How to extrapolate the fit line and uncertainty bands?

I used the function 'fit' and 'predint' to plot the data, fit line and 95% bound from the year 1965 to 1990 as below. How can I extrapolate these lines to the year 2100?

x=[1:27]';

for i=1:12
    subplot(3,4,i);

      y_var=RCM_Var_time{i,1}(:,1);

      fitresult=fit(x,y_var,'poly1');
      a=coeffvalues(fitresult);

      p11=predint(fitresult,x,0.95,'functional','on');
      if (a(1,1)>0)
          plot(fitresult,'b',x,y_var,'.k');
      else
          plot(fitresult,'r',x,y_var,'.k');
      end

      hold on;
      plot(x,p11,'m-.');

      hold on;

      set(gca,'XTick',1:5:30);
      set(gca,'XTickLabel',{1965:5:1995});
      set(gca,'YTick',0:0.5:3.5);
      set(gca, 'YLim', [0 3.5])
      title([Month{1,i}]);
      xlabel([]);
      ylabel('Q4 Variance');
      legend off;
  end