Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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063 FXUS65 KPSR 012009 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 109 PM MST Mon Jul 1 2024 .SYNOPSIS... Isolated shower and thunderstorm activity is expected this afternoon and evening across south-central Arizona. Daily rainfall chances will last into Wednesday, with most 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 areawide by the 4th of July. Above-normal temperatures will persist over the next several days, with excessive heat conditions for parts of southeast California and the Lower Colorado River Valley. && .DISCUSSION... Current atmospheric analysis reveals the persistent sub-tropical ridge continuing to center itself over the Southern Plains, while a weak area of troughing migrates across the Intermountain West. This disturbance will break the pattern that we have seen over the past several days, helping to erode positive height anomalies over the Desert Southwest, and pushing the stubborn high pressure toward the southeastern CONUS. Drier air will also accompany this troughing, slowly spreading across our forecast area over the next few days. There is already a noticeable moisture gradient being observed across the region, with PWATs of 0.7-0.8" over southeastern California, reaching towards 1.9-2.0" over south- central Arizona. Before these drier conditions become fully encompassed across Arizona, afternoon shower thunderstorm activity will once again be possible today within the axis of greatest moisture. Hi-res guidance shows a plume of instability setting up over much of south-central, and parts of southwest Arizona, with MUCAPE values ranging between 750-1000 J/kg. Model soundings and HREF guidance do indicate a little CIN this afternoon, but the environment should be mostly uncapped, priming the atmosphere for at least some convective development. There will not be much large scale ascent to promote widespread convection, so the most likely initiating mechanism will be enhanced terrain features, with coverage remaining generally isolated. The consensus among ensemble members is that showers and thunderstorms will develop across the the high terrain areas east of Phoenix, and around terrain features in southwest Maricopa and Pinal Counties. With steering flow becoming more southwesterly, a few storms that develop southwest of Phoenix may move over the metro, but not everyone will see rainfall. The main concerns with this round of activity will be heavy downpours, gusty winds, and localized areas of blowing dust. The morning Phoenix soundings showed DCAPE values around 800 J/kg, favorable for some marginally strong downbursts. However, model soundings for this afternoon have values rising towards 1300 J/kg, which would be supportive of stronger thunderstorm outflows. As a result, the HREF is highlighting most of Maricopa, Pinal, and Gila Counties in a 30-60% chances of seeing outflow gusts exceeding 35 mph. It would also not be surprising to see isolated instances of minor flooding due the ample moisture availability, and weak steering flow, resulting in some heavy, slow moving showers and storms Rain chances will continue to decrease over the next few days as dry air continues to push across the region. Any further rainfall activity through Wednesday will be focused primarily over the Arizona high-terrain. Further drying is expected to occur later in the week as a strong area of high pressure stretches from the eastern Pacific toward the Great Basin, shifting flow across the Desert Southwest out of the north. PWATs by the 4th of July will approach seasonal normals, with most remaining moisture confined in the boundary layer, muting rain chances even further as regionwide PoPs for Thursday and Friday drop to 10% or less. Temperatures through the week will follow a gradual warming trend, with today likely being the "coolest" over the next several days. Lower desert highs this afternoon will range between 103-107 degrees across south-central Arizona, while highs closer to 110 degrees can be expected further west, before these higher readings become more common across the remainder of the lower elevations through the middle of the week. Temperatures will climb even further once the previously-mentioned area of high-pressure extends closer to our forecast area, with Friday likely being the hottest day so far this year for many areas, especially out in southeast California. Temperatures near and in excess of 115 degrees will be common, with some communities potentially reaching 120 degrees. These abnormally hot conditions will result in widespread coverage of Major HeatRisk, especially over the western Deserts. An Excessive Heat Warning remains in effect for parts of southeast California through Friday. It is likely that this warning will need to be extended both in time and area to accommodate for the dangerous heat. && .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