Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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993 FXUS65 KPSR 010536 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1036 PM MST Sun Jun 30 2024 .UPDATE...Updated Aviation Discussion. && .SYNOPSIS... Shower and thunderstorm activity will increase this afternoon and evening across much of southern Arizona, with the best chances of rain extending from Phoenix eastward. Daily rainfall chances will last into Wednesday, with potential activity becoming focused over higher terrain locations. High pressure will usher in a period of drying later this week, with rain chances becoming more muted by the 4th of July. Above-normal temperatures will persist through the week, with excessive heat conditions impacting parts of southeast California and the Lower Colorado River Valley. && .DISCUSSION... Hi-res guidance continues to point toward an active monsoon day across southeast and south-central Arizona this afternoon through tonight. Moisture advection has increased over the region with the help of an MCS located over northern Mexico last night. Morning soundings from Phoenix and Tucson measured PWATs ranging between 1.5- 1.8", with low-level mixing ratios hovering around 10-11 g/kg. With this moist profile in place and the expected increase in insolation this afternoon, the environment will be conducive for the development of numerous showers and thunderstorms later today. According to the HREF, the axis of greatest instability will setup over southeastern Arizona, up through southern Gila County, where MUCAPE will be around 1000 J/kg. Initial convection will spark over these areas early this afternoon before advancing to the north and northwest. Over Maricopa and Pinal Counties, a slightly more stable environment will be in place as MUCAPEs are expected to range between 500-750 J/kg, with perhaps even a little bit CIN that will need to be overcome in order to get convection over these areas. Regardless, the northward/northwestward propagating convection from the Tucson area will be in an environment supportive of strong outflows as forecast soundings indicate DCAPE values exceeding 1300 J/kg. These potential outflows will become the focal point for further convection over our forecast area, as they should provide more than enough lift to break the cap and set off at least some strong updrafts. Depending on how long potential outflows retain their strength and how far they advance, further activity may initiate over western Maricopa and La Paz Counties late tonight into early Monday morning. The main impact of this activity will be gusty, to potentially damaging winds. The HREF shows a 70-90% probability of winds exceeding 30 kts across Pinal County. However, it since backed off on the 10% probability, mentioned in the previous discussion, of seeing winds exceed 50 kts over the same area. Even with ensemble guidance not being as bullish now regrading severe winds (gusts of 50+ kts), it would not be surprising to see gusts reach or exceed this mark across Pinal County and even parts of Maricopa and Gila Counties. Strong outflow winds are expected to traverse most of the Phoenix metro, with chances of seeing gusts 30+ kts standing at 50- 70%. Areas of blowing dust generated by enhanced winds will also be a concern this evening, especially across the usual dust prone areas of Pinal County. Though confidence is not high regarding what areas may see the heaviest rainfall, isolated instances of minor flooding cannot be ruled out. Thunderstorm activity may once again reemerge Monday afternoon across south-central and parts of southwestern Arizona, though the forecast still appears uncertain. The regional flow will shift out of the southwest as a weak area of troughing migrates across the Intermountain West, providing some slightly drier air over our CWA. However, model guidance still favors PWATs between 175-200% of normal for areas mentioned above, likely leading to sufficient instability with minimal CIN, supporting more convective development. Something that may limit this activity is subsidence behind a remnant MCV from the showers and thunderstorms we expect this evening, but this should move out far enough to allow for what could be another busy monsoon day. Decent moisture will likely stick around until Wednesday, but confidence surrounding rain chances, mainly across the lower deserts, is not high at this time. However, it does appears likely that terrain-induced convection will continue to occur for areas north and east of the Phoenix metro, as PoPs for these areas range between 40-60% through Wednesday. If mid-week rainfall were to occur over the lower deserts, it would be heavily dependent on outflows originating from high terrain storms. Models continue to show a strong area of high pressure stretching from the eastern Pacific toward the Great Basin during the latter half of the week. Based on its forecasted position, this system will shift flow out of the north across the Desert Southwest, allowing for much drier air to be funneled over the region, with PWATs forecasted to drop closer to normal for this time of year. Moisture in the lower-levels is not expected to be completely scoured out, but noticeably dry air aloft should limit rain chances for Independence Day and through the start of the weekend. It is possible to see a very isolated, high-terrain shower or thunderstorm get squeezed out on the 4th, but max PoPs are around 20%, with lower probabilities (<10%) for the lower deserts. Temperatures during much of the upcoming week should remain relatively steady, while continuing to hover above seasonal normals. Lower desert highs will range from 106-113 degrees for south-central Arizona, with slightly hotter readings between 108-115 further west. This will result in widespread Moderate HeatRisk, with isolated areas reaching into the Major category across southeastern California. In response, an Excessive Heat Warning has been posted for parts of Riverside and Imperial Counties from today through the end of the week. && .AVIATION...Updated at 0536Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: A preponderance of spotty showers with embedded thunder is expected through the rest of tonight, primarily just north and west of the metro. However, a 15% chance in the metro will continue. There is uncertainty in wind directions through the night as the showers to the north and west may lead to a wind shift to the W or N, but if this happens, when, and for how long is uncertain. Otherwise, expect SE to E winds to prevail through Monday morning. Any lingering SHRA/TS should diminish/move out toward sunrise Monday. SE-E winds will shift SW around midday Monday with afternoon gusts into the teens. There will be another slight chance (10%) for SHRA/TS Monday afternoon, but confidence and model probability is too low at this time for inclusion in the TAF. Lowest cloud bases will remain around 10K ft, aside from in SHRA/TA, with SCT to BKN coverage at times. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation aviation weather concerns expected through the TAF period. Winds will generally be out of the southeast at KIPL and out of the south at KBLH. Winds are expected to gust upwards of 20-25 kts late Monday morning and afternoon at KBLH, with weaker guest out of the west for a brief period Monday evening at KIPL. Skies will remain mostly clear. && .FIRE WEATHER... Moisture levels and storm chances will increase today with good chances for showers, scattered storms and strong outflow winds late this afternoon and evening across south-central AZ. MinRHs today will still see upper teens over much of the lower deserts and 25-30% in higher terrain areas before improving another 5% on Monday. Overnight recoveries will be good over much of the area tonight with 40-50% RHs over much of the eastern districts to 20-35% over the western districts. Outside of thunderstorm activity, winds will follow fairly typical diurnal trends but with more of a south southwesterly dominant direction, especially across the western districts. Daily monsoon storm chances should persist Monday through Wednesday across south-central Arizona, but coverage is likely to be fairly limited while favoring higher terrain areas. MinRHs of 20-25% across the lower deserts to upwards of 35-40% over the eastern Arizona high terrain can be expected through Wednesday with drying conditions and rain chances mostly ending starting Thursday. Temperatures will remain several degrees above normal each day this week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ530. CA...Excessive Heat Warning until 8 PM PDT Friday for CAZ562-566-567- 569-570. && $$ DISCUSSION...RW AVIATION...Benedict FIRE WEATHER...Kuhlman