Tornadoes/Thunderstorms

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Thunderstorms, Tornadoes and Lightning brochure (.pdf)

Your Emergency Services Division takes severe weather preparedness very seriously. Since severe weather is the #1 potential widespread risk to Washtenaw County residents and businesses, storm preparedness activities takes top priority over everything else that we do. As StormReady accredited coordinators for the National Weather Service Skywarn Spotter program, we are engaged in numerous severe weather related activities year round.


Skywarn Program

Basic Spotters' Field Guide (.pdf)
Advanced Spotters' Field Guide (.pdf)

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Your Emergency Services Division conducts several Skywarn Spotter training programs every year. The courses are held throughout the community at the beginning of every severe weather season. The presentations are free of charge and are open to anyone at least 18 years old who is interested in being trained on severe weather recognition, reporting and protection procedures.

The basic course is two and one half hours long, and Skywarn Spotter identification codes are issued to all who complete the training. Washtenaw County currently has approximately 400 trained citizens, amateur radio operators, police officers, firefighters, paramedics and public works officials.


Severe Weather EOC Activation

When the National Weather Service issues a severe thunderstorm or tornado watch, the Emergency Services Division staff is notified immediately via our weather teletype in the EOC, by radio and pager if out of the office, or even by fax at home... detailed NWS bulletins are immediately sent to our home fax machines during off hours. We then immediately activate the Emergency Operations Center with the communications, warning, direction and control, and public information duties being staffed. The EOC's communications system is activated including the Amateur Radio Skywarn network. Our weather radar and storm tracking system is immediately fired up and monitored closely for approaching or developing severe weather, matching Skywarn spotter reports to real time radar data and issuing warnings to the public in conjunction with NWS meteorologists. Here's an example of some of our tracking capabilities:

Satellite Storm Tracking EOC Status Map Doppler Reflectivity Doppler Velocity
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This is a weather satellite image (infrared and color enhanced) from the EOC's tracking system of a line of intense storms clearly indicated from near Lansing stretching all the way down into the Texas panhandle. The more red the color is, the colder the cloud tops are and therefore the higher they are in the atmosphere which indicates their relative severity. These images are updated in the EOC every 15 minutes, and animates to show overall direction of travel. The EOC's weather tracking map, showing several aerial watch boxes drawn in black and thunderstorm or tornado warnings indicated in red for each county as the storm (shown in the satellite column) develops along a cold front. This is a simple but effective mapping system that helps us to see severe weather trends and provides for an excellent storm history and summary of events. EOC Doppler radar showing a distinct "V-notch" with "hook echo" as spotters report a tornado actually on the ground in Shiawassee County. The tornado damaged several buildings and downed trees and power lines as it moved to the ESE at 30 miles per hour. Numerous Spotters followed the storm all the way to St. Clair county before going into Lake St. Clair. The same storm, a few minutes later but using a special velocity display showing intense local rotation (look at the very center of the picture where the red and blue colors appear to touch. This indicates that winds are going away from and going towards the radar station in the same general area.) This display is extremely useful at detecting tornadoes in the absence of a trained spotter by using Doppler shift technology and color enhanced imagery.

Local Severe Weather Reference Guide

Washtenaw County is covered by NOAA Weather Radio Station KEC-63 at 162.550 MHz.

Map of NOAA Weather Radio coverage in Michigan

  • Severe Thunderstorm Watch

    Conditions are favorable for the development or approach of severe thunderstorms in and close to the watch area. Stay tuned to NOAA Weather Radio or local media and be prepared to take cover indoors.

  • Tornado Watch

    Conditions are favorable for the development or approach of severe thunderstorms and tornadoes in and close to the watch area. Stay tuned to NOAA Weather Radio or local media and be prepared to take cover indoors.

  • Severe Thunderstorm Warning

    A severe thunderstorm (a storm with winds in excess of 58 miles per hour or with 1" or larger hail, or both) is indicated on radar or has been reported by a Skywarn spotter. Take cover immediately in a sturdy building. Stay away from windows and do not use the telephone or appliances unless it is a life threatening emergency. To keep informed until the storm passes and the warning expires, use a battery powered radio tuned to: WEMU (89.1 FM)

  • Tornado Warning

    A tornado (violently rotating column of air in contact with the ground) or funnel cloud (developing tornado) approaching the ground surface has been indicated on radar or has been reported by a Skywarn spotter. Take cover immediately in a sturdy building. Go to the lowest level of the structure preferably into a small windowless room and crouch under a sturdy desk or table. Stay away from windows and do not use the telephone or appliances unless it is a life threatening emergency. To keep informed until the storm passes and the warning expires, use a battery powered radio tuned to: WEMU (89.1 FM)

  • Flood and Flash Flood Watch

  • Conditions are favorable for flooding and flash flooding (inundation of flooding waters within 6 hours) in and close to the watch area. Stay tuned to NOAA Weather Radio and local media. Be aware of current conditions, especially if you live or work near a flood prone area or are near a river, creek or stream. Prepare to take immediate action to protect life and property.

  • Flood and Flash Flood Warning

    Flooding or flash flooding is imminent or is occurring now. If rising water nears, immediately evacuate to higher ground. Do not attempt to drive through flooded roadways or underpasses. To keep informed until the flooding subsides and the warning expires, use a battery powered radio tuned to: WEMU (89.1 FM)

Wind Speed Estimation (in MPH)

Wind Speed

Description

0

Smoke rises vertically

1-3

The direction of the wind is shown by smoke but not wind vanes

4-7 Wind is felt on the face, leaves rustle, wind vanes move
8-12 Leaves and small twigs are in motion, small flags are extended
13-18 Dust and loose paper is raised, small branches move
19-24 Small leafy trees sway, crested wavelets form on lakes & ponds
25-31 Large branches are in motion, whistling is heard on power lines
32-38 Whole trees in motion, inconvenience in walking against wind
39-46 Twigs break off trees, difficult to walk against the wind
47-57 Minor structural damage such as chimneys and shingles
58-72 * Damage to chimneys and antennas, shallow rooted trees uprooted
73-113 * Roof surfaces peel, windows break, moving cars pushed off road
113-157 * Roofs, weak buildings, mob. homes destroyed, large trees uprooted

 

 

[* indicates severe thunderstorm criteria]

Hail Size Estimation

Size

Description

1/4 inch Pea size
1/2 inch Marble size
3/4 inch Dime size
1 inch * Quarter size
1 3/4 inch * Golf ball size
2 3/4 inch * Baseball size

[* indicates severe thunderstorm criteria]

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