U.S. had most extreme spring on record for precipitation

By: Dr. Jeff Masters , 2:20 PM GMT on June 14, 2011

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Nature's fury reached new extremes in the U.S. during the spring of 2011, as a punishing series of billion-dollar disasters brought the greatest flood in recorded history to the Lower Mississippi River, an astonishingly deadly tornado season, the worst drought in Texas history, and the worst fire season in recorded history. There's never been a spring this extreme for combined wet and dry extremes in the U.S. since record keeping began over a century ago, statistics released last week by the National Climatic Data Center (NCDC) reveal. Their Climate Extremes Index (CEI) looks at the percentage area of the contiguous U.S. experiencing top 10% or bottom 10% monthly maximum and minimum temperatures, monthly drought, and daily precipitation. During the spring period of March, April, and May 2011, 46% of the nation had abnormally (top 10%) wet or dry conditions--the greatest such area during the 102-year period of record. On average, just 21% of the country has exceptionally wet conditions or exceptionally dry conditions during spring. In addition, heavy 1-day precipitation events--the kind that cause the worst flooding--were also at an all-time high in the spring of 2011. However, temperatures during spring 2011 were not as extreme as in several previous springs over the past 102 years, so spring 2011 ranked as the 5th most extreme spring in the past 102 years when factoring in both temperature and precipitation.


Figure 1. Nine states in the U.S. saw their heaviest precipitation in the 117-year record during spring 2011, with record-breaking precipitation concentrated in the Pacific Northwest and along the Ohio River. Seven other states had top-ten wettest springs. Texas had its driest spring on record, and New Mexico and Louisiana had top-ten driest springs. When compared with Figure 2, we see that this is a classic winter La Niña pattern, but at extreme amplitude. Image credit: NOAA/NCDC.


Figure 2. La Niña events since 1950 have brought wetter than average conditions to the Pacific Northwest and Ohio River Valley in winter, and drier than average conditions to the South in both winter and spring. Spring 2011 (Figure 1) had a pattern very similar to the classic winter La Niña pattern (left image in Figure 2.) Image credit: NOAA Climate Prediction Center.


Figure 3. The percent area of the Contiguous U.S. experiencing much above average heavy 1-day precipitation events in spring 2011 hit a record high, nearly 16%. The 102-year average is 9%. The previous record of 15.5% was set in 1964. Heavy springtime 1-day precipitation events in the U.S. have been increasing since 1960, in line with measured increases in water vapor over the U.S. due to a warming climate. See also Figure 4 below. Image credit: NOAA/NCDC.


Figure 4. Percent increase in the amount falling in heavy precipitation events (defined as the heaviest 1% of all daily events) from 1958 to 2007, for each region of the U.S. There are clear trends toward more very heavy precipitation events for the nation as a whole, and particularly in the Northeast and Midwest. Climate models predict that precipitation will increasingly fall in very heavy events, similar to the trend that has been observed over the past 50 years in the U.S. Image credit: United States Global Change Research Program. Figure updated from Groisman, P.Ya., R.W. Knight, T.R. Karl, D.R. Easterling, B. Sun, and J.H. Lawrimore, 2004: Contemporary changes of the hydro-logical cycle over the contiguous United States, trends derived from in situ observations. Journal of Hydrometeorology, 5(1), 64-85.

What caused this spring's extremes?
During a La Niña episode in the Eastern Pacific, when the equatorial waters cool to several degrees below average, abnormally dry winter weather usually occurs in the southern U.S., and abnormally wet weather in the Midwest. This occurs because La Niña alters the path of the jet stream, making the predominant storm track in winter traverse the Midwest and avoid the South. Cold, Canadian air stays north of the jet stream, and warm subtropical air lies to the south of the jet, bringing drought to the southern tier of states. La Niña's influence on the jet stream and U.S. weather typically fades in springtime, with precipitation patterns returning closer to normal. However, in 2011, the La Niña influence on U.S. weather stayed strong throughout spring. The jet stream remained farther south than usual over the Pacific Northwest and Midwest, and blew more strongly, with wind speeds more typical of winter than spring. The positioning of the jet stream brought a much colder than average spring to the Pacific Northwest, with Washington and Oregon recording top-five coldest springs. Spring was not as cold in the Midwest, because a series of strong storms moved along the jet stream and pulled up warm, moist Gulf of Mexico air, which mixed with the cold air spilling south from Canada. The air flowing north from the Gulf of Mexico was much warmer than usual, because weaker winds than average blew over the Gulf of Mexico during February and March. This reduced the amount of mixing of cold ocean waters from the depths, and allowed the surface waters to heat up. Sea surface temperatures (SSTs) in the Gulf of Mexico warmed to 1°C (1.8°F) above average during April--the third warmest temperatures in over a century of record keeping (SST anomalies were a bit cooler in May, about 0.4°C above average, due to stronger winds over the Gulf.) These unusually warm surface waters allowed much more moisture than usual to evaporate into the air, resulting in unprecedented rains over the Midwest when the warm, moist air swirled into the unusually cold air spilling southwards from Canada. With the jet stream at exceptional winter-like strengths, the stage was also set for massive tornado outbreaks.


Figure 5. A La Niña-like positioning of the jet stream, more typical of winter than spring, brought much colder air than normal to the Pacific Northwest and Upper Midwest during the spring of 2011. Washington and Oregon had top-five coldest springs, and near-record snowfalls and snow packs were recorded in portions of the Northern Rockies and Northern Plains. South of the mean position of the jet stream, top-ten warmest springs were recorded in Texas, New Mexico, and Louisiana. Image credit: NOAA/NCDC.

Was climate change involved?
Whenever an unprecedented series of extreme weather events hit, it is natural to ask how climate change may be affecting the odds of these events, since our climate is undergoing unprecedented changes. This spring's unusual precipitation pattern--wet in the Northern U.S., and dry in the South--does fit what we'd expect from a natural but unusually long-lived winter La Niña pattern (Figure 2). However, it also fits the type of precipitation pattern climate models expect to occur over the U.S. by the end of the century due to human-caused warming of the climate (though shifted a few hundred miles to the south, Figure 6.) This drying of the Southern U.S. and increased precipitation in the Northern U.S. is expected to occur because of a fundamental shift in the large scale circulation of the atmosphere. The jet stream will retreat poleward, and rain-bearing storms that travel along the jet will have more moisture to precipitate out, since more water vapor can evaporate into a warmer atmosphere. The desert regions will expand towards the poles, and the Southern U.S. will experience a climate more like the desert regions of Mexico have now, with sinking air that discourages precipitation. A hotter climate will dry out the soil more, making record intensity droughts like this year's in Texas more probable. So, is it possible that the record extremes of drought and wetness this spring in the U.S. were due to a combination of La Niña and climate change. It is difficult to disentangle the two effects without doing detailed modelling studies, which typically take years complete and publish. One weakness in the climate change influence argument is that climate models predict the jet stream should retreat northwards and weaken due to climate change. Indeed, globally the jet stream retreated 270 miles poleward and weakened during the period 1970 - 2001, in line with climate model expectations. Thus, a stronger and more southerly jet stream over the U.S. during the spring is something we should expect to see less and less of during coming decades.


Figure 6. The future: simulated change in precipitation during winter and spring for the years 2089 - 2099 as predicted by fifteen climate models, assuming we continue high emissions of heat-trapping carbon dioxide. Confidence is highest in the hatched areas. Compare with Figure 7, the observed change in precipitation over the past 50 years. Image credit: United States Global Change Research Program.


Figure 7. U.S. annual average precipitation has increased by about 5% over the past 50 years, but there has been pronounced drying over the Southeast and Southwest U.S. Even in these dryer regions, though, heavy precipitation events have increased (see Figure 4.) Thus, rainfall tends to fall in a few very heavy events, and the light and moderate events decrease in number. Image credit: United States Global Change Research Program. Data plotted from http://www.ncdc.noaa.gov/oa/climate/research/ushc n/.

Keep in mind, though, that climate models are best at describing the future global average conditions, and not at predicting how climate change might affect individual continents--or at predicting how rare extreme events might change. Major continent-scale changes in atmospheric circulation are likely to result over the coming few decades due to climate change, and I expect the jet stream will shift farther to the south in certain preferred regions during some combination of seasons and of the natural atmospheric patterns like La Niña, El Niño, and the Arctic Oscillation. For example, there has been research published linking recent record Arctic sea ice loss to atmospheric circulation changes in the Arctic Oscillation that encourage a southwards dip of the jet stream over Eastern North America and Western Europe during late fall and winter. Until we have many more years of data and more research results, we won't be able to say if climate change is likely to bring more springs with a circulation pattern like this year's.

One thing we can say is that since global ocean temperatures have warmed about 0.6°C (1°F) over the past 40 years, there is more moisture in the air to generate record flooding rains. The near-record warm Gulf of Mexico SSTs this April that led to record Ohio Valley rainfalls and the 100-year $5 billion+ flood on the Mississippi River would have been much harder to realize without global warming.

I'll have a new post by Thursday.

Jeff Masters

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Quoting stormwatcherCI:
I will say though I take heed at your forecasts or outlooks over many established meteorologists.


I do too. He is an excellent tropical weather forecaster, and he should work for the National Hurricane Center one day.
Member Since: July 6, 2010 Posts: 113 Comments: 34213
1214. Levi32
Quoting Chicklit:
Afternoon, looks inhospitable for tropical development in the Caribbean at the moment.



Should remain that way for another 3-4 days.
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Afternoon, looks inhospitable for tropical development in the Caribbean at the moment.

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Quoting weathermanwannabe:


I've lost most of my hair so humidity not a problem but the Southern Ladies around here having a bad hair day when they get outside........ :)
I used to keep my hair to my waist but couldn't take it anymore and cut it off short. This is one of the hottest years in a long time. I fear for Aug-Oct . I think we might melt. :(
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Quoting stormwatcherCI:
You have earned my respect and you deserve it. Not many young men your age that I KNOW could even begin to walk in your shoes.


I second that, which is why I put the tropical tidbits on the front page of my website. I find them informative, well spoken and full of educational knowledge that everyone interested in weather should learn. Kudos to you Levi and keep up the awesome work!
Member Since: August 28, 2006 Posts: 6 Comments: 2899
Quoting stormwatcherCI:
Current temp here is 90.3F heat index 109.5F. It is the humidity that gets to me.


I've lost most of my hair so humidity not a problem but the Southern Ladies around here having a bad hair day when they get outside........ :)
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1209. Levi32
JMA has the ridge over the western Gulf of Mexico breaking down on Day 7. If there is any moisture available to move through that break, there could be hope for the gulf coast.

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Western Hills, Del Rio, Texas (PWS)
109.5 °F
Clear
Humidity: 22%
Dew Point: 62 °F
Wind: 0.0 mph

Wind Gust: 0.0 mph
Pressure: 29.72 in (Falling)
Heat Index: 113 °F

Member Since: July 14, 2008 Posts: 2 Comments: 9784
Quoting Levi32:


Well gosh, I'm flattered :)
You have earned my respect and you deserve it. Not many young men your age that I KNOW could even begin to walk in your shoes.
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Member Since: July 14, 2008 Posts: 2 Comments: 9784
1205. Levi32
TPW imagery is showing our tropical waves well today, along with the first big African dry air outbreak of the year:

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1204. Levi32
Quoting stormwatcherCI:
I will say though I take heed at your forecasts or outlooks over many established meteorologists.


Well gosh, I'm flattered :)
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Gilbert Field
Lat: 28.05 Lon: -81.75 Elev: 144
Last Update on Jun 15, 3:53 pm EDT

Thunderstorm Heavy Rain Fog Squalls and Windy

70 °F
(21 °C)
Humidity: 87 %
Wind Speed: N 29 G 63 MPH
Barometer: 29.96"
Dewpoint: 66 °F (19 °C)
Visibility: 0.50 mi.


This is in Polk County FL
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Today in San Juan the high was 92F with heat index of 103F. We were in the sinking side of the wave that will move thru tonight. After the axis passes,the rain will come and the NWS has a 70% chance of rain for tonight and tommorow.
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Quoting DEKRE:


Very corrosive - it can kill you by destroying your lungs; it is the main component of what was known as the London Smog (Smoke + Fog).

The vapour emitted by Sulfuric Acid is SO2.
And, in the other direction, SO2 is/was behind acid rain.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting weathermanwannabe:
Current Temp at Tallahassee Airport (away from all of the concrete and asphalt downtown):

Temperature
104 °F
Feels Like 106 °F



Pocatello, Pocatello Regional Airport (KPIH)
Lat: 42.92028 Lon: -112.57111 Elev: 4449
Last Update on 15 Jun 13:53 MDT


Partly Cloudy

74°F
(23°C) Humidity: 34 %
Wind Speed: W 18 G 29 MPH

Barometer: 29.91 in (1008.80 mb)
Dewpoint: 44°F (7°C)
Visibility: 10.00 Miles


feels like 74.:)
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Oh come on! This isn't even fair!! :(
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Quoting Levi32:


As you should. They are never perfect.
I will say though I take heed at your forecasts or outlooks over many established meteorologists.
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Western Hills, Del Rio, Texas (PWS)
109.4 °FClear
Humidity: 22%
Dew Point: 63 °F
Wind: 4.6 mphfrom the ESE

Wind Gust: 14.7 mph
Pressure: 29.72 in (Steady)
Heat Index: 113 °F

Member Since: July 14, 2008 Posts: 2 Comments: 9784
Quoting Hurrykane:


I'm a little cooler than you. 89F...Heat Index 106F
Where exactly are you ?
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1194. Levi32
Quoting stormwatcherCI:
Levi, I have all kinds of faith in your knowledge of tropical weather but I take ALL forecasts with a grain of salt.


As you should. They are never perfect.
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Quoting Levi32:


Yes, but predicting the unexpected is another matter. That's why caution exists. Recognizing the potential for the unexpected is the first step.
Levi, I have all kinds of faith in your knowledge of tropical weather but I take ALL forecasts with a grain of salt.
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Quoting weathermanwannabe:
Current Temp at Tallahassee Airport (away from all of the concrete and asphalt downtown):

Temperature
104 °F
Feels Like 106 °F
Current temp here is 90.3F heat index 109.5F. It is the humidity that gets to me.
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1189. Levi32
Quoting stormwatcherCI:
It seems to me that a good percentage of the time when development is not expected in that area something does develop.


It's true. Many developments are never seen by the models.
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1188. Levi32
Quoting stormwatcherCI:
I understand that no models develop it but it looks a little bit too good to ignore. They always say expect the unexpected .


Yes, but predicting the unexpected is another matter. That's why caution exists. Recognizing the potential for the unexpected is the first step.
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Quoting Hurrykane:


Agreed. That's the "art" of forecasting.
It seems to me that a good percentage of the time when development is not expected in that area something does develop.
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Current Temp at Tallahassee Airport (away from all of the concrete and asphalt downtown):

Temperature
104 °F
Feels Like 106 °F
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1184. aquak9
Ike- let's go get ice cream...
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1183. beell
Prevailing NW/NNW low level winds over inland central FL creating a cloud free shadow to the SE of Lake O.

Warm air rising over land and replaced by cooler and slightly more stable air from the lake inhibiting cloud formation on the mesoscale downwind of the lake.

Photobucket

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Quoting Levi32:


I'm saying it will look "nice" by the time it reaches the Yucatan, meaning it will be healthier than it is now, and I expect with more convection, given the upper pattern it is running into, since tropical waves like to blow up near upper troughs. Beyond that, when the upper trough lifts out, the upper pattern may be marginally favorable, but the wave will have land to deal with, so I wouldn't expect it to do a whole lot, though it may get caught up in the 2nd mess in ~8-10 days when the monsoonal trough comes north and the other tropical wave comes crashing in behind it.

No models develop this wave. I'm just watching it because it could look more impressive before reaching central America based on the pattern that I'm seeing.
I understand that no models develop it but it looks a little bit too good to ignore. They always say expect the unexpected .
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Quoting StormFreakyisher:
shopping carts were literally speeding down the street at night.

That reminds me of college...
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I hope the trough that's supposed to get into the NE/E Gulf won't treat SW Florida the way the last ULL did, blasting us day in and day out with dry air.
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1179. IKE
I'm at 98.4 w/a heat index....Heat Index:

107 °F.
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I'm not sure what to make of this, or if its even a tropical cyclone.

12z GFS 162 hrs, off US East Coast.


12z ECMWF 144 hrs, off US East Coast.


12z CMC, lower pressures off US East Coast by 144 hrs.


nada on the NOGAPS.
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1175. NRAamy
yes, but the silent but deadly kind are the worst...
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Quoting Levi32:
This upper shortwave currently moving into Missouri is expected by the models to dig southeastward and form an upper trough over the eastern Gulf of Mexico during the next 3 days.



Such an upper trough over the Eastern Gulf of Mexico would help ventilate the Caribbean and keep Florida in an unstable weather pattern.
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Tall storms in SEFL.

[Hail] S3 61 dBZ 49,000 ft.
Member Since: August 19, 2005 Posts: 5 Comments: 5657
1172. Levi32
Quoting stormwatcherCI:
So over a few days it could possibly begin to develop ?


I'm saying it will look "nice" by the time it reaches the Yucatan, meaning it will be healthier than it is now, and I expect with more convection, given the upper pattern it is running into, since tropical waves like to blow up near upper troughs. Beyond that, when the upper trough lifts out, the upper pattern may be marginally favorable, but the wave will have land to deal with, so I wouldn't expect it to do a whole lot, though it may get caught up in the 2nd mess in ~8-10 days when the monsoonal trough comes north and the other tropical wave comes crashing in behind it.

No models develop this wave. I'm just watching it because it could look more impressive before reaching central America based on the pattern that I'm seeing.
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1171. Skyepony (Mod)
Blowing up here & RAINING. Got a Thunderstorm Warning. None too soon. My high was 102.6ºF. I think the sand from the drought, in the area around my PWS is making it read warmer this summer.

Member Since: August 10, 2005 Posts: 300 Comments: 41241
1170. DEKRE
Quoting PrivateIdaho:
true that!


Same is true for ozone, another deadly gas. As long as you can smell it, it's ok.
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Quoting IKE:
Here comes the seabreeze front...but no rain so far...I've got 97.5 outside my window....heat index around 105......




We're under a Severe Thunderstorm Watch here but I look outside and see nothing but sun. Doesn't look like anything is even trying to pop. think it'll all be in Polk County and east today.

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Quoting HimacaneBrees:


H2S can only be smelled in low concentrations. The longer you're exposed, or a high concentration, can not be smelled. It deadens your sense of smell.
true that!
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1167. Levi32
This upper shortwave currently moving into Missouri is expected by the models to dig southeastward and form an upper trough over the eastern Gulf of Mexico during the next 3 days.

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1166. NRAamy
SQUAWK, you crack me up!!!!!

;)
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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