daily record highs and 4511 record warm lows, compared to 147 record cold highs and 147 record lows. Despite the intense cold in the eastern U.S. early in 2015, this year will end up with more than twice as many U.S. daily record highs as lows, just one more statistic for a year that is wrapping up in remarkable fashion.
Bob Henson (tornadoes, blizzard, record warmth) and Jeff Masters (flooding)
Figure 5.
No comments:
Post a Comment