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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.
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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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