Surface Analysis Charts and Graphical Forecasts for Aviation: How to Read Modern Aviation Weather Charts

Nathan Hodell
Aug 27, 2025
9 min read

Updated: May 3

Aviation weather charts deliver enormous amounts of information in a compact visual format — but only if you know how to read them. The Surface Analysis Chart shows the current state of the atmosphere across the country, from pressure systems to fronts to actual reporting station observations. The Graphical Forecasts for Aviation (GFA) — the modern tool that replaced the legacy Low-Level Prognostic Chart in 2017 — provides forecast weather hazards for the next 15 hours in a way that's far more useful than the old paper charts ever were.

This post covers both products in practical depth: how to read surface analysis charts including station model symbols, how to use the modern GFA tool, what other prognostic products are available, and how all of this fits into modern flight planning.

Study this full length lesson (video, podcast, flashcards, and quiz) here: Full Length Lesson >

Surface Analysis Charts

The Surface Analysis Chart shows the current state of the atmosphere at the surface, depicting pressure systems, fronts, and weather observations. It's issued every 3 hours by the Weather Prediction Center (WPC) of the National Weather Service.

What it shows:

Sea level pressure isobars
High and low pressure systems
Frontal positions
Station observations
Pressure tendencies
Trough and ridge axes

How it's produced:

Meteorologists analyze observations from thousands of weather stations and apply them to a base map showing pressure values. The result is a hand-drawn or computer-generated chart showing the current atmospheric pattern.

Updates:

Issued at 00, 03, 06, 09, 12, 15, 18, 21 Z (every 3 hours)
Available within about 1.5 hours after the observation time
The chart represents the snapshot at the observation time, not when it's published

Reading Surface Analysis Chart Features

Isobars:

Lines of equal sea level pressure, drawn at 4 millibar intervals (typically 1004, 1008, 1012, 1016, etc.). The pattern of isobars tells you everything about the wind:

Tightly packed isobars = strong pressure gradient = strong winds
Widely spaced isobars = weak pressure gradient = light winds
Curving isobars around H or L = wind flowing parallel to isobars (geostrophic at altitude, slightly across at surface due to friction)

High Pressure Systems (H):

Marked with a blue H at the center of an area of relatively high pressure. The pressure value is sometimes shown next to the H (e.g., "1024" for 1024 millibars).

In the Northern Hemisphere:

Wind flows clockwise around the high
Wind spirals outward from the center (due to friction)
Generally clear, calm, stable conditions

Low Pressure Systems (L):

Marked with a red L at the center of an area of relatively low pressure. The pressure value is sometimes shown.

In the Northern Hemisphere:

Wind flows counterclockwise around the low
Wind spirals inward toward the center (due to friction)
Generally cloudy, unsettled conditions
Most aviation weather hazards associated with low pressure systems

Frontal Symbols:

Fronts are depicted with specific symbols pointing in the direction the front is moving:

Front Type	Symbol	Color
Cold front	Triangles pointing direction of movement	Blue
Warm front	Half-circles pointing direction of movement	Red
Stationary front	Alternating triangles and half-circles on opposite sides	Blue triangles, red half-circles
Occluded front	Both triangles and half-circles on same side	Purple
Trough	Dashed line	Brown
Squall line	Solid line with double dashes	Red
Dryline	Dashed line with scallops	Yellow or brown

Reading Station Model Symbols

Each weather station that reports surface observations is depicted on the chart using a standardized "station model" — a symbolic representation of weather conditions at that point.

A typical station model:

        Cloud Symbol
            │
Temp ───  ─●─── Wind direction & speed
            │
Dewpt ─── Pressure
            │
        Pressure tendency

Decoding components:

Cloud cover (the circle in the center):

○ — Clear sky
◐ — 1/8 covered
● (filled) — Overcast
⊗ — Sky obscured

Wind:

The line extending from the circle shows wind direction (the line points FROM the wind direction). Barbs on the line indicate speed:

Half barb = 5 knots
Full barb = 10 knots
Pennant (triangle) = 50 knots

So a line pointing south with one full barb and one half barb = wind from the north at 15 knots.

Temperature/Dewpoint:

Numbers above and below the wind line
Top number = temperature in °F (US charts)
Bottom number = dewpoint in °F

Pressure:

Three digits to the right (with implied first 9 or 10 and decimal)
"012" = 1001.2 millibars (or 0.12 inHg above some baseline)
"984" = 998.4 millibars

Pressure tendency:

Symbol below pressure showing whether pressure is rising or falling
/ rising
\ falling
― steady
⋀ rising then falling
⋁ falling then rising

Significant weather:

Various symbols between the cloud cover and temperature
Common: rain (●●), snow (***), thunderstorm (lightning bolt symbol), fog (≡)

Practical use:

The station models give you actual reporting station observations rather than just the synthesized analysis. Looking at multiple station models across an area helps you understand what's actually happening at the surface, complementing the broader pattern shown by isobars and fronts.

Pilot Use of Surface Analysis Charts

Flight planning workflow:

Identify pressure systems along your route
- Highs (favorable weather, light winds)
- Lows (active weather, stronger winds)
- Pressure trends
Locate frontal boundaries
- Are any fronts crossing your route?
- What direction are they moving?
- When will they affect your departure, en route, or destination?
Estimate wind patterns
- Tightly spaced isobars = strong winds
- Wind direction parallel to isobars (above friction layer)
- Surface winds cross isobars at 20-45° toward lower pressure
Anticipate weather changes
- Falling pressure ahead = approaching low/front
- Rising pressure = improving conditions
- Pressure tendency at stations along route
Apply Buys Ballot's Law
- Back to wind, low on left (NH)
- Helps locate weather systems by feel

For VFR pilots:

Check for fronts that might bring IFR conditions to your route
Identify stagnant high pressure areas (often hazy, sometimes fog)
Recognize approaching weather

For IFR pilots:

Determine optimal altitude based on wind patterns
Plan around frontal systems
Anticipate pressure changes that affect altimetry

The Graphical Forecasts for Aviation (GFA): The Modern Replacement

In October 2017, the FAA discontinued the traditional Low-Level Significant Weather Prognostic Chart and replaced it with the Graphical Forecasts for Aviation (GFA) tool, available at aviationweather.gov.

Why the change:

Static paper-style charts couldn't keep up with rapidly changing weather
Pilots needed more flexible, interactive products
Modern computing allows for time-progression and overlaying of multiple data sources
The legacy "prog chart" was based on outdated forecasting methods

What the GFA replaces:

Low-Level Significant Weather Prog Chart (12 and 24 hour)
Some legacy text products
Many static graphical products

Using the GFA Tool

The GFA is an interactive web tool at aviationweather.gov/gfa. It's now also integrated into most EFB apps and flight planning tools.

What the GFA shows:

The GFA provides forecast information in 3-hour intervals from current time out to 14 hours in the future, plus a "current observation" view. You can select different layers showing:

Clouds:

Cloud coverage
Cloud bases and tops
Sky condition

Visibility/Weather:

VFR, MVFR, IFR, LIFR conditions
Precipitation type and intensity
Restricted visibility (fog, haze)

Icing:

Forecast icing severity by altitude
Severity color-coded (light, moderate, severe)
Altitude bands

Turbulence:

Forecast turbulence severity
By altitude
Color-coded for intensity

Winds:

Wind speed and direction
Multiple altitude options
Visualizes jet stream and other wind patterns

Convective:

Thunderstorm potential
Severe weather forecasts
Convective outlook integration

Time progression:

A time slider lets you see how conditions evolve over the forecast period:

Current observation
03 hours forecast
06 hours forecast
09 hours forecast
12 hours forecast
15 hours forecast

This is particularly useful for understanding how a frontal system or weather pattern will affect your route at various points during your flight.

The Other Modern Forecast Products

Beyond the GFA, several other forecast products are available for pilots:

Area Forecast Discussion (AFD):

Plain-language discussion from local NWS offices
Provides forecaster's reasoning behind forecasts
Highlights uncertainties and confidence levels
Excellent context for the numerical forecast

Forecast Models (HRRR, NAM, GFS):

Numerical weather prediction models
Available on aviationweather.gov and various meteorological sites
Useful for understanding multiple forecast solutions

Convective Outlook (SPC):

Storm Prediction Center forecasts
Days 1-8 outlook for severe thunderstorms
Day 1: detailed convective probabilities
Days 2-8: progressive less detail

Winds Aloft Forecasts:

Forecast winds and temperatures at altitude
Standard altitudes (3,000, 6,000, 9,000, 12,000, 18,000, etc.)
Critical for fuel and altitude planning

Constant Pressure Charts (300mb, 500mb, etc.):

Upper-level patterns
Jet stream position
More important for high-altitude flying

Reading Sample GFA Information

Imagine the GFA showing your planned route from KDFW to KDEN at the 6-hour forecast time:

Cloud layer shows:

Light blue area covering your route — VFR conditions likely
Magenta patch over Eastern New Mexico — IFR conditions
Yellow area over Central Texas — MVFR

Icing layer at 9,000 feet:

Green areas — light icing potential
Yellow areas over your route — moderate icing
No red (severe) areas

Turbulence layer at 9,000 feet:

Light green over most of route — no significant turbulence forecast
Light yellow patch in northern New Mexico — light turbulence

Convective layer:

Storm Prediction Center 1-day outlook overlay shows enhanced risk over your destination
Possible thunderstorm development

Pilot interpretation:

Departure conditions VFR
Possible IFR/MVFR conditions in eastern New Mexico — plan deviation
Moderate icing forecast at typical cruise altitude — consider lower altitude or aircraft capability
Thunderstorm potential at destination — monitor and have alternates

This is where the GFA shines — it integrates multiple weather hazards in a single visual that you can move forward in time to see how conditions evolve.

How to Access These Charts

Surface Analysis Charts:

aviationweather.gov (Surface Analysis page)
WPC (Weather Prediction Center) website
ForeFlight, Garmin Pilot, FltPlan Go apps
1800wxbrief.com graphical briefings

Graphical Forecasts for Aviation (GFA):

aviationweather.gov/gfa
ForeFlight (Maps section)
Garmin Pilot (Weather Maps)
Other modern EFB apps
AOPA Pilot Information Center

Combined briefings:

1800wxbrief.com — provides surface analysis and GFA together in graphical briefings
Phone briefings with specialists who can describe charts to you
EFB integrated weather features

Practical Flight Planning Workflow

The recommended sequence:

Check the synoptic situation with the surface analysis chart
- Where are the highs, lows, fronts?
- What's the general weather pattern?
Look at the GFA at the time of your flight
- Conditions at departure
- Conditions en route
- Conditions at destination
- Conditions at arrival time
Check progression
- Step through GFA forecasts in 3-hour intervals
- Watch how systems move and evolve
- Identify trend (improving or worsening)
Cross-reference with TAFs and METARs
- Verify GFA matches actual conditions at airports
- Note any discrepancies
Check AIRMETs and SIGMETs
- Ensure no severe weather warnings affect your route
Develop your plan
- Departure timing
- Route choices
- Altitude selection
- Alternate airports
- Decision points and abort criteria

Common Misconceptions

"The Prog Chart is the standard product." No — the legacy Low-Level Significant Weather Prog Chart was discontinued in 2017. The GFA replaced it.
"Surface analysis is a forecast." No — it shows current conditions, not forecasts.
"The GFA only shows clouds." No — it shows clouds, visibility, icing, turbulence, winds, and convective forecasts in different selectable layers.
"Charts replace text products." No — surface analysis and GFA complement METARs, TAFs, AIRMETs, SIGMETs. Use them all together.
"You can ignore the surface analysis if you have GFA." No — the surface analysis shows current synoptic situation; GFA shows forecasts. Both are useful.

On the Written Test and Checkride

Surface analysis and prog charts (or now GFA) appear on tests and oral exams. The most commonly tested topics:

Surface analysis chart symbols (frontal types, station models)
Use of isobars to determine wind speed and direction
Buys Ballot's Law applied to charts
Difference between current and forecast products
GFA capabilities and access (modern)
Decoding station models

Quick Reference

Surface Analysis Chart:

Issued every 3 hours
Shows current sea-level conditions
Available on aviationweather.gov

Frontal Symbols:

Front	Symbol	Color
Cold	Triangles	Blue
Warm	Half-circles	Red
Stationary	Alternating	Mixed
Occluded	Both same side	Purple

Pressure Systems:

H (blue) — High pressure, generally fair weather
L (red) — Low pressure, generally unsettled

Wind Indicators on Station Models:

Half barb = 5 knots
Full barb = 10 knots
Pennant = 50 knots

Graphical Forecasts for Aviation (GFA):

Replaced legacy prog chart in 2017
Available at aviationweather.gov/gfa
Time progression in 3-hour intervals
Layers: clouds, visibility, icing, turbulence, winds, convective
14-hour forecast horizon

Key flight planning use:

Surface analysis for current synoptic situation
GFA for forecast conditions during flight
METARs/TAFs for specific airports
AIRMETs/SIGMETs for hazardous conditions
Combine all for complete weather picture

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Author: Nathan Hodell

CFI, CFII, MEI, ATP, Creator and CEO

Nathan is an aviation enthusiast with thousands of hours of flying and dual instruction over the past 15+ years. Through his aviation career he has been able to earn his ATP, fly as an airline pilot, own/operate flight schools, and create and host wifiCFI.