In the below two strings (weather mesures) I need to find with a regex expression the first `"xxxFT"` value after `"BKN"` then extract only numerical value : `xxxx`

In the 1st String final value will be `2400` and `700` in the second.

Between `"BKN"` and `"xxxxFT"` ther could be an additionnal word or not, it depends. ie : `"BKN CB 2400FT"` or `"BKN 700FT"`

```
String str1 = "4000M WX MODTSRA CLD FEW 600FT BKN CB 2400FT BKN CB 2900FT T 21 DP 18 QNH 1010.7HPA MET QFE 1004.1HPA TREND TEMPO MOD TSRA"

String str2 = "1500M CLD BKN 700FT BKN 4600FT T 16 DP 17 QNH 1014.7HPA MET QFE 1004.1HPA TREND TEMPO MOD TSRA"

```

Which regex pattern could I use for this ?