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Oct 3, 2024 · According to the National Weather Service, the warning terms for frosts and freezes are defined as follows: Frost Advisory: Issued when minimum temperatures are expected to be between 33° and 36°F (0.5° and 2°C). Skies are generally clear, and winds light.
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May 22, 2023 · A heavy frost returns to northeastern Ontario by Wednesday morning as a sharp cold from tracks in. Another trough gives temperatures near the freezing mark, even across southern Ontario,...
- Digital Writers
- Overview
- Sky condition
- Chance of precipitation
- Precipitation
- Precipitation amounts
- Wind
- Temperature
- Frost
- Obstructions to visibility
- Wind Chill
Note: These are the general rules for including weather elements in the forecast. Slight variations of these rules do exist, however they are not included in this document.
Included in the forecast for Day 1 & 2? - Yes
Included in the forecast for Day 3 to 7? - Yes
Indicates the degree of cloudiness of the sky
Days One and Two: Sky Condition is replaced by a precipitation term when the Chance of Precipitation (COP) is equal or greater than 80 per cent. It is also replaced by the following terms when they are expected to occur: Fog, Ice Fog, Blowing Snow, Local Blowing Snow, Blizzard, or Snow Squalls.
Days Three to Seven: Sky Condition is replaced by a precipitation term when the Chance of Precipitation (COP) is equal or greater than 80 per cent. It is also replaced by the following terms when they are expected to occur: Fog, Blowing Snow, Blizzard, Near Blizzard Conditions, or Snow Squalls.
No-transition phrases such as: “Becoming a mix of sun and cloud late this afternoon,” are used in Days Three to Seven.
Included in the forecast for Day 1 & 2? - Yes, if it meets the criteria.
Included in the forecast for Day 3 to 7? - Yes, if it meets the criteria.
The Chance of Precipitation (COP) is the chance that measurable precipitation (0.2 mm of rain or 0.2 cm of snow) will fall on “any random point of the forecast region” during the forecast period.
Whenever the COP is expected to be between 30 and 70 per cent inclusive, it is indicated in the forecast. The COP values are stated in increments of 10 per cent.
The term Risk is used in association with the terms Thunderstorm(s), Thundershower(s), Hail, Freezing Rain and Freezing Drizzle, when there is a 30 or 40 per cent chance of occurrence of these phenomena. In these cases, the percentage value is not stated.
The use of 50 per cent is not permitted.
Included in the forecast for Day 1 & 2? - Yes, if it meets the criteria.
Included in the forecast for Day 3 to 7? - Yes, if it meets the criteria.
Precipitation is included in the forecast when the Chance of Precipitation (COP) is equal to or greater than 30 per cent.
Days Three to Seven: Only the following types are permitted: Rain, Snow, Drizzle, Showers, Flurries, and Thunderstorms. Additionally, the term Freezing Rain is used when the freezing rain amount is forecast to be greater than 5 mm There are no precipitation type changes indicated in the extended forecast bulletin.
The following table indicates Precipitation Amounts by Region
OR The snowfall amount, ice pellet amount, or a combination of snowfall and ice pellet amounts are expected to be equal or greater than 2 cm for the full length of the forecast (Day One, Day Two, and Day Two night). Days Three to Seven: Precipitation amount is NOT forecast.
Included in the forecast for Day 1 & 2? - Yes, if it meets the criteria.
Included in the forecast for Day 3 to 7? - Yes, if it meets the criteria.
Days One and Two:
Wind is included when the mean speed is greater than or equal to 20 km/h.
The terms Light or Calm are only used in a diminishing wind situation. For example: “Wind west at 20 km/h becoming light this evening.”
A wind speed change is indicated only when the average sustained speed is expected to change by at least 20 km/h. (i.e. “Wind south 20 km/h increasing to 40 this evening.”)
Included in the forecast for Day 1 & 2? - Yes
Included in the forecast for Day 3 to 7? - Yes
A single value of temperature is used. The following applies to both the maximum and minimum temperature:
•Temperature equal to 0ºC, write the term "zero"
•Temperature below 0ºC, add the qualifier "minus"
•Temperature from 1 to 5ºC, add the qualifier "plus"
Included in the forecast for Day 1 & 2? - Yes, if it meets the criteria.
Included in the forecast for Day 3 to 7? - No.
When the minimum temperature is forecast to be at, or close to, the freezing point, the term Frost may be used to describe where freezing is expected. The usage of this term is dependent on the extent of the freezing conditions.
For the chance of local frost, the following phrases are used: "Risk of frost," "Patchy frost," "Frost in low lying areas," and "Frost in valleys."
For extensive frost or when frost is likely, the following phrases are used: "Frost," "Widespread frost," "Extensive frost," and "Frost likely."
The inclusion of frost in the forecast is regionally dependent on the time of season.
Included in the forecast for Day 1 & 2? - Yes, if it meets the criteria.
Included in the forecast for Day 3 to 7? - Yes, if it meets the criteria.
Day One and Two
Obstructions to visibility include:
•Fog
•Haze
Included in the forecast for Day 1 & 2? - Yes, if it meets the criteria.
Included in the forecast for Day 3 to 7? - No.
Days One and Two: Wind Chill is included in the forecast when temperatures are below zero and wind speeds are 5 km/h or greater. Both the minimum and maximum wind chill value can be indicated in the forecast.
Further information on wind chill.
- 11 or higher
- UV Index Range
- 6 to 7
- 8 to 10
Nov 13, 2019 · While the National Weather Service does not keep track of ‘frost’ in observations per se, we do keep track of when temperatures hit the freezing mark or fall below. Frost becomes more widespread when the temperature falls below 32°F with some freeze possible.
Oct 22, 2020 · Colloquially, a “frost” is any time the temperature drops to that 36 - 32 degree range, whether or not we see the ice crystals form. Many plants, our hardiest and cool weather crops, can survive a frost without help from gardeners.
- Lauren O'laughlin
Jan 16, 2024 · If the temperature of the air falls below 0 °C, it is referred to an air frost. The most common type of frost is called hoar frost. It is formed of tiny ice crystals and generally occurs when the air temperature falls between 0 °C and 4 °C on a night with little or no cloud and light winds.
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