A surface chart (also called surface map or sea level pressure chart) is an analyzed chart of surface weather observations
Surface Analysis Charts are computer-generated charts with frontal and pressure analysis issued from the Weather Prediction Center (HPC) at https://www.wpc.ncep.noaa.gov/html/sfc2.shtml
Surface Analysis Charts:
Surface Analysis Chart
Surface Analysis Charts provide a snapshot for regional/cross-country flights, providing:
An isobaric (lines of equal pressusure are isobars) analysis showing identifiable, organized pressure patterns
Also includes the positions of highs, lows, ridges, and troughs, and the location and character of fronts and various boundaries, such as drylines, outflow boundaries, and sea breeze fronts
A variety of charts are created for various regions that provide varying number of overlays
Additionally, they provide a look across the country as to where weather patterns are located and how they have developed
A trough of low pressure with significant weather will be depicted as a thick, dashed line running through the center of the trough and identified with the word "TROF"
The symbol for a ridge of high pressure is very rarely, if at all, depicted
Notes:
The observations from various stations are plotted
These are referred to as station models
Round station symbols indicate observations taken by an observer
Square station symbols indicate the sky cover was determined by an automated machine
Models appearing over water are data from ships, buoys, and offshore oil platforms
An outflow boundary will be depicted as a thick, dashed line with the word "OUTBNDY"
A dry line will be depicted as a line with unshaded pips or a through symbol identified with the words "DRY LINE"
Pressure is plotted in tenths of millibars, with the leading 10 or 9 omitted
A legend is printed on each chart stating is name, valid date, and valid time
Frontal & Pressure Markings:
Trough:
Trough
An elongated area of relatively low atmospheric pressure; the opposite of a ridge
On HPC's surface analyses, this feature is also used to depict outflow boundaries
Dry Line:
Dry Line
A boundary separating moist and dry air masses
It typically lies north-south across the central and southern high Plains states during the spring and early summer, where it separates moist air from the Gulf of Mexico (to the east) and dry desert air from the southwestern states (to the west)
Squall Line:
Squall Line
a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms
Tropical Wave:
Tropical Wave
A trough or cyclonic curvature maximum in the trade wind easterlies
Frontal Change:
Frontal Change
A hash mark denotes a change in frontal type
The hash mark will always be drawn perpendicular to the boundaries
They are not drawn at "triple points" (the intersection of an occluded, cold and warm or stationary front) and where a low pressure center separates the different frontal types
Frontogensis:
Frontogensis
Refers to the initial formation of a surface front or frontal zone
Depicted on HPC's surface analysis and forecast charts as a dashed line with the graphical representation of the developing frontal type (the blue triangle for cold fronts, the red semicircle for warm fronts, etc...) drawn on each segment
Frontolysis:
Frontolysis
the dissipation or weakening of a front
depicted as a dashed line with the graphical representation of the weakening frontal type drawn on every other segment
Station & Ship/Buoy Plot Models:
Station Plot Models
Ship/Buoy Plot Models
Regional surface analysis chart products provide station plot models [Figure 9/10]
Land, ship, buoy, and C-MAN stations are plotted on the chart to aid in analyzing and interpreting the surface weather features
These plotted observations are referred to as station models
Some stations may not be plotted due to space limitations; however, all reporting stations are used in the analysis
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