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Advanced Shallow Weather and Orographic. Boundaries. Thunderstorm Outflows Lake Breezes. Gust Fronts. Very shallow feature, emanate from a thunderstorm. Recall the depth-detection discussion. Reflectivity “thin lines”. Arc of blowing dust. Example of Boundary in Reflectivity -10 to 20 dBZ.
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Boundaries Thunderstorm Outflows Lake Breezes
Gust Fronts Very shallow feature, emanate from a thunderstorm. Recall the depth-detection discussion. Reflectivity “thin lines” Arc of blowing dust
Rapid Storm Evolution (Time lapse < 5 hours) Animation 120 km
Movie Loop Showing Cold Front, Gravity Wave and Dry Line Interactions International H20 Water Vapor Project (IHOP) May 11, 2002
Gravity Waves International H20 Water Vapor Project (IHOP) May 11, 2002
S = r θ s θ r • 1o = 180/pi = 0.0175 radians • At r=100 km then s = 100 * 0.0175 • S = 1.75km = beamwidth at 100km • For flat Earth, for beam at 1o elevation angle, height of beam centre ~= 1.75km H = sqrt ( r^2 + 2*Ke*ae*r + sin ( theta_e ) ) – ke * ae
What is the approximate Height / Width the Beam Arc distance = r theta 1 deg = 180 / pi = 0.01745329
Pat King and Dave Sills Lake Breezes and Tornados
Lake Breeze Boundaries Lake Huron Lake Ontario Lake St Clair Lake Erie Mid Afternoon “Pure” LB example Enhance convergence Morning
Lake Breezes + + = Pure lake breeze Moderate SW Flow
Spring (15 Mar - 15 Jun) Tornado Touchdown Points Confirmed and probable only
Spring (15 Mar - 15 Jun) Tornado Touchdown Points … overlaid with boundaries from 31 July 1994 ... Forecasters use knowledge of lake breeze positions in their severe weather forecast for weak tornadoes … tornadoes are suppressed in regions where Southwest winds are onshore ... … and enhanced in regions where lake breeze boundaries often form.
Lee Side Troughing On a very small terrain feature
Topography of Southern Ontario Georgian Bay Lake Huron Lake Ontario Southern Ontario is relatively flat. Elevations rise from about 200m on Lake Huron to about 400m just south of Georgian Bay. Lake Erie
Dissipation of Clouds in a SW Flow Moderate WSW flow Dissipation of thin SC cloud in downslope flow SC cloud forming beneath an inversion at 1500 m above ground Topography of Southern Ontario Average of six GOES images over a 3-hour period
Niagara Escarpment Topography of Southern Ontario Average of six GOES images over a 3-hour period
20 February, 2008 2008 NWA Conference - Louisville, KYSam Lashley – National Weather Service Northern IndianaJon Hitchcock – National Weather Service Buffalo, NY
Mountain Top Radars Show Rodger Brown Paper graphs
Negative Elevation Scans Show DEM and the one degree beam Show negative elevation angle Discuss caveats – need gc filtering Need 3dB filling Show
Scanning in Complex TerrainValley Radars Show the v10 radar DEM and discuss with respect the weather NOT surveillance
Radar Detection Issues CAPPI (too high) 0o PPI
Lake Breezes and Convection Initiation/Suppression • Review the wilson boundary rules/Aurora did a poster on this • Show Pat King Lake Breeze and Prevailing Wind Analysis • Show Pat King Tornado climatology and Lake Breezes • Show AF358 or another case
Lake Effect Snow Bands Show the EGPM lake effect snow bands Show single bands Show multiple bands Show the convergence in the middle of the band Talk about TREC tracking
Orographic Effects Precipitation Enhancement upslope condensation and development Precipitation Suppression lee side troughing Blocked flow Radar Blockage – can not see Explanation Impact of Froude Number