Principles of Freeze Protection for Fruit Crops
For a long time Alabama as well as much of the rest of the United States was provided with specific agricultural forecasts by the National Weather Service (NWS). However, in April, 1996 in a budget cutting move, the NWS closed all of its agricultural weather service centers including the one located at Auburn University. As a result, growers who desire specific agricultural weather information must now subscribe to one of two private agricultural weather firms, one located in Auburn, AL and the second in the Northeast. Some growers have contracted with private meteorologists for weather information.
The NWS continues providing similar forecasts to what has been provided in past years, but this information is of a general type and is not intended for direct agricultural application. The NWS Birmingham office serves most of Alabama while the Mobile office serves several southeastern counties. Weather information from NWS can be obtained by NOAA radio, special bulletins via TV and radio, newspaper and the internet. General weather forecasts and current conditions are always available via TV and internet links provided by special weather channels and local TV stations.
Frost/Freeze warnings are issued by the National Weather Service according to forecast conditions. Table 1 explains how the wording of these warnings should be interpreted. The type of warning given will assist the grower in understanding which if any of his freeze protection methods may be effective. For example, a "Freeze" warning implies that winds may be too high for successful use of helicopters, wind machines or overhead irrigation.
|WARNING||AIR TEMPERATURE||WIND SPEED|
|Frost||Above 32F||Below 10 mph|
|Frost/Freeze||Below 32F||Below 10 mph|
|Freeze||Below 32F||Above 10 mph|
Until April of 1996, Alabama's Agricultural Weather Program at Auburn University was providing over 900 individual weather products via the internet. Part of this information was originating from 15 remote weather stations located strategically throughout the state. Currently some 15 remote stations are supplying weather information (Table 2). Previously, each of these stations supplied hourly (real time) information that was made available via internet to anyone and via specific networks to university workers. Today, only information for the past 30 days and the past 24 hours (ending at 7 AM each morning) is available via the internet or internal university networks. Presently growers can only access this information via the internet through a private firm. Efforts are being made to enable growers to access real time information from the remote weather stations as could be done previously via internet or bulletin board. A voice modem that provides real time information for growers is being currently operated at one of the remote weather stations.
NAME OF STATION
|Grand Bay||Mobile county, 5 miles NW of Grand Bay||30.52||88.28||110|
|Fairhope||Baldwin county, at Gulf Coast Substation off Hwy AL 105 in Fairhope||30.55||87.88||230|
|Semmes||Mobile county, beside Hwy US 98 at Mary Washington High School in Semmes||30.70||88.25||210|
|Brewton||Escambia county, at Brewton Experiment Field about 4 miles northeast of downtown Brewton, some 3 miles off US Hwy 31||31.14||87.05||160|
|Headland||Henry county, beside Hwy US 31 at Wiregrass Substation in Headland||31.58||85.39||370|
|Union Springs||Bullock county at Turnipseed/Ikenberry Place Substaion 6 miles east of Union Springs||
|Marion Junction||Dallas county, at Black Belt Substation near Marion Junction off US 80 onto County road 45||32.47||87.22||200|
|Milstead||Macon county, at E.V. Smith research Center one mile north of I-85 near Shorter||32.45||85.88||251|
|Auburn||Lee county, on old Agronomy farm one mile east of Auburn University main campus, beside US 29||32.60||85.50||652|
|Prattville||Autauga county, at Prattville Experiment Field on County Rd. 4, off US 31, 4 miles south of Prattville||32.43||86.45||200|
|Thorsby||Chilton county, 50 yds. from Chilton Area Horticulture Substation Hdqts. beside county Road 29. (4 miles west of I-65)||32.92||86.67||680|
|Cullman||Cullman county, at North Alabama Horticultural Substation, 4 miles east of I-65||34.18||86.85||800|
|Belle Mina||Limestone county, at Tennessee Valley Regional Extension Center located 2 miles north of Belle Mina (1 1/2 miles east of I-65)||34.70||86.88||600|
|Meridianville||Madison county, on agricultural research farm of Alabama A&M University, beside US 431, 3 miles north of Meridianville||34.97||86.50||850|
|Ider||Dekalb county, located in Ider near city hall||34.70||85.67||1000|
1 All remote weather stations are comprised of Campbell Scientific CR-10 units.
Growers are reminded that forecasts by the NWS are generally based on temperatures for warmer, urban areas. Many of the locations are for airports where temperatures are almost always warmer than surrounding areas. The more rural farm areas most often experience temperatures during freeze events that are three to six degrees colder than forecasts. In some cases, the very coldest locations in an area may be as much as eight to ten degrees colder than the forecast. It is also possible to have frosts in rural areas when temperature forecast for urban areas are for mid to high 30's with no frost.
When using forecasts, no matter who is issuing them, it is always wise to continue relying on the updated, latest forecast for the freeze event. In addition, it is worth noting that forecasts are given for temperatures in an area at the 5-foot height. On calm nights, temperatures at the soil surface may be several degrees below those at the 5-foot height. This is especially applicable to crops such as strawberries that are located on the soil surface.
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