Boats

GREAT LAKES SEVERE WEATHER OUTLOOK

Welcome to our "Great Lakes Severe Weather Outlook" mainpage! This page, and attendant pages herewith are designed to provide critical hazardous weather information to all mariners and major shipping interests alike. Coverage will focus on lakes "Superior" and "Michigan", with complete detailed information on the type(s) of hazards expected, location, and timing of occurance. The forecast products will be issued in two (2) formats. The first is a "categorical" version, which is traditionally used in all forecast products. The other is a "probablistic" version, which was started at our office in 2004. Both versions should provide enough details of what is to be expected so as to help mariners make sound decisions about venturing out.
This product will only be available from spring until fall, to cover the primary boating season. The specific outlooks contained herein will be available only when a threat for severe weather exists across either lake. The breakdown between the categorical risk and associated probabilities is shown in the table below. Note: the probabilities here are different then those in our other outlook products.
Very Important: If you find any errors on these pages, or would like to make a comment about this product, we would love to hear from you so just E-Mail us.

Legend Slight Moderate High
Large Hail 10% 30% 60%
Damaging Winds 10% 30% 60%
Waterspouts 01% 08% 15%

While the primary purpose for this product will focus on severe weather potential for each lake, there are other hazards which can also impact mariners and shipping interests alike. A few of the more common hazards are highlighted below.

Alert Type What It Means What Actions To Take
SMALL CRAFT ADVISORY This means sustained winds of between 18-33 knots with higher gusts are likely with waves of 4 feet or higher. Boaters with small vessels are urged to avoid going out, even in nearshore zones.
GALE WATCH This means that gale force winds (34-47 knots inclusive) and waves building to 10-15 feet are possible within 24 hours. All mariners and boaters should keep up with later forecasts and statements.
GALE WARNING This means gale force winds (34-47 knots inclusive) are imminent, or now occuring. Boaters with small vessels are advised not to venture out, but extreme caution is advised for medium sized vessels.
STORM WATCH This means storm force winds of 48-63 knots inclusive, and waves up to, and exceeding 18 feet are possible within 24 hours. All marine interests, including major shipping vessels, are strongly urged to keep up with later forecasts and statements. Major ship captains should consider delaying your departure, or depart immediately.
STORM WARNING This means storm force winds of 48-63 knots inclusive, and waves up to, and exceeding 18 feet are imminent, or now occuring. All marine interests are advised not to venture out. This is a particulary dangerous and life threatening situation! Ship captains are urged to stay at safe port, but if departure is necessary, use extreme caution and be in contact with appropriate people.
SEVERE THUNDERSTORM WATCH This means atmospheric conditions are favorable for the possible development of severe thunderstorms over the next several hours. Boaters who will be out on the water should keep an eye to the sky every so often. Watch for cumulus clouds that tower up into the atmosphere. If you see a storm building, head for safe harbor quickly.
TORNADO WATCH This means that atmospheric conditions are favorable for the possible development of severe thunderstorms and waterspouts over the next several hours. Boaters who will be out on the water should keep an eye to the sky every so often. Watch for cumulus clouds that tower up into the atmosphere. If you see a storm building, head for safe harbor quickly.
*SPECIAL MARINE WARNING This means that severe thunderstorms with wind gusts of 34 knots or higher, large hail, frequent deadly lightning, and possible waterspouts are imminent, or now occuring. If caught out on the open water and your vessel has no cabin, get to safe harbor at once. If your vessel has a cabin, your best option is to get to safe harbor. However, if there is little time, drop anchor and get into the cabin. Don't touch metal surfaces.

Note: * - Special marine warnings can also be issued for high non-thunderstorm winds, dense fog, and other hazards.

THE OUTLOOKS

In the graphics below, click on the link for a more detailed discussion of the outlook. To obtain the latest nearshore forecasts, and other marine products, click here.

CATEGORICAL Lake Michigan Synopsis Discussion PROBABLISTIC
Lake Michigan Lake Michigan
CATEGORICAL Lake Superior Synopsis Discussion PROBABLISTIC
Lake Superior Lake Superior

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