I’ve received a handful of requests from folks asking about Growing Season frosts during the rest of March and April. This is a tricky thing to forecast because frosts – especially late-season frosts, have as much to do with topography as they do with weather. Since cold air is more dense, it will tend to ooze down valleys and along riverbanks. That means cold air can make it much further south along in a valley or along a river as it would generally.
It also means that forecasting a frost for every person at every point, six weeks out – trying to estimate a very specific number at a very specific site – is nearly impossible.
That said, estimating a percent-chance of a frost for general areas is something that is a bit more feasible. So I wanted to give it a shot. And, full disclosure: I’ve never done this kind of a forecast before. So, take this for what it is worth. I’m going to try to balance a six week forecast against topography.
Where we talkin’?
Generally, for this blog, when I talk about the Gulf Coast, I’m talking about parts of Louisiana, central and southern Mississippi, central and southern Alabama, and the western Florida panhandle.
Saying “Gulf Coast” isn’t perfect, but I’ve yet to find a name for this region that I’m comfortable using. For a while I tried to make LaMsAL (pronounced “Lam-suhl” rhymes with damsel) but it never felt right. I tried “northern Gulf Coast” but people in houston and Tallahassee felt left out.
So I just say “Gulf Coast” and leave it at that.
Underneath that, for this forecast, I’m taking that same area and chopping it up further.
The difficult thing for frost is that there is also a wide spread of frost potential from west to east within Zone 3 due to Cold Air Damming against the southern tier of the Appalachians. And I can’t really slice this up further, but I will try to notate (where I can) when the potential for a frost is limited to a particular direction.
Current Frost estimates
| Date in March | %-Chance Frost Zone 1 | %-Chance Frost Zone 2 | %-Chance Frost Zone 3 |
| 9th | 0 | 0 | 5 |
| 10th | 0 | 0 | 5 |
| 11th | 0 | 0 | 0 |
| 12th | 0 | 0 | 0 |
| 13th | 0 | 0 | 0 |
| 14th | 0 | 0 | 0 |
| 15th | 0 | 0 | 0 |
| 16th | 0 | 0 | 0 |
| 17th | 0 | 5 | 15 |
| 18th | 1 | 15 | 30 |
| 19th | 1 | 20 | 40 |
| 20th | 0 | 15 | 20 |
| ate in March / April | %-Chance Frost Zone 1 | %-Chance Frost Zone 2 | %-Chance Frost Zone 3 |
| 21st | 0 | 5 | 5 |
| 22nd | 0 | 0 | 5 |
| 23rd | 0 | 0 | 5 |
| 24th | 0 | 0 | 5 |
| 25th | 0 | 5 | 5 |
| 26th | 0 | 10 | 10 |
| 27th | 0 | 10 | 20 |
| 28th | 0 | 15 | 20 |
| 29th | 1 | 20 | 20 |
| 30th | 1 | 20 | 20 |
| 31st | 1 | 20 | 30 |
| 1st | 0 | 10 | 20 |
The reality of the situation
The toughest part is that frosts can occur in very specific spots and be highly localized, while somewhere a few miles down the road sees no frost. I can recall a few years ago when along the Pearl River Valley through parts of Mississippi and Louisiana there was a reasonable frost because cold air, that was trapped north of I-20, leaked down the valley and made it all the way into Louisiana.
No where else was below 39 degrees. But along that valley, temperatures tumbled down to 33 degrees.
Those are events that can’t really be forecast more than a day or two out. And that is why many people wait to put seeds into the ground until mid-April. It is the safest way to be sure that your area isn’t the “odd spot” that sees a random late-season frost.
