FXUS65 KPSR 032321 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 420 PM MST Sat May 3 2025 .UPDATE... Updated Aviation && .SYNOPSIS... A potent low pressure system will enter the Desert Southwest resulting in breezy to locally windy conditions focused over Southeast California this evening, then areawide Sunday. Scattered showers and isolated thunderstorms will be possible across portions of the area on Sunday. Lingering chances for showers will continue Monday and possibly Tuesday mainly across the Arizona higher terrain. Below normal temperatures will persist through Tuesday followed by a quick warmup during the latter half of next week. && .DISCUSSION... Early afternoon mid-level water vapor imagery reveals a ridge positioned over the Intermountain West, the influence of which our area still falls under, and a deep trough just off the West Coast. A weak cutoff low still lingers over AZ, helping to spark some convective showers mainly over the northern AZ high terrain this afternoon, though this low will have little influence on thermal profiles over the lower deserts. As such, we'll see one more day with temperatures slightly above seasonal normals, reaching the lower to middle 90s across the lower deserts. The upper level trough off the West Coast will become a closed low over the next 24 hours or so, as it makes its way onshore over SoCal tonight into early Sunday morning. The increasing gradient aloft ahead of the low as it follows this trajectory will allow for strong winds to develop at the surface over the typical wind prone areas of SE CA this evening and through the overnight hours, particularly Western Imperial County. Therefore, a Wind Advisory remains in effect for that area starting 5 PM PDT this afternoon. By Sunday afternoon, the strongest winds aloft will have shifted east of the forecast area, though some near Advisory-level gusts between 30-40 mph will be possible, especially along ridgetops, to the east/southeast of the Phoenix Area. These windy conditions may result in patchy areas of blowing dust across central Pinal County during the afternoon into the early evening hours. Aside from breezy to locally windy conditions, the strong dynamics of this upper low and modest northward moisture transport, mostly in the mid-levels, will result in the development of scattered showers and isolated thunderstorms Sunday afternoon into the evening. NAEFS mean PWAT values increase to just upwards of 0.75", which is in excess of the 90th percentile of climatology for the time of year. Additionally, latest HREF mean MUCAPE reflects the increase in moisture and steepening lapse rates as the core of the low moves overhead, with a corridor of values upwards of 250-500 J/kg stretching from Western Maricopa into La Paz and Eastern Riverside Counties. This setup should support scattered coverage of convective showers, with a few thunderstorms capable of producing gusty outflow winds and pea sized hail. Rainfall amounts Sunday are not expected to be very high with most areas actually seeing rain receiving less than a tenth of an inch, but very localized areas may see up to around 0.25-0.50" from any thunderstorms. Much cooler air will also move into the area on Sunday as a cold front pushes through during the morning hours. Forecast highs Sunday are only in the upper 70s to around 80 degrees across the lower deserts with Monday's readings even a few degrees cooler. The upper level low will be slow to exit the region early next week as a secondary shortwave is expected to dive southward down the backside of the low late Monday into Monday night. With the center of the low remaining in place on Monday and moisture staying elevated, some areas could see another round of isolated to scattered light showers with the best chances likely across eastern Riverside and La Paz Counties, and over the higher terrain north and northeast of Phoenix. Tuesday may also bring some higher terrain showers, but the bulk of the activity will stay outside of our area. As the upper low continues to weaken and fill over our region going into the middle of the workweek, temperatures will begin to climb as highs warm back into the mid to upper 80s on Wednesday. This warming trend will continue through the latter half of the workweek, especially Thursday into Friday as a ridge moves back over our region. This should easily push daytime highs well into the 90s with some areas even flirting with 100 degrees by next Friday. Ensemble guidance even suggests we may see highs top 100 degrees for next weekend. && .AVIATION...Updated at 2320Z. South Central Arizona including KPHX, KIWA, KSDL, KDVT: The greatest weather impacts will be concentrated on Sunday in the form of several hours of gusty, cross runway winds followed by scattered late afternoon/evening SHRA/TSRA with the potential for erratic winds, periodic cigs developing in a 5-7K ft range, and lofted BLDU impacting slantwise visibility. This evening, confidence is moderate that W/SW winds (with localized 160v230) with occasional gusts around 20-25kt will prevail before trending more towards the SE overnight. Several hours of a southerly cross cross runway wind with gusts 20-25kt appear likely Sunday mid morning through early afternoon before veering to SW by mid afternoon. Otherwise, very low confidence exists for much of Sunday due to a complicated weather pattern and local loss of important model guidance. There may be a period of at least SCT decks 040-060 during parts of the morning, but more likely cloud development will be delayed until the afternoon. Wind directions should veer more SW by mid afternoon, but may retain some 160v240 with gusts 20-25kt. TCU/SHRA should build during the late afternoon with low confidence on proximity to the terminals, however direct impacts from SHRA in the form of cigs below 060 and/or gusty erratic outflow winds are certainly possible. A 20% chance of embedded TSRA even exists. Confidence is somewhat better that more concentrated scattered SHRA and lowering cigs will sweep through the PHX metro Sunday evening. Southeast California/Southwest Arizona including KIPL and KBLH: Strong gusty winds will be the main weather impact at KIPL through Sunday afternoon while the chance for TSRA will be the greatest potential impact at KBLH. Winds should quickly veer to westerly at KIPL this evening with good confidence of gusts 25-35kt through the overnight. These winds may incur periods of BLDU across the area, though confidence in sfc restrictions are too low to include in this package. Model suggest speeds partially relax Sunday afternoon. S/SW winds will not be as pronounced at KBLH, yet still occasionally gust 20-25kt. Confidence is moderate that SHRA/TSRA with erratic winds will form in the vicinity of the terminal late Sunday afternoon. && .FIRE WEATHER... A strong weather system will promote a substantial cool down from Sunday into early next week. The approaching weather system will result in increased winds across the Imperial Valley and Lower Colorado River Valley this afternoon and evening. On Sunday, elevated conditions will shift eastward to the AZ high terrain where gusts could reach 30-40 mph. However, MinRHs will improve areawide to around 20% by Sunday afternoon. There will be a slight chance for showers and thunderstorms in southcentral AZ on Sunday, however the chances for wetting rainfall remains low (<20%). Any storm that develops will be capable of producing gusty and erratic winds. Chances for showers will linger across the AZ high terrain through early Tuesday. High pressure will likely to move back over the region by the middle to latter half of next week, leading to warmer and drier conditions. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...Wind Advisory until 2 AM PDT Monday for CAZ562. Wind Advisory until 5 AM PDT Sunday for CAZ566-567. && $$ DISCUSSION...Whittock/Kuhlman AVIATION...18 FIRE WEATHER...Kuhlman