4/11/2013 Frost Warning

Unseasonably Cold Temperatures Likely Friday Morning, and Again Sunday through Tuesday Mornings

Nic Loyd, Meteorologist, 509-786-9357
Gerrit Hoogenboom, Director, 509-786-9371

Time Period
High risk: Friday, Sunday, Monday, and Tuesday mornings
Lower risk: Saturday morning

Locations Affected
All of central and eastern Washington, and possibly colder areas of western Washington like Olympia and Sequim.

Low to mid 20s in colder, wind-sheltered locations, to 30s in cloudy or windy areas.

Confidence Level
The presence of a deep and cold air mass: Very High
The extent of clouds and wind: Lower

The upcoming period of cool weather will promote an increasing frost risk in the coming days, with the most critical periods occurring Friday morning and again from Sunday morning to Tuesday morning.

On Friday morning, a more stable atmosphere will allow colder locations to fall into the mid to upper 20s, although some areas will remain above freezing. A strong frontal passage on Saturday morning will usher a colder air mass into the region, although generally safe conditions will result from the very windy conditions during this time.

Frost protection will likely be necessary for several days beginning on the morning of Sunday, April 14, and continuing through early next week. During this time, lows will average in the upper 20s to mid 30s in central and eastern Washington. The potential exists for widespread critical temperatures on any given morning in the Sunday to Tuesday period, although not all locations will experience critical temperatures each morning.

While periodic clouds and wind will keep some areas in the 30s, clear and wind-sheltered areas are likely to drop into the mid to upper 20s each night and morning. The potential exists for the coldest areas to drop into the low 20s. Despite the uncertainty in the extent of the cloud cover and atmospheric mixing on any given night, the prolonged nature of the event suggests that most areas will see critical temperature values at some point during the next seven days.

It is important to note that surface based inversions will be variable and rather weak in places, especially on Sunday morning, such that wind machines may have limited efficacy in increasing surface temperatures. The cold air mass will be deep and somewhat well mixed, and areas at slightly higher elevations are as likely to experience sub freezing temperatures as typically cold low lying areas.

If cold temperatures persist into the middle of next week, wind machines could become increasing effective due to warming temperatures aloft and increasingly stable conditions. By mid to late next week, the frost risk will decrease significantly, although the timing of the warming is unclear.

Please continue to monitor AgWeatherNet for weather forecast updates during this variable and critical time period. The Frost Risk page is updated daily, and additional frost risk detail will be available in the Friday outlook. For questions or further information, please contact Nic Loyd, (509)786-9367, nicholas.loyd@wsu.edu.

Washington State University