Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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487 FXUS65 KPSR 292119 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 219 PM MST Sat Jun 29 2024 .SYNOPSIS... Above normal temperatures will persist into next week, especially for the western deserts, where daily highs are expected to be near or above 110 degrees. Shower and thunderstorm activity will be limited today before becoming more widespread over south- central Arizona by Sunday. Enhanced monsoonal moisture will keep rain chances elevated through at least the middle of next week, with the best chances focused over high terrain areas north and east of the Phoenix metro. && .DISCUSSION... Current WV analysis reveals a sharp contrast in the environment between each end of our forecast area, with very dry conditons being observed over Southeast California, while parts of south-central Arizona have seen better moisture that lead to some light showers this morning. Meanwhile, the sub-tropical ridge has now become centered over the Southern Plains, which will help to keep favorable monsoonal flow over the region through this weekend. However, the ridge will strengthen through the day today, stretching out over the Desert Southwest once again. This will provide renewed subsidence aloft, which should limit convective activity for most of our CWA this afternoon and evening. Nonetheless, with the relatively enhanced moisture profile (PWATs 1.3-1.5") over much of southern Arizona, it is not out of the question that areas in Pinal, Gila, and southern Maricopa Counties see terrain influenced convection once the atmosphere starts to destabilize this afternoon. If storms do initiate, the environment will be be favorable to see some enhanced to potentially damaging downbursts with stronger storms. As mentioned in previous discussions, an easterly wave, currently seen in WV imagery over northern Mexico, will advance towards the Desert Southwest through tonight, helping to turn our mid-level flow toward the southeast, providing increased moisture flux over the region. This wave will also help to spark an MCS over Sonora later today, which may play in part in setting off some elevated showers over southeastern and south-central Arizona Sunday morning due to additional moisture advection and any associated gravity waves. Model guidance has shown a consistent signal regarding Sunday being an active monsoon day across parts of Arizona. The dynamics associated with the above-mentioned easterly wave will tap into what will be a relatively unstable environment (MUCAPE 500-1000 J/kg) over southeast Arizona and up through Gila County Sunday afternoon. Hi-res data has convection developing near the Tucson area during the afternoon hours, before advancing towards Pinal and Maricopa Counties Sunday evening. The environment over the Phoenix metro and down along the I-10 corridor will be slightly more stable, but would still support further convective development, with MUCAPE values between 500-750 J/kg. Model soundings do point toward at least some CIN being present, but strong outflows from the previously-mentioned activity should provide enough lift to overcome this capping, likely sparking further thunderstorm initiation. Best chances to see shower and thunderstorm activity over our CWA will be focused over the high terrain areas north and east of Phoenix, where a greater axis of instability will be present, with current Pops between 60-80%. Closer to the Phoenix metro, rain chances range between 30-40%, likely due to the slightly lower instability, and greater projected CIN. Nonetheless, even with these more subdued rain chances, there is good confidence that areas around the metro will see activity. Some storms are likely to be strong to severe with, damaging winds possible. Stronger outflows will also have a high potential of generating areas of blowing dust, especially across the usual dust prone areas in Pinal County. With ample moisture available, heavy rainfall, with potentially minor flooding, will also be potential hazard with Sunday`s activity. One potential limiting factor to all of this will be lingering cloud cover from tonight`s storms over northern Mexico, with models hinting at decent cloud cover over south-central Arizona through Sunday morning. If these were to stick around into the afternoon hours, it could limit convective activity and coverage due to more limited insolation. However, models seem to agree that clearing should take place by late morning/early afternoon, favoring a more active solution. The GFS continues to show the development of and MCV over south- central Arizona late Sunday. This feature will drift of towards Flagstaff on Monday, leaving a good portion of our CWA under the influence of subsidence, likely limiting shower and thunderstorm development, at least over the lower-elevations, Monday afternoon and evening. Regional flow will also shift out of the southwest during the start of the week, providing some slight drying, creating another inhibiting factor for more widespread thunderstorm activity. Nonetheless, terrain driven convection looks likely as moisture levels remain above normal, with current PoPs over northern Maricopa and southern Gila Counties ranging between 40-70%. Forecast confidence for Tuesday and Wednesday is still somewhat low due to the lack of any good forcing as we will fall in between a developing high pressure ridge off the coast of California and the ridge center over the Lower Mississippi Valley. A couple of weak upper level shortwave troughs are also expected to pass by to our north Tuesday and Wednesday with potentially a little bit of upper level forcing over Arizona on Wednesday. This may help with some convection, but a southwesterly steering flow is generally not very favorable for convection impacting the lower deserts. Even with this level uncertainty, NBM shows PoPs over Gila County upwards of 50-60% through Wednesday, so daily terrain- driven convection is still possible through mid-week. By late next week, the aforementioned Pacific high will move onshore, shifting flow over the Desert Southwest out of the north, resulting in further drying, which would limit monsoon activity though at least next weekend. Temperatures during the next seven days will continue to exceed seasonal-normals, especially out in the deserts of southeastern California. Daily readings across south-central Arizona will range between 104-112 degrees, while temperatures near and above 110 degrees will be common further west. These temperatures, combined with expected dew points in the 50s, will result in in widespread Moderate, to locally Major, HeatRisk. In response, the Excessive Heat Watch for parts of southeast California has now been upgraded to a warning and will be in effect through the end of the upcoming work-week. && .AVIATION...Updated at 1720Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Some things to watch for this TAF period are more clouds and whether or not precipitation will materialize. Winds will tend to follow their typical diurnal patterns with westerly into this evening, shifting around to the southeast overnight. Although, magnitude will be AOB 10 kts outside of maybe a few late day gusts to 20 kts. Otherwise, monitoring the cloud and precip trends. We will continue to see SCT mid and BKN high clouds for the most part. Most of the showers/storms will stay south of the valley terminals this evening, but outflows may push north (10% chance) into the valley, but not expecting to be too strong and little impacts. Something that will be watched in the very short term trends. There is also a low chance (10-20%) that a few showers could develop north into the valley overnight into early Sunday. For now, confidence is too low to include in the area TAFs. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will continue to follow their typical diurnal patterns through the TAF period. At KIPL, wind speeds will be aob 8 kt. At KBLH wind speeds will be more elevated and generally aob 13 kt, with some gusts of 20-25 kt this afternoon. Skies will remain mostly clear through the TAF period. && .FIRE WEATHER... Very limited monsoon activity is expected today before fairly widespread showers and thunderstorms are expected over south- central and eastern Arizona Sunday afternoon and evening. Humidity levels today will drop slightly from yesterday with MinRHs in the upper teens across the lower deserts to 20-30% over the higher terrain with only very slight improvement through Sunday afternoon. Overnight recoveries will be fair tonight and good Sunday night as moisture increases over much of the area. Winds will follow typical diurnal trends through Sunday afternoon with occasional afternoon breeziness near 20 mph, while strong outflow south southeasterly winds look likely Sunday evening into south- central Arizona. Daily monsoon storm chances should persist through at least south-central Arizona into the middle part of next week, while humidities rebound to 20-25% across the lower deserts to upwards of 35-40% over the eastern Arizona high terrain. Temperatures next week will remain several degrees above normal each day. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning from 10 AM Sunday to 8 PM MST Friday for AZZ530. CA...Excessive Heat Warning from 10 AM Sunday to 8 PM PDT Friday for CAZ562-566-567-569-570. && $$ DISCUSSION...Kuhlman/RW AVIATION...Frieders FIRE WEATHER...Kuhlman