Marine Weather Primer

Transcription

1 1 of 73 Marine Weather Primer Mark A. Thornton LakeErieWX: Marine Weather Education and Forecasting Resources

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3 3 of 73 Marine Weather Seminars & Workshops Learn a little meteorology and reduce some of the uncertainty of coastal and offshore boating... Great Lakes Basic Marine Weather Seminar Great Lakes Wind Forecasting: A Workshop For Sailors Coastal and Offshore Marine Weather Preparing Your Mac Forecast: A Workshop For Sailors

4 4 of 73 Marine Weather Dashboards

5 5 of 73 Weather and Boating Three Steps To Safer Boating 1. Basic understanding of meteorology. 2. Understand the forecast before your outing begins. 3. Monitor the weather while underway and remain alert for rapidly changing conditions.

6 6 of 73 Weather and Boating Three Steps To Safer Boating 1. Basic understanding of meteorology. 2. Understand the forecast before your outing begins. 3. Monitor the weather while underway and remain alert for rapidly changing conditions.

7 7 of 73 Basic Meteorology Low Pressure Systems

8 8 of 73 A Typical Low Pressure System

9 9 of 73 Low Pressure Systems and Weather Temperature Changes Fog Wind Shifts Strong, Gusty Winds High Waves Thunderstorms, Tornadoes, Waterspouts

10 10 of 73 Frontal Boundaries

11 11 of 73 Stationary Fronts Stationary Fronts a boundary with less than five knots of forward movement. Can promote widespread cloudiness and prolonged precipitation. Can also be a focal point for the development of severe weather.

12 12 of 73 Cold Fronts Cold Fronts a boundary between colder and drier air and warmer, moister air. Temperature and moisture differences can be significant. On average, a cold front moves forward at approximately 20 knots. Shifty and gusty wind conditions along and behind the front. Very often a focal point for the development of thunderstorms and squall lines due to dynamic lift and wind shear.

13 13 of 73 Warms Fronts Warm Fronts boundary between warm, moist subtropical air and cooler, maritime polar air. Warm front is less steep (in cross-section) than a cold front. Warm fronts typically progress forward at around 10 knots. The lifting of warm moist air over the boundary may result in a stratus cloud deck and persistent rain. Can be a source of elevated thunderstorms, but the risk of tornadoes is limited.

14 14 of 73 Basic Meteorology Forces Controlling The Wind

15 15 of 73 The Flow Associated With Surface High and Low Pressure Clockwise & Outward Counterclockwise & Inward

16 16 of 73 Wind Speed & Pressure Gradient

17 17 of 73 Fluids Flow From HIGH Pressure to LOW Pressure

18 18 of 73 The Pressure Gradient Force 1015 mb High minus 1005 mb Low = 10 Millibar Difference 1015 mb High minus 1000 mb Low = 15 Millibar Difference High High Low Low 500 Miles 500 Miles High Low High Low Wind Speed 50% Stronger

19 19 of 73 Isobars - Pressure Gradient On A Weather Map Contours of equal barometric pressure. Typically plotted at 4 mb intervals. H L H H H

20 20 of Pressure Gradient Force October 26,

21 21 of 73 Low Pressure Systems Wind Direction By Quadrant

22 22 of 73 Above Of The Warm Front L

23 23 of 73 L Below The Warm Front

24 24 of 73 L Ahead Of The Cold Front

25 25 of 73 Behind The Cold Front L

26 26 of 73 Basic Meteorology Thunderstorms

27 27 of 73 The Warm Sector Beware Of Thunderstorms The Warm Sector

28 28 of 73 Definitions Are Important! Severe Thunderstorms- According To The NWS NWS Severe thunderstorm thresholds: Hail >= 1 Surface wind gust >= 50 kts The storm produces at least one tornado The potential of reaching severe status increases as the duration of the storm increases.

29 29 of 73 The Thunderstorm Life Cycle Stages of Development -- Summary A single cell may pass from the cumulus to the dissipating stage in sixty minutes. Not all cumulus columns reach the mature stage due to a lack of instability or moisture. Warning -- lightning may occur several miles ahead of the approaching storm.

30 30 of 73 Thunderstorm Types

31 31 of 73 Single cell storms are characterized by a single, nonrecurring updraft and downdraft. The garden variety summer thunderstorms that tend to build and dissipate quickly (typically 1 hour or less). Also called pulse, pop-up, or air-mass storms. Generally form in response to localized instability in the absence of synoptic frontal boundaries and weak wind shear. Capable of producing severe weather. Single Cell Storms

32 32 of 73 Multi-Cellular Storm Systems Multi-cellular thunderstorms are those storms where cells in various stages of development coexist in a cluster. The outflow boundaries from mature cells contribute to the cumulus stage of development by acting as mini cold fronts. This is the most common form of thunderstorm development and is responsible for most severe weather reports around the Great Lakes. A multi-cellular thunderstorm cluster may persist for several hours and contain severe thunderstorms squall lines are an excellent example. Squall Line Cluster or Complex

33 33 of 73 Thunderstorm Downdrafts A Significant Hazard To Boaters

34 34 of 73 Thunderstorm Downdrafts Wind from a thunderstorm downdraft (outflow) can be quite strong 100 kts (microburst & macrobursts). May come from a direction that is very different from the large-scale wind.

35 35 of 73 The Direction Of A Downdraft Is Unpredictable

36 36 of 73 The Direction Of A Downdraft Is Unpredictable

37 37 of 73 Thunderstorm Motion

38 38 of 73 Determining Storm Motion Don t trust the speed and direction of the surface wind to judge motion of storm systems. Storms are typically steered by the winds in a deep layer (to 6 km) of the atmosphere. Doppler radar is an effective method of monitoring storm motion. 50 kts 20 kts

39 39 of 73 Thunderstorm Development Is Difficult To Predict

40 40 of 73 Weather and Boating Three Steps To Safer Boating 1. Basic understanding of meteorology. 2. Understand the forecast before your outing begins. 3. Monitor the weather while underway and remain alert for rapidly changing conditions.

41 41 of 73 The Best Weather Forecasting Resources On The Web The National Weather Service

42 42 of 73 WPC Issues Surface Forecasts To Seven Days

43 43 of 73 WPC Issues Surface Forecasts To Seven Days 12-Hour 24-Hour 36-Hour 48-Hour

44 44 of 73 Forecasting Thunderstorms

45 45 of 73 Thunderstorm 4-Hour Intervals 7 am to 11 am 11 am to 3 pm 3 pm to 7 pm 7 pm to 11 pm

46 46 of 73 Assessing The Risk of Thunderstorms NWS Hazardous Weather Outlook HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 449 AM CDT SAT AUG THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS... NORTHEAST ILLINOIS AND NORTHWEST INDIANA..DAY ONE...TODAY AND TONIGHT. WEATHER HAZARDS EXPECTED: SCATTERED THUNDERSTORMS...THE STRONGEST MAY PRODUCE: HAIL TO ONE INCH. STRONG DAMAGING WIND GUSTS IN EXCESS OF 60 MPH. LOCALLY HEAVY RAINFALL. AREAS AFFECTED AND TIMING: THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS WESTERN ILLINOIS THIS AFTERNOON AND CONTINUE EAST THROUGH ALL OF NORTHEAST ILLINOIS AND NORTHWEST INDIANA LATE THIS AFTERNOON INTO THE EVENING AND OVERNIGHT HOURS. THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS NEARSHORE WATERS OF LAKE MICHIGAN AND THE INDIANA NEARSHORE WATERS OF LAKE MICHIGAN..DAY ONE...TODAY AND TONIGHT. THUNDERSTORMS ARE LIKELY THIS EVENING AND TONIGHT WITH SOME POTENTIALLY PRODUCING WINDS IN EXCESS OF 50 KNOTS.

47 47 of 73 Marine Forecast

48 48 of 73 National Weather Service - Chicago Offshore and Nearshore Marine Forecast

49 49 of 73 A Page For Each Lake Forecast Graphics In 3-Hour Increments To 84 Hours National Weather Service Wind Speed and Direction Wind Gust Wave Height Wave Period

50 50 of 73 Wind Speed / Direction In 3-Hour Increments

51 51 of 73 Wind Speed / Direction In 3-Hour Increments Stepping Through Time

52 52 of 73 Wind Gusts In 3-Hour Increments

53 53 of 73 Wind Gusts In 3-Hour Increments Stepping Through Time

54 54 of 73 Wave Heights In 3-Hour Increments

55 55 of 73 Wave Heights In 3-Hour Increments Stepping Through Time

56 56 of 73 Weather and Boating Three Steps To Safer Boating 1. Basic understanding of meteorology. 2. Understand the forecast before your outing begins. 3. Monitor the weather while underway and remain alert for rapidly changing conditions.

57 57 of 73 A Digital Barometer A Valuable Resource

58 58 of 73 Watch The Pressure Trend It is the trend, not the absolute value, of barometric pressure that is important. Falling barometric pressure may signal the potential arrival of inclement weather. The steepness of the decline in pressure can provide clues to the strength of the approaching system an accurate barometer will monitor changing conditions.

59 59 of 73 VHF Radio Marine Forecasts Marine Observations/NDBC Buoy Reports Severe Weather Watches/Warnings

60 60 of 73 Always Use The NWS Weather Channel Closest To Your Location Best Reception Watches/Warnings For Your Location.

61 61 of 73 Keeping An Eye To The Sky - Cloud Characteristics Clouds in stable environments tend to be wider than they are tall due to weak upward motion. Clouds in unstable (thunderstorm) environments are typically taller than they are wide due to stronger upward motion.

62 62 of 73 Oh No, Your Forecast Has Gone Awry!

63 63 of 73 National Weather Service NWS Weather Forecast Offices Severe Weather Watches and Warnings Marine Weather Warnings

64 64 of 73 NWS Marine Forecast Zones

65 65 of 73 Understanding Doppler Weather Radar

66 66 of 73 How Radar Works Radar stations transmit pulses of energy within the microwave portion of the electromagnetic spectrum. A very small portion of this transmitted energy is backscattered by objects toward the station s antenna. The station spends 59 minutes 53 seconds of each hour measuring backscattered energy (listening). Rain, snow, hail, etc., all backscatter radar pulses, but so do planes, birds and insect swarms.

67 67 of 73 Beam Curvature & Earth Curvature = Absence of Radar Data

68 68 of 73 Doppler Weather Radar-Reflectivity Base Reflectivity Composite Reflectivity Base Reflectivity Composite Reflectivity

69 69 of 73 The Earth Throws A Curve Ball The curvature of the Earth results in an ever-increasing beam elevation as distance from the site increases. Low levels storms at a distance from the radar site may not be properly sampled.

70 70 of 73 Use The NWS Radar Station Closest To The Weather Feature You Are Concerned About.

71 71 of 73 Warning: Radar Images Are Not Live! Images Are Refreshed At 4 to 5 Minute Intervals

72 72 of 73 On Your ipad or iphone RadarScope Base Reflectivity With NWS Warnings and Lightning

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