NC ALERT: Another Cold Event Anticipated by Weekend (3:30pm, Tue., 3/24/15)

— Written By Barclay Poling
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fulks-sunset low resFig. 1. During the EASTER FREEZE of April 7-8, 2007, strawberry growers like Donnie Fulks, Fredericksburg, VA, had to pull out all the stops to bring his strawberry crop through this epic freeze event with the crop in full bloom, and temperatures in the teens! Not to mention winds that were gusting well above 10 mph in the early evening. The combination of row covers + irrigation was needed to pull the crop through. I don’t think we should be anticipating anything like the Easter Freeze of April 2007, but we do have some serious cold weather headed our way this weekend, and growers will need to study local weather forecasts closely, and take into consideration their crop stage, to come up with the correct protection strategy for their farm.

Good afternoon,

Fortunately, the strawberry crop in NC is not as far along in development today as it was when the 2007 “Easter Freeze” hit our state on April 7-8, but we do have “enough open blooms and exposed flower buds,” that strawberry growers should take quite seriously what may be our most severe “pre-blossom/blossom” cold event of the 2014-2015 season on  Saturday night/Sunday morning (March 28/29).

1. What makes this such a serious cold event? Note the very cold minimum temperatures that AWIS is now forecasting for Sunday morning, 3/29 (Fig. 1).

7daytemp.nc.10Figure 1. Note the dark gray areas across much of the central piedmont – these areas will be in the mid-20s on Sunday morning, 3/29, and that is cold enough to kill all open blossoms and even emerged flower buds (Fig. 2). In the light red areas (WNC and Foothills), the temperature minimums may  be in the low 20s, and the dark red areas will be close to 20 F. This is what makes this a potentially very dangerous cold event for then entire state. Temperatures of close to 20 F could be quite serious even for plants in the mountains that have just now begun to show a few emerged flower buds. Note the yellow areas may experience upper teens.

emerged critical tempFig. 2. At this stage in season, strawberry plants have lost their late winter “hardiness” and where an emerged flower bud could possibly tolerate a minimum temperature of even 20 F in early and mid-March, by the end of March we need to respect the possibility of even 25 F being critical to the emerged flower buds. By this weekend, strawberry plants in the central and western piedmont will have numerous “emerged flower buds,” and even some open blossoms (where row covers have forced the crop), and these could be damaged by temperatures in mid-20s. The open blossoms will likely be killed at 27-28 F.

AWIS 7-day Minimum temperature forecast for the state of NC:  AWIS NC Mar 24-31

Note these minimums in WNC on March 29th:

wncTable 1. Asheville may drop to 22 F; in the western piedmont, locations like Yadkinville will experience low 20s as well.

Please take this opportunity to investigate now what may be in store for you area with the much more detailed 10-Day Hourly forecast that AWIS produces for these locations in NC:

10-DAY DETAILED HOURLY WEATHER FORECASTS 

Ahoskie-Tri-Cou Albemarle_AP Andrews Asheboro
Asheville_Munic Beaufort-Michae Boone_NC Burlington-Burl
Cape_Hatteras_AG Chapel_Hill-Hor Charlotte Cherry_Point
Clinton_NC Concord_NC Currituck_NC Edenton-Northea
Elizabeth_City Elizabethtown_NC Erwin-Harnett_C Fayetteville_AP
Fort_Bragg/Simm Franklin/Macon_C Gastonia-Gaston Goldsboro_AFB
Goldsboro_NC Greensboro Greenville_AP_NC Hickory
Jacksonville Jacksonville_(A Jefferson_AP_NC Kenansville-Dup
Kill_Devil_Hills Kinston_AP Lexington-David Lincolnton_AP
Louisburg_NC Lumberton_AP_NC Mackall_AAF Manteo/Dare_Co
Maxton Mcalf_Bogue_Fiel Monroe_AP_NC Morganton-Morga
Mount_Airy-Moun New_Bern North_Wilkesbor Oxford_NC
Piney_Island_Bom Pope_AFB Raleigh-Durham Reidsville_AP
Roanoke_Rap_AP Roanoke_Rapids_R Rockingham_NC Rocky_Mount-Wils
Roxboro_AP Rutherfordton Salisbury-Rowan Sanford_NC
Shelby_AP_NC Smithfield_AP Southern_Pines Southport_NC
Statesville-Sta Tarboro_AP Wadesboro_AP Washington-Warr
Whiteville_NC Wilmington_AP_NC Winston-Salem

Example scenarios:

IMG_3310Fig. 3. A fairly “dormant looking” crop that I visited last week near Greensboro. But, I would say that by next weekend, 3/28-3/29, there will be a significant number of emerged flower buds on these plants. Some fairly new row covers are ready to be pulled back over the crop this week in anticipation of temperatures that might be damaging to emerged flower buds on Sunday morning, 3/29.

AWIS Detailed forecast for Greensboro, NC:

greensTable 2. The air temp minimum forecast for Sunday morning is only 26 F. That is cold enough to damage open blooms, but I would anticipate less threat to emerged flower buds (I don’t think any will be hurt at this temperature). Looking at Saturday morning, please note the min of 29 F. Also note winds of 7-8 mph. There should be good air mixing and canopy temps will be same as weather shelter of 29 F. Virtually no risk of any damage if this holds true for open blossoms (which there will be few), and emerged flower buds are safe. At this time, they (AWIS) see high winds in forecast on Sunday night/Monday morning. That can easily change. Note that dewpoints will be up a lot on Sun/Mon (mid 20s) compared to night before (low teens). Technically, Sat/Sun is shaping up to be what some call a “dry air” cold event, or black frost (in winds stay below 5 mph). There will be very little possibility of frost on Sat/Sun. The situation will flip the next night due to the higher moisture content of the air. If winds die down enough on Sun/Mon, there could be “white frost.”  Right now, my rec. would be to apply a row cover prior to the Sat/Sun cold event. I realize there are all kinds of crazy issues to work out with getting the covers on, and possible precipitation events later this week AS WELL AS WINDS. With so few blossoms on these plants, and only the emerged flower buds to primarily consider, just pulling those row covers on top the plants will provide an excellent margin of safety. I would keep them on through Monday morning, even though frost is not expected at this time (that can change if winds die down).

Rocky Mount: (please send me a crop photo if you are grower in this area). In this Table it is important to note that the minimum for Sunday morning is actually a little bit colder than for Greensboro, and with a minimum of 24 F (air at weather shelter), I would be quite concerned about open blossoms being killed, and this region of state is further ahead in blossom development than Greensboro. In other words, this region is more at risk with this cold event than Greensboro due to colder temp and more advanced crop. Even so, a single 1.2 oz row cover will provide adequate protection with this minimum (24 F), and no need for sprinkling on top of covers. Further, please note that winds will be an issue “all the way through” this period from Sat night (13-15 mph) through the morning on Sun (7-10 mph). The air will also be relatively dry (DP 16). Whenever you are dealing with high winds and low dewpoints, you are better off not getting involved with sprinkling (to be safe). The temperatures are not going to be low enough to justify sprinkling on top of covers.

rocky mount scen

Take a look at the AWIS 10-day hourly forecast for a location near you, and if you have some questions about what might be a good strategy for this coming weekend, send me an email. We can discuss your question(s), and perhaps assist some other growers who have similar concerns. If you do contact me, please tell me what your SkyBit is saying (if you have this service) for your farm this weekend.

Barclay

p.s. here is my evening SkyBit for Clayton. It looks like rains coming on Thursday. And, minimum in canopy of 26 on Sunday morning – that will make toast out of open blooms!

20150324st2.NCCLY

In looking at AWIS 10-day hourly for RDU (closest location to Clayton for this product), it is obvious that low DPs on  Sat night/Sun morning will be one factor to consider AGAINST usage of sprinkling:  If someone were to attempt sprinkling, they would need to start up at 1700 (5 p.m.) on Saturday afternoon (before wet bulb drops below 31 F), and run continuously  through Sunday morning at 8:30 a.m. Winds could also be a source of problem, as they might be as high as 13 mph when starting the system up on Sat. The conditions in the early evening will be quite winy, but then winds will begin to drop down into 7-8 mph range in morning hours. This is technically a frost/freeze event – these are always harder to handle with sprinkling. Row covers should be a better way to handle this.

rdu

Updated on Mar 24, 2015
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