Marine Weather Forecasting The United States Power Squadrons® Webinar/Seminar Guide 2011 Copyright USPS® Acknowledgements The Marine Environment Committee gratefully acknowledges NOAA’s continuing support of the United States Power Squadrons® weather education mission and its contributions to this Webinar/Seminar Guide including: • The Mariners Weather Log article – Mariner’s Guide to the 500 – Millibar Chart – co-authored by Joe Sienkiewicz (NOAA/NWS) and Lee Chesneau (Lee Chesneau’s Marine Weather), and • Images from NOAA/NWS’s weather web pages, including the images used on the cover. The committee appreciates very much the contributions of Stf/C Robert F. Anderson, AP, an Assistant Chair of the Committee, who originated the idea for this Seminar/Webinar and did much of the work in putting it together. We also gratefully thank the Chairperson, R/C S. Patricia Greer, SN, and members, of the Publications Support Committee who reviewed and formatted this Guide for publication. R/C Ronald Kessel, SN Marine Environment Committee, Chairman The following are registered trademarks and service marks of the UNITED STATES POWER SQUADRONS® AMERICA’S BOATING COURSE PARTNER IN COMMAND AMERICA’S BOATING CLUB SEA VESTER DESIGN (Cartoon caricature) BOAT SMART and Design THE ENSIGN BOATING IS FUN --- WE’LL SHOW YOU HOW THE ENSIGN (Stylized) CHART SMART THE UNITED STATES POWER SQUADRONS and Design ENSIGN FLAG DESIGN UNITED STATES POWER SQUADRONS ENSIGN FLAG DESIGN IN A SHIP’S WHEEL USPS JET SMART USPS UNIVERSITY PADDLE SMART WATER SMART FROM THE START THE UNITED STATES POWER SQUADRONS® also owns the USPS AQUA TRADE DRESS OF ITS SEVERAL PUBLICATIONS (Left side of front covers, including text and graphics) One or more of these trademarks or service marks may be found in this publication. Copyright 2011, United States Power Squadrons All rights reserved Printed in the United States of America United States Power Squadrons 1504 Blue Ridge Road P.O. Box 30423 Raleigh, NC 27622 Voice: (919) 821-0281 1-888-FOR-USPS (367-8777) Fax: (919) 836-0813 www.usps.org This publication is designed to provide general information on boating safety, piloting, and navigation. It was prepared by the United States Power Squadrons and its members, and is sold with the understanding that professional nautical services are not being provided. Do not use this publication as a substitute for original sources of nautical information, including government publications, rules, regulations, laws, and manufacturers’ recommendations, where appropriate. The subject matter of this publication is likely to become outdated over time, and may have changed since our last publication date. Consequently, you must research original sources of authority to update this material and ensure accuracy when dealing with specific “on the water” conditions or boating problems. Marine Weather Forecasting Webinar/Seminar Guide “ I must go down to the seas again, to the lonely sea and the sky…” John Masefield These familiar words of John Masefield capture some of the wonder and fear that the sky and the sea can evoke. It is no surprise that ever since mariners set out to sea they all shared the same awe and fear. The sails and courses they set, their livelihoods, and even their lives were weather dependent. The effect of weather on the sea always was for them, and still is for us, a vital concern. The Marine Weather Forecasting webinar deals with these same ages‐old concerns, but in a modern way taking full advantage of today’s meteorological advances and presenting a seminar via the Internet as a webinar. Marine Weather Forecasting has been designed with coastal and offshore cruisers in mind, but it will also be of interest to all boaters and those generally fascinated by the weather. Seminar topics include: Review of Surface Maps and Winds Upper‐Air Winds and Charts The 500 mb Chart GRIB Forecasts NWS Marine Weather Forecasts. The 500 mb chart is a major important tool in forecasting the weather for those in coastal/offshore areas as well as those on the high seas. It is no accident that understanding and interpreting this upper air chart is a major focus of the webinar. In addition to this Webinar/Seminar Guide participants will be able to download in pdf format the classic article co‐authored by Joe Sienkiewicz and Lee Chesneau: Mariner’s Guide to the 500‐ Millibar Chart. Webinar participants reviewing the intricacies of the 500 mb chart are encouraged to read this article. The illustrations will be easier to see and the more detailed explanations accompanying them will be particularly helpful. This guide consists of slide images and complete notes that cover all the webinar subjects. There may be some minor differences from the slides the presenter selects for the actual webinar presentation, but they will not be major ones. This Webinar/Seminar Guide with its images and notes will serve as a review and will be a useful reference for years to come. Marine Weather Forecasting 1 Slide 1 Welcome to Marine Weather Forecasting This seminar is presented by: • The United States Power Squadrons® (USPS) • USPS is a non‐profit educational organization made up of 450 individual squadrons throughout the US and the Caribbean. • This seminar on Marine Weather Forecasting is only one of many USPS courses and seminars designed for the recreational boater. • Other subjects include seamanship, piloting, navigation, engine maintenance and marine electronics. • The National Oceanic and Atmospheric Administration (NOAA) and its National Weather Service (NWS) • The National Weather Service provides weather, hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas. • Its products are used by both government entities and the private sector. • The NWS accomplishes this mission through a collection of national and regional centers, and 122 local weather forecast offices. • The NWS collects meteorological data from all over the globe. Slide 2 Acknowledgements • The United States Power Squadrons® gratefully acknowledges NOAA’s continuing support of the USPS weather education mission and its contributions to this webinar: • The Mariners Weather Log article – Mariner’s Guide to the 500 – Millibar Chart – co‐authored by • Joe Sienkiewicz (NOAA/NWS) • Lee Chesneau (Lee Chesneau’s Marine Weather) • Content from NOAA/NWS’s weather web pages • The webinar’s NWS Instructor Slide 3 Seminar Instructor • Joseph Sienkiewicz Chief ‐ Applications Branch Science and Operations Officer Ocean Prediction Center NOAA National Weather Service USPS University Series 2 Marine Weather Forecasting Slide 4 Seminar Materials • Mariner’s Guide to the 500 – Millibar Chart article– co‐ authored by Joe Sienkiewicz (NOAA/NWS) and Lee Chesneau (Lee Chesneau’s Marine Weather) appearing in the December 2008 issue of the Mariners Weather Log (Vol. 52 No.3). • The article contains a more detailed explanation of the 500 mb chart and the slides relating to it. • It is available to the public at no cost and can be downloaded at: www.vos.noaa.gov/MWL/dec_08/milibar_chart.shtml • Where the slide notes contain references to figures, the references are to the illustrations in the Mariner’s Guide to the 500 – Millibar Chart. • Marine Weather Forecasting Seminar Guide prepared for this webinar. • The guide contains thumbnail images of the slides in this presentation together with notes for each slide. • The images, however, are smaller than the same 500 mb chart images in the article. • The guide is available only to webinar participants at no extra cost and can be downloaded at www.usps.org/eddept/webinars/wx/wx_forecasting_guide.pdf Slide 5 Seminar Focus • Coastal and Offshore Marine Forecasting • Topics: • Review of Surface Maps and Winds • Upper‐Air Winds and Charts • The 500 mb Chart • GRIB Forecasts • NWS Marine Weather Forecasts Slide 6 Seminar Topic Review of Surface Maps and Winds USPS University Series Marine Weather Forecasting 3 Slide 7 Surface Weather Maps Surface Weather Maps show: • High – an area of comparatively high pressure with winds spiraling out • Low – an area of comparatively low pressure with winds spiraling in • Trough – an elongated region of comparatively low pressure • Ridge – an elongated area of comparatively high pressure • Front – the boundary between two air masses of different temperatures • Isobar – a line of equal pressure drawn on a weather map Slide 8 Surface Weather Map Symbols • Pressure Regions • Highs are designated with a blue H. • Lows are designated with a red L. • Troughs are designated with a tan dashed line. • There are four main types of fronts (boundaries) between two air masses. • Warm: advancing surface front with warm air mass behind it depicted by red domes. • Cold: advancing surface front with cold air mass behind it depicted by blue triangles. • Stationary : a surface front that is not moving depicted by alternating red domes and blue triangles on opposite sides. • Occluded: a front where warm and cold air masses meet above the surface depicted by domes and triangles on the same side usually colored purple. • Dry Line: a front that separates warm dry and warm wet air masses depicted by gold domes on the same side. Dry lines occur over the plains. Slide 9 Isobars • Isobars (line of equal pressure) are normally drawn at 4 mb intervals with 1000 mb being the base value. • The isobars are drawn on a “best fit” basis and smoothed to make the map more readable. • The patterns of isobars are useful in forecasting weather and identifying weather systems. • This weather map clearly shows different weather systems: • Low pressure systems where the weather is usually foul; and • High pressure systems where the weather is usually fair. USPS University Series 4 Marine Weather Forecasting Slide 10 Surface Analysis (Fig. 1) • This surface analysis shows the features of a typical surface weather map: • highs; • lows; • troughs; • fronts (warm, cold, stationary, and occluded); and • isobars. • It adds • red and blue Xs – 24 hr forecast positions of lows and highs • ship observations; and • a satellite overlay.