Forecasting II: Exam 2

Effective Inflow Layer

Layer of the atmosphere a storm ingests air from

• Where parcels have at least 100J/kg of CAPE and less than –250J/kg of CIN

• Cyan layer on a sounding

Bunkers Storm Motion

Used to diagnose left- or right-moving supercell thunderstorms

• Draw shear vector connecting average 0–0.5km and 5.5–6 km wind vector tips

• Draw perpendicular line through centroid of hodograph

• Intersection is right-mover storm motion, the opposite is left-mover

Low/High LCL Height

• Low: large boundary layer RH

• High: small boundary layer RH

Teleconnection

A linkage between weather patterns and changes occurring in widely-separated regions of the globe

El Niño

Anomalous warming of the SSTs in the eastern tropical Pacific

• The “Niño 3.4” region is most commonly used for El Niño and La Niña assessment

La Niña

Anomalous cooling of the SSTs in the eastern tropical Pacific

• Stronger trade winds enhance upwelling of cooler water along the west coast of South America

El Niño impacts in U.S. and tropics

• Stronger subtropical jet, increase in winter precipitation across southern U.S.

• Increased shear over western Atlantic suppressed hurricane development June–August

La Niña impacts in U.S.

• Amplified flow during winter because of an increased blocking pattern over the Gulf of Alaska

• Northern U.S.: colder and stormier weather, increased frequency of cold air outbreaks

• Southern U.S.: warmer and drier conditions

Pacific Walker Circulation

Large east-west overturning cell across the tropical pacific driven by SST differences

• Neutral: convection over western Pacific, sinking air over eastern Pacific

• La Niña: intensified version of the neutral state

• El Niño: convection over eastern and central Pacific, sinking air over western Pacific

Arctic Oscillation

See-sawing pattern between pressures over the Arctic versus pressures over the surrounding midlatitudes

• Time Scale: weeks to decades

• Positive Phase: lower than average pressures in Arctic. Jet stream stays north, milder winter.

• Negative Phase: higher than average pressures in Arctic (blocking pattern). Jet stream dips, cold air outbreaks.

North Atlantic Oscillation

Pressure difference between the Icelandic Low and Azores High

• Positive = stronger pressure difference

• fewer cold-air outbreaks and decreased storminess (eastern U.S.)

• Negative = weaker pressure difference

• stronger cold-air outbreaks and increased storminess

Pacific-North American Pattern

A pattern of air pressure anomalies at four locations over the Pacific Ocean and North America

• Positive = high west, low east

• Negative = low west, high east