Lee

... Patchy frost possible tonight...

An unseasonably strong area of surface high pressure is expected
to dominate the weather across the mid and upper Mississippi
Valley tonight. The combination of clear skies and light winds
under this high will allow temperatures to drop into the middle
to upper 30s across northern Illinois tonight. Temperatures this
cold could result in the development of some patchy frost across
the area later tonight... especially in low lying areas. Although
widespread frost is not expected... any frost that does form could
result in damage to sensitive vegetation if left unprotected.
Temperatures should quickly warm after sunrise on Friday... ending
the threat.


Kjb

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334 PM CDT Thu may 23 2013

... Patchy fog possible tonight...

An unseasonably strong area of surface high pressure is expected
to dominate the weather across the mid and upper Mississippi
Valley tonight. The combination of clear skies and light winds
under this high will allow temperatures to drop into the middle
to upper 30s across northern Illinois tonight. Temperatures this
cold could result in the development of some patchy frost across
the area later tonight... especially in low lying areas. Although
widespread frost is not expected... any frost that does form could
result in damage to sensitive vegetation if left unprotected.
Temperatures should quickly warm after sunrise on Friday... ending
the threat.


Kjb

Visit US at http://weather.Gov/Chicago (all lowercase)

Follow US on facebook... twitter... and youtube at:
www.Facebook.Com/US.Nationalweatherservice.Chicago.Gov
www.Twitter.Com/nwschicago
www.Youtube.Com/nwschicago

... Lake Michigan Beach forecast season begins may 24th...

The National Weather Service Chicago office will resume issuing
surfzone forecasts for the shoreline of lake and Cook counties in
Illinois and lake and Porter counties in Indiana for the Summer
swim season beginning Friday may 24th.

New for this year: beach hazard statements...

Beach hazard statements will be issued over the Summer on days
when dangerous swimming conditions are expected. The beach hazard
statement addresses various beach hazards and replaces the rip
current statements that have been issued in past years. See the
service change notice at...
www.NWS.NOAA.Gov/om/notification/scn13-33bhs_expansion.Htm for
more details on this transition.

Swim hazard risk replaces rip current risk in the surfzone
forecast...

Part of the transition to beach hazard statements will include the
surfzone forecast. The surfzone forecast will no longer refer to
rip current risk... but instead low... moderate and high swim risk.

Factors contributing to dangerous swimming conditions...

... High waves...

High waves pose several dangers to swimmers at Lake Michigan
beaches. First... high waves will cause swimmers to become
fatigued. Large waves are very powerful and can push a person off
a sandbar and into deeper water... requiring them to swim through
a rapid succession of waves to get back to more shallow water.

... Rip currents and structural currents...

Also... high waves result in strong rip currents and strong
structural currents. Rip currents are strong channels of water that
form rapidly and flow quickly away from shore through breaks or
low spots in The Sandbar. Structural currents are strong currents
which frequently flow along piers... breakwalls... and jetties
toward deeper water offshore.

... Strong offshore winds...

Dangerous swim conditions can also develop with strong offshore
winds. Although wave heights would tend to be lower with offshore
winds... strong winds can still cause dangerous structural currents
in the Chicago area. Southerly winds over 35 mph resulted in
dangerous currents near a pier at Loyola Park beach on may 24
2012... a contributing factor in the tragic drowning of a 15 year
old female.

Furthermore... particularly at the Indiana dunes beaches... strong
southerly winds pose a unique hazard to those on rafts. These
winds can create a current that pulls rafts well away from shore
into deeper water. A 31 year old male drowned on June 18 2012 at
Lake View beach in Beverly Shores when his raft capsized and blew
away from him after drifting over a quarter mile from shore due
to 30 mph southerly winds.

Criteria for issuance of beach hazard statements...

NWS Chicago will issue a beach hazard statement when there is a
high swim risk due to either of the following:

1) high waves of at least 3 to 5 feet and dangerous currents.

2) winds of 30 mph or higher.

We will no longer be issuing statements for a moderate risk... but
a moderate risk will be highlighted in the surfzone forecast.

People heading to Lake Michigan beaches this Summer should...

1. Check www.Weather.Gov/Chicago or NOAA Weather Radio to see if
any beach hazard statements are in effect... and if they are...
plan to stay out of the water on that day.

2. Swim on lifeguarded beaches when possible.

3. Refer to warning flags at local beaches for the latest
information before going into Lake Michigan waters (flag
definitions... green: OK to swim... yellow: caution is urged...
red: hazardous to swim).

Swimming at Lake Michigan beaches is a wonderful part of living
or visiting this area... but on days when waves are high and/or
currents are strong... it is a very dangerous activity and one
that should be postponed until the hazardous conditions subside.
Please stay informed and safe this Summer... and enjoy the
beaches!