How to Manage Pests

California Weather Database: Description

Date

The date of the observation.

Hour or Time of Observation

Time of observation on the 24-hour clock, from 0001 through 2400 represented by four-digits in the format HHMM, where HH is hours and MM is minutes. Some elements of a weather observation occur at the time of observation, e.g., dry-bulb, wet-bulb temperatures. Others are from the 24-hour period prior to time of observation, e.g., precipitation. If maximum and minimum temperatures are the only data entered for a date, it is assumed that they are for the midnight to midnight period for that date.

Precipitation

Amount. The amount of precipitation (rain or liquid equivalent of frozen precipitation) during the 24 hours prior to the time of observation. Amounts are in inches (to hundredths), except where more than 10 inches fell in one day; then amounts are in inches to tenths. Also,

• *TR indicates that a trace (less than 0.005 inches) of precipitation fell in the past 24 hours. (In data file formats, traces of precipitation are listed as "0.00.")
• *SM indicates that the amount for this 24 hours is included in Subsequent Measurement. (In data file formats, the day's precipitation is then listed as "0.00.")

Type. The predominant type of precipitation that fell. Abbreviations are:

Air Temperatures

Air temperatures are measured at a height of 5 to 6 feet.

Maximum and minimum. The highest and lowest, respectively, temperatures (F or C) that has occurred during the 24 hours prior to the time of observation, or that has occurred during the midnight to midnight period on the given day if no time of observation is specified. Temperatures below zero are indicated by a "-".

Observation. The air temperature (F or C) at time of observation. Temperatures below zero are indicated by a "-".

Weather Type

"Weather type" contains information about the weather at the observation time. Also, if a significant weather event occurs during a day, hail or a tornado for instance, the occurrence may be noted in this field.

Wind

Climate and TouchTone stations: speed and direction at the time of observation are reported. Automatic and PestCast stations: average speed and direction for the date are reported.

The format is DDSS, where DD is direction from which the wind is blowing with direction noted to 8 points of the compass (N, NE, E, SE, S, SW, W, NW), and SS is speed in miles per hour or meters per second. Calm or no wind is indicated by 0000.

Bulb Temperatures

Wet-bulb and dry-bulb temperature readings are made from a psychrometer, to be used in calculating dew point and relative humidity. Wet-bulb and dry-bulb temperature readings are made at the time of observation. They are entered to a tenth of a degree when the value is less than 100F. Above 100F, only whole degrees are entered. Values are in Fahrenheit or Celsius.

Soil Temperatures

Maximum. Maximum soil temperature (F or C) at the depth indicated in the station description during the 24-hour period prior to time of observation.

Minimum. The lowest soil temperature (F or C) at the depth indicated in the station description that has occurred during the 24 hours prior to the time of observation.

Pan Evaporation

The amount of water evaporated from the surface of a water-filled evaporation pan. The amount is in inches and hundredths, for the 24-hour period prior to the time of observation. A value of "*SM" indicates that the amount is included in subsequent measurement.

Relative Humidity

The maximum and minimum values of relative humidity for the 24 hours prior to the time of observation are reported for Automatic stations. Values are in percent.

ETo

The daily reference evapotranspiration (ETo) is calculated by the California Department of Water Resources CIMIS Project for its Automatic stations and it is also calculated for some PestCast stations. ETo is reported in inches or millimeters.

Solar Radiation

Global solar radiation is found in this field. Solar radiation is in langleys/day (cal/cm²/day) or Watts/m². The value is for the 24 hours prior to the time of observation.

Leaf Wetness Duration

Leaf wetness is reported as the number of hours (and fractions) of a day that the sensor indicates it is wet.

The set of variables reported by each PestCast station is likely to be different from other stations. However, within a network, the reported variables are usually very similar. See a station's description to find out which variables are reported.

Measured variables may include (* indicates that the measurement may be reported more frequently)

• Air temperature (daily maximum and minimum with the time each occurred, daily and hourly* average) for up to three instruments at one station
• Relative humidity (daily and hourly* average) for up to two instruments at one station
• Precipitation (daily and hourly* total)
• Soil temperature (daily maximum and minimum with the time each occurred, daily and hourly* average)
• Wind (daily and hourly average speed and direction, daily and hourly* max gust with its direction and time that it occurred)
• Solar radiation
• Leaf wetness

Calculated variables may include

• Dew point
• Hours when temperature is 32F or less
• Chilling (Number of hours when temperature is 45F or less)
• Thresholds (Number of hours when temperatures relate to specified thresholds)

Definitions of measured variables

Date

The date on which the observation was made.

Obs Time (Time of Observation)

Time is Pacific Standard Time year round. The elements of a weather observation occur at the time of observation or cover the reported collection period prior to time of observation, e.g., precipitation total or average relative humidity.

Reports are for the interval prior to the time reported. For daily observations, reports are for the 24 hours prior to the time of observation. For hourly or sub-hourly reports, reports are for the hour or other interval prior to the reported time.

Air Temperatures

Air temperatures may be reported for up to three probes: AIR TEMP, AIR TEMP2, AIR TEMP3. Temperatures below zero are indicated by a "-".

Maximum and minimum. The highest and lowest temperatures (F or C) that have occurred during the 24 hours prior to the time of observation.

Time. Time at which the maximum or minimum temperature occurred, on a 24-hour clock. Time is always Pacific Standard Time.

Average. The air temperature (F or C) averaged over the measurement interval prior to the time of observation.

Relative Humidity

Maximum and minimum. The maximum and minimum values of relative humidity for the 24 hours prior to the time of observation. Values are in percent.

Average. The relative humidity averaged over the period prior to the time of observation.

Precipitation Amount

The amount of precipitation (rain, since gauges are not heated to measure liquid equivalent of frozen precipitation) during the period prior to the time of observation. Amounts are in inches (to hundredths).

Solar Radiation

Global solar radiation is found in this field."English" units are langleys accumulated over the reported period. Metric units are Watts/m2.

Wind

Average. The average speed and direction over the prior period, in miles per hour or meters per second. Direction is in degrees, with 0 as North.

Maximum speed, direction, and time. The speed and direction of the maximum gust during the period prior to time of observation, and the time at which it occurred.

Soil Temperatures

Maximum and minimum. Highest and lowest soil temperatures (F or C) at the depth indicated in the station description during the 24-hour period prior to time of observation.

Time. Time at which the maximum or minimum soil temperature occurred, on a 24 hour clock. Time is Pacific Standard Time year round.

Average. The soil temperature (F or C) averaged over the period prior to the time of observation.

Leaf Wetness

For daily reports, the number of hours that the sensor indicates "wet." For hourly or sub-hourly reports, the numbe of minutes that the sensor indicates "wet."

Definitions of calculated variables

Hours <= 32F

Number of hours that the temperature was at or below 32 degrees Fahrenheit.

Chilling

Number of hours that the temperature was at or below 45 degrees Fahrenheit, often called "chilling hours."

Thresholds

Number of hours that the temperature was at or below the threshold temperatures given, usually provided for use in a biological model such as grape powdery mildew.

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