A situation that is noticeably favorable to tornado activity is cold air advection aloft. When mP air moves across the United States, it becomes heated in the low levels in the western plateaus. The resulting density of the now warm mP air is then equal to or less than that of mT air moving northward over the Mississippi Valley. The mP air rides up over the mT air. The mP air still maintains low temperatures at higher altitudes causing extreme instability. The  following  conditions  may  indicate  possible tornado activity: 1. Pronounced   horizontal   wind   shear.   (Wind shear   is   the   rate   of   change   of   wind   velocity   with distance.) 2. Rapidly moving cold front. 3. Strong convergent flow at the surface. 4. Marked convective instability. 5. Dry air mass superimposed on a moist air mass and  abrupt  change  in  moisture  content,  usually  below 10,000 feet. 6. Marked   convection   up   to   the   minus   10°C isotherm. WATERSPOUTS Waterspouts  are  tornadoes  that  form  over  ocean areas. This phenomenon consists of two types: tornado in origin and locally induced. The difference between the two types is significant in that the tornado type has potential  for  inducing  substantial  damage  and  injury over a broad area, while the local type has potential for causing   only   minor   damage   in   a   small   area.   The following information is provided to help you to better understand the two types of waterspouts. Tornado Type These  waterspouts  form  at  the  cloud  and  extend down   to   the   surface.   They   originate   from   severe convective  cells  associated  with  a  cold  front,  squall line,    or    large    convective    cluster.    Whenever    the conditions  for  tornado  development  are  present  over coastal areas and the triggering mechanism extends into the adjacent maritime area, then potential for waterspout development is high. The tornado waterspout has a relatively short life span and usually stays   over   water.   However,   when   one   does   come ashore,    there    is    potential    for    it    to    assume    the characteristics  of  a  tornado;  although  its  life  span  is limited,   the   initial   intensity   is   sufficient   to   cause property damage and injury to personnel. Local Type These    waterspouts    originate    from    convective clouds of moderate vertical extent which form a line or a small cluster. Their existence is sensitive to wind and temperature in that surface winds of 20 knots or greater, or   a   cooling   of   the   atmosphere   by   precipitation, dissipates  them.  Additionally,  when  local  waterspouts come  ashore,  the  friction  induced  by  the  land  rapidly dissipates  them.  The  biggest  threat  posed  by  these waterspouts is to small craft, recreational boating, and to   support   facilities   such   as   harbor   operations   and marinas. REVIEW QUESTIONS Q5-1.    Describe  the  major  difference  between  rain and drizzle. Q5-2. What  altitude  range  do  clouds  occur  in  the tropics? Q5-3. What is the altitude range of middle clouds in the temperate regions? Q5-4. Describe the difference between sea fog and steam fog. Q5-5. What criteria must be met for a hydrometeor to be classified as blowing spray? LITHOMETEORS LEARNING    OBJECTIVE:    Identify    the characteristics  of  lithometeors  (haze,  smoke, dust, sand, and dust devils). Lithometeors   comprise   a   class   of   atmospheric phenomena of which dry haze and smoke are the most common examples. In contrast to hydrometeors, which consist largely of water, lithometeors are composed of solid  dust  or  sand  particles,  or  the  ashy  products  of combustion. HAZE Haze   is   composed   of   suspended   dust   or   salt particles    that    are    so    small    that    they    cannot    be individually  felt  or  seen  by  the  unaided  eye.  They reduce  visibility  and  lend  a  characteristic  opalescent appearance  to  the  air.  Haze  resembles  a  uniform  veil over the landscape that subdues all colors. This veil has a bluish tinge when viewed against a dark background 5-12