What changes have been made to the WPC North American analysis?
There are two changes to the North American analysis. The
domain of the chart has been reduced by eliminating a portion of the analysis
over the Atlantic and Pacific Oceans. The analysis over this smaller domain
is issued approximately 15-30 minutes earlier than analyses prepared before June 3, 2003.
These changes only apply to the North American analysis. The
other charts available from the WPC web site, including the CONUS area
charts have not changed.
Why has WPC reduced the size of the North American surface analysis
The previous, larger domain for the North American surface analysis was designed
for a time when the chart was distributed by facsimile and only one chart
could be sent for each analysis time. Most users of NWS products were able
to receive only the WPC analysis and it needed to cover a wide area to
meet the needs of all users. The analysis domain and issuance time
were a compromise between the need for a wide area of coverage and a timely
analysis. NCEP now has three centers preparing surface analysis charts
over much of the Northern Hemisphere and all are available to all users.
The oceanic areas eliminated from the WPC analysis are better
served by the Ocean Prediction Center (OPC) and the National Hurricane
Center (NHC). Their later deadlines allow more observational data to be
incorporated into OPCs' and NHCs' analyses, resulting in a more accurate product.
How much data over the oceans does the analyst have available for the
preparation of the North American surface analysis?
The WPC analyst relies heavily on satellite imagery for the placement
of fronts and pressure centers over the oceans. Very few ship observations
are available by the time the WPC North American surface analysis is issued.
The National Hurricane Center and the Marine Prediction Center provide
later analyses that take into account a fuller set of observations.
What if I need an analysis covering an area larger than the North
NCEP plans to provide a composite analysis that covers the entire domain
of the analyses produced by the three NCEP centers producing surface analyses.
Why are surface analyses prepared at three different centers?
Each of the three NCEP Service Centers producing a surface analysis
has expertise in a different area. The Ocean Prediction Center (OPC)
concentrates on marine weather, the National Hurricane Center (NHC) is
the source of expertise in tropical weather, and the Weather
Prediction Center (WPC) focuses on weather over North America. Each
center brings its unique skills to the problem of surface analysis.
The preparation of the surface analysis is an important part of the forecast
process. Each center prepares the surface analysis over its own area
of responsibility as the first step in the forecast process.
How do the three NCEP analysis centers coordinate their analyses?
Until recently, each NCEP center prepared its own surface analysis independent
of the other centers. Now that each center prepares its analysis
on a computer workstation, they can exchange files and each center can
see the analyses prepared by the other centers before they are released.
If centers disagree on a feature, they can coordinate via chat software
or telephone. Through this collaboration process, the three centers
arrive at a consistent analysis.
What are the areas of responsibilities for the three analysis centers?
The Weather Prediction Center is responsible for the analysis
over North America north of 30N. The NHC is responsible for the area
south of 30N including oceans and land areas. The Ocean Prediction
Center is responsible for the Atlantic and Pacific Oceans north of 30N.
How are the analyses prepared at the three centers combined to make
the analysis products available on the web?
After the three centers have coordinated, each sends their completed
analysis to the other two centers. Each center then electronically
“clips” the analyses from the other two centers into its analysis.
A meteorologist then manually blends the analyses along the borders to
ensure a smooth fit. This process is designed so that each center
brings its particular expertise to the analysis process and each center
can issue an analysis over an area beyond its area of responsibility without
any duplication of effort.
What surface analyses are available from NCEP?
The following surface analysis charts are available from NCEP:
|Time after synoptic hours (e.g. 00 UTC)
||Surface Analysis Chart
||WPC Operational North American analysis (every 3 hours)
|2 1/2 hours
||NHC Operational Tropical analysis (every 6 hours)
||MPC Operational Marine analysis (every 6 hours)
|3 1/2 hours
||NCEP Final analysis (every 6 hours)
Why are the OPC and NHC analyses issued so much later than the WPC
The WPC analysis area is mostly over land and is covered by a dense
network of observations available within minutes of observation time. These
observations are augmented by radar and satellite imagery. The analyst
can begin the analysis within minutes of the observation time.
The Ocean Prediction Center and the National Hurricane Center cover
large areas of ocean. There are much fewer observations and it may
take several hours for these observation to reach NCEP. Furthermore,
these observations are taken by volunteer observers often under difficult
conditions and are subject to quality control. There is no radar
imagery over most of these ocean areas. Satellite data is used extensively
over the oceans, but some of the processed satellite data is not
available until hours after observation time. For these reasons, the analysts
cannot begin their analyses over the oceans until much later than the WPC
Why does the WPC issue an analysis every three hours while the OPC and
NHC issue analyses only every six hours?
The dense network of observations, radar, and satellite imagery that
form the basis for the Weather Prediction Center (WPC) analyses
are available every hour. Observations are much more limited over
the oceans, where, by international agreement, observations are only required
to be taken every six hours.
Because of the rich set of observational data over North America, the
WPC can analyze relatively small scale features, such as dry lines and
outflow boundaries. In order to track these meso-scale features,
we need to have frequent analyses. The data over the oceans do not
support that kind of detail. The analyses prepared by the National
Hurricane Center and the Ocean Prediction Center depict primarily synoptic
scale systems that are adequately tracked at six hour intervals.
Where can I find the surface analyses from the three NCEP centers?
Analyses over North America from the Weather Prediction
Analyses over the Tropics from the National Hurricane Center:
Analyses from the Atlantic and Pacific Oceans from the Ocean prediction
Why do the analyses from the various centers look different?
Each center developed their surface analysis for a different set of
customers. While the three NCEP centers collaborate to produce one
NCEP analysis, the depiction of these weather features will vary from center
The Weather Prediction Center produces a detailed analysis
over a data rich area. Most users receive the analysis in electronic
format. For these reasons, the WPC analysis is more detailed than
those produced by the other two centers and the graphics use finer lines.
The National Hurricane Center (NHC) and the Ocean Prediction Center
(OPC) provide analyses of synoptic scale features over areas with less
data. Their analyses are distributed primarily by lower resolution
radio facsimile which dictates thicker lines and less detail. The NHC and
OPC also include forecast positions for some weather features on their
analyses as an aid to shipping.
How can I contact the Weather Prediction Center?
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