Mike Bardou National Weather Service Chicago/Romeoville, Il • Radar Has Limitations

Mike Bardou National Weather Service Chicago/Romeoville, Il • Radar has limitations

• Spotter reports are used to verify what we see on radar

• Spotter reports are a vital part of the Warning Decision Making Process Why we need spotters

Radar Horizon

AA B

Radar ?

Radar beam cannot see lower portion of storm “B” NWS Warning Forecaster NWS Doppler Radar Data

Spotter Reports

Warning Issued

Environment • Safety • Plan ahead • Identify Updraft/Downdraft • Positioning • Be Patient • Proper reporting Updrafts Downdrafts • Area where warm, moist • Area often identifiable air rises into the storm by heavy rain (possible hail) falling • Identified by dark, rain-free cloud base • Heavy rain/hail have under cloud towers dark, murky appearance in distance

. . UPDRAFT WARM

COLD UPDRAFT COLD

WARM WARM DOWNDRAFT DOWNDRAFT

Cumulus Stage Mature Stage Dissipating Stage

...... Updraft Downdraft • Wall cloud • Shelf Cloud • Rotation • Downbursts • Funnel Cloud • Gust Fronts • Tornado • “Dust Whirls”

. . • Rain-Free Base: Dark, flat, cloud base under the updraft, with little or no visible precipitation & tall cumulus towers above • Wall Cloud: Isolated lowering attached to the rain-free base, indicates inflow and updraft into the storm • Shelf Cloud: Low, horizontal cloud attached to a thunderstorm often wedge shaped & elongated, occurs with the downdraft. Storm Anatomy

• Funnel Cloud: rotating cloud protruding from the base of a thunderstorm that is not in contact with the ground • Tornado: violently rotating column of air extending from the base of a thunderstorm that is in contact with the ground • The tornado is the wind, not the cloud! • Not all tornadoes will have condensation funnel visible all the way to the ground • Gustnado/Dust Whirl: ground-based, usually short-lived dust whirl, not connected to cloud base, usually along leading edge of gust front. A gustnado is NOT a tornado Updraft & Rain Free Base Wall Cloud

WARM

. Downdraft & Heavy Rain/Hail COLD Squall Lines • Most common multicell type storm

• Many squall lines have shelf clouds along leading edge

• Worst is first with squall lines, wind then heavy rain Movement The shelf cloud is often at the leading edge of squall lines . Dark, turbulent, windy, Concave appearance. Spotters may see some swirling but tornadoes are highly unlikely in the cool outflow/downdraft. Jim Zandonai – Freeport IL

Lorraine Mahoney – Campton Hills, IL Similar to shelf cloud but tubular, detached from storm base, and takes on a slow horizontal rolling motion Supercells • Rarest type, potentially most dangerous

• Have a rotating updraft (mesocyclone)

• Most common spring & early summer

Supercells • Often discrete storms

• Many have a distinctive radar signature

• “Hook echo” often present

• Mesocyclone, possible tornado located in hook

Light Rain

Forward- Moderate/Heavy flank Rain & Hail downdraft Gust Front

Rear-flank downdraft

Anvil Edge “Hook echo” WARM

Flanking line 0 5 10 miles Overshooting top

Same storm from last slide, Anvil panoramic view Main storm tower Mammatus COLD clouds Flanking line Downdraft

Updraft Shelf cloud WARM Rain-free base Wall cloud Heavy rain & Hail ...... Storm motion Storm Motion “Right Hand Rule” LightLight Rain Forward- Forward-flank Moderate/HeavyModerate/Heavy flank When spotting a downdraft (FFD) RainRain & HailHail downdraft GustGust Front Front supercell, try to position yourself with heavy rain, Rear-flank hail to your right and downdraft (RFD) updraft to your left

You should be here COLD Possible rotation

WARM WARM

Looking northwest North . West