FRIDAY MORNING FROST: NC and Regional Update at 3:30pm (4/23/15)

— Written By Barclay Poling

7daytemp.se.2Fig. 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).

frost spring ncFig. 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.

7daytemp.nc.2 (1)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.

7daytemp.nc.4Fig. 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):

7daytemp.nc.2 (1)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).

greenTable 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!

stateTable 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 

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

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 

Aiken_AP Anderson_Co_Air Barnwell_AP Beaufort_Cnty_AP
Beaufort_SC Bennettsville_Je Camden_AP Charleston_Exec_
Charleston_Muni Cheraw_AP Chester_AP Clemson-Clemson
Columbia-Columb Columbia/McEnti Columbia_Metro Conway_AP
Darlington Florence_SC Georgetown_AP_SC Greenville_Donal
Greenville_Down Greenville-Spart Greenwood-Green Hartsville_AP
Hilton_Head_AP Kingstree_AP Lancaster-McWhir Laurens_AP
Manning_AP Marion_AP_SC Moncks_Corner_AP Mount_Pleasant_A
Myrtle_Beach Newberry_AP North_Myrtle_Be Orangeburg-Oran
Pickens_AP Rock_Hill Spartanburg_Down Summerville_AP
Sumter_AP Sumter_SC Walterboro_AP Winnsboro_AP

VA Minimum Temp Map for tomorrow morning:

7daytemp.at.2Fig. 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 

Abingdon Ashland_VA Charlottesville Chesapeake-Ches
Culpeper Danville Dublin/New_Riv Emporia_VA
Farmville Fentress_Naval_A Fort_Belvoir/Da Fort_Eustis/Fel
Franklin/J_B_Ro Hillsville Hot_Springs/Ing Jonesville_AP
Langley_AFB Leesburg/Godfre Louisa-Louisa_C Lynchburg
Manassas_Muni(A Marion/Wythev Martinsville Mecklenburg/Bru
Melfa/Accomack Newport_News Norfolk_Hampton_ Norfolk_NAS
Norfolk_VA Oceana Orange_VA Petersburg_(AWO
Quantico Richlands_AP Richlands_VA Richmond
Richmond_Chester Roanoke Shannon_Arpt Stafford_AP_VA
Staunton-Shenan Suffolk-Suffolk Tappahannock_AP Virginia_Tech_A
Wakefield_AP Wallops_Island Warrenton_Fauqui Washington_Dulle
West_Point_VA Williamsburg_VA Winchester_Rgnl Wise/Lonesome_P

TN: 10-DAY DETAILED HOURLY WEATHER FORECASTS 

Chattanooga/Lov Clarksville_TN Crossville_AP Dyersburg
Elizabethton_AP Jackson_TN Knoxville_AP Memphis_AP
Millington Nashville_Metro Oak_Ridge_TN Smyrna
Tri-City_RGNL_AP

KY: 10-DAY DETAILED HOURLY WEATHER FORECASTS 

Bowling_Green Covington Danville-Powell_ Fort_Campbell
Fort_Knox/Godma Frankfort_AP Glasgow_KY Henderson_City
Jackson_KY Lexington_KY London_Corbin Louisville_AP
Louisville/Bowm Middlesboro_AP Monticello_KY_AP Murray_AP
Owensboro_AP Paducah Richmond_Madison Somerset(AWOS)

MD: 10-DAY DETAILED HOURLY WEATHER FORECASTS 

Aberdeen Andrews_AFB Annapolis_Naval Baltimore_Sci_Ce
Baltimore/Wash Cambridge/Dorche College_Park_AP Cumberland_AP
Easton_MD Fort_Meade Frederick_MD Gaithersburg_AP
Hagerstown_AP Leonardtown Middle_River Oakland_MD_AP
Ocean_City_AP Patuxent_River Salisbury Stevensville_AP
St_Inigoes/Webst Washington_DC_AP Westminster_AP

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!

Dr. E. Barclay Poling
Professor Emeritus (Strawberry Plasticulture Researcher)
Department of Horticultural Science
Campus Box 7609, 162A Kilgore Hall
NC State University
Raleigh, NC 27695-7609
“An idealist believes the short run does not count. A cynic believes the long run does not matter. A realist believes that what is done or left undone in the short run determines the long run.”

Sidney J. Harris, In: Reclaiming a Lost Heritage – Land-Grant & Other Higher Education Initiatives for the Twenty-first Century