Changes to Local Hazardous Weather Outlook
National Weather Service Chicago routinely issues a Hazardous Weather Outlook (HWO) daily at 430 AM and 430 PM Central Time. The HWO highlights any potentially hazardous weather that is anticipated over the next several days. It can be found at the NWS Chicago web page, http://weather.gov/chicago. From the main menu on the left, under “Current Hazards”, click on “Outlooks”. The top item on the Outlooks page is “Latest Local Hazardous Weather Outlook”.
Effective April 15, 2008 the HWO will be also updated at 1100 AM during the warm season from March through September 30. This will be mainly to enhance the forecast thunderstorm threat. When thunderstorms are forecast in the Day 1 period, the HWO will be enhanced with three sections;
1. The “WEATHER HAZARDS EXPECTED” section will list the hazards expected during the day one period, including the potential magnitude and coverage or probability of occurrence.
2. The “AREAS AFFECTED AND TIMING” section will highlight the portions of the outlook that are expected to be impacted, as well as the time(s) that the hazards are expected to occur.
3. The “DISCUSSION” section will be used to briefly elaborate on the hazardous weather that is expected during the day one period.
Here is a sample HWO with thunderstorms;
HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
430 AM CDT FRI OCT 26 2007
ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
270945-
WINNEBAGO-BOONE-MCHENRY-LAKE ILLINOIS-OGLE-LEE-DE KALB-KANE-
DUPAGE-COOK-LA SALLE-KENDALL-GRUNDY-WILL-KANKAKEE-LIVINGSTON-
IROQUOIS-FORD-LAKE INDIANA-PORTER-NEWTON-JASPER-BENTON-
430 AM CDT FRI JUN 26 2008
THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
ILLINOIS...NORTHEAST ILLINOIS AND NORTHWEST INDIANA.
.DAY ONE...TODAY AND TONIGHT.
WEATHER HAZARDS EXPECTED:
ISOLATED SEVERE THUNDERSTORMS...A FEW MAY PRODUCE:
DAMAGING WINDS IN EXCESS OF 70 MPH.
HAIL TO THE SIZE OF NICKELS.
HEAVY RAINFALL WHICH COULD LEAD TO LOCALIZED FLOODING.
AREAS AFFECTED AND TIMING:
A LINE OF THUNDERSTORMS IS EXPECTED TO DEVELOP OVER NORTH CENTRAL ILLINOIS...WEST OF I-39...BETWEEN 2 AND 4 PM. THIS LINE OF STORMS IS EXPECTED TO MOVE EAST INTO NORTHEAST ILLINOIS AFTER 4 PM AND INTO NORTHWEST INDIANA AFTER 7 PM. THUNDERSTORMS WILL EXIT THE OUTLOOK AREA BETWEEN 9 PM AND MIDNIGHT.
DISCUSSION:
THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A STRONG COLD FRONT THIS AFTERNOON OVER NORTH CENTRAL ILLINOIS. WINDS ALOFT ARE QUITE FAVORABLE FOR THE DEVELOPMENT OF SEVERE THUNDERSTORMS...HOWEVER SOME UNCERTAINTY EXISTS ON HOW UNSTABLE IT WILL BECOME THIS AFTERNOON. IF CLOUDS BREAK AND TEMPERATURES WARM INTO THE 70S...THEN THE THREAT OF SEVERE WEATHER WILL BE HIGHER THAN IF SKIES REMAIN CLOUDY AND TEMPERATURES COOLER. IF THUNDERSTORMS DO BECOME SEVERE THEN THE PRIMARY SEVERE WEATHER THREAT WILL BE DAMAGING WINDS...POSSIBLY IN EXCESS OF 70 MPH...WITH A LESSER THREAT OF SOME HAIL AS WELL.
.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY.
THUNDERSTORMS ARE POSSIBLE AGAIN ON MONDAY.
.SPOTTER INFORMATION STATEMENT...
SPOTTERS WILL LIKELY BE NEEDED THIS AFTERNOON AND EVENING.
&&
COMPLETE FORECAST INFORMATION IS AVAILABLE ON THE NWS CHICAGO
WEBPAGE: WEATHER.GOV/CHICAGO
Comments or suggestions on the HWO can be sent to w-lot.webmaster@noaa.gov
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