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22Wxhzd&Polar Lows Lecture 22 Weather Hazards Weather Hazards in Winter Storms and Polar Lows Polar low seen in an infrared image from a polar orbiting satellite Hazards associated with Midlatitude Cyclones 1 2 Weather Hazards Winter Storm - Hazards • High Winds – Nor’easter, Blizzard Conditions, Turbulence • Frozen Precipitation Blizzard – Blizzard Conditions, Snow, Sleet and Freezing High winds Sleet and ZR Rain, Aircraft Icing, Riming, Snow Avalanches • Heavy Rain Severe T-storms Tornados – Flooding, Flash Floods, Mud Slides High winds • Large Ocean Swell and Waves – High Surf, Storm Surge • Severe Thunderstorms – Tornados, Large Hail, High Winds, Lightning Where are the hazards? 3 4 High Winds Where do the Hazards Occur? Where do we find the strongest winds in a midlatitude cyclone? Blizzard conditions occur N and NW of • Surface surface-low center. – Where the pressure gradient is largest, often on NW side of storm. – Near convective clouds (including tornados) – Near the fronts Nor’easters • Upper Air • Strong low pressure systems moving up – Where the pressure gradient is largest Atlantic seaboard – In pulses superimposed on the jet stream • Strong winds and heavy – these pulses are sometimes called jet streaks precipitation (blizzards). – turbulence is found near jets in regions of large wind shear 5 6 Hazards – High Winds Precipitation Patterns Radar View of Precipitation Where does air rise • Along the fronts • In areas of convection • Around surface the low center 7 8 Hazards – Sleet and Freezing Rain Hazard – Freezing Rain The Rain – Snow Line • North of the warm front there is a transition from rain to snow called the rain- snow line. Kansas City, MO, January 31, 2002. • Freezing rain and sleet fall on the warm Frozen precipitation causes side of this line. significant disruption of transportation and resulting economic impact. 9 10 ‘93 Blizzard Freezing Rain Television Tower Raleigh, NC January 1990 Blizzard conditions include heavy snowfall and blowing snow with strong winds. Note the tight spacing of isobars at left. 11 12 Hazards – Blizzard Hazards – Heavy Snow Blizzard conditions include winds !35 mph and visibility less than 1/4 mi. Snowstorms leave a band North Dakota: A March 1966 blizzard of heavy snow in their wake. nearly buried utility poles. 13 14 Hazards – Heavy Snow Hazard – Snow Avalanche Death in blizzards comes from exposure to cold. Western U.S. mountains generally record over 100,000 avalanches every winter. Some avalanche slides can reach speeds of over 100 miles per hour . 15 16 Hazard – Snow Avalanche Hazards – Heavy Rain and Flooding An ice storm in New York In US roughly 25 deaths also caused flooding of per year due to snow water front properties in avalanches. the region, January 1998. 17 18 Hazards – Heavy Rain and Flooding Hazards – Large Waves Oahu, North Shore January 1998. Flash floods often cause Peggotty Beach, Massachusetts fatalities by drowning February 9, 1978 when people try to drive across flood waters. Oahu flood, November 1995 19 20 Hazards – Large Swell Hazards – Severe Thunderstorms Surf's up! Heavy surf on the Columbia River bar tests a Coast Guard Large Hail vessel approaching the mouth of Tornados the Columbia River. High Straight-line winds 21 22 Where do the Hazards Occur? Weather Hazards in Winter Storms Severe Thunderstorms Produce: • Tornados Severe Thunderstorms • Large Hail associated with a cold • High Straight-line Winds front. (and Lightning) Occur where jet stream crosses the cold front. 23 24 Questions? What is a Polar Low? A small-scale (typically 200-300 mi in diameter) cyclone that forms in a cold air mass poleward of major jet streams or frontal zones. Blizzard High winds Sleet and ZR Severe T-storms Tornados High winds Three areas with distinct hazards in winter storms. 25 26 Small Scale Polar Low Characteristics Polar low seen in an infrared image • Non-polar frontal low-pressure systems from a polar orbiting satellite • Cyclonic wind circulation (in Northern Hemisphere) • Anticyclonic outflow at upper levels • Warm Core • Winds decrease with height • Vertical structure, spiral or symmetric about clear "eye" • Sensible and latent heat from the ocean primary energy source • Formation over high latitude oceans adjacent to snow or ice covered surfaces NOAA-5 infrared satellite photograph of a polar low over the Bering Sea and Bristol bay; at 21:27 GMT on 19 January 1979. 27 28 Forecast Challenge Weather Related Hazards: • High winds (up to 90 kt observed) • Large waves and swell • Low visibility, heavy snow, icing of ships • Thunderstorms and in some cases tornados Polar Low over the Barents Sea area at 0240 UTC 13 December 1982. • Small scale - 200 - 300 mi in diameter • Data sparse habitat - over high latitude oceans • Rapid development - ~12 hour spin up 29 30 Form to the North and West Comma Clouds of the Polar Front Polar lows do not form on the polar front Schematic Model 31 32 Comma Cloud a) Schematic depiction of a series of developing comma clouds forming within a 500 mb cold-core low (L). b) NOAA-7 infrared- satellite image at 1508 PST, 16 January 1982, showing high clouds associated with the incipient comma cloud Case 1 and a mature comma cloud that preceded it. This one produced tornados in CA! 33 34 Schematic Model Schematic Model 35 36 Prerequisites for Formation Schematic Model • Cold temperatures in the upper troposphere • Air passing from snow or ice covered surface over the open ocean leading to enhanced surface sensible and latent heat fluxes • Curved flow (large vorticity or spin) at the surface and aloft 37 38 Prerequisites for Formation Habitat Polar Low Climatology Paths of polar lows over the Norwegian Sea 1978-1982. Closed Sea-surface temperature and extent of the ice edge circles indicate point of origin, open circles indicate final position. (shaded area) for 9-12 February 1984 39 40 Polar Low Habitat Polar Low Climatology Mean sea-surface temperature (°C) and extent of the ice edge (heavy dashed line) for the Bering Sea and the North Pacific Ocean; Histogram of the number of days per month on which polar lows 20 year mean (1957-1978) for January. were observed in polar-orbiting satellite imagery over the Gulf of Alaska or the Bering Sea during the period 1975-1983. 41 42 Polar low and cloud streets over the Barents Sea: NOAA-7 Polar Low over the Norwegian Sea area at 1340 UTC infrared satellite photograph for 0320 GMT, 22 November 1983 27 February 1984. 43 44 Polar Low over the Norwegian Sea area at 1340 UTC Sea-level pressure analysis of Polar Low over the 27 February 1984. Norwegian Sea area at 1340 UTC 27 February 1984. 45 46 Polar Lows over Mediterranean Sea Polar Low in Southern Hemisphere Polar lows are sometimes called extra tropical hurricanes. NOAA-6 enhanced infrared-satellite photograph of a polar low 25 January 1982 near the ice edge just west of the Palmer Peninsula, Antarctica 26 January 1982 at 18:25 GMT on 15 march 1985. 47 48 NOAA-5 infrared satellite photograph of a polar low and cloud NOAA-4 infrared satellite photograph of polar low and cloud streets over the Bering Sea at 22:24 GMT on 23 January 1979. streets over the Gulf of Alaska at 20:21 GMT on 22 March 1975. 49 50 Summary Questions? • Conditions favorable to Polar Low Development – Strong cold air advection over water. – Cold temperatures at 500 mb - unstable air • Forecast Challenge – Small scale - subsynoptic – Data sparse habitat - over high latitude oceans – Rapid development - ~12 hour spin up • Weather Related Hazards – High surface winds (up to 90 kt observed) – Large waves and swell – Low visibility, heavy snow, icing of ships – Thunderstorms and in some cases tornados Why can’t I show you a nice satellite loop of a polar low? 51 52.
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