463 FXUS65 KPSR 121728 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1028 AM MST Thu Jun 12 2025 .UPDATE...Updated 18z Aviation Discussion. && .KEY MESSAGES... - Dry conditions with temperatures remaining 3 to 5 degrees above average across the region through Friday. - A strong ridge of high pressure will build over the Desert Southwest this weekend, promoting the hottest temperatures so far this year. - An Extreme Heat Watch is in effect from Saturday morning through Monday evening for high temperatures ranging from 106 to 114 degrees across the lower deserts. && .DISCUSSION... Very little has changed since yesterday with the sub-tropical ridge still centered west of Baja, while providing higher than normal H5 heights of 588-590dm over our region. The dry air mass will also remain in place allowing for continued clear to mostly clear skies with only some passing high cirrus clouds. Temperatures will continue to run at least a few degrees above normal with highs mostly topping out between 104-109 degrees today and Friday. Models continue to show the sub-tropical ridge shifting eastward into northern Mexico later today into Friday before moving northeastward on Saturday, centering itself near El Paso, TX. A subtle shift in the upper level pattern over the northern tier states by the weekend will also allow the ridge to extend well to the north through the central U.S., while the ridge gains some strength. The closer proximity of the ridge to the Desert Southwest and the slight strengthening will boost H5 heights over our region beginning Saturday before peaking on Sunday. The latest model run has shifted H5 heights over our region ever so slightly lower for this weekend, but we are still likely to see H5 heights somewhere between 591-594dm on Sunday before starting to lower by Monday. The latest NBM run has also lowered forecast temperatures by a degree or two overall for Sunday and Monday with Sunday`s readings likely being the highest at 110-114 degrees across the lower deserts. As a result, the areal coverage of the Major HeatRisk has dropped and mostly only shows up on Sunday. The Extreme Heat Watch remains in effect due to some uncertainty still remaining in the forecast temperatures. Guidance is also showing a higher probability of a modest cool down by next Tuesday as an even higher majority of members show a dry trough moving into our region from the west. Despite the increasing forecast confidence in this trough, there is still some uncertainty with its strength and how much it may drop our temperatures. For now, the NBM shows highs dropping more into a 103-107 degree range on Tuesday before already starting to trend back higher Wednesday into Thursday. This cool down will likely just be a brief dip in temperatures as guidance favors the ridge to quickly build back into our region late next week with 110 degree temperatures likely returning for at least some locations. The weather pattern over at least the next 7 days will continue to promote dry conditions, but there looks to be some potential for increasing moisture returning as early as next weekend. && .AVIATION...Updated at 1730Z. South Central Arizona including KPHX, KIWA, KSDL, KDVT; Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns will exist through Friday afternoon under FEW-SCT high clouds. Winds will continue to follow their typical diurnal tendencies. Periods of light and variable to nearly calm winds are expected, especially during diurnal transitions. In the Phoenix Metro Area, occasional wind gusts to 15-20 kts are likely (>70% chance) this afternoon, with a period of even stronger westerly gusts to 20-25 kts possible for a period late this afternoon into the evening (00-04Z). && .FIRE WEATHER... Little to no change in the weather pattern through Friday will keep temperatures 3-5 degrees above normal and humidities seasonably low. Winds will follow typical diurnal tendencies with periods of modest afternoon upslope breeziness (gusts to around 20 mph at times). Minimum afternoon humidity will continue to bottom out between 8-12% with poor to fair overnight recovery mainly between 20-35% region-wide. Temperatures are forecast to get even hotter this upcoming weekend with afternoon highs reaching 110 or hotter as early as Saturday across the lower deserts as Min RHs lower in the 5-10% range. By early next week, the arrival of a dry weather system may result in an uptick in winds across much of the area. These gusty winds combined with dry fuels and very low humidity could result in elevated fire weather concerns. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Extreme Heat Watch from Saturday morning through Monday evening for AZZ530>544-546>556-559>562. CA...Extreme Heat Watch from Saturday morning through Monday evening for CAZ562>567-569-570. && $$ DISCUSSION...Kuhlman AVIATION...Whittock/Berislavich FIRE WEATHER...Salerno/Kuhlman