Thes dates are based on "statistical probabilities". There is no such thing as "average"
Acording to data collected over many years they come up with a
"statistical distrubutin" of the last frost date.
I dont know what the general practic is, but normaly you can say a 90% probability. MEANING; that after that date there is a 10% probability of frost. As you go further out, That 10% becomes smaller and thinner (but not zero).

Having said all this, last couple of years' data is nut
scientifically sufficient to come up with a reiable probabilty and date.

Cleo

I see you don't want a future estimated last frost date but the real magilla for years past.

Georgia fortunately has that information, but it's reputed to be one of the few states that does. It would certainly be easy enough for states to publish.

To see how it's presented for Georgia, just enter 30115 or any other Georgia zip code in the little zip code block, and then click on "Last Frost Date" in the next window. For this area of Georgia, the actual date is listed by year. You have to ignore 2010, of course.

You've probably seen this chart with various Massachusetts towns and dates with the probability of the last spring frost. But I don't think that's what you want.

I wonder if your Extension Office could help you, at least point you in the right direction?

This data from NOAA will tell you the max and min temperature on any date in the last few years for MASS and several other NE states.

Hope this helps.

to be safe assume frost temperature is 34* F

Here is a link that might be useful: Weather Data

This link will tell you the max,min and mean temperatures as well as growing degree days (used to calculate harvest date) for any US zipcode going back several years.

Here is a link that might be useful: Historical weather data

anny, Thanks for the link. Has a lot of data and info.

If I use their 15 years LAST FROST DATE for my area, with only 10% of probability after that, it will APRIL 14.
If I am willing to take a 25% chance it would be APR 5.

But luckily we have extended forcasts nowadays.
lets say that we are on March 25 and the forecast indicate a frost on Apr. 2,. Then I will be ready to jump.,
depending on what the revised forecast is on APR 2. If there is no more frost for the next two weeks, I am better than 98% covered, with only less than 2% probability.

Cyrus, you should be warned that extended forecasts are not all that acurate. say it's april first and the forecast shos everything will be ok till april 15. Your probally fine to april 6 becuase the first 5 or 6 days are pretty acurate but 15 days out is kind of a toss up. those forecasts are based on model runs and those computer models flip flop so often for anything more then 5 days out it is hard to go by a two week forecast.

if you want you can see the actual models by going to NOAA's website.

DAYLILY, you are right about that. But there are statistical odds. Say, we in GA take April 8 as sort of LF
bench mark. This means that probablity of frost after that is very small. And on the other hand, extended c@omputer
model forecast also shows no frost. So putting those two together
is a pretty good bet that there won't be any frost.

We must undestand that there are small risks.

Ok I Understand what your saying in our area the 90% no frost date is april 30th. I was looking back at some of the historical data for my area and in 1994 it got down to 32* F on June 28. I'm not sure I think that thats true because the day before and after both had lows in the upper 50s / low 60s. However what I'm trying to say like you pointed out is that there is always some risk. I would be crazy to wait until June 30th to put out frost tender plants and I'll continue to plant my crops the first two weeks of may. I am just saying which you obviously understand that just because your past you last AVG frost date and the computer shows no frost for the next two weeks does not mean your safe.

Easy. Go to weather.com. Type in your zip. Click on Ten Day. Scroll down to near page bottom and click Averages. You can see acual low temps per month or day by using java drop down. Click on daily averages to see what I mean.

I don't think cleo was looking for AVG temp more actual temp for past years.

Not only do you have to watch out for low temperatures, I watch wind and cloud cover. The absolute worst is cold, clear and perfectly still. We have had this happen to us the last several years on our last cold snap of the spring.

Jay

What Jay said is a good point.
A lot of times when the lows get down to freezing mark(frost),
it is the wind that can cause more damage than actual
temperature. That is why a simple cover can protect plants.

Plants are living things, just us. We loose more body heat and
moisture when it is windy and FEEL as if it is much colder than
thermometer reading.

daylilyfan, yes I know, but Weather.com also shows you ACTUAL record lows for all 365 days which I find helpful.

bigdaddyj

I couldn't find those actual temps for 365 days for years past. All I see are averages for time spans.

I also use weather.com to check on current temps as well as using the other link I posted for current and past actual temps.

anney, sorry if I confused anyone. What you will see is the RECORD high and low for all 365 days. Along with average temps per day. For instance, lets take March 15. It won't show temps for every March 15 in recorded history! But it will show the average high and low for all March 15's and it will show the record high and lows for all March 15's. If I click on Averages, then Daily, then scroll to March 15 I'll see this:

15 7:14 AM 7:10 PM 54°F 32°F 43°F 81°F (1990) 10°F (1993)

That's sunrise, sunset, avg H, avg L, Mean, Record high 81 in 1990 and Record low in 1993. I find these record Hs and Ls meaningful. Looking at that month's worth you can plan good plant out dates.

Not exactly what the poster was after but useful info and easy to get to.

This one does High, Low & Average temps, Dew points, Barometric pressure, Wind speed, Wind gusts, wind Direction, Precipitation and rainfall, and will graph it automagically by the day, week, month, year, for the location, day, week, month, year of your choosing.
www.wunderground.com

Have you tried weather.com or accuweather.com, then go to history section for your zipcode?

We have a full moon this year April 28th and again on May 27th. May 27th is kinda late but around the 23rd could get dicey.

If you have high pressure overhead anytime 4 days before or after the full moon (April 24th thru May 2nd) You can get a frost.

You heard it here first! I'll bump this post up around April 25th. Anyone sporting the big "H" will be scrambling, you'll see.

I built a 'Frost Date Finder' based on the NCDC's Freeze/Frost data. Se if this helps...

Here is a link that might be useful: Frost Date Finder

Bump,Bump...Frost warnings here tonight. Then, Low pressure coming in till Tues. And a frost warning again next weds after the low pulls out.

Hmmmmmmm...