Meteorology 302.01, spring 2004
Class Notes for February 16, 2004

Glenn Scott

Nate Henke

Active Weather

We review the latest 4km Visible Image

-There is a band of clouds over CA and the West Coast

-To locate rainfall, compare visible image with infrared (IR) image

We review the latest 4km IR Image

-Cold cloud tops can imply rain

We review the latest 4km IR Loop

-The loop can be set to “rock” (move forward and backward) or “loop” (run forward repeatedly)

-Clouds are collections of condensed water droplets that float in and move with the air

-The clouds are moving from the SE to the NW

-Therefore the wind in the upper atmosphere is blowing from the SE

-This relates to the Jet Stream, a fast moving ribbon of air in the upper atmosphere

We review the latest 16-KM (IR) IR Loop

-The clouds extend approximately to the Hawaiian Islands

Bay Area Winds

We view the Bay Area Winds link

-It is produced by the San Jose State University Dept. of Meteorology

-It is a map plotted with conventional arrows showing wind speed and direction

-The map shows southerly winds (S -» NW air movement) in the Bay Area

-Therefore, the nearest low pressure must be to the NW (Because air flows from high to low)

California Regional Weather Server

We view the California Regional Weather Server link:

(CA Regional Weather Server -» Sub-regions of CA -» Northern CA)

-Shows report of Northern California (both buoys and land stations)

-Wind symbols show sustained 15-25 mph. SW winds

-Rain shown at most, but not all, land stations (do not report on present weather or cloud cover)

-Pressures are higher to the SE (Fresno: coded as 229, which translates to 1022.9mb), and are lower to the NW (Livermore: 1018.1mb, Ukiah: 1014.7mb)

Surface Weather map

We review the Surface Weather Map

-There is a reading of 989.0mb off the north coast, indicating a low-pressure area

National Weather Service forecasts across the country

We view the NWS Forecasts Across the Country link

-This shows all of the forecasts produced by the NWS (unlike private meteorological forecasts found in newspapers, etc.)

-They are responsible for issuing watches and warnings for given areas

We view the San Francisco Office link

(Office located in Monterey)

-Has IR image and map of area with color- coded areas representing various advisories, watches and warnings in effect

We view the Flood Warning issued for the Sacramento River

We view the S.F. Part of the Map

-There is a table with probabilities of (measurable) precipitation

-It is 100% today and 60% tonight

-There is an urban and small stream flood advisory to the north of us

-An "Urban and Small Stream Flood Advisory" means that small creeks may overflow their banks, but there is no danger to human life

Frequently Used Graphics: 72 hour forecast

We view the 60-Hour Precipitation Total link

-PST = UTC minus 8 hours

-Colors on map indicate predicted inches of rainfall

-2½ inches predicted in S.F., 8” predicted for the coast range

-Maps are updated every 6 hours

Homework Assignment One

-Assignment is due Friday

-The typos have been corrected

Foundations of the Scientific Method

We view Foundations of the Scientific Method link

-Features quotations from Zebrowski pertaining to Determinism (P.38)

Definition: Determinism: every effect has a cause

We review the Units of Pressure link:

-The rule of thumb is deterministic

-Air moves from areas of high pressure to areas of low pressure (in the absence of other conditions)

We review the Surface Weather Map link:

-Lows (L) appear in red and highs (H) appear in blue

-The atmosphere weighs more at a high and less at a low

Definition: Weather map: a weather chart drawn for a specific level (e.g. sea level)

Pressure Features

We view the Pressure Features link:

Definition: Cyclone: area of low pressure completely encircled by at least one isobar

-Analogous to the Tahoe valley

-Do not confuse these phenomena with tornadoes, which are referred to as cyclones in Kansas

Definition: Anti-cyclone: area of high pressure completely encircled by at least one isobar

-Analogous to a mountain peak

-Wind direction is opposite that of a cyclone

Definition: Ridge: an area of high pressure not completely encircled by at least one isobar.

Storms

We review the Storm link:

-Note the term, tropical cyclone

-Tropical cyclones are also known as hurricanes

-Hurricane is a general term for severe, non-frontal synoptic scale cyclones that originate over the tropical/sub-tropical area

-West of the International Date Line, hurricanes are called typhoons

We view IR Loop of Hurricane Mitch (1998):

-At the center of the storm, there is a clear area called an Eye

-It is moving slightly north of West

-There is a ring of cumulonimbus clouds (Colored gold in the image) clustered around the eye

-The storm is moving to the NW, but the clouds are circling it counterclockwise

-In the Northern Hemisphere, cyclones spin counter-clockwise and anti-cyclones spin clockwise

-The opposite is true in the Southern Hemisphere

-There are three stages of tropical cyclone development:

1-Tropical depression

(Winds under 38 mph)

2-Tropical storm

(Winds btw 38 mph--74 mph)

(When storm is named)

3-Hurricane

(Winds greater than 74 mph)

National Hurricane Center

We view the National Hurricane Center web site:

-Currently there are no hurricanes listed

-Hurricane season normally runs from May--October

The Corriolis Effect

The Corriolis Effect causes air to spiral when it moves from high to low pressure (It does not move in a straight line)