Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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171 FXUS65 KPSR 011750 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1050 AM MST Mon Jul 1 2024 .UPDATE...Updated 18z Aviation Discussion... && .SYNOPSIS... Current shower and isolated thunderstorm activity across south- central and southwestern AZ will persist through the morning with the activity winding down by the early to mid-morning timeframe. Another round of isolated to scattered showers and storms is expected this afternoon and early evening across south-central AZ. Daily rainfall chances continue through Wednesday, with most of the activity confined to the higher terrain locations. Dry conditions return on the 4th of July and continue into the weekend as high pressure starts to move into the region. Above normal temperatures will continue through the weekend, with excessive heat conditions for portions of the Lower Colorado River Valley and southeastern California. && .DISCUSSION... There is ongoing activity stretching from northeast Arizona to southwest Arizona, with some activity within the Phoenix Metro. On upper-level water vapor we can see a weak easterly wave moving through southern Arizona along with a broad trough moving into northwest Arizona. These features along with southerly flow advecting some moisture into into the region are likely causing the ongoing shower activity. A few isolated lightning strikes are also possible. This activity is expected to come to an end around sunrise, or mid-morning at the latest. Hi-res guidance differs on how this afternoon will play out and will likely depend on how quickly activity ends this morning and how quickly clouds can clear out causing more sunlight to heat the surface and increase instability. Current PWATs are in the 1.7-1.9" range and are forecasted to stay within that range throughout the day. Most of the hi-res guidance does keep any activity this afternoon and early evening confined to the higher terrain locations. However, the HRRR does show some isolated showers and storms across portions of the lower deserts, mainly in western Maricopa County and locations to the east. GFS soundings also depict an uncapped environment this afternoon. So if we can get some of the clouds to clear out across the lower deserts this afternoon the environment would be poised to produce some shower and thunderstorm activity. The 00Z HREF indicates the greatest instability will set up over southern Arizona and extend up into western Maricopa County, with MUCAPE values of around 1000 J/kg and around 750 J/kg in the Phoenix Metro. The HREF also shows no CIN in place across south-central Arizona this afternoon and early evening. Activity is expected to initiate over the higher terrain locations to the east of Phoenix as well as to the southwest of Phoenix. The steering flow today will be southwesterly, so the activity to the southwest of Phoenix will be important to watch for it to either potential move into Phoenix or produce an outflow that moves through the Phoenix Metro that can kick off some storms. The environment today will also be supportive of outflow boundaries with soundings showing DCAPE values in the 800- 1000 J/kg range. While todays activity is a lot more conditional than yesterday`s activity, any storms that form will be capable of producing gusty winds, and brief localized heavy downpours. The HREF shows a 30-50% of winds exceeding 30 kts across Maricopa County and 50-70% of exceeding 30 kts across Pinal County. These wind speeds could cause areas of localized blowing dust, especially across the usual dust prone areas. Some minor flooding cannot be ruled out, especially if storms move over areas that have already seen a lot of rain. Ensemble guidance still depicts a change in the synoptic pattern by Thursday, with a strong high pressure system stretching from the eastern Pacific to the Great Basin. The position of this high pressure system will give our region dry northwesterly flow which will usher out a lot of our moisture, especially at the mid- and upper-levels. While, some moisture will remain within the boundary layer, the much drier mid- and upper-levels will suppress any convection. NBM PoPs have lowered for Thursday and Friday and are now around 5-10% across the higher terrain and <5% across the lower deserts. Ensemble guidance does start to show some moisture starting to move back in to the region by late this weekend. Temperatures for much of this week will remain above normal and will not fluctuate a whole lot. Lower desert high temperatures will be in the 105-113 degree range across south-central Arizona and in the 110- 115 range across southeastern California and far southwestern Arizona. Overnight lows will be in the low-to-mid 80s across the rural deserts and in the upper 80s to low 90s in the urban areas. The hotter temperatures in southeastern California and far southwestern Arizona will result in widespread Moderate HeatRisk, with isolated Major HeatRisk. Due to this, an Excessive Heat Warning is in effect for portions of southeastern California and the Lower Colorado River Valley through Friday. Speaking of Friday, it looks to be the hottest day of the week this week with afternoon high temperatures 2-5 degrees warmer than the rest of the week. && .AVIATION...Updated at 1745Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Wind pattern through the forecast period will exhibit diurnal tendencies with speeds aob 10 kts. There is a slight chance (15%) of TSRA activity, mainly from 22-02z, but confidence in occurrence is too low at this time to include in TAF package. There is a better chance for TSRA activity east of Phoenix, which could send an outflow boundary into the metro this evening but confidence of occurrence is low as well. If an outflow boundary were to impact the metro, wind direction would most likely shift out of east this evening. Otherwise, conditions should remain relatively tranquil with lowest cloud bases remaining aoa 10 kft, with SCT to occasionally BKN coverage prevailing through this evening before diminishing to FEW during the overnight period. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under mostly clear skies expected through the TAF period. Winds will favor the typical diurnal tendencies with occasional afternoon gusts upwards of 20-25 kts at KBLH. && .FIRE WEATHER... Moisture levels remain high today with additional chances for isolated to scattered showers and storms and gusty outflow winds late this afternoon and evening across south-central Arizona. Min RHs will be in the 25-25% range over south-central Arizona and in the teens across southeastern California and far southwestern Arizona.Overnight recovery will be good and in the 40-60% range in the eastern districts and in the 30-40% range in the western districts. Outside of thunderstorms, winds will tend to follow their typical diurnal patterns. Daily monsoon storm chances continue through Wednesday, although most of the activity will be confined to the higher terrain locations. Min RHs will be in the 15-25% range Tuesday and Wednesday with overnight recoveries in the 30-50% range. Dry conditions and ending rain chances start on Thursday and continue into the weekend. Temperatures will remain above normal through the week, with Friday being the hottest 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...Berislavich AVIATION...Lojero FIRE WEATHER...Berislavich