Strategy for Tonight – for NC Growers but Relevant to Other States and Regions (11:20am, 3/26/14)

— Written By Barclay Poling

pecip rate

Table 1. This irrigation rate table will be very important to growers in the Carolinas tonight

Intro:  This will be an “irrigation night” for many growers in Carolinas, and this table tells you the sprinkling rate needed for the minimum air temps shown. You can see that with no winds, a sprinling system can be very effective! Even with lows of 20 F and 2-4 mph winds, a precipiation rate of 0.21 inch/hr is adequate.

RECAP OF LAST NIGHT AND THIS MORNING

It was a very difficult night across the Carolinas and I am still waiting to hear back from many of you who I spoke with yesterday. As with any of these types of events, there were some “unexpecteds”…take for example, a conversation I had with Ron Cottle, Faison, NC, at 8 p.m. last night…he had very high winds in forecast the whole night, but guess what happened at 4 a.m. today? Right, the winds dropped to below 5 mph, and he could see frost beginning to form in low spots AT THAT TIME, so he went with this “gut” and turned on the irrigation in just those fields that had the worst air movement – woods surrounding these fields. He did not run at the home farm that is very open – winds stayed up. The minimum was 28 F, and I said that blossoms could have survived to that absolute temperature, but if “ice crystals” are forming, that’s a different ball game! He just sent texxt message now, and things turned out ok – no apparent cold jolt issues from turn on below wet bulb of 31 F (fortunately his dew points were quite high relative to other regions, like our western piedmont where DPs were incredibly low). For Ron, who is in our eastern NC region, his interest is now tonight. The plan is to start irrigation up this evening sometime between 6 and 6:30 p.m. – before the wet bulb drops below 31. This is not up for negotiation folks! Tonight, Ron’s area and just about every place I’ve studied on the map here is going to have very dry air. In fact, dewpoints are so low that this is what I talk about on my personal phone greeting today – the need to start irrigation up early!

720 a.m. cronos

Figure 1. Later today if time permits, I will do some more “digesting” about how things played out last night and this morning, but I did pull this surface obs map off of AccuW at 7 a.m. for winds (next figure), and the winds truly were all over the map last night.

winds

Figure 2. The black areas are no winds, and you can interpret the wind speeds from the color gradient bar below. Dark blue was 6-8 mph at about 7 a.m. this morning. Earlier in the evening, the northwestern piedmont had incredibly high winds, and I am very glad decisions were made out in that part of the state to not attempt sprinkling (alone) – it would have been potentially devastating! This area of the state was not “at risk” like eastern areas, and they truly lucked that minimum temps were not any colder. This is where the forecast was “off” a lot in some areas – it was calling for several degrees colder than it turned out.

7 a.m. temp

Fig. 3. Min. temps at about 7:05 a.m. are shown in this map – we definitely lucked out! I just got my call from Kenneth Rudd in Greensboro (10:20 a.m.), and he reported their minimum was only about 27-28 F. Their covers on the home farm did freeze up last night (lots of rain yesterday), but they still kept the buds about 33 F underneath! This is some very good information to have, as no one has done any research on how much warmth to expect under a frozen cover. He said they probably lost blossoms in touch with frozen cover. He did not run water on the home farm, but did at another location where they had row covers and cranked up at 2 a.m. when the blossoms to 33 F, and the irrigation on the covers kep the blossoms at 34 F all night. At 8:30 a.m. they cut off when blossoms got to 35 F. When I asked Kenneth what it was like last night, he said, “It was really different!”  At one point in the early evening it was even snowing for a while, and the winds would start and stop. He will share his final report later today.

Much colder tonight?

Yes, I believe it will be. We definitely did not get the low temps they were calling for this morning (and we did not get blossom damage either, so it is worth reading these advisories ’cause you got something worth keep’n), but though I am concerned about low temperaturess tonight for the ROW COVER PEOPLE OUT THERE (those 1.25 oz covers are definitely going to be at their limit with temps in low 20s), I am not so focused on the minimum temperature tomorrow morning if you are an IRRIGATION ONLY person.

What is far more important to those of you who have only sprinkler irrigation is:

  • 1) knowing that  winds will not be a factor tonight – that’s right, “0” mph for long periods, and
  • 2) the air is incredibly dry today!  You don’t care so much about the final minimum temperature in the canopy as a ROW COVER person must be. Nope, you need to focus on WHEN TO START THE SYSTEM UP.

IRRIGATION PEOPLE:

So, yes, it is well to see these minimum temps at maybe 6 a.m. tomorrow morning, but what does that really mean if you are running sprinklers?

thur monrFig. 4. So, here you can see the minimum temp for tomorrow morning will likely be very cold in all those dark gray areas (24-26) across eastern piedmont, all of interior coastal plain, some coastal areas, and the Sandhills.

But, if you are sprinkling, THE TABLE at the beginning of this advisory is the main thing you need to know as far as minimum temperature information. Even with lows of 20 F (not likely), and 2-4 mph winds (??), a precipiation rate of 0.21 inch/hr is adequate.

Let’s provide an example for the IRRIGATION PEOPLE on when they should start tonight. For example, “irrigation” growers who live near me in Raleigh/Durham,  will need to start at 7 p.m. (sunset 7:31 p.m.).

AWIS Hourly Forecast For Raleigh-Durham, NC     
Produced at 10:00 a.m. CDT on Wed Mar 26 2014
Day-Length = 12:21 / Sunrise at  7:10 a.m. / Sunset at  7:31 p.m.

Local               Forecast For  Wednesday     March 26, 2014 
Hour  00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
                      MIN= 27                    MAX= 47
TEMP  38 37 35 34 33 31 30 29 27 30 33 36 38 40 43 44 47 47 44 41 38 36 34 32
DEWP  28 27 26 25 25 23 22 21 19 18 15 11 10  7  6  6  5  5  6  7  7  8  8  9
WETB  34 33 32 31 30 28 27 26 25 26 28 29 30 30 32 33 34 34 33 31 29 28 27 26
WNDS   9  9  9  8  7  6  6  5  5  7  9 13 13 13 13 13 11 10  8  5  1  1  1  0
WNDD       WNW      WNW        W       NW       NW      WNW      WNW        N
CLDC       CLR      CLR      CLR      CLR      CLR      CLR      CLR      CLR
INV    0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  1  4
DEWF                        F                                                
POP6        11        3        0        1        1        0        0        1
Q1     0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0

Local               Forecast For   Thursday     March 27, 2014 
Hour  00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
                      MIN= 25                    MAX= 58
TEMP  31 30 29 29 28 25 25 27 28 32 37 42 46 50 54 55 58 58 56 54 52 52 51 49
DEWP   8  7  7  8  9 11 11 10 11 11 12 11 12 12 12 13 14 14 18 20 22 26 29 31
WETB  25 24 23 24 23 21 21 22 23 26 29 32 35 37 39 40 42 42 42 41 40 41 42 41
WNDS   0  0  0  0  0  1  1  1  2  6  9 13 13 14 15 15 16 17 15 13  9 10 11 13
WNDD         N      ESE      SSE        S      SSW      SSW        S        S
CLDC       CLR      CLR      BKN      SCT      SCT      FEW      CLR      CLR
INV    5  6  7  7  8  7  7  6  4  1  0  0  0  0  0  0  0  0  0  0  0  0  0  0
DEWF

Table 2. In RDU area the wet bulb reaches 31 F at 7 p.m. (1900). This is 30 min before sunset! It is crucial to have water running by this hour to avoid causing a “cold jolt” at start up. Both high winds (not a factor tonight) and low dewpoints (10 F is an incredibly low DEWP at 7 p.m.), DRIVE evaporative cooling, which is the biggest enemy so sprinkler irrigation for frost/freeze protection. Note the air temp will be 41 F at 7 p.m. NEVER EVER START SPRINKLING ON A LOW DEWPOINT NIGHT AT A WET BULB OF LESS THAN 31 F, unless you are interested in running a science experiment on your crop?

No doubt, if you are starting irrigation at 7 p.m., this means that it will be a very long night and morning. You will not be able to shutdown in the morning until the wet bulb reaches 31-32 F, which is not going to occur until almost 11 a.m. on Thursday.

In my next post, I will elaborate on stategies for the ROW COVER PEOPLE, but let me say now that if your area is likely to experience lows in the very low 20s, and you have an irrigation set-up, I would plan on using it. Even if you don’t need it, get it ready as an insurance policy against a forecast that may not be cold enough, or a row cover that doesn’t perform up to its “billing”.  I will be sharing information in the next advisory showing we got 25% bloom damage at Clayton last year from a 20 F minimum and a 1.25 oz cover. So, I don’t trust a row cover of this weight for temperatures this low. I would set up the irrigation system today so that you have the option to run water on the covers in case it gets seriously cold out there tonight and tomorrow morning. I will also review the basics on how to run water on covers (again) in the next advisory.

FYI here is my SkyBit for Clayton for tomorrow morning. It is helpful to me for you to forward your SkyBit to me if you have questions. My text number is 9194189687. Very little time for calls today.

Notes on this SkyBit:

    1. Min in canopy Thur is 22 F (this will kill open blossoms, ALL popcorns and could do major damage to larger tight buds)
    2. Min at weather shelter 26 F (4 F higher than ground level)
    3. Note in very bottom table that wet bulb will be 31 F at 6 p.m., and air temp 41 F – that is when you must start irrigation up

Dewpoint is only 12 F – very very dry air

clayt

Updated on Mar 26, 2014
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