Huntsville Tornado, Nov. 15, 1989 - Southern Region Disaster Survey

Part II

Summary of Warning Services

 

On the morning of November 15th, a short wave trough over the central Rocky Mountain region was forecast to move rapidly east-southeast across the middle and lower Mississippi Valley. The trough was forecast to assume a negative tilt across the southeastern United States by 6:00 am (1200 UTC) on the morning of the 16th.

Associated with the trough was a strong cold front pushing eastward along a line from the mid-Mississippi Valley to Texas. The front was expected to reach a line from the southern Appalachians to the Florida panhandle by 6:00 am on the 16th. The air mass over the southeast ahead of the cold front was unstable with surface dew points in the lower to mid 60s. The upper air sounding at Weather Service Meteorological Observatory (WSMO) Centreville, AL, at 6:00 am on Wednesday, November 15th, confirmed the unstable nature of the air mass. The Lifted Index on that sounding was -4 with a K- index of 29.

The 500 millibar (MB) wind over the frontal boundary was forecast to increase from around 50 knots on the morning of the 15th to near 70 knots by the morning of the 16th. The 850 MB jet blowing from the south-southwest was also forecast to strengthen to over 40 knots. By 6:00 pm (0000 UTC) on the 15th, the 850 MB jet was expected to be aligned along a line from southeast Louisiana to the southern Appalachians.

The combination of strong upper dynamics and moderate instability was expected to result in a significant development of severe weather from the mid-Tennessee Valley southward to the Gulf coast.

Severe weather potential for Alabama on Wednesday was first identified in the State Forecast Discussion (SFD) issued at 2:47 pm, Monday, November 13th. This discussion mentioned that a squall line would likely move through Alabama Wednesday, and the potential for severe weather would have to be monitored. The 4:05 pm Alabama Zone Forecast on Monday included a forecast of thunderstorms likely for the fourth period, Wednesday. The local forecast for Huntsville, issued by the Huntsville WSO, included the same information.

By Tuesday, November 14th, it became evident that a severe weather outbreak for Alabama was likely the following day. The evidence included strong positive vorticity advection and warm air advection accompanied by a rapid rise in dew points throughout the area. Additionally, a vigorous cold front was to push into the state adding to the already unstable conditions. The 3:34 am State Forecast Discussion on Tuesday expressed expectation of a line of thunderstorms ahead of the cold front with the mention of possible severe thunderstorms in the Wednesday forecast. The 5 am Zones and Huntsville Local Forecast included the wording "...showers and thunderstorms... some may be severe". This wording was carried forth in the 11 am forecasts.

The Tuesday afternoon forecast discussion, issued at 2:47 pm on the 14th, described the developing system as very strong with a severe weather producing squall line a possibility for Wednesday and Wednesday night ahead of the cold front. Projections in the SFD placed the cold front in Northwest Alabama by late Wednesday afternoon. The wording of "showers and thunderstorms...some may be severe" was continued in the forecast for Wednesday.

The Convective Outlook issued by the NSSFC in Kansas City at 12:16 am (0616 UTC) placed Alabama and Mississippi within an area of moderate risk of severe thunderstorms.

The early morning State Forecast Discussion on Wednesday, November 15th, further emphasized the strong severe weather threat. The SFD was followed by a Special Weather Statement (SPS) from the WSFO highlighting the significant threat of severe weather to Alabama. This information was repeated in the 5:40 am issuance of the Alabama Weather Summary.

At 9:30 am, NSSFC forecasters issued a Public Severe Weather Outlook describing the weather situation and indicating that an outbreak of tornadoes and severe thunderstorms was forecast to develop Wednesday afternoon into Wednesday night across the Tennessee Valley. It was further described as a potentially dangerous weather situation and encouraged people to monitor the weather closely.

A 9:44 am State Forecast Discussion amplified on the developing weather situation and the severe weather threat. It also advised all Alabama and Northwest Florida Weather Offices to review staffing requirements and line up additional personnel for late in the afternoon and evening.

The Public Severe Weather Outlook from NSSFC was followed at 10:50 am by a Special Weather Statement from WSFO Birmingham. The statement was headlined "MAJOR SEVERE WEATHER THREAT POISED FOR ALABAMA AND NORTHWEST FLORIDA!" The statement did a quick recap of the expected weather and encouraged people to review severe weather safety rules. All law enforcement and emergency management agencies (EMA) were encouraged to make plans for adequate staffing for the afternoon and evening. A paragraph was included to appeal to the media for assistance in distributing weather watches, warnings, and statements. This SPS was followed within 20 minutes by safety rules for severe thunderstorms and tornadoes.

The 10:45 am Zone Forecast continued the mention of some thunderstorms being severe. The 11:20 am Alabama Weather Summary devoted two paragraphs to highlighting the potentially dangerous situation expected.

 At 12:01 pm, the NSSFC issued Tornado Watch Number 750, which included part of Northwest Alabama, valid from 12:30 pm to 8:00 pm. The areal outline, prepared by WSFO Birmingham, was transmitted on the NOAA Weather Wire Service (NWWS) at 12:09 pm. The watch included 19 counties in North Alabama, one of which was Madison County, and one county in South Alabama. The Zone Forecast for the affected zones was updated at 12:30 pm to include the tornado watch. At that time, the wording in the forecast text was changed to read "...showers and thunderstorms...some will be severe".

Because of the staff shortage at WSO Huntsville, the Alabama Area Manager coordinated with the Huntsville Acting Official-in-Charge (AOIC) on staffing requirements shortly after 8:00 am on Wednesday, November 15th. A meteorologist intern at WSFO Birmingham was available for detail to Huntsville. Around 10:30 am, the intern departed Birmingham to go to Huntsville, arriving there shortly after noon.

Prior to noon, the issuances from NSSFC and WSFO Birmingham were placed on the NOAA Weather Radio broadcasts from the Huntsville office. With the arrival of the NSSFC Tornado Watch, all EMA offices within Huntsville's county warning area were notified via telephone. Continuous weather radar coverage was begun, and the first radar observation was sent at 12:35 pm.

At 12:45 pm, a Special Weather Statement was issued detailing radar indications and reiterating the Tornado Watch and the need for people to review safety rules. Between 12:30 and 1:00 pm, the Huntsville-Madison County EMA office activated the amateur radio spotter network interface in the WSO radar room. An amateur radio operator is normally detailed to the WSO whenever a tornado watch affects the Huntsville area.

From 12:45 pm to 3:30 pm, the staff of WSO Huntsville collected information on various storms and interfaced with EMA and law enforcement agencies and media outlets. Severe Thunderstorm and Tornado Warnings and statements were issued primarily involving the counties in the western half of the Huntsville county warning area. A 3:15 pm Severe Weather Statement included the wording that "...These storms are dangerous and not to be taken lightly ... the storms should reach the Huntsville area between 4 and 5 pm CST."

The WSO received a number of reports of severe weather. The reports, however, were mostly of hail and high wind including some reports of wind damage such as trees blown down. Specific details from the Huntsville warning log are contained in Appendix B.

At 3:40 pm, a Tornado Warning was issued for Lawrence and Morgan Counties. The warning was based on a possible hook echo on the Huntsville local warning radar. At 3:48 pm, three-quarter inch hail was reported in Decatur area of Morgan County which is just southwest of the city of Huntsville.

Due to the nature of the storm reports and to the dissipation of the hook echo configuration, the 3:40 pm Tornado Warning was changed to a Severe Thunderstorm Warning at 3:54 pm. Limestone County was also added to the warning. At this time the radar echo was exhibiting a bow shape with a cell top to 55,000 feet.

At 4:09 pm, large hail was again reported in the city of Decatur in Morgan County. Another hail report, this of "pea-size" hail at County Line road between Madison and Limestone Counties, was received at 4:10 pm.

A Severe Thunderstorm Warning was issued at 4:13 pm and included Morgan, Madison, and Limestone Counties. The warning was based on radar and the numerous hail reports. As the thunderstorm moved into Madison County, it moved across the Huntsville International Airport, location of the WSO. At 4:15 pm, a wall cloud was observed by WSO personnel. The wall cloud was not rotating and dissipated rapidly.

A 4:24 pm Severe Weather Statement highlighted the reports of hail and damaging winds in the warned areas. By 4:27 pm heavy rain and hail were falling at the WSO; the rain severely attenuated the radar.

The WSO received a report around 4:30 pm through the amateur radio spotter network of a tornado in the old airport area in Huntsville. Another spotter report at 4:32 pm said there was no tornado. Additional tornado reports were received at 4:33 pm.

The WSO staff began preparing a Tornado Warning for Madison County at 4:35 pm. The warning was broadcast "live" on NOAA Weather Radio (NWR) with the tone alert at this time. A problem with data lines between the SRWARN computer and AFOS was quickly cleared and resulted in only a slight transmission delay. The Tornado Warning was sent to AFOS from the SRWarn computer at 4:39 pm and sent immediately on the NWWS. SRWarn refers to a PC-based program used by NWS offices to rapidly compose and transmit warning messages. AFOS refers to the main on-line computer system used throughout the NWS.

At 5:02 pm a Tornado Warning was issued for Jackson, Madison, and Marshall counties as the tornado-producing cell continued eastward. A 5:18 pm Severe Weather Statement canceled the tornado warning for Madison county, but continued the warning for Jackson and Marshall Counties.

Additional statements and warnings were issued through 7:00 pm as the weather continued to affect the eastern portion of the Huntsville county warning area. By 7:00 pm, the extra staff was being released.

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