Watching the Weather

Dark stormy sky over our hoophouse and solar panels. Photo Wren Vile

Farmers and gardeners have always watched the weather, and now, as the climate crisis gets worse and the weather more chaotic, we need to hone our skills. I’ve written in the past about

Where does your weather come from?

Our mid-Atlantic weather mostly comes from one of three directions,

  • mainly from the Gulf of Mexico, (wet, maybe windy)
  • the Bermuda High Pressure area in summer, (hot and dry)
  • recurrent waves of cold air from Canada in winter (from a disrupted polar vortex).
  • Due to the erratic movement of thunderstorms, some parts of our area may experience long periods of drought. September–November is the dry season but also the hurricane season.
Such grey weather! But will it rain?
Photo Wren Vile

Find a weather station that is a good match for your area, and learn how to adapt it

We use Wunderground.com for Louisa Northside, but subtract 5F° from their forecast night lows, and mentally downgrade the chance of rain by 10%, as rain often passes us by as it scoots along the river valley north of us. I use the ten-day forecast to get the general idea, the hourly one when planning tasks, the Roanoke animated radar on the daily page to see what’s on the way and when it’s likely to arrive, and the alerts, watches and warnings. The forecast for the month is under the Calendar tab, although the further out the forecast is, the less reliable it will be. In hurricane season I check the Severe Weather tab with the Hurricane and Tropical Cyclones information.

Make yourself a Frost Alert Card of conditions that are likely to lead to an early or late frost, so you can quickly take avoiding actions without dithering.

Learn about recent average weather at your location.

I recommend Weather Spark for browsing on a rainy day, or a too-hot afternoon. “The weather year round anywhere on earth”

Weather Spark chart of average daily temperatures in Louisa County, Virginia

I rechecked our area on Weather Spark recently and realized how much has changed since I started quoted information from our Extension Service twenty or more years ago.

  • The climate in Louisa County, Virginia, is changing on average in the past ten years to drier weather with milder winters, hotter summer nights.
  • Twin Oaks is in USDA Winter Hardiness Zone 7a: the average annual minimum winter temperature is 0°F–5°F (–18°C to –15°C).
  • The average rainfall for a year is 37” (100 cm), fairly evenly distributed throughout the year, at 2.2”–3.6” (5.6-9.1 cm) per month. October is the driest, May the wettest.
  • The average daily maximum temperatures are 49°F (9.4°C) in December and January, 89°F (31.7°C) in July. The average night low temperatures are 29°F (–1.7°C) in January, 69°F (20.5°C) in July.
  • The season from last frost to first frost, is around 211 days. The average date of the last spring frost is April 24 (later than May 7 only happens one year in ten); the average date of the first fall frost is Oct 14 (earlier than Oct 1 only happens one year in ten).

Weather SparkOn Weather Spark you can study artfully-made colorful charts of temperature, precipitation, cloud coverage, humidity and tourists (!) month by month. There is a chart of average high and low temperatures over the year, and one showing the average hourly temperature over the year (we are currently in the big red blob of hot afternoons). There’s a grey and blue chart of cloud coverage, and a green one of the daily chance of rain (with touches of blue and purple frozen precipitation). The average monthly rainfall chart is all greys, as is the snowfall one. Our greatest chance of snow is February with an average of 4.2” for the month.

You can compare your nearest city to another you might dream of moving to.

There are charts of hours of daylight and twilight, sunrise and sunset, the solar elevation and azimuth (for those planning greenhouses); moon rise, set and phases for a choice of years; and – oh – humidity! Color-coded from a comfortable green, humid yellow, tan mugginess, pink oppressive and orange misery (over 75%).

There’s a chart of average wind speed over the year; wind direction, which shows my wrong belief that most of the wind here comes from the west (true in July, December and January only). There’s also (keep scrolling) a chart about the growing season, by which they mean the longest continuous period on non-freezing temperatures, although the chart provides a very visual bigger picture of periods in various temperature bands.

There’s a Growing Degree Days chart! We’re on average at 2000 F GDD at this point in July. Next is a chart of solar energy (average daily incident shortwave solar energy), with kWh peaking in June at 6.9 per day.

There’s more details, but I’m moving on.

Check extreme weather

Lightning Strike map

For when you need to know, check out Real Time Lightning Maps.org. On the map, enlarge the area you are concerned about., and watch for the activity sparking, or click for sound. There’s an explanation of how the data is gathered and what the various color dots mean.

Windy.com has a colored map with streaming arrows, and other settings for rain and thunder, clouds, temperature and more. For those at seas, you can check the waves and swell.

AirNow.gov has a quick-to-read dial of air quality, fire and smoke maps, ozone, fine particulates, lots of information about air quality

Not exactly weather, but if you experience an earthquake, go to Did You Feel It? And register your experience. It helps USGS build a clearer picture of earthquake events in your area. You can see maps of recent earthquakes globally or a world map to give understanding of tectonic plates.

 

Winter Preparations for Vegetable Gardens

 

Frosty daikon radish
Photo by Bridget Aleshire

Winter-Kill Temperatures

My annual blogpost of Winter-Kill Temperatures for Cold-Hardy Vegetables is always very popular. In fact, it’s my most popular title! Usually searches for this info increase in October and peak in early November, so here are quick links for those of you who have been meaning to look something up.

Winter-Kill Temperatures of Cold-Hardy Vegetables 2020

Winter Kill Temperatures of Cold-Hardy Vegetables 2019

Winter-Kill Temperatures of Cold-Hardy Vegetables 2018

Winter Kill Temperatures of Winter-Hardy Vegetables 2016

Trimming roots from a leek in December.
Photo Pam Dawling

For several years, starting in 2012, my friend and neighboring grower Ken Bezilla of Southern Exposure Seed Exchange and I have been keeping records of how well our crops do in the colder season. Ken provided much of the original information, and has suggested the morbidly named Death Bed idea: set aside a small bed and plant a few of each plant in it to audition for winter hardiness. Note each increasingly cold minimum temperature and when the various crops die of cold, to fine-tune your planting for next year (and leave me a comment!) Each year I update the list, based on new things I learned during the recent winter.

We are in zone 7a, with an average annual minimum temperature of 0-5°F (-18°C to -15°C).

The winter 2019-2020 was mild, with our lowest temperature being a single night at 12°F (-11°C). The Koji greens became completely unmarketable but did not completely die. Yukina Savoy is indeed hardier (as I expected), being OK down to 10°F (-12°C). We had one night at 13°F (-10°C) and two each at 17°F (-8°C), 18°F (-8°C also) and 19°F (-7°C). That winter I noted the death of rhubarb stems and leaves at 25°F (-4°C), rather than 22°F (-6°C), as I noted a year or two ago. I also added some cover crop hardiness temperatures.

Rhubarb in spring.
Photo Kathryn Simmons

I also learned that there is more damage when the weather switches suddenly from warm to cold. And that the weatherman in Raleigh, NC says it needs 3 hours at the critical temperature to do damage. Also note that repeated cold temperatures can kill off crops that can survive a single dip to a low temperature, and that cold winds, or cold wet weather can destroy plants quicker than simple cold. All greens do a lot better with row cover to protect them against cold drying winds.

Winter hoophouse lettuce
Photo Kathryn Simmons

It’s worth noting that in a double-layer hoophouse (8F/5C warmer at night than outside) plants can survive 14F/8C colder than they can outside, without extra rowcover; at least 21F/12C colder than outside with thick rowcover

Salad greens in a hoophouse in zone 7 can survive nights with outdoor lows of 14°F (-10°C). A test year: Lettuce, Mizuna, Turnips, Russian kales, Senposai, Tyee spinach, Tatsoi, Yukina Savoy survived a hoophouse temperature of 10.4°F (-12°C) without rowcover, -2.2°F (-19°C) with. Bright Lights chard got frozen leaf stems.

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Seeking Reader Participation

Your experience with your soils, microclimates and rain levels may lead you to use different temperatures. I’d love to hear from readers if they’ve found my numbers work for them, or if they have a different experience. You can leave a comment here, and it will appear on the website, for others to consider. Or you can fill out a Comment Page and only I will see it, although I’ll pass on the information without your name, if I think others would like to know too.

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Preparing for winter

Rowcover rolling with crank handle.
Photo Rodaew Institute

I’ve also written posts about winter preparations

Getting ready for frost. This post includes info on DIY weather-forecasting, our Frost Prediction checklist, and our Frost Alert Card. Also a link to a 126 page book which includes explanations of freezes and frosts to help us make sense of advice we’ve not understood. FrostProtectionFundamentalsPracticeandEconomicsFAO.pdf

Preparing for Frost and Cold Weather. This post includes our Frost Alert Card, a Frost Predictions checklist of what to do when the first fall frost is expected; how to use sprinklers overnight to stop tomatoes from freezing; four ranges of cold-hardiness (some crops can wait in the garden till it gets colder); and different levels of crop protection, including rowcover, low tunnels, Quick Hoops, caterpillar tunnels and hoophouses (aka high tunnels).

Season Extension and Frost Preparations. This post includes my Season Extension slideshow; the Frost Alert Card and Frost Predictions checklist again; a diagram of our winter double hoop system to hold rowcover in place during the worst weather;

Double hoop system for winter rowcover.
Pam Dawling

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Changing Winter Temperatures

Here’s an article from the Virginia Mercury by Sarah Vogelsong, giving info about changing winter temperatures, particularly later fall frosts in Virginia:

The frozen Potomac River. (Sarah Vogelsong/Virginia Mercury)

Autumn’s first frost is falling later. For farmers, the consequences are wide-ranging

by Sarah Vogelsong, November 3, 2020

Halloween has come and gone. The clocks have been set back. Every evening darkness falls just a little bit earlier.

But for much of Virginia, the first frost still remains elusive.

Over the past century, the average date of the first frost has been moving progressively backward throughout the commonwealth, today landing a week or more later than it did at the turn of the 20th century.

“This is one of the clearest signs of not only the changing climate but … its impact on our systems,” said Jeremy Hoffman, who as chief scientist at the Science Museum of Virginia conducts extensive research on climate change in Virginia. “It’s not just here, it’s everywhere.”

As global temperatures have warmed, largely due to the release of greenhouse gases into the atmosphere, frost seasons have shrunk. The Fourth National Climate Assessment released by the Trump administration in 2018 reported that “the length of the frost-free season, from the last freeze in spring to the first freeze of autumn, has increased for all regions since the early 1900s.”

How the shifts have played out in different states with different geographic, ecological and topographic features varies. Data from the U.S. Environmental Protection Agency show that between 1895 and 2016, the average date of the first fall frost moved back by 7.1 days in Virginia.

On the local level, the changes may be even starker. Estimates of how much the average date has changed vary depending on the time range used and how scientists fit a line to their data points, but in most Virginia cities, they show unmistakable upward trends. Looking at first frost dates between 1970 and 2016, Climate Central, a nonprofit staffed by scientists and journalists, calculated that on average, the first frost today is 5.9 days later in Lynchburg, 8.9 days later in Harrisonburg, 12.8 days later in Roanoke, 15 days later in Charlottesville and 18.5 days later in Richmond. While their data show Norfolk’s first frost occurring about six days earlier on average, Hoffman said that longer-range data going back to 1940 show the first frost moving back by about five days. Still, he cautioned, variation does occur: “Localized things like weather” can “work against that dominant signal in datasets like these.”

First freeze dates for Richmond, 1930-2019. (Jeremy Hoffman, Science Museum of Virginia)

The implications of the shifts in the freezing season go beyond a few more days to enjoy warm weather, say scientists and policymakers. Perhaps most affected are farmers, whose livelihood is intimately tied to fluctuations in both short-term weather and long-term climate.

“Some things you can sort of manage around and some things you can’t,” said Wade Thomason, a professor of crop and soil environmental science at Virginia Tech and the state’s grain crops extension specialist.

For most farmers, the last frost of the year in the spring is the riskier of the season’s two endpoints, falling as it does when most plants are young and more vulnerable to temperature extremes. But ongoing changes in the first frost in the fall also have ripple effects.

“It can be a beneficial thing for some instances. We might get more grazing days for livestock operations in a year,” said Thomason. For some crops, like double-cropped soybeans that are planted following the harvest of another crop — typically a grain like wheat — “it can extend the season.”

Other effects are less immediately apparent. Many wheat farmers who typically plant in mid-October have begun to push back their planting dates to ensure plants don’t grow too quickly during the freezing months, making them susceptible to disease or falling over in the field. Specific types of forage rely on long periods of cool weather to thrive: in Northern Virginia and the Shenandoah Valley, farmers have noticed that orchard-grass stands are only living for four to five years instead of the once-standard 10.

“For years now, we’ve heard from farmers that the stands don’t persist like they used to,” said Thomason. Research has shown that one factor contributing to less persistence is warmer nighttime temperatures, he added, but because most operations rely on cultivars developed decades ago, “we haven’t adapted orchard grass that thrives in a warmer climate.”

Other crops affected by longer warm seasons? Tree fruits and wine grapes

“Virginia’s one of those places that we expect to get hotter and we also expect to get wetter,” said Benjamin Cook, a climate scientist with the National Aeronautics and Space Administration’s Goddard Institute for Space Studies whose research includes the effects of climate change on vineyards. Neither of those conditions are necessarily good for high-quality wine prospects, he said. Furthermore, farmers working in these areas face special risks because of the long time to maturity of their crops.

“Those are parts of the agricultural world that adaptation eventually becomes a lot more challenging, because you can’t switch crops from year to year,” he said. “You have to make a bet on something and wait four years to see if it pays off.”

Regardless of their specialty, all farmers face another consequence of shorter freeze seasons: more weeds and more pests.

“With longer growing seasons, with these warmer winters, the populations of insects are increasing, the mortality is lower, they can produce more generations a year, and that potentially presents a problem for agriculture and plants in general,” said Cook.

Those effects can be seen on the ground, said Thomason: “Maybe 30 years ago, we could stop worrying about them in early October, and now it may be a week or 10 days later.”

https://www.virginiamercury.com/ Virginia Mercury is part of States Newsroom, a network of news outlets supported by grants and a coalition of donors as a 501c(3) public charity. Virginia Mercury maintains editorial independence. Contact Editor Robert Zullo for questions: info@virginiamercury.com. Follow Virginia Mercury on https://facebook.com/thevirginiamercury and https://twitter.com/MercuryVirginia

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