Central Plains Blizzard: Snow Amounts Likely to Take Many By Surprise


A Blizzard Warning and Winter Storm Warning has been issued parts of the Southern and Central Plains, the second such blizzard in a week for some residents.  However a concept in disaster preparedness can be readily displayed with the forecast for this event.  Currently, the National Weather Service is forecasting a foot as the upper limit to the snowfall values in Kansas and 15″ as the upper limit to snowfall values in extreme Northeastern part of the Texas Panhandle.  But the highest snowfall totals for this storm could be much much higher….

Recently, the NOAA Hydrometeorological Prediction Center (HPC) began issuing probabilistic snowfall graphics (shown below) that show snowfall forecasts where snowfall values are exceeded 90%, 75%, 50%, 25% and 10% of the time.

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HPC 50th Percentile Snow Forecast
(Click for larger image)

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HPC 90th Percentile Snow Forecast
(Click for larger image)

Essentially a 50th percentile snow forecast is the forecast that 50% of the time the amounts will be higher and 50% of the time, the amounts will be lower.  For planning purposes, this is the likely amount forecasted if you’re going to play the middle of the road.

However the 90th percentile forecast is quite different.  It shows the amounts that will be exceeded only 10% of the time.  While many people want to forecast snow amounts accurately, the 10% probability event is a great resource to “Plan for the worst” and the 50% probability event is “hoping for the best”.

The wild card in events like this is thunder snow. Essentially, areas where thunder snow occurs can receive locally higher snowfall amounts. The snow probabilities point to this potentiality, although the bands of intense snowfall will not cover the entire area. Depending on where the most intense bands set up, it will dramatically impact the amounts of snow received in those areas. This again points to the importance of the 10% exceedance threshold. Most people will receive snow amounts closer to the 50th percentile amount, but there will be pockets where people receive substantially higher amounts.

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Comparison between NWS forecast (left) and HPC 90th percentile / 10% exceedance forecast (right) Current as of 0800CT on 2/24/2013

You may be saying right now, “that’s great but I hate math and hate probabilities”.  Communicating potential risk, especially in low probability, high impact events is critical for anticipating the worst and taking protective action while hoping for the best.  If there was a 10% chance of an intruder in your house, going after you and your family, would you take protective action?  If there was a 1 in 10 chance that you could lose your job, would you start developing a backup plan?

We’ll see how this specific event unfolds, but the current forecast (left in map above) isn’t even at the levels depicted in the 50th percentile event (likely underestimating snow  amounts).  Between that and the incredible disparity between the forecast and 10% potential snowfall amounts, this is a classic example where people can and likely will be caught surprised by the event.

Mayor: “We Were Blessed” – No Fatalities as Tornado with Winds Up to 170mph Tears Through the Deep South


Damage to Music Building at University of Southern Mississippi (WDAM)

Damage to Music Building at University of Southern Mississippi (WDAM)

UPDATE: 536pm CT – The National Weather Service office in Mobile, AL has released the preliminary storm survey results confirming two tornado tracks in their forecast area produced by the same storm that impacted Hattiesburg, MS.  The storm survey team found EF-1 intensity damage in Wayne County with a tornado tracking nearly 17 miles in a discontinuous path.  The tornado first touched down near the community of Clara and then tracked to Denham before lifting.

Additionally, EF-0 damage was found in Northwest Perry County – an extension of the track of the same tornado that moved through Hattiesburg and Petal, MS.

Additional details will be forthcoming over the next few days after survey teams complete their data, especially looking on Tuesday in the Washington and Clarke County areas in Southwest Alabama.

UPDATE: 505pm CT – The National Weather Service in Jackson, MS has just upgraded the intensity from the Hattiesburg / Oak Grove tornado that impacted Lamar and Forrest Counties yesterday.  The tornado was preliminarily rated EF-3, but that rating has since been upgraded as damage consistent with 170mph winds was observed in the area of Oak Grove High School.  This violent tornado was only the second violent tornado (EF-4 or EF-5) recorded in Lamar or Forrest Counties since record keeping beginning, the other tornado being the April 24, 1908 Purvis tornado which was on the ground for 155 miles and impacted a wide ares from Louisiana into Mississippi (Source: NWS Jackson MS).

The  NWS storm survey teams have also preliminarily confirmed EF-2 tornado damage in Southwest Marion County – a separate track from the tornado that hit Hattiesburg.  This confirms the suspicions in the original  post that the storm “cycled” and produced separate tornadoes – as indicated by radar signatures.

— Original Post Below:

“We were blessed”.  That is what the Mayor of Hattiesburg, Mississippi said repeatedly when interviews on CNN after a strong tornado tore through the city on an otherwise calm Sunday afternoon in February.  As he stated repeatedly, even though the University of Southern Mississippi, several high schools, and the American Red Cross center were all directly hit by this storm, there were only limited injuries and not fatalities.  The fact that we’re reporting on damage to buildings, NOT fatalities is key in this story, and with storms like these, timing is everything.

First off, with students already on a long weekend break with Mardi Gras coming up, so the tornado occurring on the middle day in a four-day weekend meaning that the campus was relatively quiet.  Throw in the fact that the campus is a short two-hour drive from New Orleans, many students were likely out of town for one reason or another.  Additionally, the Elam Arms residence hall was hit by the tornado, blowing out windows to the multi-story residence hall… But the residence hall has not been used for some time, and according to a July 15, 2011 story from WDAM in Hattiesburg, the university was hoping to tear down the dormitory because “it’s considered to be in a prime location, for a developer to put in a business…. An excellent site for a hotel.”

According the University website, several structures in the southern portion of the campus were damaged including Jazz Station, the Mannoni Performing Arts Center, Ogletree Alumni House, and Elam Arms.

Mississippi is no stranger to strong tornadoes as we have seen in years past in places like Yazoo City.  This storm was similar to previous supercells producing long-lived tornadoes.  The supercell tracked from Southern Walthall County in Southern Mississippi through the counties of Marion, Lamar, Forrest, Perry, Jones and Wayne.  The same storm was also responsible for damage near Millry and Coffeeville in Washington and Clarke Counties in Southwest Alabama.

Based on an initial review of the radar data from this storm, the same supercell appeared to have cycled at several points along this 3.5 hour, nearly 170 mile long path.  The National Weather Service Offices in New Orleans, Jackson and Mobile will likely be performing damage assessments over the next several days.  It will be interesting to see where the damage paths are confirmed to have started/stopped, but the most likely points for breaks in the paths appear to be located near the following locations in that path:

  • Near the Marion / Lamar County, MS line – slight jog in the storm path to the right
  • Southwest Wayne County, MS – Just west of Camp Eight Road in the De Soto National Forest
  • Clarke County, AL – The storm appears to have crossed US-84 roughly 5 miles east of Coffeeville, AL
Radar-based rotation path for the Hattiesburg, MS supercell.  Note the path changes and possible locations for breaks in the path (cycling supercell).

Radar-based rotation path for the Hattiesburg, MS supercell. Note the path changes and possible locations for breaks in the path (cycling supercell).

In all, it is pretty likely that there were multiple tornadoes along this path.  The worst of the damage appears to be EF-2 to EF-3 in intensity, with the Hattiesburg tornado causing damage consistent with a tornado of at least EF-3 strength.  EF2 and greater tornadoes are rated as strong, so regardless of the damage, it is clear to say that the area was impacted by a strong tornado.

Tornadoes are rated by the damage they produce.

EF0…WEAK……65 TO 85 MPH
EF1…WEAK……86 TO 110 MPH
EF2…STRONG….111 TO 135 MPH
EF3…STRONG….136 TO 165 MPH
EF4…VIOLENT…166 TO 200 MPH
EF5…VIOLENT…>200 MPH

On a related topic the National Weather Service in Mobile tweeted the following graphic.  Incredibly their 30 minute forecast for this supercell was HIGHLY accurate both temporally and spatially.  The storm passed within a mile of Robinson’s Junction at 0027 UTC – right in line w/ the forecast graphic below.  The use of Social Media in this case to not only get out the tornado warnings, but to EMPHASIZE areas that are at greater risk represents a MAJOR opportunity for the National Weather Service to enhance their communication with customers.

NWS Mobile – Projected Path of Tornadic Supercell – VERY ACCURATE 30 MIN FORECAST – Storm passed w/in a mile of Robinson’s Junction at 0027 UTC.

Hurricane Storm Surge Scales – What Does the National Hurricane Center Think?


Link: NHC Views on Storm Surge Scales
Released September 10, 2010

There are scales for tornadoes, hurricanes, earthquakes, and other natural hazards.  In the aftermath of Hurricane Isaac, there were numerous calls for the National Hurricane Center to add back in a storm surge scale into the hurricane scale.  In an August 31st article from the New York Times, “Climatologists like Kerry Emanuel of the Massachusetts Institute of Technology have said that any classification should include both wind speed and surge. Otherwise, he argues, coastal residents can be easily misled.”

In 2010, the National Hurricane Center removed verbage in the Saffir-Simpson Scale that referred to storm surge in hurricanes.  In a one-page document posted on the National Hurricane Center (NHC) website earlier this week, the NHC Public Affairs staff shared the reason why storm surge was removed from that scale.  Additionally, they elaborated on why: Continue reading

Radar-Based Maps of the Henryville, IN Storm Tracks


NWS Louisville Statement on the Challenges in Damage Assessment for the Henryville, IN Tornado.

UPDATE: MARCH 6 – The National Weather Service in Louisville has published their initial findings including descriptions of the areas impacted.  That information is available at: NWS Louisville Damage Surveys – March 2, 2012.

Also, I have put together an initial version of an interactive web-map at ArcGIS.com that combines information from the second map below with the damage path information from the NWS in the link above.  The map is accessible at: Web Map of the Henrysville damage path and radar based-storm tracks at ArcGIS.com

ORIGINAL POST: March 4, 2012 – 630pm ET:

The past two days have been full of media reports, tweets and information being shared on the tornado outbreak that occurred on March 2nd, 2012 affecting towns like Henryville, IN.  As you can see from the statement below from the NWS Louisville Forecast Office, there were two supercell storms that impacted the area, with the first one producing the tornado that most people are talking about.  There was in fact a second storm behind the first one that also produced tornadoes and tornadic damage.  To make things more complicated for damage assessment teams, the paths essentially paralleled one another, and even crossed in places, making it difficult to attribute the damage to one storm versus the other.

I’ve put together the following the following map based on the NWS Radar information from the March 2nd tornado outbreak.  The map shows the paths of the two storms and paint the clear challenge that the NWS professionals have in identifying and differentiating between the two damage paths. Continue reading

Tornado Fatailities and the NWS Dual-Polarization Radar Upgrades


One of the fatalities occurred in this area near Jackson Gap. The NWS warnings for this storm were very clear, telling people to “seek shelter underground” and that a debris signature was appearing on radar.

Some people might ask is it worth it to upgrade the National Weather Service (NWS) radars to this “new” dual-pol technology.  While only 25% of the 160 radar sites around the country have been upgraded, the performance in the March 2, 2012 Tornado Outbreak is quite an impressive statement to the effectiveness of the technology.

During the March 2nd tornado outbreak, many of the tornadoes occurred in areas where the radars have already been upgraded.  When the debris was detected by the dual-pole technology, meteorologists could enhance their tornado warnings, confirming that a damaging tornado was indeed on the ground.  These signatures are essentially as good as visually confirmation of the tornadoes being on the ground.  The technology works because when the radar beams hit debris (leaves, shingles, branches, parts of houses, etc), there is a different signature from what is seen by the radar.  In the graphic above, you can see the blue area in a circle.  This area means that the radar is seeing a “different” signature from the surrounding areas.  When this is in the same location as strong rotation as seen by the doppler velocity products, it is essentially a confirmation of a tornado on the ground at the time of the radar sweep, or just before that time.

This will be significant with difficult-to-see tornadoes, especially ones that are either rain-wrapped or occurring in the overnight hours. Continue reading

NCDC Weather/Climate Toolkit BETA v 3.5.0 Released


The beta version of the National Climate Data Center (NCDC) Weather and Climate Toolkit (WCT) has been released and is now available for download from http://lwf.ncdc.noaa.gov/oa/wct/install.php.  This beta release adds support for several new functions including Level 2 and Level 3 Dual-Polarization products like the graphic below.  The tool is available for use in Windows, Mac OS/X and Unix/Linux environments.  I personally use the standalone download because it’s easier to save versions locally to test out the features of the newer release. Continue reading

There are Cat 3 Hurricanes & EF-3 Tornadoes, But Do Winter Storms Get Categories Too???


Many people are aware of the Enhanced Fujita (EF) Scale for tornadoes.  Most also know about the Saffir-Simpson Hurricane Wind Scale.  However there is also a rating scale for Winter Storms that fewer people know about. In 2004, Paul Kocin and Louis Uccellini from the National Weather Service (Kocin and Uccellini, 2004) developed the Northeast Snowfall Impact Scale (NESIS).    Below is a description from the National Climate Data Center (NCDC) website for NESIS:

“The index differs from other meteorological indices in that it uses population information in addition to meteorological measurements. Thus NESIS gives an indication of a storm’s societal impacts. This scale was developed because of the impact Northeast snowstorms can have on the rest of the country in terms of transportation and economic impact.

NESIS scores are a function of the area affected by the snowstorm, the amount of snow, and the number of people living in the path of the storm. The diagram below illustrates how NESIS values are calculated within a geographical information system (GIS). The aerial distribution of snowfall and population information are combined in an equation that calculates a NESIS score which varies from around one for smaller storms to over ten for extreme storms. The raw score is then converted into one of the five NESIS categories. The largest NESIS values result from storms producing heavy snowfall over large areas that include major metropolitan centers. Continue reading