There are a couple reasons why. First, we have not had a strong ridge of high pressure establish itself over the region yet. This usually does in the summer months and it's not a question of "if", but "when".
Second, we have had a very wet spring. With all that moisture in the ground, it will make the hurdle to and above 90° a little more difficult. The suns energy really goes into evaporation before efficient heating can take place.
The latest "first" 90° was June 20, 1910. While I don't think we will reach the 20th without hitting 90, 2017 could rank in the top 20 latest.
The Saturday morning run of the GFS does show Little Rock hitting 90° next weekend and beyond, but the Euro does not. However, the Euro does show upper 80s and with this being in the long range, it could easily change one way or the other.
|From top to bottom, the latest it has reached 90° or higher at Little Rock|
|GFS next Saturday (June 10th) shows we'll be very close.|
|GFS on Monday June 12th says 91° for a high. Remember, forecasting the temperature to the exact degree in the long range is very difficult, but it does appear we'll be in that range.|