Hazardous Weather Detection
How PlaneWX detects and assesses thunderstorms, icing, turbulence, and other hazardous conditions along your route.
Convective Watch
The Convective Watch section appears in your briefing whenever thunderstorm or convective activity is detected along your route. It combines data from three sources to build a comprehensive threat picture:
1. Numerical Weather Models
Regional and global model soundings (for example HRRR, HRDPS, ICON-EU, ICON-D2, AROME, GFS, ECMWF — whichever apply to your route) are sampled at multiple points along your route to extract convective indices (CAPE, K-Index, Lifted Index). These indices measure the atmosphere's potential for thunderstorm development.
2. Weather Prediction Center (WPC)
WPC short-range and extended discussions are analyzed for convective language. PlaneWX classifies WPC text into 4 severity tiers using 80+ phrase patterns sourced from real aviation weather products.
3. TAF Convective Phrases
TAFs at departure, arrival, and en-route airports are scanned for convective weather codes (TS, TSRA, VCTS) and probability groups (PROB30, PROB40) containing thunderstorm activity.
Convective Indices Explained
In Enhanced View, the Convective Watch card displays five key atmospheric indices with gauge bars showing where each value falls within its range. Here's what they mean for your flight:
CAPE (Convective Available Potential Energy)
Measures how much energy is available to fuel thunderstorm updrafts. Higher CAPE means stronger potential storms. Measured in Joules per kilogram (J/kg).
0–500
Weak
Little convective potential
500–1,500
Moderate
Isolated storms possible
1,500–3,000
Strong
Organized storms likely
3,000+
Extreme
Severe storms possible
K-Index
A composite index measuring thunderstorm potential based on temperature lapse rate, moisture content, and dewpoint depression. Higher values indicate greater thunderstorm probability.
<20
Low
Thunderstorms unlikely
20–30
Moderate
Isolated possible
30–40
High
Scattered storms likely
40+
Very High
Numerous storms expected
Lifted Index (LI)
Measures atmospheric stability by comparing the temperature of a lifted air parcel to the environment at 500 mb (~18,000 ft). Negative values indicate instability. The more negative the value, the more unstable the atmosphere.
>0
Stable
No thunderstorm support
0 to −3
Marginally Unstable
Weak storms possible
−3 to −6
Unstable
Strong storms likely
<−6
Very Unstable
Severe storms possible
Cap Strength — CIN (Convective Inhibition)
The atmospheric “cap” that suppresses storm development even when energy (CAPE) is high. Low CIN means the cap is weak or gone and storms can fire with little or no trigger. High CIN means energy is strongly suppressed. The gauge runs red-to-green: red = dangerous (weak cap), green = suppressed (strong cap).
<25 J/kg
Cap Gone
Storms fire with no trigger
25–50 J/kg
Eroding
Weak forcing enough
50–150 J/kg
Present
Trigger needed to breach
>150 J/kg
Strong
Storms unlikely despite CAPE
Storm Trigger — LFC (Level of Free Convection)
The altitude where a rising air parcel becomes warmer than the surrounding atmosphere and starts rising on its own — creating a self-sustaining storm. A low LFC (<6,500 ft) means storms need minimal lift to initiate and intensify rapidly. SPC research links low LFC environments to elevated tornado probability when strong wind shear is also present.
<6,500 ft
Low
Storms self-sustain easily
6,500–9,800 ft
Moderate
Adequate forcing needed
>9,800 ft
Elevated
Stronger forcing required
Sounding Profile Badges
When CAPE and CIN combine into a dangerous pattern, PlaneWX displays a colored badge and a Threat Brief paragraph explaining the risk in plain English. The badge also appears in your Gotchas and Briefing Summary.
CAPE ≥ 1,000 J/kg + CIN 50–150 J/kg
Energy building under the cap. A trigger like peak heating or a frontal passage could breach it.
CAPE ≥ 1,000 J/kg + CIN 25–50 J/kg
Cap is eroding. Weak afternoon heating or a minor boundary can fire storms.
CAPE ≥ 2,500 J/kg + CIN <50 J/kg, or any CAPE ≥ 1,000 with CIN <25 J/kg
Cap is essentially gone. Rapid storm development possible at any time with no external trigger.
How PlaneWX uses these indices: No single index tells the full story. PlaneWX evaluates all five together across multiple sample points along your route and combines them with WPC discussions and TAF convective phrases to determine the overall threat level (Isolated, Scattered, or Widespread).
Multi-Model Icing Analysis
PlaneWX analyzes icing with multi-model soundings (HRRR, GFS, ECMWF, and regional models where available), plus CIP nowcast and DAFS IFI when your flight is inside their CONUS windows. Climb and descent use phase-local hybrid peaks; a cloud-top vs freezing-level check can clear icing when there is no supercooled liquid water on the path. Full detail is on the Multi-Model Icing Analysis help page.
What's Assessed
- •Freezing level: Altitude where temperature drops below 0°C along your route
- •Icing layer: The altitude band where icing conditions exist (base to top)
- •Severity: None, Trace, Light, Moderate, or Severe based on humidity and temperature profiles
- •Phase exposure: Whether icing affects your climb, cruise, or descent
- •FIKI status: Whether your aircraft has Flight Into Known Icing equipment
Freezing level warning: If your cruise altitude is above the freezing level, an amber indicator appears in the Icing grid. This doesn't necessarily mean you'll encounter icing — it means you're flying in an altitude range where icing is possible if moisture is present.
Multi-Model Turbulence Analysis
PlaneWX combines two turbulence data sources into a single per-waypoint hybrid assessment:
GTGN Nowcast (near-term)
The FAA/NCAR Graphical Turbulence Guidance Nowcast provides EDR-based turbulence severity computed from actual aircraft sensor data, updated every 15 minutes. For departures within approximately 2 hours, GTGN is the primary turbulence source along your route.
NWP Models (all departures)
Regional and global NWP soundings (HRRR, HRDPS, ICON-EU/ICON-D2, AROME, GFS, ECMWF — whichever apply to your route) provide wind shear and Richardson number analysis at 24 pressure levels. Thresholds are calibrated for light GA aircraft — roughly 40% lower than transport-category standards, because your SR22 feels the same air very differently than a 737.
Severity Scale
Why you may see SEVERE when other tools don't: PlaneWX uses GA-calibrated thresholds that are roughly 40% lower than the transport-category standards used by most aviation weather products. What shows as Moderate in a 737-calibrated tool can legitimately be Severe in a light GA aircraft at 3,400 lbs. The easy path would have been to display the same numbers every other tool shows — we chose not to, because those numbers aren't calibrated for the airplane you're flying.
For the full methodology including exposure time, severity smoothing, Richardson number analysis, mountain wave detection, and PIREP normalization, see the Turbulence Analysis help page.
Wildfire Smoke
PlaneWX overlays NOAA HMS smoke plumes on your route map and samples estimated visibility along the corridor. For VFR flights, en-route smoke visibility is scored against your VFR soft/hard visibility minimums (departure and arrival terminals still use METARs/TAFs). For IFR flights, smoke is informational only and does not change the WX Score by itself.
Full details — data sources, VFR vs IFR scoring, and map interactions — are on the Wildfire Smoke help page.
AIRMETs & SIGMETs
PlaneWX automatically detects active weather advisories that intersect your route corridor and affect your cruise altitude. These are shown in the AIRMETs/SIGMETs section with their type, affected area, and valid time. For Convective SIGMETs, corridor intersection means the product is relevant enough to show — the WX Score then applies time-aware encounter scaling (storm motion vs your track) so a polygon you are flying away from is not treated the same as one you will punch through. See Convective Watch scoring for tops, deviation difficulty, and SIGMET/TAF dedup.
G-AIRMET Types
- SierraIFR conditions and mountain obscuration
- TangoModerate turbulence and sustained surface winds ≥30 kt
- ZuluModerate icing and freezing levels
SIGMETs
- •Convective SIGMETs: Severe thunderstorms, tornadoes, or embedded thunderstorms. Highest priority.
- •SIGMETs: Severe icing, severe or extreme turbulence, volcanic ash, sandstorms.
- •CWAs (Center Weather Advisories): Short-term hazards not covered by SIGMETs.
Impact on WX Score: Severe convective SIGMETs you are still expected to encounter (high tops, difficult deviation, near-term validity) can drive large deductions or a NO-GO in the pre-flight window. Polygons only in the search corridor that you are departing away from are scaled down or omitted from the en-route penalty. The same storm is not fully double-counted when it also appears in a TAF thunderstorm group. G-AIRMETs still deduct points proportional to severity and distance.
Related Help Pages
Multi-Model Icing Analysis
CIP/IFI hybrid, cloud-top veto, and ForeFlight VCS cross-check
Convective Watch Scoring
Time-aware SIGMETs, ledger dedup, and threat scores
Understanding Your Briefing
How to read the Enhanced and Classic briefing views
WX Score Explained
How hazardous weather deductions affect your score
Wildfire Smoke
Plume overlays and VFR en-route visibility scoring
Weather Decisions
How weather products are selected and filtered for your flight