373 FXUS65 KPSR 011158 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 458 AM MST Sun Jun 1 2025 .UPDATE...Updated Aviation Discussion... && .DISCUSSION... Key Messages: - Showers and isolated thunderstorms will spread across the region today, with some lingering higher terrain shower activity into Monday. - A few strong thunderstorms with gusty winds, small hail, and localized heavy rainfall are possible on Sunday, anticipated to be strongest in southeastern California, which could preclude a minor flash flood threat as well as localized blowing dust impacts. - Temperatures will drop below normal with highs in the nineties for several days starting today, though temperatures will warm each day after that resulting in a return to above normal temperatures by the end of the workweek. The long awaited and unusual weather pattern for this time of year is finally upon us, as early morning radar depicts scattered to numerous showers spreading across mainly south-central and southwestern Arizona. Some embedded thunder has also been observed with these showers, as they rotate northwestwards over the next couple of hours around the low circulation situated offshore of the Baja Peninsula. While hi-res guidance did not do a good job depicting this early morning convection, its anticipated that the vort lobe that is aiding in this shower activity will lift northwards, resulting in a lull in shower coverage in a few hours until later this morning. As the low circulation meanders eastward this morning, this will result in the main event creeping into southwestern Arizona and then spreading into south-central Arizona, with the Phoenix metro seeing the bulk of shower/storm activity during the afternoon and evening hours. The thunderstorm threat is much more muted, as very little daytime instability is being depicted by the HREF (100 J/kg or less) across south-central Arizona. Thus, don`t expect much more than some embedded thunder throughout the day, with some improving thermodynamic profiles post-front this evening, but then showery activity will be much more scattered by then. On the other hand, more robust thunderstorm activity will be possible further west, particularly across southeastern California this afternoon and early evening. Due to being closer to the low center (cooler temperatures aloft/steeper lapse rates), better instability will be available (500-1000 J/kg) with maybe enough clearing after this initial wave of showers/clouds early this morning to spark some thermally induced thunderstorms during the afternoon hours. Should this be the case, a few strong storms will be possible with gusty outflow winds (30-50% chance of 35+ mph gusts), patchy blowing dust, small hail, and heavy downpours that could preclude to a minor flash flood threat all potential threats from these storms. Overall, the vast majority of the region should see some level of shower activity, with accumulating rains anywhere from 0.10" to upwards of 0.50" in upslope enhanced locations. In areas that have multiple rounds of showers/storms or a strong storm (such as southeastern California), localized areas receiving 1.00"+ accumulations is not out of the question, but still generally less than a 25% chance of that occurring in any one spot across the region. Otherwise, hi-res guidance depicts the main frontal band progressing northeastward concentrated across southern Arizona and extending into south-central Arizona, thus the more widespread higher accumulations for the AOR are anticipated to be more centered across south-central Arizona. As the low continues to progress eastward, post-frontal showery activity will continue to linger into the overnight hours tonight across the lower deserts, but become primarily confined to higher terrain areas east of Phoenix during the daytime hours on Monday. Otherwise, cooler temperatures several degrees below normal persisting through early this week. A secondary shortwave will dive southward across the West Coast early in the week and eventually progress eastward across the Desert Southwest. This feature will unfortunately not bring much in terms of moisture to increase rain chances again Tuesday into Wednesday, as the main moisture is in the lower levels and will remain offshore as this trough progresses eastward. Thus, this trough will, at most, spark some higher terrain showers and temper the warming the trend set to take place late this week. Subtropical ridging will take hold across northern Mexico starting mid to late week, resulting in warming conditions to above normal as early as Thursday. Temperatures will continue to warm as the ridge remains anchored across northern Mexico, with considerably above normal temperatures by late this upcoming weekend. Ensemble guidance is in good agreement of the general pattern setup mid- week onward, with the main differences being the strength of the sub-tropical high. Regardless, the IQR of NBM temperatures remain around five degrees through the extended period, thus will have to keep a watch on whether the higher end scenario could creep into extreme heat concerns for early June. && .AVIATION...Updated at 1155Z. South Central Arizona including KPHX, KIWA, KSDL, KDVT: Lowering cigs, periods of showers, and gusty winds will be the main weather concerns today into tonight. Light showers early this morning with southeasterly winds should move out of the metro by around 13-14Z. Winds should quickly return to a west component by late morning and become gusty by the afternoon as another round of more robust showers and maybe a few embedded thunderstorms progresses through the Phoenix Metro. This VCSH/SHRA will persist for around 6 hrs before slowly shifting NE of the region by mid to late evening. There is still low confidence (<30%) in cigs falling below 6 kft at KPHX, however could be a brief reduction to MVFR cigs and/or vsby if showers become heavy enough. Southeast California/Southwest Arizona including KIPL and KBLH: Lowering cigs, periods of SHRA/TSRA through this afternoon, and gusty and erratic winds will all be the main weather concerns. Scattered light showers will become a bit heavier and more persistent after sunrise before becoming fairly isolated in the afternoon. Winds will predominately be out of the south for much of the period with KIPL more out of the southeast and KBLH more often out of the southwest. Gusts increasing to around 20-25 kts later this morning are likely, particularly at KBLH. After the morning shower activity, another round of SHRA with the potential for isold TSRA will become the main concern heading into the evening hours, particularly at KIPL. && .FIRE WEATHER... An unseasonably wet weather system will track through the area today bringing widespread wetting rain chances of 50-80% and chances for thunderstorms (15-30% chance). Afternoon minRHs will rise to 20-40% areawide today, with similar values anticipated Monday. The elevated humidities Sunday-Monday will begin to lower starting Tuesday, but MinRHs should mostly stay above 15% through the middle of the workweek. A drier weather system is likely to move through the region on Tuesday possibly bringing some isolated showers and a few thunderstorms focused over higher terrain areas. Hotter and seasonably dry conditions are likely to return later this week, with minRH`s dipping below 10% late week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Young AVIATION...Kuhlman FIRE WEATHER...Young/Whittock