PORTLAND, Ore. (KOIN) – We are starting to approach the infrequent territory of reaching the month of June without having an 80-degree day in Portland. Believe it or not, that accomplishment doesn’t happen very often.

Going all the way back to 1940, it has only occurred eight times. We may make it number nine this year, as we are going to be on the fringe of the upper 70s and lower 80s on Tuesday, Wednesday, and even potentially on Thursday. This is going to be the warmer temperatures that get us all excited for summer activities.

Here is the deal: It sure seems like we are going to only get a brief taste of that milder air mass, eventually turning back the other direction. Will this hold through the first week of June? It’s tough to say. It sure seems like we could at least contest the record in the graphic below if we happen to avoid 80 this week.

Latest First 80-Degree Day June 12, 2010

Right now, we have a rolling jet stream that is going to keep the weather pattern changing. The constant battle to balance, keeps the weather interesting! If you follow the weather graphic below, you will see the ups and downs of the jet stream. We will exchange one air mass for another as we work through the week. There are no signs of pausing this action with a blocking high or cut-off low. That means you can count on a wavering forecast for the next five to seven days. What does this mean? Temperatures and conditions are going to feel and look different from the start of the week to the weekend.

Extended Weather Pattern: Monday – Friday: Ridge and Trough

If you navigate the Temperature Departure slider below, you will find the exchange of cool air with the mild air mass that is on the way. Temperatures should find a way to the lower 70s without much effort now, but it takes some work to keep them below or above average. The blue and purple colors are representing anywhere from 5 to 15 degrees below average. The yellow and orange colors are representing warmer temperatures, anywhere from 5 to 15 degrees above average. Doing the quick math, if we end up a good 10 to 15 degrees above average, we will surely be in the 80s. We do not see that in the forecast just yet.

National Temperature Departure: Monday – Wednesday: Air Mass Exchange

Weather data is projecting a forecast high in the mid to upper 70s for the last day of May and the start of June. Quickly behind that, the dynamic jet stream will usher in a trough that will bring us right back down to the 60s. The chance for 65 degrees or above is 85% in the month of June. That means if we only hit 65 degrees, we are floating in the 15% range. That means we do not see high temperatures in the mid-60s very often in the month of June. We will watching the extended forecast closely for that first significant wave of summer temperatures!

Forecast Trend: (May 30 – June 9)