EF1 tornado, Urbana to Monrovia, Maryland, July 31, 2009

1. EF065 to 85 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mphthis tornado

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mph

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF1

Date

July 31, 2009

Touchdown

2:06 PM EDT (18:06 UTC)

Lifted

2:13 PM EDT (18:13 UTC)

On the ground

7 minutes

Path length

2.6 miles (4.2 km)

Path width

125 yards (114 m)

Deaths

0

Injuries

0

County

Frederick County

Touchdown point

39.351, -77.358

Lift-off point

39.371, -77.317

Record number

0907311206-01

A cold front and its associated trough of low pressure triggered showers and thunderstorms across Maryland. A southwest flow ahead of the front ushered in plenty of moisture from the Gulf of Mexico, resulting in an unstable atmosphere. The moderate amounts of instability combined with the forcing from the front and strong winds aloft for some thunderstorms to become severe.

Sporadic tree damage was noted along Tabler Road, where large branches were broken from hardwood trees. The circulation impacted several residences along Ball Road between Tabler Road and Ijamsville Road. One residence suffered roof structure damage and broken windows. In this location the roof was uplifted and shifted northward. An air conditioner unit on the north side of the home was lifted and transported fifteen feet to the east. ||Many trees were snapped along Mussetter Road. A large home suffered roof damage and structural damage and a barn was destroyed. |||A second residence also experienced an uplift of roofing. Several metal-sided barns were also destroyed.

Several trees were snapped or uprooted along Ijamsville Road and Price Distillery Road. Several hundred hardwood and softwood trees were snapped or uprooted along Whiskey Road and Whiskey Court. One home bearing specialty shingles to withstand winds up to 100 mph suffered some dislodging of its shingles. A clubhouse on the golf Course also lost many shingles from its roof.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down. One was issued for the county at another hour that day.

The county was under a severe thunderstorm watch, issued at 17:20 UTC and running to 20:56 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 16:22 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

Frederick Municipal Apt (FDK), 7 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The Sterling radar (KLWX), 45 km away, was scanning. The volume nearest the touchdown began at 18:08 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2009 tornado in MarylandEvery tornado in Maryland since 1950Warnings in force in Maryland nowThe forecast where you are

10 more were confirmed in the United States that day.

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.