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Introducing the LCR (Vehicle Loss-of-Control Risk) (v1.0 Beta)

The LCR scale is a tool for classifying, forecasting and warning the public about hazardous winter driving events. The value of the 15-point scale is calculated from observed or numerical model-derived meteorological data. Charts of LCR values can be plotted from either realtime or model data, allowing quick identification of geographical areas posing the highest risks to drivers. The LCR Scale is a nonprofit project, and the script/code is being released under a GNU license.

DISCLAIMER: The LCR project is experimental, independently produced, and is not affiliated with or endorsed by any official government agency, NOAA or the National Weather Service.

Purpose | Justification | Applications | Scale & Color Scheme | Methodology | Script | Development Goals | Limitations | Collaboration


LCR is designed to display the risk of a motor vehicle encountering a hazardous (reduced road surface friction) condition that can lead to a loss of control incident. Higher LCR values indicate a greater risk to a driver, as well as a corresponding increase in the following human impacts:
  • Number of accidents
  • Number of injuries
  • Number of fatalities
  • Demand on police/fire/EMS first responders
  • Road closures/restrictions
  • Property damage losses
  • Demand on towing services
  • Shipping and commerce impacts


The majority of hazardous road conditions develop when any type of precipitation falls with a surface temperature at or below the freezing point (32°F / 0°C). There are additional meteorological factors that can increase the risk from this baseline condition.

No shorthand way to represent this risk has existed in publicly-available forecast tools. For example, discerning the simple condition where precipitation is falling at below-freezing surface temperatures has involved toggling back and forth between QPF (precipitation) and 2m temperature charts. LCR consolidates all of the meteorological factors that produce and increase the hazardous road condition risk into a single, easy-to-understand parameter.


  • LCR charts can be generated from realtime meteorological data
  • LCR forecast charts can be generated from numerical model data
  • LCR can be easily manually calculated for any in-progress event at a given location
  • LCR can be manually calculated for past events at a given location
  • LCR charts for past events can be generated from meteorological data archives

Approximate human impacts

Low 1 Isolated incidents, mainly involving vehicles traveling at speeds faster than 65mph.
Marginal 2 Scattered incidents, mainly involving vehicles traveling at speeds faster than 65mph. Isolated injury crashes.
Slight 4 Elevated number of incidents, mainly involving vehicles traveling at speeds faster than 55mph. Scattered injury crashes.
Enhanced 6 Numerous incidents, mainly involving vehicles traveling at speeds faster than 45mph. Some localized EMS/first responder strain. Multiple injuries. Isolated fatalities.
Moderate 8 Numerous incidents. Isolated multi-vehicle pileups. Multiple road closures. Regional EMS/first responder strain. Numerous injuries, multiple fatalities. Towing bans placed in effect.
High 10 Widespread incidents. Major multi-vehicle pileups. Widespread road closures. EMS/first responders overwhelmed. Numerous injuries and fatalities. Travelers stranded. Shipping, commerce and other economic impacts. Towing bans placed in effect.


LCR is calculated using a series of conditional statements that apply pre-set values in a cumulative (additive) fashion. LCR is intended to be an hourly value for a given location. 6, 12 and 24-hour period LCR maximum charts can also be derived from the hourly values.

Prerequesite data

LCR requires the following data for each gridpoint (latitude/longitude):

For numerical model data forecast charts:

  • 2m temperature
  • 2m dewpoint
  • 2m relative humidity
  • 2m surface pressure
  • 6-hour 2m temperature history
  • Hourly QPF
  • Hourly QPF (freezing rain/drizzle)
For realtime analysis:
  • Latitude/longitude
  • ASOS or AWOS observations of:
    • 2m temperature
    • 6-hour 2m temperature history
    • 2m dewpoint
    • 2m relative humidity
    • 2m surface pressure
    • Precipitation rate/type
  • NWS-issued winter watch/warning/advisory in effect (yes/no):
    • winter weather advisory
    • winter storm watch
    • winter storm warning
    • freezing rain advisory
    • freezing fog advisory
    • ice storm warning
    • blizzard warning
    • snow squall warning
The LCR script code contains a function to calulate the 2m wet bulb temperature with a standard formula using 2m temperature, 2m dewpoint and 2m surface pressure.

Baseline LCR (v1.0 Beta)

Non-activated gridpoints have an LCR value of zero (0). LCR is activated at a gridpoint where precipitation of any type (hourly QPF above zero) is falling during the following conditions:
  • 2m temperature at or below 35°F
  • 2m wet bulb temperature at or below 32°F
If the above conditions are met for a gridpoint, the baseline LCR value is set as follows:
  • For hourly liquid-equivalent QPF of less than 0.1", LCR is set to 1.
  • For hourly liquid-equivalent QPF of more than 0.1" and less than 0.25", LCR is set to 2.
  • For hourly liquid-equivalent QPF of 0.25" or more, LCR is set to 3.
For realtime LCR analysis, if ASOS/AWOS observations indicate:
  • Light precipitation, LCR is set to 1.
  • Moderate precipitation, LCR is set to 2.
  • Heavy precipitation, LCR is set to 3.

Factors that increase LCR (v1.0 Beta)

Each of the following condition factors, when true, add to the baseline LCR value. The script does not apply these factors if the baseline LCR is zero (a no-QPF condition).

  • Below-freezing factor: If the 2m temperature is below freezing, the gridpoint's LCR value is increased by 1. Justification: Well-bonded ice layer begins forming on road surfaces when temperatures fall below freezing.
  • Below-freezing temperature history factor: If the average 2m temperature of the previous 6 hours is below freezing, the gridpoint's LCR value is increased by 1. Justification: A longer period of below-freezing temperatures allows road surfaces to cool enough to support the efficient development of hazardous conditions.
  • Optimal ice bonding, melting/refreezing cycle factor: If the 2m temperature is between 24°F and 29°F, the gridpoint's LCR value is increased by 2. Justification: A more solid bonding of an ice layer to a road surface occurs during temperatures below 29°F. With temperatures between 24°F and 29°F, vehicle traffic introduces a melting-refreezing cycle of falling/fallen precipitation on a road surface. The result is a uniform, well-bonded ice layer that is significantly more hazardous to drivers.
  • Freezing rain/freezing drizzle factor: If the precipitation type is freezing rain or freezing drizzle, the gridpoint's LCR value is increased by 2. Justification: Freezing rain and freezing drizzle produce a treacherous road surface lacking in visual cues for drivers.
  • Regional de-icing capacity factor: If the gridpoint's location is at or south of the 35° latitude, the LCR value is increased by 3. Justification: Regions with reduced de-icing capacity suffer the greatest and most widespread hazardous conditions during subfreezing precipitation. The driving public in these regions is also much less experienced with hazardous winter driving conditions.
  • Pre-existing winter weather watch/warning/advisory factor (realtime analysis only): If the gridpoint's location has not been under an active winter weather watch/warning/advisory for at least 3 hours, the gridpoint's LCR value is increased by 3. Justification: Short-fuse "surprise" events suffer from fewer available de-icing crews and equipment, resulting in greater and more widespread hazardous conditions. This factor is not applied to LCR forecast charts derived from model data.
Freezing Fog

Freezing fog is indicated when QPF is zero, 2m temperature is at or below 31°F and 2m relative humidity is 99 percent or greater. Freezing fog LCR values are not applied if QPF is greater than zero. At this time, the Regional de-icing capacity factor and Pre-existing winter weather watch/warning/advisory factor are not applied to a freezing fog LCR value.

Numerical models: For 2m RH at or greater than 99% and temperature at or below:

  • 31°F, LCR is set to 1.
  • 29°F, LCR is set to 2.
  • 27°F, LCR is set to 3.
Realtime analysis: ASOS/AWOS reporting heavy fog or freezing fog and temperature at or below:
  • 31°F, LCR is set to 1.
  • 29°F, LCR is set to 2.
  • 27°F, LCR is set to 3.
Maximum LCR value

The maximum LCR value is 15, which would occur during the following conditions:
  • 0.25" or greater of freezing rain in one hour
  • 6-hour average 2m temperature below freezing
  • 2m temperature between 25°F and 29°F
  • Occurring in a southern US state
  • No NWS winter watch, warning or advisory in effect for at least 3 hours
LCR values for select past events

  • February 11, 2021 - Fort Worth, Texas: LCR = 10
  • December 16, 2016 - St. Louis, MO: LCR = 10
  • February 15, 2021 - Houston, Texas: LCR = 10
  • January 6, 2017 - Birmingham, AL: LCR = 10
  • January 18, 2015 - New Brunswick, NJ: LCR = 9
  • November 27, 2021 - Dubuque, IA: LCR = 8
  • November 1, 2021 - North Platte, NE: LCR = 4

Script Development

Pre-release scripting progress (Updated December 28, 2021)
The first script is intended to run in the NCO toolkit.

To download, right-click on the following files and choose "Save As".

You can also download the script from Github.


  • Numerical model chart script (Phase I): A LCR script for numerical model charts is in development, with a release date in December 2021. This script (currently being developed in C++) will be capable of processing standard NOAA grib files to produce a final NetCDF file containing a latidude/longitude array of LCR values. This code is being made available under a standard GNU license to any and all outlets that display numerical model data charts.
  • Realtime analysis script (Phase II): Realtime LCR chart generation will be possible using METAR (surface) observations and mesonets. Development of this code is scheduled, but no date of completion has been set. Mesoanalysis charts can be generated using the numerical model data script.

Future Development Goals

Planned updates to the LCR data processing script include:
  • De-Icing Capacity refinements. Currently, the 35° latitude is used as a proxy for demarcating between regions of adequate vs reduced de-icing capacity (salt/brine trucks, plows and crews). Future plans call for a detailed county-by-county database of de-icing capacity across the US that can be used to apply a granular GIS-based De-Icing Capacity factor in LCR calculations. This data will also allow for a multiple-step grading of de-icing capacity that will allow application of this factor in an incremental manner.
  • RWIS integration. Current realtime analysis will use AWOS/ASOS observations. Later editions of the script will include RWIS (Roadway weather information systems) data, where available.
  • Radar integration. The possibility of using radar reflectivity for realtime LCR calculations is being investigated. Radar may be used to augment or replace the QPF/precipitation rate factor for realtime LCR analysis.


LCR does not address lingering hazardous road impacts. Several factors can cause a hazardous road condition to persist for some time after the event is over. These include:
  • Temperatures remaining below freezing with no road treatment applied. As long as roads remain untreated and temperatures remain below freezing, the hazardous condition will remain at is previous LCR maximum until either of those factors has changed. It will remain possible for LCR values calculated in the time following an event to not show this ongoing hazard.
  • Temperatures rising above freezing immediately following a high-LCR event. Road surfaces can remain hazardous for an interval of time even if temperatures rise above freezing immediately afterward.
Significant accumulations (snowstorms) and blizzards: LCR does not consider non-road-surface-friction hazards from significant winter storms (cold temperatures, blowing snow, reduced visibility), nor road impassability due to large snow accumulations or drifts. In other words, LCR does not consider the risk of a vehicle getting stuck. Such hazards are already well-covered by the current watch, warning and advisory products. Vehicle loss-of-control incidents are also less of a factor during significant snowfall events (+5") due to these accumulations inherently limiting vehicles' top speeds.

LCR does not take into account rain (wet road) impacts. Rain does correlate with an increase in accident rates, but only at a marginal level compared to the increase during winter precipitation conditions. Rain, a very common condition in most locations, rarely results in the acute, widespread impacts that winter precipitation produces. The presence of precipitation during the warm season is already well-represented using radar and model QPF charts. In addition, including rain in the LCR equation would create unneccessary noise in the data. These all influenced the decision to not include an LCR factor for rain.


Assistance in development, refining and implementation of the LCR Scale would be welcome! Please email Dan Robinson at [email protected].

Educational Winter Driving Videos - Watch for Free:

Video: How to correct a slide on an icy road (and how to prevent them)Video: Icy Bridges: Weather's underrated killerVideo: Deadliest Weather: Freezing Rain

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