Frost and Frost / Freeze Conditions in WNC (4/17/10)
Find this article at:
go.ncsu.edu/readext?1643
go.ncsu.edu/readext?1643
en Español / em Português
Español
Português
English
El inglés es el idioma de control de esta página. En la medida en que haya algún conflicto entre la traducción al inglés y la traducción, el inglés prevalece.
Al hacer clic en el enlace de traducción se activa un servicio de traducción gratuito para convertir la página al español. Al igual que con cualquier traducción por Internet, la conversión no es sensible al contexto y puede que no traduzca el texto en su significado original. NC State Extension no garantiza la exactitud del texto traducido. Por favor, tenga en cuenta que algunas aplicaciones y/o servicios pueden no funcionar como se espera cuando se traducen.
Português
Inglês é o idioma de controle desta página. Na medida que haja algum conflito entre o texto original em Inglês e a tradução, o Inglês prevalece.
Ao clicar no link de tradução, um serviço gratuito de tradução será ativado para converter a página para o Português. Como em qualquer tradução pela internet, a conversão não é sensivel ao contexto e pode não ocorrer a tradução para o significado orginal. O serviço de Extensão da Carolina do Norte (NC State Extension) não garante a exatidão do texto traduzido. Por favor, observe que algumas funções ou serviços podem não funcionar como esperado após a tradução.
English
English is the controlling language of this page. To the extent there is any conflict between the English text and the translation, English controls.
Clicking on the translation link activates a free translation service to convert the page to Spanish. As with any Internet translation, the conversion is not context-sensitive and may not translate the text to its original meaning. NC State Extension does not guarantee the accuracy of the translated text. Please note that some applications and/or services may not function as expected when translated.
Collapse ▲berry mg
vol 11 no 33
April 17, 2010 (1 p.m.)
vol 11 no 33
April 17, 2010 (1 p.m.)
The NWS has issued a FREEZE warning for the blue shaded counties (Haywood, Jackson, Swain) in NC tomorrow morning as well as for counties near Boone. I know that we are getting ready for a busy weekend of cold protection at the Upper Mountain Research Station, Laurel Springs (forecast is for possibly a low of 34 F low tonight, but winds above 7 mph should keep us out of any frost problem – we will nonetheless have the frost alarm set at 37 F). Then, for Sunday night/Monday morning, the weather forecast is for 33 F as our low. Since winds are going to be much lower the 2nd night, we are looking for potential frost on Monday morning at this location.
What is different about a National Weather Service FREEZE WARNING is that this is a cold event in which there is potential for both sub-freezing temperatures and high winds (above 10 mph), and if you read the official NWS Freeze Text Warning below Table 1, you will see that they have indeed issued a FREEZE WARNING, but what I am trying to figure out sitting in Raleigh at my computer, is this the “real Mckoy?” My conclusion is that it is not. Depending on the area your farm is located in WNC, you may be dealing with a standard frost event (white frost), or in some areas where winds will be up all night as well as having potential to dip below 32 F, you are then dealing with a frost/freeze. But, I do not see any areas where there is true advective freeze potential tonight (winds above 10 mph and air temps < 32).
If you are a mountain grower, the simplest thing to do is to apply a row cover today – I hope they are not wet though? If they are wet from showers, they could be difficult to now handle and you will be forced to use sprinkling (if you have it). This is basically a 2-day cold event in WNC and so the covers would stay on until Monday (at least that’s what it looks like now). If you are in an area where winds will be sustained all night above 5 mph, row covers would definitely be the easiest way to protect (assuming they are dry). But, in the windy areas you will need to start irrigation up before the wet bulb drops below 32 F (much more detail about this problem below).
So, in order to kill some time on my day off, I thought I would begin to investigate in further detail several cities in the NWS Freeze Warning blue zone (above map), namely Waynesville (Haywood Co), Sylva (Jackson Co) and Bryson City (Swain). And, guess what I found out? I learned that with the exception of Waynesville, we are dealing with what would appear to be pretty classical radiation frost conditions in Bryson City and Sylva for both nights! You can hardly call winds of 2-3 mph a FREEZE? And, AccuWeather is showing no temperatures below 32 F on either night for Bryson City and Sylva. My advice to growers in these areas of the blue zone is to look for radiation frost.
If we examine Waynesville (town closest to Asheville), it is very interesting to see that this is what could be called a FROST/FREEZE, or a hybrid event in which you do have winds above 5 mph plus potential for temperatures below 32 F (but not for long – maybe 60-90 minutes before sunrise). Nonetheless you must prepare for a FROST/FREEZE differently than a Radiation Frost (which I believe that Bryson City and Sylva may encounter), and the main difference is that if you are sprinkling for cold protection, you must start the watering before the wet bulb temperature of 31 F is reached – that would be about 4 a.m. in Waynesville tomorrow morning. That would be the time to start irrigation up to avoid the “cold jolt” at start up. Now, on Monday morning, the Waynesville area is in what I would classify as a Radiation Frost condition, and in this case its a BLACK FROST. In a black frost the blossom can reach a killing point without the grower ever seeing evidence of ice crystals. So, in Waynesville on the 2nd night, your cut on for watering is at 2 a.m. (when wet bulb reaches 31 F). You will note that there is no wind the second night anywhere in these several mountain counties.
Table 1. A detailed investigation of the NWS Freeze Zone doesn’t support the warning of a FREEZE event, but there is potential for a FROST (white) tomorrow morning in Bryson City and Sylva, and in Wayesville it may be a hybrid cold event involving sustained winds and a brief period below 32 F.
| Sunday morning | Min Temp & | 6 a.m. | Hour when | ||
| Cloud cover | Dewpoint | Winds | Hours< 32 | WB at 31 F | |
| Bryson City | 10% | 36 (30) | 2-3 mph | none | Wb is 34 F |
| Sylva | 10% | 36 (30) | 3 mph | none | WB is 34 |
| Waynesville | 8-11% | 31 (25) | 5-6 mph | 1? | 4:00 a.m. |
| Asheville | 11% | 39 (32) | 7-8 mph | none | WB is 36 F |
| Monday morning | 6 a.m. | Hour when | |||
| Cloud cover | Min Temp | Winds | Hours< 32 | WB at 31 F | |
| Bryson City | 25% | 35 (30) | 1 mph | none | WB is 33 F |
| Sylva | 25% | 34 (29) | 1 mph | none | WB is 32 F |
| Waynesville | 25% | 31 (26) | 1 mph | 1-2? | 2:00 a.m. |
| Asheville | 26% | 37 (30) | 2-3 mph | none | WB is 34 |
What about Asheville? Skip down below and you can see the entire hour by hour forecast from AWIS in Table 2. Basically, from what I can tell about Asheville is that your winds will be sustained all night and morning and I do not see frost potential (even thought AWIS says there could be frost at 7 a.m.?). The key thing to do in this area is to set your frost alarm and then if it goes off monitor field conditions closely. A white frost is possible if the winds die down enough. I can assure you, that a minimum temperature forecast of 35 F could easily lead to a frost if winds die down. If you are using irrigation, there is little issue with evaporative cooling problems as your wet bulbs are above 32 both nights. Practically speaking, you do not have to be quite so careful about turning on and getting a cold jolt problem – that’s a good thing not to have to worry about!
Meanwhile, if you are in an area that is prone to a radiation frost tonight, like Bryson City or Sylva, then please set your frost alarm to go off at about 37 F, and then go to the field and monitor conditions the rest of the night (sorry about that). You would need to start irrigation as soon as you see evidence of ice crystals on plants. This could occur soon after your alarm goes off, and there is no point in my trying to estimate when that may be! In areas with sustained winds above 5 mph (like Waynesville), you have to be prepared to irrigate when the wet bulb temperature reaches 31 F, and if you wait past this time you risk causing evaporative cooling damage at start-up tonight. It looks to me like around 4 a.m. tonight the wet bulb will be 31 F in Waynesville and then at 2 a.m. tomorrow night.
WNC Freeze Warning
URGENT - WEATHER MESSAGE NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 424 a.m. EDT SAT APR 17 2010 ...FREEZING TEMPERATURES EXPECTED ACROSS PORTIONS OF THE NORTH CAROLINA MOUNTAINS TONIGHT... .GUSTY NORTHWEST WINDS WILL DEVELOP ACROSS THE MOUNTAINS THIS EVENING FOLLOWING THE PASSAGE OF A COLD FRONT. THE NORTHWEST WINDS WILL BRING MUCH COLDER TEMPERATURES ACROSS THE SOUTHERN APPALACHIANS TONIGHT. TEMPERATURES WILL CONTINUE TO FALL THROUGH TONIGHT...WITH LOWS RANGING FROM THE UPPER 20S TO LOWER 30S ACROSS THE NORTHERN MOUNTAINS AND PORTIONS OF THE SMOKIES. NCZ033-049>052-059-063-172100- /O.NEW.KGSP.FZ.W.0002.100418T0400Z-100418T1300Z/ AVERY-YANCEY-MITCHELL-SWAIN-HAYWOOD-NORTHERN JACKSON- SOUTHERN JACKSON- INCLUDING THE CITIES OF...NEWLAND...SPRUCE PINE...CHEROKEE... WAYNESVILLE...SYLVA 424 a.m. EDT SAT APR 17 2010 ...FREEZE WARNING IN EFFECT FROM MIDNIGHT TONIGHT TO 9 a.m. EDT SUNDAY... THE NATIONAL WEATHER SERVICE IN GREENVILLE-SPARTANBURG HAS ISSUED A FREEZE WARNING...WHICH IS IN EFFECT FROM MIDNIGHT TONIGHT TO 9 a.m. EDT SUNDAY. NORTHWEST WINDS WILL BRING A COLD CANADIAN AIR MASS ACROSS THE SOUTHERN APPALACHIANS TONIGHT. TEMPERATURES WILL FALL STEADILY OVERNIGHT...WITH SEVERAL HOURS OF FREEZING TEMPERATURES EXPECTED ACROSS THE NORTHERN MOUNTAINS AND PORTIONS OF THE SMOKIES AFTER MIDNIGHT TONIGHT. TEMPERATURES SHOULD WARM ABOVE FREEZING SHORTLY AFTER SUNRISE SUNDAY MORNING. PRECAUTIONARY/PREPAREDNESS ACTIONS... A FREEZE WARNING MEANS SUB-FREEZING TEMPERATURES ARE IMMINENT OR HIGHLY LIKELY. THESE CONDITIONS WILL KILL CROPS AND OTHER SENSITIVE VEGETATION.
The Asheville AWIS hour by hour table is provided below and note the “F” for FROST at 7 a.m. Sunday!
Table 2. AWIS Hourly for Asheville (MIN 35 F) for April 18 (Sunday morning).
Agricultural Weather Information Service, Inc. 60-Hr Detailed Forecast For Asheville_Munic, NC
Produced at 508 a.m. CDT on Sat Apr 17 2010
Day length= 13:12 / Sunrise at 6:54 a.m. / Sunset at 8:06 p.m. EDT
Saturday April 17, 2010 Sunday April 18, 2010
HR 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6
MAX= 73 MIN= 35
TDB 54 58 62 65 68 70 72 73 73 73 68 63 59 55 52 50 48 48 45 43 41 40 38 36
TDP 46 45 44 43 42 41 41 40 40 40 40 38 36 34 35 35 36 36 35 35 34 34 33 33
TWB 50 51 53 53 54 55 56 56 56 56 53 51 48 45 44 43 43 43 41 40 38 38 36 35
WSD 5 6 7 8 9 10 13 14 14 15 15 15 14 14 13 12 10 10 9 9 9 9 9 9
WDR NNW NNW NNW NNW NNW NNW NNW NNW
CLD SC SC SC SC SC SC CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL
INV -- -- -- -- -- -- -- -- -- -- -- -- -- -- 0 0 1 1 1 2 2 2 3 3
DFR -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
Sunday April 18, 2010 Monday April 19, 2010
HR 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6
MAX= 64 MIN= 36
TDB 36 41 46 51 56 59 62 63 64 64 60 57 54 51 49 47 46 45 43 42 41 39 38 37
TDP 32 32 31 30 29 28 27 26 25 25 24 25 25 26 27 29 30 31 31 32 32 32 32 32
TWB 34 37 40 42 44 46 47 47 47 47 45 44 42 41 40 40 39 39 38 38 37 36 36 35
WSD 8 8 9 10 12 13 13 14 14 13 13 12 12 10 12 12 13 10 9 7 7 7 7 7
WDR NNW N N NNW N E SSW NE
CLD CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL CL
INV 4 2 1 0 -- -- -- -- -- -- -- -- -- -- 0 0 0 1 1 2 2 2 3 3
DFR F -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
The light blue (38-40) is problematic! The dark green in north central piedmont is not without its potential for frost on Sunday morning should all the conditions needed for frost fall into place, especially light winds and temperatures at the canopy level that get down to below 32 F. You will see that AWIS is allowing the possibility of frost in north central piedmont tomorrow morning - table below
VIRGINIA
You will note there is a very large area covered in dark green for Sunday morning (30-35), so I am afraid this could be a long night for Virginia strawberry growers in these areas where minimums will be below the 37-38 F "frost threshold" and all growers in these areas must set their frost alarms! I would also have it set the in 35-40 range zones as well.
THE SOUTHEAST - SOUTH CAROLINA AND GEORGIA "APPEAR" TO HAVE DODGED THE BULLET, BUT NOT TENNESSEE!
able 2. AWIS FROST/FREEZE FORECAST for April 18 (Sunday morning)
AWIS Weather Services, Inc. North Carolina Frost/Freeze Forecast Produced at 516 a.m. CDT on Sat Apr 17 2010 ... Forecast for Tonight ... Northeast NC Coast Currituck/Camden/Pasquotank/Tyrrell Counties *** No Frost And/Or Freeze Danger Tonight *** -------- East Central/SE NC Coast Carteret/Pamlico Counties *** No Frost And/Or Freeze Danger Tonight *** -------- Southeast NC NWS FORECAST ZONES 87-90,96-101 *** No Frost And/Or Freeze Danger Tonight *** -------- North-Central NC Franklin County Area ** SCATTERED FROST COLDEST LOCATIONS ** Lowest Temperatures: 38 - 47 Louisburg Min 38 Range Dewpoint Temps: 32 - 38 Range Wetbulb Temps: 37 - 49 AVG Wind Direction/Speed: N 5 Long Periods of Calm AVG Sky Condition: Partly Cloudy
-------- North/Central NC Alamance County Area ** SCATTERED FROST COLDEST LOCATIONS ** Lowest Temperatures: 39 - 44 Graham_AG Min 42 Range Dewpoint Temps: 30 - 38 Range Wetbulb Temps: 37 - 49 AVG Wind Direction/Speed: N 6 Long Periods of Calm AVG Sky Condition: Partly Cloudy -------- South/Central NC Richmond County Area *** No Frost And/Or Freeze Danger Tonight *** Lowest Temperatures: 43 - 47 Ellerbe Min 47 -------- For more detailed information visit www.awis.com or call 888-798-9955. Copyright 2010 AWIS Weather Services, Inc. All rights reserved.
Good luck
Dr. E. Barclay Poling
Professor and Extension Specialist (Small Fruits)
Dept. of Horticultural Science
Campus Box 7609
NC State University
Raleigh, NC 27695-7609
919-515-1195
919-515-2505 fax
919-418-9687 cell
email: barclay_poling@ncsu.edu
Professor and Extension Specialist (Small Fruits)
Dept. of Horticultural Science
Campus Box 7609
NC State University
Raleigh, NC 27695-7609
919-515-1195
919-515-2505 fax
919-418-9687 cell
email: barclay_poling@ncsu.edu