Perfect Conditions for FROST on Tuesday Morning (5:30pm, Mon, 3/21/16)

— Written By Barclay Poling
en Español

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Collapse ▲ 1. It will definitely be cold enough for frost in most areas of NC tomorrow morning – with so much of the crop in tender bloom stage, this could be a serious cold event if growers don’t take precautions! A majority of growers have already applied row covers. But, some growers may be using sprinkler irrigation for frost protection tomorrow morning, and this can also be very effective. This advisory contains some review information about correct usage of sprinkling for a radiation frost.

Dear Agents, Agronomists and Growers,

Tonight’s conditions are perfect for a Radiational frost. This type of cold event is caused by longwave radiational losses of heat from the ground and solid objects (like a strawberry blossom) and occurs when clear skies and calm winds allow an inversion to develop and temperatures near the surface drop below 32 F. Also,  dewpoint (DP) temperatures tonight are near or above the freezing point (0 F), and this indicates the lower atmosphere is relatively moist, and if you are using sprinkler irrigation, you will need to pay very close attention to the start of ‘‘ice crystal’’ formation on strawberry plant tissues. Any surface moisture, including ice crystals, can serve as an important extrinsic agent on the plant surface  along with Ice-Nucleic Active (INA) bacteria. Surface nucleators may trigger ice formation inside plant tissues, and whenever ice forms in the plant tissue, there will be damage regardless of how long it took to reach that point.

For growers using sprinkler irrigation, the  sprinkling should be initiated at the first appearance of frost ice crystals to avoid damage to open blossoms. If you have already applied row covers to prevent frost damage tonight, there is nothing else to be done.  But, if you are using sprinkling, you must plan on visiting your strawberry planting on a frequent basis during the night to observe with a flash light when ice crystals start forming on vegetation near the ground level, or even on top of row covers that be rolled to the side. As soon as you detect any frost forming on exposed strawberry plant tissues, turn the water on!

If you are in the Raleigh-Durham area, AWIS weather services is forecasting that the first signs of FROST might be around 5 a.m. tomorrow morning (table below). Frankly, this is only a guess! It could be that FROST could start forming much earlier in the morning than 5 a.m., and I am aware of situations when AWIS called for frost at say 5 a.m., but then I would later learn from someone in the area that they saw ice crystals as early as say 2 a.m.!

So, the AWIS forecast is best utilized to get an idea about whether conditions might favor a frost (and they do in many areas tonight), BUT never count on them to Time the Frost for you! If you are using sprinkling, it is your job to monitor field conditions yourself to see when ice crystals start forming.

rduTable 1. Please note how winds will die down this evening (Mon) and by Tue morning will be “0 mph” at 5 a.m. In addition to no winds, skies will be clear in RDU area, and dewpoints are in the perfect range for frost formation on Tuesday morning (27-29)…there is plenty of moisture in the air for frost to form. Though the air temp minimum for RDU will be 35 F, that is definitely cold enough for frost formation at canopy level where it will drop below 32 F. AWIS is saying the FROST will occur at 5 a.m., but it could be MUCH EARLIER IN THE NIGHT! Growers using sprinkling are 100% responsible for monitoring their crop during the night to see when ice crystals begin to form.

When to shut down sprinkling?

Wet bulb temperature can be used to safely determine when sprinkling can be
shutdown in the morning – water can be safely turned off when the wet bulb
temperature is above 32oF. In the Raleigh Durham area, please note wet bulb will be at 35 F at 7 a.m. – that is when it “should be” safe to shut down. But, I would wait a little longer and make sure the ice is nicely melting. Waiting for all of the ice to melt is an older method that can also be effective tomorrow morning for knowing when to safely shut down under the kinds of conditions expected tomorrow morning.

You can look at the bottom of the SkyBit forecast below to see an hourly  table that shows when the wet bulb will be above 32 F at Clayton tomorrow morning (answer is sometime between 7 a.m. and 8 a.m.)

20160321st2.NCCLYTable 2. Clayton is about 20 miles southeast of Raleigh, and at this location the minimum at canopy level is going to be 31 F. That is cold enough for good frost formation! We cannot know exactly when ice crystals may begin to form at the canopy level, so a grower would need to monitor the crop directly. Most growers using sprinkling will set a FROST ALARM at a specific temperature, and it might be well to consider setting it around 37-38 F for tonight (to be safe).

If you wish to become a real expert on Sprinkler Irrigation for Strawberry FROST and FREEZE protection, you may wish to download this document: StrawberryPlasticulureAdvisoryApril1505

Here is the latest update from AWIS for our region:

Detailed forecasts for MD, VA, NC, SC and GA

MD minimum temps for tomorrow morning in Mid-Atlantic


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



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



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

SC minimum temps for tomorrow morning across Southeast, including SC


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



Albany_Municipa Alma/Bacon_Co Americus_AP Athens_Municipa
Atlanta/DeKalb Atlanta/Fulton Atlanta_Intl_Ar Atlanta_Paulding
Augusta/Bush_Fi Augusta_Daniel_F Bainbridge_GA Blakely_AP
Brunswick_GA Brunswick/Glync Canton_GA Carrollton_AP
Cartersville_AP Claxton_AP Columbus_GA Covington_GA_AP
Dalton-Dalton_M Douglas_Muni Dublin/WHBarron Fitzgerald_AP
Fort_Benning Ft_Stewart/Wrig Gainesville_AP_G Greensboro_GA
Homerville_AP Hunter_(AAF) Jesup_AP La_Grange
Lakeland Lawrenceville_AP Macon_AP Marietta
Marietta/Cobb Milledgeville_AP Moultrie_Muni_AP Newnan-Newnan_C
Peachtree_City Rome_GA Savannah Statesboro_GA
Swainsboro_AP Sylvania_AP_GA Thomaston_AP Thomasville_AP
Thomson_GA Tifton_AP Valdosta Valdosta/Moody
Vidalia Warner_Robins_A Washington_GA Washington_GA
Waycross_AP Winder_AP

Good luck!

Dr. Barclay Poling,

Retired Strawberry and Muscadine Grape Specialist

p.s. If you are using sprinkling, remember the saying, “Those who snooze, lose.”  Be sure to set that frost alarm!