Figure 3d
sociated with an occlusion are mixed and Fax schedules on page 808 for times of
“pocket thunderstorms” may occur. In mid- transmissions, Internet addresses and e-mail
northern latitudes in winter, rain is likely if retrieval methods.
r
you are located east of the center of the low-
Surface Charts
pressure area associated with the occlusion.
If you are west of the center, snow is likely.
A surface analysis chart is like a weather
e
athe
Figures 3a-d depict the various stages of a
snapshot showing weather features at a spec-
W
typical developing frontal system.
ified time. A forecast chart projects into the
future—some are 12 or 24 hours ahead, oth-
Weather Charts
ers provide extended forecasts at lengthening
There are four primary types of charts is- intervals up to five days. This discussion of
r
sued by the National Weather Service (NWS): surface charts focuses on surface analysis
surface, upper air, streamline, and sea state. charts.
Within each type are analysis (current con- Every six hours (0000, 0600, 1200, and 1800 e
athe
ditions) and forecast (future conditions) GMT), the National Weather Service Marine
charts. The NWS also issues imagery from Forecast Branch produces synoptic (large-
geostationary and polar-orbiting weather area) surface analysis charts for the Atlantic,
satellites. Before and during an ocean voy- Pacific, and the Gulf of Mexico. The surface
age, you should study a variety of types of analysis charts are usually available within
charts and satellite images. The more pieces 3.5 hours of the “valid” time. These surface
r
standing W
of the weather puzzle you have, and the more charts are based on information from satel-
familiar you are with the imagery, the more lites, weather buoys, weather balloons, ship
nde
accurate your interpretation can be. reports, and observations from aircraft and
U
NWS charts are transmitted via radio as fax individuals.
images that can be received by either a dedi- Surface Analysis Format: Surface analysis
cated weather fax receiver, or with a com- charts cover a very large area so that mari-
puter equipped with a modem connected to ners can use them to plot the locations and
an SSB receiver. Additionally, the charts are tracks of many weather systems, and to show
available online and via e-mail. See Weather the systems’ locations relative to land.
Each ocean basin is shown on a Merca-
tor projection with latitude and longitude
787