Fig. 1. Minimum temp map for the region, Friday, 4/24 – more details in this advisory about areas that may be at real risk of frost tomorrow morning – a frost can be devastating to open blooms. What is especially interesting about this cold event is how late in the season it is occurring!

“Frost” is a word that ALL strawberry growers would rather not hear at this juncture in the strawberry season. But, the truth is that frost is very possible across much of piedmont and western areas of North Carolina tomorrow morning. What is remarkable is how late in the spring season this frost event is happening (Fig. 2).

Fig. 2. From Weather and Climate in NC, AG-375, 1988, p. 8.

BIg Frost in KY this morning!

For your information, there was a BIG FROST out in Kentucky this morning – they are usually a day ahead of us on cold events. So, I think we now need to take this potential frost event  seriously in areas of NC,  and around the region, where there is a forecast for temperatures in the mid-30s tomorrow morning.

Fig. 3. Current minimum temp forecast for NC. Most of the problem areas for frost are going to be in areas with teal color (36-38), and colder. In areas with blue, navy blue, pink, purple and gray, there is an excellent chance of frost tonight. And, if you are in one of these frost prone regions, I would take this opportunity NOW to pull a row cover…in the event you don’t have sprinkler irrigation. If you don’t have pipe in the field, and cannot make arrangements to get a row cover back on, then you might try running drip early tomorrow morning. Some growers have reported  success with using drip alone! You can start running the drip if your see frost crystals forming at the ground level. This is not a well researched technique, but who would ever have “thunk” we need to frost protect this late in April?

I am rushing this advisory a bit because I know that there are a number of growers who rely on row covers, and they will need as much lead time as possible to get the crop re-covered before tonight.  Of course, this type of frost episode is easily handled with sprinkler irrigation. Growers who have both options may wish to go with sprinkling because of convenience.

Specific disadvantages of row covers. Relative to sprinkler irrigation for blossom protection, row covers do require a tremendous amount of labor and lead time for deployment. For this and other reasons, many growers prefer sprinkler irrigation to row covers for frost protection at the strawberry crop bloom stage. Another reason why growers may prefer sprinkling in a heavier frost situation (and, this might be one), is that open blossoms in direct contact with a “frosted” row cover (a heavy frost will cause the covers to stiffen like cardboard) are often killed, and this type of “row cover” injury could affect up to 5% of the open blossom.  Another  point in favor of sprinkler use during bloom has to do with rapidly changing weather systems in North Carolina during the spring. As we have witnessed this week, weather systems and forecasts do “turn on a dime”  in this new era of climate change. Two days ago, I did not really think this was going to materialize into serious event, and now I am rushing to get this alert out to let North Carolina growers in the northern and western piedmont know that this could  be a damaging frost tomorrow morning! There are still a lot bloom out there! Thus, growers without access to a sprinkling system face a considerable challenge to quickly procure a labor force and apply row covers at 4-5 p.m. in the afternoon because of a last minute forecast for frost!! Growers with an “easy on, easy off” sprinkler system can more easily respond to the rapidly changing weather conditions that typically occur in North Carolina in late April.

Set those frost alarms on 37 F for irrigation and dripping

I would definitely be setting my frost alarm tonight at 37 F — to be safe in any growing region with a forecast of 37 F, and below. Here is how you can quickly gauge the danger you may be in if you are a NC grower:

NC Minimum Temp Table for the entire state: AWIS NC Apr 23-30

And, for some regions of NC, AWIS produces this frost/freeze alert (not for western piedmont, foothills, or mounatins)

AWIS Weather Services, Inc. North Carolina Frost/Freeze Forecast
Produced at  505 a.m. CDT on Thu Apr 23 2015

... Forecast for Tonight ... Northeast NC Coast                      
Currituck/Camden/Pasquotank/Tyrrell Counties      
** PATCHY FROST COLDEST PROTECTED AREAS **

Lowest Temperatures:      40 - 47
Elizabeth_City Min          41 
Range Dewpoint Temps:     28 - 42
Range Wetbulb  Temps:     39 - 50
AVG Wind Direction/Speed:  NW 10                          
AVG Sky Condition:     Partly Cloudy

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   45 - 52   54 - 60   48 - 55   45 - 52   48 - 54   54 - 60
--------

East Central/SE NC Coast                
Carteret/Pamlico Counties                         

*** No Frost And/Or Freeze Danger Tonight ***

Lowest Temperatures:      43 - 47
Morehead_City Min           46 

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   43 - 50   60 - 61   54 - 54   48 - 51   53 - 54   59 - 60
--------

Southeast NC                            
NWS FORECAST ZONES 87-90,96-101                   
** PATCHY FROST COLDEST PROTECTED AREAS **

Lowest Temperatures:      40 - 46
Elizabethtown Min           42 
Range Dewpoint Temps:     32 - 47
Range Wetbulb  Temps:     39 - 53
AVG Wind Direction/Speed:  NW  8                          
AVG Sky Condition:         Clear    

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   45 - 50   58 - 64   50 - 56   45 - 50   49 - 56   53 - 60
--------

North-Central NC                        
Franklin County Area                              

**** NEAR FREEZING COLD LOCATIONS  ****
** FROST COLDEST LOCATIONS **

Lowest Temperatures:      33 - 43
Louisburg Min               33 
Range Dewpoint Temps:     29 - 34
Range Wetbulb  Temps:     34 - 45
AVG Wind Direction/Speed:  NW  5     Long Periods of Calm 
AVG Sky Condition:         Clear    

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   42 - 49   50 - 58   43 - 51   40 - 47   43 - 50   45 - 56
--------

North/Central NC                        
Alamance County Area                              

**** NEAR FREEZING COLD LOCATIONS  ****
****  FROST LIKELY ****

Lowest Temperatures:      35 - 40
Graham_AG Min               38 
Range Dewpoint Temps:     23 - 34
Range Wetbulb  Temps:     34 - 45
AVG Wind Direction/Speed:  NW  5     Long Periods of Calm 
AVG Sky Condition:         Clear    

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   43 - 49   53 - 57   45 - 50   42 - 47   44 - 49   47 - 51
--------

South/Central NC                        
Richmond County Area                              
** FROST COLDEST LOCATIONS **

Lowest Temperatures:      40 - 42
Ellerbe Min                 42 
Range Dewpoint Temps:     28 - 36
Range Wetbulb  Temps:     39 - 47
AVG Wind Direction/Speed:  NW  7                          
AVG Sky Condition:         Clear    

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   47 - 52   56 - 60   49 - 52   46 - 49   49 - 52   48 - 56
--------

Interior/EC-SE NC                       
Wayne County Area                                 
** PATCHY FROST COLDEST PROTECTED AREAS **

Lowest Temperatures:      40 - 44
Goldsboro_AG Min            44 
Range Dewpoint Temps:     34 - 38
Range Wetbulb  Temps:     40 - 47
AVG Wind Direction/Speed:  NW  7                          
AVG Sky Condition:         Clear    

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

  04/25/15  04/26/15  04/27/15  04/28/15  04/29/15  04/30/15
  --------  --------  --------  --------  --------  --------
   44 - 47   56 - 60   49 - 52   45 - 48   48 - 51   54 - 59
--------

For more detailed information visit www.awis.com or call 888-798-9955. Copyright 2015 AWIS Weather Services, Inc. All rights reserved.

Fig. 4. Just for the historical record,  this was the NC forecast for Friday, 4/24, as of yesterday (4/22). You can see a pretty significant change occurred overnight if you glance at this map, and then look at the current one in Fig. 3. For example, RDU (Raleigh Durham) was in the green zone yesterday (40-42), but now in teal (36-38). That is a significant drop in just 24 hours!!

Looking at this new minimum temp map (the current one is reproduced again below):

Fig. 5. Current minimum temp map for NC on Friday morning

Special map notes (2 locations with 37 F minimum; one with frost forecast, and the other not?)

GSO (Greensboro) was looking quite safe yesterday, but I would definitely be setting a frost alarm in Greensboro tonight! In fact, I spoke to Mr. Kenneth Rudd this morning (Greensboro grower), and the real concern about this possible frost event in his area is with all the other transplants they have recently set out in the field, as well as with Chandler and Camarosa strawberry plants that are in bloom. Anyway, I took a look at the latest AWIS hourly detailed forecast for Greensboro, and there is NOT an indication for frost at this time (3:30 p.m., Thur). But, they are right on the edge. And, with winds not being quite so high tonight, I can easily see where frost could occur in this location (Table 2).

Table 2. Frost is not in Greensboro forecast at this time for FRI morning, but if those winds die down tonight, it is possible things could really change in a hurry. Growers in areas where the strawberry patch is protected by woods, are going to be very frost prone tonight.

If we drive west of Greensboro in I-40 for about 45 min we reach Statesville (depending on traffic and how fast you drive?), and what is most interesting is that Statesville does have a forecast for FROST at 5 a.m.. Note that he minimum air temp is the same as Greensboro!

Table 3. To give you an idea of what a fine line we are dealing with regarding frost potential tomorrow morning, Statesville has the SAME minimum air temp (37) as Greensboro, and winds are very similar. The one difference is the slightly higher dew point in Statesville (31 F at 6 a.m. vs. 28 DP in Greensboro). Thus, having a DP  a few degrees higher could make the difference tomorrow morning.

Now it’s your turn to check on the AWIS location nearest your farm to get an idea of whether or not there is potential for FROST in the morning:

10-DAY DETAILED HOURLY WEATHER FORECASTS 

To assist growers in other states, here are your respective AWIS  hourly forecasts for SC, VA, TN, KY and MD. Sorry, we did not have funds to purchase additional state licenses from AWIS.

SC:  10-DAY DETAILED HOURLY WEATHER FORECASTS 

VA Minimum Temp Map for tomorrow morning:

Fig. 3. Much of VA will be 35 F and colder, but frost is possible in areas in light green (35-40) as well! Be sure to check an AWIS location close to your farm to see what AWIS believes the potential may be for a frost tomorrow morning?

Here you go!

10-DAY DETAILED HOURLY WEATHER FORECASTS 

TN: 10-DAY DETAILED HOURLY WEATHER FORECASTS 

KY: 10-DAY DETAILED HOURLY WEATHER FORECASTS 

MD: 10-DAY DETAILED HOURLY WEATHER FORECASTS 

AWIS frost forecasts are there for your guidance only – you may, or may not get a frost:

NO WEATHER SERVICE IS CAPABLE OF FORECASTING FROST RELIABLY!!!
The reason why this is so difficult to get right has to do with the extreme difficulty of forecasting with accuracy wind speeds and cloud covers.

Another precauation:  AWIS can be off by a few hours!!!

I have observed this season that the AWIS forecasts for frost are often 1-2 hours “late”…meaning that if they (AWIS) see frost potential at 5 a.m., it could be 3 a.m. when ice crystals begin to form. The only way for you not to get blindsided is to set that alarm to go off at 37 F, and then go out into your patch to see for  YOURSELF what the actual situation may be? You may find, as one grower did in Maryland this early morning, that the forecast for 7 mph winds at 6 a.m. was dead wrong (the winds were completely still), but overcast skies moved in overnight, and there was no frost formation. There simply is NO SUBSTITUTE for the grower heading out to his/her field to see what is actually taking place. So, if you get anything from this advisory, please remember to be sure to set you frost alarm at 37 F tonight, especially for growers in areas where there is a good chance of air temperature minimums of 37 degrees F, and lower.

Remember, those who snooze, lose!