Tucson, AZ 
157 FXUS65 KPSR 181121 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 421 AM MST Mon Aug 18 2025 .UPDATE...Updated 12Z Aviation Discussion. && .KEY MESSAGES... - High pressure will strengthen over the region this week, causing temperatures to climb to near record levels and result in the return of widespread major HeatRisk. - Extreme Heat Watches remain in effect across the majority of the region Wednesday through Friday. - Monsoon thunderstorm activity will remain primarily confined to the high terrain of E and SE Arizona through the first half of this week before rain chances expand to the lower deserts by the end of the week and into this weekend. && .SHORT TERM /Today through Tuesday/... The overall upper air pattern has not changed much over the past 24 hrs as our forecast area remains centered between troughing over the Pacific NW and ridging over the Southern Plains. The subtropical ridge is forecast to retrograde back to the west today and set up over the Four Corners region starting Tuesday, resulting in a warming trend back to above average temperatures. Today is expected to remain dry and tranquil across the region as moisture remains quite limited, even across the higher terrain with PWAT values hovering around 1.0-1.2". There could be a few isolated storms over far SE AZ, but the chances for any outflow boundaries reaching the lower deserts of southcentral AZ will be very low (
