Transcript Sequential Weather Maps

Sequential Weather Maps
Over the USA for Eight Days
in January 2008
Assembled by
Ken Mitchell
Livermore TOPScience
Surface Map - January 12, 2008
Surface Map – January 13, 2008
January 14, 2008
January 15, 2008
January 16, 2008
January 17, 2008
January 18, 2008
January 19, 2008
How to Read a Surface Map
Surface maps depict the large-scale elements of the weather.
These elements include high and low pressure systems, cold
and warm fronts, and precipitation areas.
Cold Front
A cold front is the leading edge of an advancing cold air mass that
is under running and displacing the warmer air in its path.
Generally, with the passage of a cold front, the temperature and
humidity decrease, the pressure rises, and the wind shifts (usually
from the southwest to the northwest in the Northern Hemisphere).
Precipitation is generally at and/or behind the front, and with a
fast-moving system, a squall line may develop ahead of the front.
Warm Front
A warm front is the leading edge of an advancing warm air mass
that is replacing a retreating relatively colder air mass.
Generally, with the passage of a warm front, the temperature and
humidity increase, the pressure rises, and although the wind
shifts (usually from the southwest to the northwest in the
Northern Hemisphere), it is not as pronounced as with a cold
frontal passage.
Precipitation, in the form of rain, snow, or drizzle, is generally
found ahead of the surface front, as well as convective showers
and thunderstorms.
Fog is common in the cold air ahead of the front. Although
clearing usually occurs after passage, some conditions may
produce fog in the warm air.
Low Pressure System
A low pressure system is an area of relative pressure minimum
that has converging winds and rotates in the same direction as
the earth.
This is counterclockwise in the Northern Hemisphere and
clockwise in the Southern Hemisphere.
Stormy weather is often associated with low pressure systems.
High Pressure System
A high pressure system is an area of relative pressure
maximum that has diverging winds and a rotation
opposite to the earth's rotation.
Fair weather is typically associated with high pressure.