Freeze warning question

[Scott Patterson]

The National Weather Service has issued a freeze warning since we're supposed to drop into the 20's tomorrow night (June 18-19).

In areas that can experience frost year round, I've always wondered what the purpose of such warnings are.

It seems useful for areas where people grow plants and crops that are cold sensitive, but no one in areas with a short growing season does this anyway (actually people do try and grow things like tomatoes here, but they always bring them indoors at night).

Does anyone know why the NWS still issues freeze warnings for mountain valleys and locations with cool summer nights? It doesn't hurt anything to issue such warnings, I was just curious.

[JonathanBelles]

I'll answer that from a north Florida perspective (agriculture). Each office has it's own requirements, and yours may be different from Tallahassee's. We have a lot of agriculture that does very well in subfreezing temperatures, but below a certain mark (usually 26F) they began to die. Freeze warnings are issued when there is a threat of subfreezing temperatures sometimes to let growers know they have to glaze their crops (which keeps them between 30-32F). Freeze warnings are dropped after a few hard freezes until meteorological spring begins in March. I've never been in a situation where hard freeze warnings are dropped, but that would be the next step. I think that the main reason that hard freeze warnings would be dropped would be because all crops in the area are dead, even the hearty ones.

There are a lot of reasons that freeze warnings are issued. Agriculture is probably just one of them, but it is the main one in my area. You could probably send an email to the NWS there to ask. I know that machinery (namely the shuttles at Canaveral) were also reasons for freeze warnings in the past. These were often internal outside of the NWS though.

[Scott Patterson]

I got an answer. It is because of alfalfa. Alfalfa crops can be damaged if the temperature drops much below 28F this late in the season.

The rest of the crops grown here aren't sensitive to such temperatures.

From the local newspaper today:

http://www.craigdailypress.com/news/201 ... g-tempera/

Hagen­buch said lettuce, kale and spinach should be fine if it gets down to 28 degrees, but zucchini and tomatoes are more vulnerable (everyone brings tomatoes in doors anyway on cold nights). If it gets much colder than 28 degrees, ranchers might not be able to harvest alfalfa as soon as they want.

“Things are growing quite well right now,” Hagen­buch said.

It is not unusual for the area to see such cool temperatures in June. On average, Steamboat at 6,770 feet has only 46 frost-free days each year, according to the Western Region Climate Center. By comparison, Leadville at 10,177 feet has 26 frost-free days on average, and the heat seekers in Grand Junction see 183 days.

Anyway, here is the freeze warning, but it doesn't mention alfalfa specifically:

http://forecast.weather.gov/showsigwx.p ... 6IWSZRdWSo

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
243 PM MDT WED JUN 18 2014

COZ002-190445-
/O.UPG.KGJT.FZ.A.0010.140619T0600Z-140619T1500Z/
/O.NEW.KGJT.FZ.W.0012.140619T0600Z-140619T1500Z/
CENTRAL YAMPA RIVER BASIN-
INCLUDING THE CITY OF...CRAIG
243 PM MDT WED JUN 18 2014

...FREEZE WARNING IN EFFECT FROM MIDNIGHT TONIGHT TO 9 AM MDT
THURSDAY...

THE NATIONAL WEATHER SERVICE IN GRAND JUNCTION HAS ISSUED A
FREEZE WARNING...WHICH IS IN EFFECT FROM MIDNIGHT TONIGHT TO 9 AM
MDT THURSDAY. THE FREEZE WATCH IS NO LONGER IN EFFECT.

* TIMING...FREEZING TEMPERATURES WILL OCCUR BETWEEN MIDNIGHT
TONIGHT AND 9 AM MDT THURSDAY MORNING IN LOW LYING VALLEYS.

* TEMPERATURE...DROPPING INTO THE UPPER 20S TO LOWER 30S.

* IMPACTS...FREEZING TEMPERATURES MAY DAMAGE SENSITIVE
VEGETATION.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A FREEZE WARNING MEANS SUB-FREEZING TEMPERATURES ARE IMMINENT OR
HIGHLY LIKELY. THESE CONDITIONS WILL KILL CROPS AND OTHER
SENSITIVE VEGETATION.