Weather Definitions For the AWIS Ag Weather Forecast

Max Temperature: Highest temperature expected for the day. Typically occurs in the mid-afternoon hours.

Min Temperature: Lowest temperature expected for the day. Often occurs near sunrise.

Daytime/Nighttime Precipitation Likelihood: Probability of precipitation expected between 6AM and 6PM (day) or between 6PM and 6AM (night)

LIKELY: Greater than 65% chance with large area coverage.

UNLIKELY: Less than 20% chance of rain.

SCATTERED: Some places will get rain, but others will not.

ISOLATED: Only a few places will get some rain, most will not.

Daytime/Nighttime Precipitation Amount: Range (in inches) of precipitation expected in the time periods above. Large variations over small distances can occur, particularly during summer months.

Thunderstorm Risk: AWIS has developed an index to indicate the risk of thundershowers/thunderstorms. The risk is indicated a little/no, slight chance, chance, or likely.

Snowfall: Expected snowfall for the calendar day. Snow amounts can vary considerably in certain weather situations, so use this with caution!

Frost/Dew Intensity and Dryoff Time: Amount of frost or dew expected at a 2 ft height, and the likely dryoff time. Heavy dew can prevent or delay haymaking operations and other activities that require dry foliage.

Morning/Afternoon Wind Direction/Speed: Prevailing wind direction expected and the average wind speed in MPH expected in the morning (6AM and 12PM) and the afternoon (12PM and 6PM). Generally, spraying operations will result in excessive drift if wind speeds are much above 7 mph. This varies with equipment used, boom height, water volume, droplet size, etc. Most sprayers have detailed tables in the owner's manual to determine if wind conditions are acceptable.

Lowest Relative Humidity: Minimum humidity level for the day. The minimum relative humidity normally occurs at the time of the maximum air temperature, typically around mid-afternoon.

Highest Relative Humidity: Highest humidity level for the day. The maximum relative humidity normally occurs at the time of the minimum air temperature, typically around sunrise.

Hours of Sunshine: Expected number of sunshine hours.

Percent of Possible Sunshine: A good indication of expected cloud cover for the day.

Solar Radiation: Total solar energy received at the earth's surface (in Watt-Hours/Square Meter). It is used in crop modeling, calculating irrigation needs, water uptake, drying potential, etc.

Pan Evaporation: A forecast of the amount of water (in inches) that will evaporate from a standard 4-foot pan. The water evaporating from the surface of a bare field is approximately 37% of the water that evaporates from the pan. Pan evaporation is routinely used in irrigation scheduling and water budgeting.

Drying Potential: An indication of the potential for soil and crops to dry. It is calculated from evaporation rates. When high, fields and crops dry out quicker. For hay following guidelines apply:

VERY HIGH: Conditions favor rapid drying. Hay often dries enough for baling in only one day. "Over" drying could occur if left in field too long, lowering quality of hay.

HIGH: Conditions favor drying. Generally one or two "high" drying days are required to render hay suitable for baling.

MODERATE: It will take at least two days of "moderate" drying conditions before newly mown hay will be fit for baling.

LOW: There's little or no wind and little sunshine. Humidity is high or it is raining. Little or no drying takes place.

Livestock Safety Index: A scale referring to heat stress placed on animals. It ranges from zero to 100.

BELOW 74: Minimal threat to confined livestock

ALERT (75 - 78): Possible death losses if livestock are confined too tightly or agitated.

DANGER (79 - 83): Up to 25% death losses can be incurred among livestock in transit.
Transport in early morning hours, don't crowd as tightly and consider wetting down with hoses. Provide shade for confined livestock.

EMERGENCY (84 and higher): Up to 45% death losses can be incurred among livestock in transit. Ship overnight or early morning when temps are cooler. Provide shade. Avoid crowding or agitating animals. Consider misters and other methods to cool down animals.

Growing Degree Days (50): A forecast of the heat units above 50 degrees F that will accumulate. It is calculated by subtracting 50 from the average temperature. Negative daily values are set to zero. Generally used to monitor the physiological development of corn.

Growing Degree Days (60): A forecast of the heat units above 60 degrees F that will accumulate. It is calculated by subtracting 60 from the average temperature. Negative daily values are set to zero. Generally used to monitor cotton development.

Heating Degree Days: An indication of heating demand.

Cooling Degree Days: An indication of cooling demand.

Highest Heat Stress: The highest hourly human heat stress for the day.

Lowest Heat Stress: The lowest hourly human wind chill for the day.

Maximum Air Pressure: The highest hourly barometric pressure for the day.

Minimum Air Pressure: The lowest hourly barometric pressure for the day.