Wednesday, April 30, 2014

Record Rain in Alabama and Florida

Source: NWS Advanced Hydrologic Prediction Service
For the second time this month heavy rain has produced widespread flash flooding over southern Alabama and the western Florida panhandle. On April 14 three to five inches of rain fell from Mobile County, AL into the western Florida panhandle, with 6 to 8 inch amounts from the eastern side of Mobile Bay along I-10 into Florida.  In the past 48 hours the area was hit again, but with twice the amount of rain as on April 14.

Rainfall totals of up to 26 inches were estimated by radar in the westernmost portion of the Florida panhandle, though no actual amounts that high have been reported. Measured 24-hour rain totals in excess of 12 inches were common. The rain came in two waves, the first of which occurred Monday night into early Tuesday morning. This round of storms dropped from 3 to 8 inches of rain along the coasts of Alabama and Florida. The second wave of storms produced 10 to 15 inches of rain in roughly a period of nine to ten hours. The National Weather Service reported that 5.68 inches of rain fell between 10:00 p.m. to 11:00 p.m. CDT in Pensacola, FL on Tuesday night.

2-day radar estimated precipitation ending at 8:00 a.m. CDT April 30. The Mobile, AL radar was knocked out by a lightning strike during the storms and was not available. This image combines the radars from New Orleans (KLIX) and Eglin AFB (KEVX).  There is a slight difference between the start of the accumulation periods for the two radar sites.

Previous daily rainfall records for Mobile, AL and Pensacola, FL were annihilated Tuesday. Mobile measured 11.24 inches of rain on April 29, breaking the old record of 3.67 inches in 1996. In Pensacola, 11.13 inches of rain broke the old record of 3.06 set in 1918. The new record may in fact be a little low because a power outage resulted in the loss of an hour of data. The NWS radar estimate of rain at the Pensacola observation site was 15.55 inches.

24 hour radar estimated rainfall. KPNS is the Pensacola Regional Airport where the weather observations are made.
Credit: NWS Mobile/Pensacola

The CoCoRaHS reports coming in this morning were amazing. (The high amounts, compared to what was happening in the rest of the country, are what caused the national map to "skew to the blue", so to speak).  Six observers in southeastern Alabama and western Florida reported 24-hour totals of more than 17 inches, and 50 other observers reported more than 6 inches of rain.  Here is a list of the CoCoRaHS observers in the affected area reporting 10 inches or more of rain in the past two days. Stations highlighted in green reported that the gauge overflowed, so actual amount is likely higher.

Station No. Station Name County    4/29     4/30     TOTAL
AL-BW-45  Silverhill 5.0 SW  Baldwin 1.80 20.00 21.80
AL-BW-9  Foley 0.5 ESE  Baldwin 1.83 18.93 20.76
AL-BW-27  Orange Beach 2.1 NE  Baldwin 2.01 18.52 20.53
FL-SR-9  Milton 10.9 SSW  Santa Rosa 1.48 18.91 20.39
FL-ES-21  Pensacola 9.2 NW  Escambia 1.86 17.70 19.56
AL-MB-50  Mobile 5.1 S  Mobile 4.21 12.99 17.20
AL-BW-3  Daphne 1.2 NNW  Baldwin 3.48 12.99 16.47
AL-BW-32  Fairhope 3.1 NNW  Baldwin 3.43 12.70 16.13
AL-BW-40  Fairhope 1.5 WSW  Baldwin 2.56 12.95 15.51
AL-BW-65  Silverhill 0.9 SSE  Baldwin 2.45 13.02 15.47
AL-BW-68  Spanish Fort 1.6 W  Baldwin 3.12 12.33 15.45
FL-ES-4  Gonzalez 2.5 NNW  Escambia 1.50 13.93 15.43
AL-BW-13  Fairhope 3.7 NNW  Baldwin 3.41 10.88 14.29
AL-BW-4  Daphne 0.4 SW  Baldwin 3.33 10.90 14.23
FL-OK-29  Mary Esther 0.6 E  Okaloosa 1.72 12.43 14.15
AL-BW-1  Fairhope 2.3 N  Baldwin 2.63 11.49 14.12
AL-MB-49 Mobile 1.2 WSW Mobile 4.31 9.73 14.04
AL-MB-26 Mobile 4.4 WNW Mobile 4.82 9.18 14.00
FL-SR-12  Navarre 2.1 WNW  Santa Rosa 2.98 11.00 13.98
AL-BW-58  Spanish Fort 1.2 NE  Baldwin 2.87 10.96 13.83
AL-BW-36  Daphne 4.2 NE  Baldwin 2.61 11.20 13.81
AL-BW-26  Loxley 0.4 SSW  Baldwin 2.42 11.36 13.78
AL-MB-35 Mobile 7.4 W Mobile 4.63 8.91 13.54
AL-BW-8  Foley 7.4 SW  Baldwin 1.92 11.55 13.47
AL-BW-41  Fairhope 2.3 E  Baldwin 2.43 11.01 13.44
AL-MB-1 Tillmans Corner 4.3 WNW Mobile 4.56 8.73 13.29
FL-OK-33  Destin 1.3 NW  Okaloosa 1.02 12.20 13.22
FL-ES-15  Gonzalez 2.1 E  Escambia 1.69 11.53 13.22
AL-BW-31  Foley 2.0 SSW  Baldwin 1.87 11.30 13.17
FL-SR-2  Milton 1.4 NNE  Santa Rosa 2.06 11.09 13.15
AL-BW-20  Summerdale 4.3 WSW  Baldwin 1.78 11.25 13.03
AL-BW-60  Daphne 1.5 SSW  Baldwin 1.98 11.00 12.98
AL-MB-44  Mobile 1.8 W Mobile 3.96 8.92 12.88
AL-MB-10  Mobile 11.4 WSW Mobile 4.42 8.43 12.85
FL-SR-12  Navarre 2.1 WNW Santa Rosa 1.78 11.00 12.78
AL-BW-53  Elberta 3.1 SSW Baldwin 2.81 9.86 12.67
FL-OK-17  Ocean City 1.3 NNW  Okaloosa 1.56 11.04 12.60
AL-MB-4 Mobile 2.6 WNW Mobile 4.09 8.21 12.30
AL-MB-63 Tillmans Corner 8.7 WNW Mobile 4.43 7.66 12.09
FL-SR-17  Milton 6.0 SW  Santa Rosa 0.00 12.00 12.00
FL-WT-14  Inlet Beach 0.7 E  Walton 1.86 10.00 11.86
FL-OK-16  Shalimar 1.0 N  Okaloosa 1.25 10.38 11.63
AL-BW-30  Fairhope 3.5 E Baldwin 2.50 9.04 11.54
AL-MB-41  Theodore 8.0 SSE Mobile 2.97 8.25 11.22
AL-MB-32  Grand Bay 3.1 NNE Mobile 4.70 6.13 10.83
FL-OK-15  Niceville 4.5 SE Okaloosa 1.50 8.55 10.05
AL-BW-35  Orange Beach 1.3 E  Baldwin       M 19.00 INC
FL-ES-10  Pensacola 3.8 N  Escambia M 12.00 INC

The thunderstorms that produced the rain resulted from a "perfect storm" of factors.  There was strong upward motion in the atmosphere generated by small waves of energy rotating around the massive low centered over the central U.S.  That upward motion was aided by difluence in the upper atmosphere as well. In simple terms, difluence is the horizontal "spreading" of air at a level. As air is removed from a given level air rises from lower levels to replace it. That rising motion can aid in thunderstorm development. A third ingredient to this event was the surface cold front to the west, which helped provided lifting of the air from the surface. Lastly, warm, moist air from the Gulf flowed into the area ahead of the cold front. All of these came together to produce the conditions that gave rise to the torrential rain and resulting flash flooding.

Surface weather map at 7:00 p.m. CDT April 29.
This same area experienced a similar heavy rain and flash flooding event less than two years ago on June 9-10, 2012. Eight to 12 inches of rain fell from around Mobile Bay into the Florida panhandle. The CoCoRaHS observer at FL-ES-2 (West Pensacola) reported almost 22 inches of rain with that storm. You can read more about this in the July 2012 edition of the Florida CoCoRaHS newsletter.

More information on this event can be found at the NWS Mobile/Pensacola web site. 

Monday, April 28, 2014

A Jam in the Atmospheric Stream

500 millibar map at 7:00 a.m.CDT
Saturday, April 26.
A sluggish upper level weather pattern is setting the stage for a wet week across the eastern half of the country. The stage was set on Friday when and upper level low pressure system came ashore in the Pacific Northwest. By Saturday the low had dropped to southern California, and then kicked east on Sunday. This low is what helped produce the unstable atmosphere which spawned the tornadoes across Arkansas on Sunday and in Mississippi and Alabama on Monday.

The system currently crawling across the Midwest is called a closed low. Closed lows typically are strong systems with a distinct center of cyclonic circulation. On upper air charts the lows will be completely encircled by one or more height contour lines. Here is the 500 millibar map from May 4, 2013 showing a strong closed low centered over northern Arkansas. Note that there are three contour lines encircling the center. The more lines encircling the center, the more intense the low.

Strong closed low on May 4, 2013

Compare this to an open trough of low pressure. On the map below the trough along the west coast is open.

500 millibar map for May 17, 2013 with open trough along west coast.

Open troughs tend to be progressive. Small troughs tend to move faster than the
large troughs that extend north to south across the U.S.

Closed lows, on the other hand, move slowly. If the closed low becomes disassociated from the westerly flow of air, it is referred to as a cutoff lows. In both cases, the presence of a closed or cutoff low means an extended period of wet, cool, and stormy weather. Such is the case this week. Complicating the picture this week is the existence of what is called an "omega block", a pattern that resembles the Greek letter omega. This pattern tends to occur during the late winter and early spring in the Northern Hemisphere. It's main feature is the presence of the upper level high poleward of the jet stream. These warm highs tend to be stable and persistent, retarding the eastward movement of weather systems.The pattern is very evident on this morning's 500 millibar chart.

The 500 millibar map for 7:00 a.m. CDT April 28.with omega block pattern.
Since Friday there has been significant precipitation in the central U.S. as a result of the closed low on the west side of the omega block. Rain gauges will get a workout this week in the eastern half of the U.S. as the upper level low intensifies and moves slowly to the northeast over the next 48 to 72 hours. By Wednesday the center of the low will spin over the upper Great Lakes and this system will dominate the weather from the Continental Divide to the east coast. 

500 millibar forecast for 7:00 a.m.Thursday, May 1st.
Most precipitation will occur Tuesday and Wednesday, although wingspread cloudiness, scattered showers and thunderstorms, and cooler weather will be possible through the end of the work week. Present indications are that the closed low will open up and accelerate eastward on Friday. That should leave much of the eastern half of the U.S., except perhaps the northern Great Lakes, in good shape for the weekend.

Quantitative precipitation forecast for the five days ending 7:00 p.m. CDT Saturday, May 3rd

Wednesday, April 23, 2014

Update - CoCoRaHS Observations and NOWData

There was a lot of interest, a number of questions via Facebook, and some confusion about the inclusion of CoCoRaHS data in the NWS NOWData product.  I'll try and clear up a few things in this post, and also point you to another web site where you can also look at CoCoRaHs observations.

The data that feeds the NOWData tool on the National Weather Service web sites come from the Applied Climate Information System (ACIS) developed and maintained by the Regional Climate Centers (RCCs). The daily data from the U.S. Cooperative Network and CoCoRaHS are fed into ACIS by the Global Historical Climate Network (GHCN) Daily database which is collected, compiled, and distributed by the National Climatic Data Center in Asheville, NC. Are you following all of this? Good.

A few people have asked why their station does not appear in NOWData. The GHCN database only contains the data for CoCoRaHS stations that have submitted at least 100 observations. New active stations are added to the GHCN database once a month, so depending on timing it could be four months before a new station appears in GHCN and thus in NOWData.

Remember, to see the CoCoRaHS stations on NowData you must choose View Map, and then at the bottom of the map select "Show more stations".  The only way to identify a station is to move your mouse over the CoCoRaHS symbol.  Click on the symbol to select that station. Note that CoCoRaHS stations are only identified by the station name, not the CoCoRaHS station number.

There is another source where you can view tables and charts of CoCoRaHS data.  The Midwestern Regional Climate Center's cli-MATE system has a number of ways to view CoCoRAHS data. (Full disclosure - I was Director of the MRCC for 13 years and still work there on a part-time basis).  You do have to register for an account, but it's free. Once you have an account you have access to climate data throughout the U.S., not just CoCoRaHS.

Once you have an account you have access to the data and charts. As an example we'll look at Station Data/Daily Between Two Dates and one of the Multi-Station Summaries. You can select a station either through a sequential menu or through a map interface. For this example we'll select CoCoRaHS station CO-LR-273, FCL 2.2 NW. Note that you can select the stations only by their names at this time. cli-MATE also access the GHCN data through ACIS, so the data availability rules apply here as well (100 observations).

After the station is selected, go to Station Data/Daily Data Between Two dates. Here you can select over what time period you wish to view data, and whether you want tabular output (similar to what is on the CoCoRaHS Station Precip Summary option), or a chart. This chart has precip, snow, and snow depth data plotted on it..

Chart showing precip, snow, and snow depth for CO-LR-273

Here is the chart with just precipitation. If you move your mouse pointer over a bar on the chart the data for that bar is displayed.

You can also display summaries of precipitation data by climate division.

Input screen for multi-station precip summary

Output for multi-station precip summary. This list was truncated for display - there are many more stations in the summary

 Another option allows you to display daily data for a particular county.

Input screen for county daily data

Output for county daily data.
This output can get rather large (several screen widths) if there are a large number of stations in a county.

CoCoRaHS data is really "out there" in the world of weather and climate data. CoCoRaHS is now the largest provider of daily precipitation observations in the United States.  These new tools allow more people to have access to the observations you make and report every day. Thanks to all of our dedicated observers!

Tuesday, April 22, 2014

News from the (Lack of) Severe Weather World

NOAA's Storm Prediction Center has launched a new experimental web page for viewing storm reports.  You may be used to seeing this map of storm reports:

Storm reports for the tornado outbreak in April 2011.
In the current map and report format certain parts of the Local Storm Reports (LSRs) are truncated or ignored for the sake of brevity. The reports are listed below the map on the page.

The new, experimental system contains more information by retaining more from the listing of the report, including the source of the report, extending the remarks section to include all 500 characters, and whether the report magnitude was measured, estimated, or unknown. Also, will include LSRs related to winter weather.The map is larger and easier to read.

Experimental storm report map for the tornado outbreak in April 2011

New winter weather storm report map
One of the biggest differences between the current Storm Reports page and the new experimental page is the interactivity and the amount of information available.  Users can display subsets of reports  and can overlay counties, highways, NWS County Warning Areas (CWAs), and other features.

Tabs at the top of the map allow you to display all reports, or just tornado reports. The individual reports are listed below the map.

 Clicking on the "+" icon on the far left expands the report to show the detail. Additional detail can be seen by selecting the Map option on the far right.

SPC is seeking feedback on the experimental map, so feel free to put it through its paces and provide comments or suggestions. A link to provide comments is at the top of the page.

So far there hasn't been much to look at related to severe weather this season. The Storm Prediction Center says that 2014 tornado activity through April 21 is estimated to be at a record low level.  Through today there have been 85 severe thunderstorm watches and 84 tornado watches issued. In 2013 the corresponding numbers were 136 and 136. In 2011, when 465 EF-1+ tornadoes had been counted by this time there had been 184 tornado watches issued through April 22.

 It's hard to say if or when our luck will hold out. The system forecast to move across the country later this week is likely to produce severe weather from the Central and Southern Plains east through the lower Mississippi River Valley over the weekend. Stay up-to-date on the weather at your local National Weather Service office web page or at the Storm prediction Center web site.

Outlook outlining at a 30% or higher probability for severe thunderstorms within 25 miles of any point
for Saturday, April 26 (D5) and Sunday, April 27 (D6).

Tuesday, April 15, 2014

Winter Won't Let Go

Spring 2014 has been a roller coaster ride for much of the country. The month of March was a cold one east of the Rockies, and nationally was the 43rd coldest March on record and the coldest since 2002.  The first two weeks of April have held a little more promise, teasing us with brief periods of warm weather. The latest "bait and switch" occurred this past seven days. There was a nice warm-up this weekend as a developing low over the Central Plains combined with a high pressure system along the east coast produced strong southerly winds and boosted temperatures into the 70s and even low 80s as far north Chicago. Temperatures were a summer-like mid 80s in the Central Plains. Lincoln, Nebraska reachd 85°F on Saturday, one degree short of the record for April 12.

Surface temperatures at 4:00 p.m. CDT Saturday, April 12

24 hours later it was in the 30s and snowing. This morning Lincoln reached a  morning low of 19°F shattering the old record of 24°F.

Surface temperatures at 7:00 a.m. CDT Tuesday, April 15
While central portions of the country were enjoying warm weather snow was falling in the Rockies from Montana through Wyoming and Colorado into New Mexico as the low continued to organize over the Plains. By Sunday the system was pressing eastward, with rain changing to snow in the Arctic air behind the front.

Surface map at 1:00 p.m. CDT on Sunday, April 13.
Snow fell from Nebraska through much of Iowa, central and southern Wisconsin, and the Michigan U.P. Snow amounts ranged from 4 to 8 inches in Wisconsin and Michigan. On Monday light snow fell across northern and central Illinois, northern Indiana, lower Michigan and Ohio.

72-hour snowfall ending Tuesday morning, April 15.
As the front pushed through the Gulf States it kicked off severe thunderstorms across eastern Texas, northern Louisiana and central Mississippi. Further south, heavy rain fell from Mobile, Alabama east into the Florida Panhandle. Three to more than four inch amounts were common, but just east of Mobile Bay rainfall ranged from six to more than inches. Two CoCoRaHS observers north of Fairhope, AL reported 9.19 and 9.79 inches of rain this morning.

CoCoRaHS precipitation amounts in southern Mississippi, Alabama, and the western Florida Panhandle for the 24 hour period ending the morning of April 15.

Freeze warnings are in effect for much of the southeastern United overnight, and Winter Storm Warnings and Winter Weather Advisories extend from central Minnesota across northern Wisconsin and the Michigan U.P .through Thursday morning. Up to a foot of snow is possible across northern Wisconsin into the western U.P.

Watches, warnings and advisories as of 11:30 p.m. CDT April 15
This was probably winter's last gasp in the Plains and Midwest, but the northern Great Lakes and northern New England could see more snow this weekend.

Tuesday, April 8, 2014

CoCoRaHS Observations Served Up on NWS Web Sites

CoCoRaHS observations are now accessible through an interface on National Weather Service office web sites.  The observations are available using a tool called NOWData (NOAA Online Weather Data) found under the Local Climate option on the web site menus.

The main left-hand menu on the NWS office home page (top), and the window showing the NOWData tab (bottom)

NOWdata has been a feature on NWS climate pages for a couple of years, but a recent upgrade added new capabilities and access to CoCoRaHS observations, data from Remote Automated Weather System (RAWS) network, data from the USDA SNOTEL network, as well as from the NWS U.S. Cooperative Network stations. RAWS stations are largely used in the western U.S. for fire weather support, so your area may not have nay RAWS stations nearby depending on where you are.

If you would like to look at data from the U.S Cooperative Network stations, choose a station from the list in the list box on the left-hand side.

NOWData menu for the NWS Lincoln, IL office

CoCoRaHS and RAWS data are only accessible through the map interface. To access the map, click the View Map button on the left-hand side of the window.  The initial map that displays will show the NWS County Warning Area (CWA) shaded with push pin symbols representing the U.S. Cooperative Network stations. If you hold your mouse over a symbol on the map the name of the station will display in the lower left corner of the map window.

To view the CoCoRaHS stations available (stations that have reported in the past year), click the "Show more stations" button at the bottom of the window.  The map will get cluttered, but you will see the CoCoRaHS symbols on the map. You can zoom in on an area by dragging/panning the area you are interested in to the middle of the window, then click on the "+" symbol as many times as needed to zoom into the area you want, or you can use your mouse wheel. Again, holding your mouse over a symbol will display it's name in the lower left hand corner of the screen. Click on a symbol to select that station.

The NOWData map window displaying U.S. Coop an CoCoRaHS stations

The data is available in tables and in charts. Since we don't record temperature as part of CoCoRaHS none of the temperature products will be relevant.  here are examples of the products using data from my CoCoRaHS station, IL-CP-1.

Daily data for a month is similar to the Station Precip Summary on the CocoRaHS web site.

Daily precipitation for the current month. You can list daily precipitation for any month in the record.

The Daily Almanac provides you with your statistics for today and the month and year to date, as well as record highest and lowest amounts and accumulations.

Daily Almanac product on NOWData

Monthly and annual summary product on NOWData.
Monthly Summarized Data is also useful. With this you can view your monthly totals, the daily maximum or minimum for each month, the mean monthly precipitation, and the number of days where precipitation is equal to a great than an amount you specify. However, one serious drawback to the monthly summarized data is that it does not currently include multi-day amounts.  When I first pulled up my data I was amazed at the number of "M"s (missing) appeared in the monthly totals. If data is missing for any day in the month, then the sum is set to missing, and if any month is missing, the annual total is set to missing. I do not have any days missing in my CoCoRaHS record. However, I have a number of multi-day accumulations, as many of us do. The underlying database for the NOWData tool does not at this time assimilate the multi-day amounts, so days included in a multi-day period are set to "M". I've been told that this should be resolved in the future. In the meantime, your can use the Station Precip Summary option on the CoCoRaHS web site to get your actual monthly totals.

Accumulation graphs can also be generated for a time period you specify. The graphs display the highest, lowest, and the actual data for the period you specify.  When you mouse over a data point on one of the lines in the chart it will display the data, observed precip, accumulation to date, and the highest and lowest accumulation for the period to date for the station selected.

Accumulated precipitation for 2014 for my CoCoRaHS station.

Accumulated snow fall for my station for the winter of 2013-2014.

Take some time to jump on to your NWS office web site and play around with NOWData. It's a pretty cool tool. Here is a link to a page which lists and links to all of the NWS offices by state:

NOWData - NOAA Online Weather Data

Thursday, April 3, 2014

40th Anniversary of the April 3-4, 1974 Super Outbreak

In a little under 18 hours from April 3 to the early morning hours of April 4, 1974 the central and eastern U.S. experienced a historic damaging and deadly tornado outbreak. 148 tornadoes left a path of destruction across 13 states from eastern Missouri through Illinois, Indiana, Kentucky, Ohio, Alabama, and North Carolina, South Carolina, Michigan, Mississippi, and West Virginia.The storms were most numerous and the damage concentrated in Alabama, Georgia, Tennessee, Kentucky, Indiana, and Ohio.The storms resulted in 330 tornado-related deaths, 5,484 injuries, and $600 million in damages. The outbreak produced an astounding seven F5 tornadoes and 23 F4 tornadoes. The 1974 Super Outbreak occurred in a time before Doppler radar and well before the Internet and it's ability to rapidly and widely disseminate information. NOAA Weather radio was in its early stages of deployment.

On April 3, 1974 the early morning weather map depicted a strong low pressure system in central Kansas with a cold front trailing south into eastern Texas. and a warm front extending east from the cold front through Arkansas Tennessee, and North Carolina. South of the front warm, humid Gulf air was in place. A line of early morning thunderstorms were moving through eastern Missouri and western Illinois. Northwest of the low pressure center snow was falling in western Kansas, eastern Colorado, and southern Nebraska.

Portion of surface weather map for 7:00 a.m. CDT, April 3, 1974

Forecasters at the National Severe Storms Forecast Center (now the Storm Prediction Center) saw the potential for severe weather the day before and had notified Weather Services Offices  to be ready. However, the extent and intensity of the severe weather was still uncertain. By the morning of April 3 the potential for severe weather was coming into better focus. The first Severe Thunderstorm Watch was issued at 8:27 a.m. CDT for the Ohio Valley, and over the next 19 hours 28 severe weather watches were issued covering almost the entire area from the Gulf of Mexico to the Canadian border and from the Mississippi River to the East Coast.

Map of the tornado tracks for April 3-4, 1974
prepared by Dr. Ted Fujita
It was early afternoon when the severe weather development became explosive. A severe thunderstorm hit St. Louis at about 1:05 pm CDT. This storm, which had high winds and 2.75 in hail (baseball-size) caused 25 injuries and $45 million in damage, a record hail loss at the time.  A lot of the hail hit in the part of the city were the were a number of car dealerships, and cars in the lots were decimated by the hail.

The first tornado of the outbreak touched down in Morris, IL (Grundy County). It was a weak (F0) tornado that was on the ground for only a tenth of a mile. An hour later two more tornadoes touched down in central Illinois, quickly followed by more tornadoes in Illinois and Indiana. Storms spawned tornadoes throughout the afternoon and evening at a rapid pace.  At one point a total of 15 tornadoes were on the ground at the same time, and meteorologists in Indiana placed the entire state under a tornado warning. This was the first and only time in U.S. history that an entire state was under a tornado warning.

The F5 tornado as hit hit downtown Xenia, OH.
Photo by Kitty Marchant
The deadliest tornado to occur was the F5 tornado that destroyed much of Xenia, Ohio. 32 people were killed and 1,150 were injured. Almost half the buildings in Xenia were damaged or destroyed, and damages were in excess of $100 million (1974 dollars) About the time the Xenia tornado developed near Bellbrook, OH, another tornado touched down in Breckinridge County, KY and quickly intensified to produce F5 damage as it plowed through Brandenburg KY. As the afternoon wore on and the atmosphere became more unstable thunderstorm supercells developed eastward through the Southeast U.S.

Depiction of the upper level conditions (left) and surface conditions (righ)t at 7:00 p.m. CDT on April 3, 1974

There is no way to thoroughly write about all that occurred on the 18 hour period in April 1974 in a blog post.  It was a much-researched and documented event. You can easily spend many hours reading through the huge amount of information available on the 1974 Super Outbreak.  The Super Outbreak led to significant changes in warning procedures for severe weather.  Many communities that did not have outdoor warning sirens did so in the aftermath of the Super Outbreak. NOAA's Weather Radio network rapidly expanded in the wake of the Super Outbreak so that warnings could be quickly disseminated. It also helped spur the National Weather Service modernization program.

This short documentary on the Super Outbreak provides an overview of just what forecasters and the public were up against that day. This shows actual footage of tornadoes as they struck Xenia, Cincinnati, and Louisville, causing massive damage and numerous deaths. Includes discussion of advance tornado preparation and emergency coordination.   Courtesy of the National Archives.

Here are some sources for further reading. Many of these include numerous photographs, news accounts, and first-hand accounts of the events of that day. Several of the NWS pages contain links to other data and information about the Super Outbreak

NOAA Natural Disaster Survey Report - December 1974

NWS Nashville, TN - April 3-4, 1974 Super Outbreak

NWS Louisville, KY - 40th Anniversary of the April 3, 1974 Super Outbreak

NWS Wilmington, OH - The Super Outbreak of April 3-4, 1974

NWS Huntsville, AL - Remembering the April 3-4, 1974, Tornado Outbreak

NWS Birmingham, AL - The April 3rd and 4th 1974 Tornado Outbreak in Alabama

NWS Lincoln, IL - April 3-4, 1974 "Super Outbreak" of Tornadoes:  Impacts on Illinois

NWS Indianapolis, IN - April 3, 1974 Super Outbreak