jeudi, juin 07, 2007

Tornade, vous avez dit Tornade ?

J'ai déjà évoqué à plusieurs reprises la météo que nous avons à Chicago. Le temps est assez déroutant pour nous autres du vieux continent, habitués à des climats plus "tempérés".
Ici, les températures jouent au yoyo et les orages se multiplient.

Par exemple, hier, nous avons plafonné à 54 ° F( 12°C), et aujourd'hui nous avons atteint les 93 (presque 34)! Il y a beaucoup de vent et le ciel est très menaçant. Curieuse de nature, je me suis dit : tiens, je vais regarder la météo, je suis sûre qu'ils nous prévoient un orage.

Voici texto le "severe weather alert" pour l'Illinois... (les courageux peuvent le lire). Pour les autres, il est dit que nous avons un risque d'avoir des vents assez puissants et peut être même une tornade !
En fait nous sommes bien dans le fameux "couloir" des tornades, mais tout au bout au bout. Apparemment, ici ils voient une tornade tous les 10 ans (j'espère que ce ne sera pas pour aujourd'hui!).

BENTON-BOONE-COOK-DE KALB-DU PAGE-FORD- GRUNDY-IROQUOIS-JASPER- KANE-KANKAKEE- KENDALL-LA SALLE-LAKE-LAKE IN-LEE- LIVINGSTON- MCHENRY-NEWTON-OGLE-PORTER- WILL-WINNEBAGO- 1255 PM CDT (155 PM EDT) THU JUN 7 2007

...DAMAGING THUNDERSTORM WINDS POSSIBLE ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA THIS EVENING...

A SQUALL LINE OR SOLID LINE OF THUNDERSTORMS IS EXPECTED TO DEVELOP OVER NORTHERN ILLINOIS THIS EVENING. THE GREATEST SEVERE WEATHER THREAT FROM THESE STORMS IS DAMAGING WIND GUSTS AROUND 80 TO 90 MPH. THIS STORMS WILL EVOLVE FROM SUPERCELL THUNDERSTORMS THAT DEVELOP THIS AFTERNOON ACROSS IOWA AND NORTHWEST ILLINOIS AND THEN RACE TO THE EAST NORTH-EAST.

ISOLATED TORNADOES ARE POSSIBLE WITH THESE STORMS AS WELL... HOWEVER THE RISK OF TORNADOES WILL DIMINISH AS THESE STORMS COME FARTHER EAST ACROSS ILLINOIS AND WE GET LATER INTO THE EVENING. PRELIMINARY ESTIMATES ON THE TIMING OF THESE STORMS IS AS FOLLOWS: ROCKFORD... ORGEON... AND DIXON BETWEEN 7 AND 10 PM...CHICAGO... WAUKEGAN.. AURORA... JOLIET... OTTAWA... AND PONTIAC BETWEEN 9 PM AND 12 MIDNIGHT... AND VALPARAISO... GARY...RENSSELAER...KANKAKEE... AND WATSEKA BETWEEN 11 PM AND 2 AM.

THESE STORMS ARE BEING DRIVEN BY AN UNUSUALLY STRONG STORM SYSTEM ACROSS THE NORTHERN PLAINS. THIS STORM SYSTEM IS WINTER LIKE IN TERMS OF ITS WIND ENERGY...WITH WINDS OVER 100 MPH IN THE UPPER LEVELS OF THE ATMOSPHERE. THIS WIND ENERGY COMBINED WITH ABUNDANT MOISTURE STREAMING NORTH AHEAD OF A COLD FRONT AND HIGH INSTABILITY PROMPTED BY VERY WARM AIR NEAR THE GROUND AND COLDER AIR ALOFT WILL SET THE STAGE FOR EXPLOSIVE THUNDERSTORM DEVELOPMENT. THE GREATER MOISTURE AND INSTABILITY WILL SPILL EASTWARD INTO NORTHERN ILLINOIS LATE THIS AFTERNOON AND EVENING AS THE COLD FRONT ADVANCES EAST.

A COMPLICATING WEATHER FACTOR WITH THIS SEVERE WEATHER POTENTIAL IS WARM TEMPERATURES ALOFT...REFERRED TO AS A CAP. THIS CAP PREVENTS THUNDERSTORMS FROM DEVELOPING. THIS CAP WILL KEEP MOST LOCATIONS DRY UNTIL IT WEAKENS WHEN THE COLD FRONT GETS CLOSER TO THE AREA LATE THIS AFTERNOON AND THIS EVENING.

ALL INTERESTS ARE ADVISED TO MONITOR LATER FORECASTS AND PLAN NOW WHAT TO DO IN THE EVENT OF A SEVERE WEATHER WARNING.

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