Advanced Shallow Weather and Orographic

Boundaries

Thunderstorm Outflows

Lake Breezes

Arc of blowing dust

Reflectivity “thin lines”

Gust Fronts

Very shallow feature, emanate from a thunderstorm. Recall the depth-detection discussion.

Example of Boundary in Reflectivity-10 to 20 dBZ

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

Drizzle

A Typical Z – RBeijing Summer

Reflectivity and DrizzleBeijing Summer

How to remember beamheight numbers?

Aside

S = r θ

• 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

r

sθ

Beam Height Diagram

What is the approximate Height / Width the Beam

0.5o beamwidth 1.0o beamwidth

Elevation Angle 0.5o 1.0o 0.5o 1.0o

Range

50 km

100 km

Arc distance = r theta 1 deg = 180 / pi = 0.01745329

Forest Fires

Kelowna Forest Fires

Nocturnal bird migration looks like drizzle

Insect migration and Cb

Lake Breezes and Tornados

Pat King and Dave Sills

Morning

Mid Afternoon“Pure” LB exampleEnhance convergence

Lake Breeze BoundariesLakeHuron Lake Ontario

LakeSt Clair

Lake Erie

+

+

=

Pure lake breeze

Moderate SW Flow

Lake Breezes

Average of 6 VIS Images from 1500-1800 UTC

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 ...

… tornadoes are suppressed in regions where Southwest winds are onshore ...

… and enhanced in regions where lake breeze boundaries often form.

Forecasters use knowledge of lake breeze positions in their severe weather forecast for weak tornadoes

Lee Side Troughing

On a very small terrain feature

Southern Ontario is relatively flat. Elevations rise from about 200m on Lake Huron to about 400m just south of Georgian Bay.

Lake

Huron

Lake Ontario

Lake Erie

Georgian Bay

Topography of Southern Ontario

Topography of Southern Ontario

Average of six GOES images over a 3-hour period

Moderate WSW flow

Dissipation of thin SC cloud in downslope flow

SC cloud formingbeneath an inversionat 1500 m above ground

Dissipation of Clouds in a SW Flow

Topography of Southern Ontario

Niagara Escarpment

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

Sea Spray

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