NOAA S National Weather Service

Transcription

1 NOAA S National Weather Service Night Spotting Advanced Concepts of Severe Storm Spotting 2012 Rusty Kapela Milwaukee/Sullivan Weather.gov/milwaukee

2 Problems Spotters Encounter Spotters can only see a limited area, and much of the time the spotter view is being blocked by rain/hail, hills, trees, and buildings. Spotters have a hard time getting the big picture of what is going on around them. Mobile spotters may not have access to radar data to find where to go (safely). Spotters have a hard time judging distances to weather phenomena underestimate so don t do this besides, we don t need this information!

3 Problems Spotters Encounter Every storm is different the classic text-book images, graphics, and video clips you see in this presentation will most likely not be seen all the time in the real world. Many spotters have said things always look different in the field. If the storms are moving rapidly you will not have much time to recognize the important features and put it all together this is when you are likely to make a mistake!

4 The Big Picture Spotters should self-educate themselves with online educational material, courses, Top News of the Day stories, SkyWarn pages, etc. The NWS Southern Region Office has an on-line School for Weather entitled JetStream

5 COMET on-line spotter courses (two) ourse.php?id=23

6 Thunderstorm Development Iowa State University MesoNet Video is time lapse fast forward

7 Types of Thunderstorms Weak updraft (non-severe or severe) Moderate updraft (nonsevere or severe) Moderate updraft (nonsevere or severe) Intense updraft (Always severe) Mesocyclone - Rotating updraft Slight threat Moderate threat Moderate threat High threat Squall Line

8 Single Cell Storms May produce brief severe events

9 Multi-cell T storm Clusters Ordinary non-organized storms with low severe threat S Each cell lasts minutes, but a cluster can last for hours Courtesy Alan Switzer Heavy rain is the main problem However, strong winds, small hail and weak tornadoes are possible

10 Multi-cell Thunderstorms Ordinary non-organized storms with low severe threat

11 Multi-cell (Squall) Line Leading edge of Squall Line usually marked by shelf cloud. Do not report shelf clouds. What to expect Strong and possibly damaging wind Heavy rain/hail

12 Multi-cell Line (Bow Echo)

13 Squall Line - Bow Echo This shelf cloud is ahead of echo on right! bow Storm moving left to right (W-E) Well-developed shelf cloud is found on front side of line

14 Rain Foot Rain Foot = Strong downburst winds

15 Hail Shaft Copyright Paul Craven

16 Classic Tornado Near Central City, IA, Apr 26, 2009

17 Wedge Tornado They look wider than the distance from the ground to the cloud base

18 Rope Tornado

19 Supercell Main Features Overshooting Top Anvil Rotating & Tilted Updraft (Meso-cyclone)

20 Supercell Thunderstorm Contains a rotating updraft called a mesocyclone Only about 10% of radar-detected meso s are associated with a tornado Produce large hail, high winds, and strong to violent tornadoes Can last for several hours

21 Supercell

22 Tornadic Tstm Structure Overshooting Top Storm Motion Anvil Rear Flank Downdraft Foreward Flank Downdraft Updraft Tornado Actual tornadic structure more complicated

23 Supercell Rear Flank Downdraft Main Features Forward Flank Downdraft N Rain Free Base Wall Cloud

24 Tornadic Supercell Thunderstorm N Forward Flank Downdraft Light Rain Shelf Cloud Rear Flank Downdraft Moderate/Heavy Rain & Hail Storm motion Flanking Line T Rotating Wall cloud miles Gust Front Low-level Warm air inflow

25 Wall Cloud Movement RFD Wall Cloud Beaver Tail FFD

26 Supercell Features

27 Wall Cloud & RFD & FFD RFD Updraft FFD RFD Updraft FFD Copyright Jim Bishop Copyright Jim Bishop What a difference a few minutes can make!

28 Tornado note condensation funnel and debris spray at ground Tornado note condensation funnel and debris spray at ground

29 Storm Evolution Mike Hollingshead July 13, 2009 Kodoka SD to Valentine NE Rotating Wall Cloud

30 Storm Evolution Mike Hollingshead July 13, 2009 Kodoka SD to Valentine NE RFD Tornado

31 Storm Strength Clues Overshooting Top Flanking Line Updraft Wall cloud

32 Evaluating the Surroundings A thick, crisp anvil is another sign of a strong updraft An indication of a rapidly, intensifying storm!

33 Updraft Tilt Strong Winds Aloft Tilted updraft allows most of rain to fall downstream outside of updraft area. Updraft Downdraft (FFD) Updraft isn t choked off by rain-cooled air and lives for more than an hour!

34 Vertical Wind Shear Note the tilted storm tower Vertical wind shear Downdraft rain is shifted downstream

35 Landspouts Non-Supercell no rotating wall cloud or mesocyclone circulation starts at ground and builds upward

36 Landspout Tornado Weaker than a supercell tornado

37 Gustnadoes Aren t tornadoes since they don t extend to the cloud base Form along gust fronts Shallow vortices Report as gustnadoes if confident, otherwise report as thunderstorm wind damage if damage occurs

38 Gustnado Weak, short-lived, ground-based vortex on gust front

39 July 22, 2010

40 July 22, 2010

41 End of Class!