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National Weather Volume 1, Issue 2 Summer 2002
Service Forecast Office
Baltimore/Washington How Do Meteorologists Use Doppler Radar
to Warn for Tornadoes?
Inside this issue: By John Margraf, Information Technol-
ogy Officer
How Meteorologists 1 Prior to the installation of the WSR-88D
use Doppler radar (Doppler) radar in the early 1990s, mete-
Regional Weather 2 orologists had a very difficult time issuing
Review tornado warnings. Occasionally, there
Regional Weather 3
would be a sign in the older radar images
Review
that indicated a possible tornado, but
most of the time tornado warnings were
Skywarn Spotlight 4 not issued until a funnel cloud or a tor-
Floyd Abell nado was spotted and reported back to
the National Weather Service.
Skywarn Classes 5
The Doppler radar in use today gives me-
Farewell..Jim 5 teorologists the opportunity to see tor-
Wiesmueller nadic development inside of a thunder-
storm. This provides the meteorologists
Aviation Weather 6 with the capability to issue a tornado
warning before a tornado touches the age. Our Doppler radar measures the shift
Spring 2002 7 ground, increasing the amount of time that in frequency between the transmitted sig-
people have to get themselves and their nals and return signals, and transforms
families to a safe location. that information into a display of motion
Web Site Intro 7 inside of thunderstorms. Forecasters can
So, what do meteorologists look at to de- actually detect circulations inside of a
50 Years of Service- 8
termine whether or not a tornado may oc- storm. If a storm develops a deep, strong,
Robert Dornin
cur? Our radar produces a number of dif- persistent circulation (especially one with a
ferent products that the forecasters have strong rotation near the ground), this is a
Historic Chronicle 9 at their disposal. The most commonly good indicator that a tornado may develop,
Hurricane Agnes used radar product is a reflectivity image, and a warning will be issued.
Picnic & Tell Us Your 10
which is the standard image that most
Story
people see on TV or across the internet, A velocity image from the tornado that hit
displaying where the storms are located College Park last year is displayed on the
and how intense the precipitation is inside next page. The shades of green indicate
of the storms. There are some reflectivity air motion toward the radar. The shades of
signatures that help us determine if a red indicate motion away from the radar.
storm could become tornadic, including The brighter shades of green and red indi-
the "hook echo" displayed on the image at cate the stronger velocity readings. In this
top right. (this was the storm the produced image, just to the north of College Park
a tornado in College Park, MD in Sept. (on the far right side of the image), you will
2001) see a couplet of strong motion toward the
radar and strong motion away from the
Another key radar product used for deter- radar (a bright green next to a bright red).
mining tornado potential is a velocity im- This is an indication of a strong rotation
Volume 1, Issue 2 Page 2
How Do Meteorologists Use Doppler Radar to Warn for Tornadoes? (Continued from Pg. 1)
near the surface, and when this information is combined
with data from our other radar products, we have a strong
indication that a tornado will occur with this storm.
The doppler radar installed here at Sterling in the early
1990s, and others like it across the country, have provided
NWS meteorologists with the information necessary to is-
sue timely, accurate tornado warnings, with enough lead
time for you and your family to find a safe place during
these dangerous storms. When a tornado warning is is-
sued, make sure you pay close attention to the path of the
storm, and follow the safety instructions that are given out
on NOAA weather radio or by the other local media out-
lets.
What do meteorologists look at to
determine whether or not a tornado
may occur?
Regional Weather Review
17th: Light rain fell across Allegany County, Maryland dur-
by Michelle Margraf, Forecaster ing the afternoon and early evening. . At elevations above
Here's a list of weather events that had an impact on our
1500 feet, surface temperatures were just below freezing
region in March and April of 2002. This information is
for much of the day so the rain froze on contact with side-
compiled from reports from volunteer and co-op weather
walks, metal objects, and trees. Accumulations of up to
observers, SKYWARN spotters, county and state officials,
1/8 of an inch were reported just outside of Frostburg.
and automated weather observations. This information is 21st and 22nd: A strong arctic cold front pushed through
included in the National Weather Service's monthly publi- the region during the evening of the 21st. This front ush-
cation, Storm Data and Unusual Weather Phenomenon. ered in strong northwest winds that gusted as high as 59
March 2002
MPH east of the mountains. The highest winds occurred
between 6 PM and 11 PM, but gusty conditions continued
through 4 AM on the 22nd. Minor structural damage was
9th-10th: A strong cold front which crossed the region reported in isolated locations, in addition to downed trees
late on the 9th was accompanied by strong gusty northwest and power lines.
winds. Some locations just east of the Appalachian Moun-
tain ridges reported downed trees and power lines in addi- April 2002
tion to some structural damage. In Mineral County, West
Virginia, a wind sensor on the top of a 75-foot tower in 18th: Scattered thunderstorms developed during the
Keyser recorded a wind gust of 69 MPH at 10:30 PM on early afternoon across Northern Virginia and Central Mary-
the 9th and 62 MPH at 4 AM on the 10th. In the northern land. Some of the storms produced damaging winds, very
Mineral County community of Ridgeley, the high winds heavy downpours, and frequent lightning. In Greene
caused moderate structural damage. The slanted roof of a County, a handful of lighting fires were reported. In Albe-
two-story apartment building was partially ripped off. In marle County, lighting started at least 7 brush fires. In Or-
Allegany County, a number of trees were downed, awn- ange County, lightning started an attic fire at an apartment
ings were damaged, and signs were broken.
Volume 1, Issue 2 Page 3
Regional Weather Review (Continued from Pg.2)
building. In Spotsylvania County, two homes were dam- of the damage, maps of tornado tracks, and more on our
aged by lighting fires and scattered trees and power lines web page at: http://weather.noaa.gov/lwx/Historic_Events/
were downed. Heavy downpours flooded roads in Freder- apr28-2002/laplata.htm
icksburg. In Alexandria, a lightning fire damaged an apart-
ment building. In Anne Arundel County, lighting struck at In Virginia: This storm damaged property all the way
least 10 homes, caused 35,000 power outages, and from Rockingham County to the Potomac River. It pro-
started five brush fires. High winds blew through open roll- duced an F2 tornado in Shenandoah County, a funnel
up doors on the front of an industrial building and the re- cloud in Fauquier County, large hail, heavy downpours,
sulting pressure blew out a portion of a concrete wall on and scattered wind damage along its path.
the back of the structure. Marble sized hail was reported in
Odenton. Heavy downpours flooded 20 basements and In Shenandoah County, an
numerous roads were covered by water. Rainfall of up to F2 tornado touched down
5.23 inches was recorded. In Harford County, two homes just east of Quicksburg and Across Charles County, 638
were damaged by fires resulting from lighting strikes. stayed on the ground for 4 homes were damaged, 100
miles before it dissipated homes were destroyed, 143
19th: Thunderstorms with hail and high winds moved while moving up the west
through the District of Columbia and the northern and cen- side of Massanutten Moun- businesses (mainly in
tral suburbs during the afternoon of the 19th. Winds gusted tain. The twister was about downtown La Plata) were
as high as 70 MPH. At least 82 trees were downed across 75 yards wide and it damaged, and 49 businesses
downtown Washington. Trees fell onto power lines, cars, caused a total of $1.6 mil-
homes, and several roads. A large tree fell onto a vehicle lion in damage. Along the were destroyed.
in Northeast. A 51-year-old man was killed and three path of the tornado, 15
other passengers sustained minor injuries. In Prince residential structures were
George's County, pea to quarter sized hail and 60 MPH damaged or destroyed, and 15 had minor damage. Four
winds were spotted. In Prince William County, two large poultry houses and 15 barns were destroyed. The roof of
trees were downed in the southeast portion of the county. a poultry house was ripped off and thrown onto Interstate
In Fairfax County, dime sized hail fell. In Arlington County, 81. Airborne roof debris hit a tractor-trailer on I-81 and
flooding was reported on Interstate 66. caused it to flip onto its side. The driver of the tractor-
trailer was treated for minor injuries.
22nd: Heavy rainfall over the headwater region of the
South Branch of the Potomac River caused the waterway The twister moved across Interstate 81 into the Kay Hill
to rise above flood stage in Grant and Hardy Counties in subdivision. Homes were damaged and trees were
the eastern panhandle of West Virginia. In Petersburg, downed. In Franwood Farms, a two-story home was se-
where flood stage is 10 feet, the river crested at 10.8 feet. verely damaged by debris from a neighbor's 60-foot-high
In Springfield, where flood stage is 15 feet, the river grain silo. A woman inside the structure was treated for
crested at 17.49 feet. bruises. At Franwood Farms Airport, 5 people took shelter
in a hangar. The tornado blew the roof off the building and
28th: Thunderstorms with winds gusting in excess of 58 flipped a plane on the landing strip. The tornado's path
MPH moved through the Eastern Panhandle of West Vir- was visible through the woods up to two miles east of
ginia between 5 and 7 PM. In Grant County, a power pole Framwood Farms and ended near Massanutten Mountain.
was downed and hail was reported. In Morgan County,
trees were downed, including one which fell onto a power The storm moved into Rockingham County, where it pro-
line in a mobile home park. In Berkeley County, a tree was duced dime sized hail. In Page County, golf ball sized hail
downed and a utility pole was lifted partially out of the fell and power lines were downed. In Culpeper County, a
ground. In Jefferson County, numerous trees were tree was downed. In Fauquier County, a funnel cloud was
downed and the roof of a large hay barn was blown off. photographed on a hill near Fauquier Springs. A large tree
and utility poles were downed and dime sized hail was re-
Special Report on the April 28th Tornadoes ported. In Prince William County, quarter to golf ball sized
Devastating tornadoes, large hail, and damaging winds hail caused property damage.
were produced by a long-lived supercell thunderstorm that
tracked across Central Virginia, South Central Maryland, In Maryland: The supercell crossed the Potomac
and across the Chesapeake Bay to the Eastern Shore of River from Prince William County into Charles County and
Maryland between 4:30 and 8:30 PM EDT. See pictures dropped a tornado just 2 miles east of the river. The dev-
astating tornado left a 32 mile path of destruction all the


Are UWB waveforms the best choice for Doppler radar processing? suggested that UWB waveforms are not the best choice for Doppler radar processing due to the issue of target range migration during the integration interval. However, more recent investigations 2,3 have demonstrated that this problem can be overcome by the correct choice of the matched filter in the case of UWB waveforms.

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