Chapter  15  

Blizzards  

Blizzard    

•  Where  did  the  term  originate  from?  

Blizzards  

•  Requirements  – Winds  sustained  at  35  mph  (30  knots)  or  greater  – Visibility  less  than  ¼  of  a  mile  for  three  hours  or  longer  

– Temperature  is  not  a  factor  in  determining  blizzard  condiFons  

Blizzard    

•  North  American  geography  plays  important  role  – North-­‐south  oriented  mountains  

• Why  is  this  important?  

– Long  winter  nights  contribute  to  cold  wave  outbreaks,  which  bring  the  colder  temperatures  associated  with  blizzards  

– Cyclones  reach  the  greatest  intensiFes  on  the  plains,  enhancing  the  winds  needed  for  blizzards  

Blizzard  Warnings  

•  Blizzard  Warning:  NWS  issued,  follows  definiFon  of  blizzard  condiFons  

 •  Stockmen’s  Warnings:  Issued  when  severe  winter  weather  threatens  livestock  

•  Traveler’s  Warnings:  Issued  when  winter  condiFons  make  travel  difficult  or  impossible  

Annual  Probability  of  Blizzards  

Blizzards  Reported  by  County  

Blizzard  FormaFon  

•  Ingredients  – Extremely  cold  air  

• What  helps  development  of  cold  air?  

•  Strong  High  Pressure  

– Wind  • Where  does  the  wind  come  from?  

– Snow  

Cyclones  Associated  with  Blizzards  

•  Two  types  of  cyclones  can  lead  to  blizzards.,  where  do  they  develop    

•  Which  one  typically  has  the  worst  blizzards?  Why?  

Colorado  Cyclones  

•  Caused  by  a  wave  that  moves  across  CO/NM  Rockies  

•  (Divergence,  Convergence)  alo^  triggers  formaFon  of  the  surface  low  

•  Blizzard  condiFons  require  cold  air  and  associated  high  pressure  to  already  be  in  place  

Colorado  Cyclones  

Colorado  Cyclones  

Colorado  Cyclones  

•  How  does  warm  air  play  a  role  in  enhancing  blizzard  condiFons?  

•  Where  does  the  moisture  come  from?  

Alberta  Clippers  

•  Blizzards  form  in  the  same  manner  as  the  Colorado  Cyclones  

•  Typically  produce  less  snow,  why?  

Colorado  Cyclones  

•  Why  does  the  snow  blow  around  so  easily?  

Alberta  Clipper  

Alberta  Clipper  

Snow  Rollers  

•  Log-­‐shaped  snowballs  that  form  when  wind  scoops  out  and  rolls  chunks  of  snow  

•  Move  easily  when  the  ground  has  an  icy,  crusty  surface  that  prevents  snow  from  sFcking  to  it  

•  Requires  ~  an  inch  of  loose,  wet  snow    

Snow  Rollers  

Blizzard  vs  Ground  Blizzard  

•  What  is  the  difference  between  a  blizzard  and  a  ground  blizzard?  

•  How  does  topography  play  a  role?  

Ground  Blizzards  

•  Occur  frequently  in  the  wake  of  snowstorms  •  Visibility  can  be  worse  than  during  a  snowstorm  blizzard  

•  Can  obscure  regions  of  black  ice.  What  is  black  ice?  

•   extend  only  tens  of  feet  above  the  surface  •  What  makes  them  parFcularly  dangerous?  

ForecasFng  Blizzards  

•  Have  we  goben  beber  at  forecasFng  blizzards  over  Fme?  

•  What  is  sFll  the  most  difficult  component  of  a  blizzard  to  forecast?  

Blizzard  Hazards  

•  What  hazards  do  blizzard  bring?  

Blizzards  and  Climate  Change  

•  What  effect  is  climate  change  likely  to  have  on  blizzards?