W&M ScholarWorks Reports 12-1979 The Chesapeake, a boating guide to weather Jon Lucy Virginia Institute of Marine Science Terry Ritter Jerry LaRue Follow this and additional works at: https://scholarworks.wm.edu/reports Part of the Atmospheric Sciences Commons, and the Oceanography Commons Recommended Citation Lucy, J., Ritter, T., & LaRue, J. (1979) The Chesapeake, a boating guide to weather. Educational series; no. 25. Virginia Institute of Marine Science, William & Mary. https://doi.org/10.21220/V5XB2Z This Report is brought to you for free and open access by W&M ScholarWorks. It has been accepted for inclusion in Reports by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. THE CHESAPEAKE: a boating guide to BATHER jon lucy, terry ritter, jerry larue 4 ·-Y•• ..~ .., ·"' . .· .,-.. :,- . .. ...~ ~ . "' .,'i ( ~.,..;, .. SEA GRANT PROGRAM Virginia Institute of Marine Science College of William and Mary Gloucester Point, Virginia Copies of this publication may be ordered for$ 1.00 each from the Sea Grant Communications Office, Virginia Institute of Marine Science, Gloucester Point, VA 23062 (804) 642-7170 THE CHESAPEAKE : a boating guide to WEATHER by Jon Lucy Marine Recreation Specialist Sea Grant Marine Advisory Services V irginia Institute of Marine Science And Instructor, School of Marine Science, College of William and Mary Gloucester Point, Virginia Terry Ritter Meteorologist in Charge National Weather Service Norfolk, Virginia Jerry LaRue Meteorologist in Charge National Weather Service Washington, D.C. Educational Series Number 25 First Pri nting - December 1979 Second Printing - August 1980 Third Print1ng - August ·193·1 Fourth Printing - March 1983 Fifth Printing - March 1984 Si x th Pri nting - Feb ruary 1986 Seven th Printing - September 1988 A Cooperative Pub lication of VIMS Sea Grant Marine Advisory Services and NOAA National Weather Se rvice Acknowledgements For their review and constructive criticism, appreciation is expressed to Messrs. Herb ert Groper, Chief, Community Preparedness Staff, Thomas Reppert, Meteorologist, Marin e Weather Services Branch and Michael Mogil, Emergency Warning Meteorologist, Pu blic Services Branch, a ll of NOAA National Weather Service Head­ quarters, Silver Spring, Maryland; also to Dr. Rollin Atwood, Marine Weather Instructor, U.S. Coast Guard Auxiliary, Flotill a 33, Kilm arnock, Virgini a and Mr. Carl Hobbs, Geo logica l Oceanographer, VIMS. Historical climatological data on Chesa­ peake Bay was provided by Mr. Richard DeAnge li s, Marin e Cli matological Services Branch, Nat ional Oceanographic Data Center, NOAA En vironmental Data Service, Washin gton, D.C. Thanks go to Miss Ann ette Stubbs of V IM S Report Center for pre­ paring manusc ript drafts and to Mrs. Cheryl Teagle of VIMS Sea Grant Advisory Services for com­ posing the fina l text. This work is a result of resea rch sponsored (in part) by the Virgini a Institute of Marine Science Institutional Sea Grant Program , supported by the Office of Sea Grant, NOAA, und er Grant Number (NA 79AA-D-00055). The U.S. Government is authorized to produce and distribute reprints for governmental purposes notwith standing any copy­ right notati on th at may appear hereon. DES IGN BY DICK COOK Contents PAGE CHESAPEAKE BAY CLIMATE . 3 GENERAL WEATHER FEATURES............... ... .. ...... .. ... 3 Winds. ........... .... .. ......... ... .. .. .... ..... ......... 3 Waves. 3 Clouds . 5 SEASONAL TRENDS, NOVEMBER THROUGH APR IL. ... ...... ..... .... 5 Fog. ......................... ... .... .. ... ............... ... 6 Co ld Air and Water Temperatures . 6 Co ld Fronts . 10 SEASONAL TRENDS, MAY THROUGH JULY. ....................... 10 Thunderstorms. 10 Lightning .. 12 SEASONAL TRENDS, AUGUST THROUGH OCTOBER . 13 Hurricanes . 15 Chesapeake Bay Hurricane Ho les. 15 Waterspouts . 17 SOURCES OF WEATHER INFORMATION AND FORECASTS . .... ... .. 17 WEATHER SERVICE WARNINGS -WHAT THEY MEAN . 20 WEATHER AND BOATING SAFETY..... ............ .. .. ... .. 20 CHESAPEAKE BAY CLIMATE to be southerly during warm months and northerl y during the cold portion of the year. However, the The climate of t he Bay is established by its many small er bays, inlets, islands and tributaries of location in mid latitudes on the eastern edge of the Chesapeake interfere with prevailing wind flow the North American continent. This location patterns, resulting in local wi nd s wh ich can differ results in winter climate being regul ated by the drasticall y from th e general pattern. polar continental influence, whil e summer is Differences in Bay water temperature and air characterized by continental tropical weather temperature influence wind directio n and speed, with infrequent invasions of cooler air. The particularly as compared to patterns over adjacent climate is tempered by marin e infl uences which land surfaces. During cooler months, the passage of most noticeably resu lt in mi lder wi nter tem­ light, warm preva iling win ds over cold water ca n peratures than those found inl and at simi lar result in reduced win ds on the Bay as compared to latitudes. winds inland, unl ess t he warm winds are strong. Fall, winter and spring are characterized by During warmer months, whenever cold air moves occasional storm systems producing wind gusts over warm Bay water, wi nd s will be stronger and of over 50 knots*, rarely up to 70 knots, about much more gusty over th e Bay than over ad jacent once a year. Such winds usually come from land surfaces, due to the unstab le situation o f cold the south, northwest or north, but abo ut once in air overl ying rising air warmed by the water. ten years strike the area from the east, causin g Another characteristic of wi nd s around the Bay unusuall y high storm surges. is the sea breeze effect. Occurring during warmer Summers are characterized by weak low pres­ months, sea breeze is caused by differences be­ sure systems rarely producing winds as high as 30 tween air temperatures over the land and water. knots. The Bay also experiences the majority of Basicall y, air warmed over heat-absorbing land its annual average of 30 thunderstorm days during areas is lighter than adjacent air over re latively summer, and these, of course, may produce th e cooler Bay water. The lighter air rises, causing the hi gher winds noted formerly. Often associated cooler air o ve r the Bay to move towards land to with cold fro nts, these storms occur most fre­ fil l the void . Sea breeze is noticeable when the two quently from May through August. air masses differ by as little as 5°F (about 3°C) and Hu rricanes are experienced in the Bay about increases as differences become greater. once every ten years, generall y coming in the latter The sea breeze effect is large ly responsible for half of th e boating season (A ugust-October) . the strong d iu rna l va riation in wind speeds over the The Bay's configuration and orientati o n signi fi ­ Bay during the boating season. When no major cantly affect wi nd and weather patterns im portant weather disturbances are governing the Bay's wind to boatmen (Fig. 1 ). The rel atively straight course patterns, winds wi ll tend to be ve r y light at night, of the Bay extends in a north-south direc ti on for increasing in strength during the late morning. nearl y 200 miles (332 kilometers) . The western Maximum winds occur in mid afternoon wh en shore of the lower Bay is cu t deeply by fi ve tri­ air mass temperatures over land and water differ butaries va ryin g 2-8 miles (3 -1 3 ki lometers) in the most, with wind speed fa lling off rapidl y at width at their mouths and exhibiting northwest dusk. Such winds are ge nerall y stronger near fetches of as much as 20-40 miles (32-64 kil o­ the shore, especiall y where shore elevations are meters). On the Bay's eastern shore the numerous high er, and at the mouths of ri vers. Normal tributaries arc ge nera ll y less significant in their summer day winds may be nea rl y calm in the dimensions. The width of the Bay is greatest in early mo rn ing and increase to approximately 15 Virgini a, where the distance between shores ranges knots by mid afternoon. As a result of the sea approximatel y 11 -27 miles (18-43 kilometers) . breeze effect, better conditions for hi gh speed The Maryland area of the Bay averages 5-10 miles boating occur in the morning, while afternoons (8-16 kil ometers) in width. generally favor sailors. GENERAL WEATHER FEATURES WAVES WIND S The state of the sea is governed primaril y by As a very general ru le, the prevailing wi nds over wi nd speed and duration, as wel l as the fetch the Chesapeake tend to foll ow its north-south (d istance) over which the wind blows. Wi nds o ri entation. Mid-channel wind s can be ex pected from the north or south have the greatest fetch • 1 knot = 1 nautic al mile per hour (mph). 1.15 mph or 1.85 ki lometers p e r hour. 3 Figure 1. Chesapeake Bay and its major tributaries. t & ~ ~ ~ ~ ~ 7 "" N oo' 0 t VA C 4 in the Bay, but northwest winds also have a con­ siderable fetch of 2040 miles (32-64 kilometers) off the mouths of any of the major western shore tributaries. The width of the lower Bay provides considerable fetch for strong westerly or easterly winds associated with major storm systems and cold fronts. Wind takes time to affect wave height and period ( time between successive waves) . Sudden wi nd in creases or changes in direction may take a l'l hour or more to produce maximum wave heights.