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Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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537 FXUS65 KPSR 301225 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 525 AM MST Sun Jun 30 2024 .UPDATE...Updated 12Z Aviation Discussion. && .SYNOPSIS... Monsoon shower and thunderstorm activity will increase today across much of southern Arizona with the best chances for rain from Phoenix and areas to the east and southeast of Phoenix. Daily chances for scattered showers and isolated thunderstorms should then persist through Wednesday with the activity focused more over higher terrain locations. Drier conditions are anticipated late this week with rain chances mostly ending starting Thursday. Above normal temperatures are forecast for the entire week with excessive heat conditions impacting portions of southeast California and the Lower Colorado River Valley. && .DISCUSSION... As forecast, a large MCS developed last evening across New Mexico and another in Sonora Mexico before moving into southeast Arizona over the past several hours. Convection is still ongoing across southeast Arizona, now moving into southern Pinal County, but it is now generally elevated in nature and gradually dissipating. Additional west northwestward propagating showers will remain possible through sunrise, potentially reaching portions of the Phoenix area. However, the bulk of the activity seems likely to mostly bypass Phoenix to the south, moving through the Gila Bend area before slowly dying out as it moves into Yuma County around sunrise. A remnant MCV may end up positioned somewhere just east or southeast of Yuma later this morning while having little impact on any further development later today. The 00Z HREF and the latest HRRR runs generally all point toward a busy monsoon day today across southeast Arizona into the higher terrain and then over portions of the south-central Arizona lower deserts this evening and tonight. Moisture will continue to stream into southern and central Arizona this morning and afternoon boosting area PWATs to around 1.75", while low level mixing ratios rise from the current 9 g/kg to 11 g/kg. Given the sufficient moisture and likely good insolation over much of the area by mid morning, instability should be more than adequate for shower and thunderstorm development this afternoon. The HREF indicates the best instability with MUCAPEs of around 1000 J/kg will exist across far southeast Arizona northward to around southern Gila Co. where some strong to possibly severe storms could occur. Less instability with MUCAPEs of maybe 500-750 J/kg is forecast over western Pinal into Maricopa Counties where at least some minimal CIN will also be in place. However, this area will also host much higher DCAPEs, on the order of around 1500 J/kg which will likely provide for good chances for strong outflow winds this evening. The higher terrain convection east of Phoenix mid to late afternoon may send an westward propagating outflow, but hi-res CAMs give a better shot at a strong outflow moving northwestward into Pinal County by early evening from the convection near Tucson. This outflow will likely be enough to trigger additional convective development as it progresses through Pinal into Maricopa County later in the evening. Strong gusty winds and the potential for blowing dust will likely be the main storm impacts late this afternoon and evening as the HREF shows upwards of a 90% probability of 30+ kt winds and a 10% probability of 50+ kt winds across central Pinal Co. The strong outflow winds should then progress through most if not all of the Phoenix area with a 50-70% probability of 30+ kt winds. Localized rainfall amounts upwards of an inch or more will be possible, especially within Pinal Co. By late evening into the early overnight hours, the CAMs show some further redevelopment of showers and storms within the Phoenix area through northwest Maricopa County to as far west as eastern La Paz County. After the expected busy day today, Monday could up being fairly quiet but that is far from certain. Light southwesterly flow is forecast to develop by Monday morning over at least southwest Arizona and likely into south-central Arizona and this should begin to bring some drier air into the area. Despite the southwesterly drying flow, guidance still indicates plenty of instability and overall minimal CIN across south-central and eastern Arizona. A likely remnant MCV from this evening`s convection should move north of Phoenix Monday morning/afternoon likely providing subsidence just to the north and east of Phoenix. However, more favorable conditions should be seen across southern Maricopa County which the HRRR shows as an area of development by mid afternoon. Given a weak southwesterly steering flow, some of this convection could very well make its way into the Phoenix area during the late afternoon/early evening. DCAPEs will not be as high on Monday, but with MUCAPEs potentially around 1000 J/kg we can`t rule out a few strong storms. The southwesterly drying flow is likely to persist into Tuesday, but ensemble mean PWATs still remain high at 1.5-1.7" while generally staying there through Wednesday. Forecast confidence for both Tuesday and Wednesday is not all that high as convection is likely to be conditional due to the lack of any organized forcing. There will definitely be some higher terrain afternoon convection, but with an overall weak southwesterly flow any convective development across the lower deserts will likely be dependent on colliding outflows. The synoptic pattern will begin to shift starting Wednesday as a very strong high pressure ridge develops off the California coast before likely shifting into at least western portions of the Desert Southwest by Thursday. The positioning of the high should result in dry northerly flow across our region starting Wednesday night and lasting through at least Friday. This northerly flow is not likely to completely scour out the lower boundary layer moisture, but it will bring in markedly drier air aloft which will easily be enough to squash most if not all of convective development starting Thursday. NBM PoPs for Thursday and Friday are at most 10-15% over higher terrain areas to around 5% over the lower deserts. Eventually, guidance shows some moisture beginning to seep back into the region from the east next weekend. Forecast temperatures this week remain largely unchanged and really do not change much day to day. Expect lower desert highs ranging from 107-112 degrees across south-central Arizona to upwards of 110-115 degrees for the lower deserts of southeast California into far southwest Arizona. Overnight lows will also run very warm this week with readings mainly in the low to mid 80s over the rural deserts to the upper 80s and lower 90s within the metro areas. && .AVIATION...Updated at 1220Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Current southerly/southeasterly winds with gusts 20-25 kt will taper off over the next couple of hours with speeds returning to aob 10 kt by 13-14Z. Southeasterly winds will continue through the morning with the typical westerly shift expected around 19Z. There may be some occasional wind gusts of 15-20 kt late this afternoon and early this evening. This evening, there is a high chance (>70%) of an outflow boundary arriving from the S-SE. Timing and strength of the outflow is still a bit uncertain, but there will likely be an abrupt wind shift accompanied by gusts reaching 20-40 kts and potential for blowing dust. There is also a 40% chance of TSRA at all terminals this evening, mainly after 03Z. TSRA is expected to exit the Metro by 10-12Z Monday morning. We will continue to adjust arrival time of the outflow and possible TSRA in subsequent forecasts. Southeast California/Southwest Arizona including KIPL and KBLH: Winds will continue to follow their typical diurnal patterns with southeasterly flow continuing at KIPL and southerly flow persisting at KBLH. Speeds should generally remain 8 kts or less. Decaying showers near the Colorado River Valley will likely send an outflow boundary through the region reaching the terminals around 15-16Z causing winds to gust up around 20 kt. After a few hours wind speeds at KIPL will go back to aob 10 kt. At KBLH, wind speeds will remain elevated through the afternoon with gusts up around 20-25 kts. Skies will remain mostly clear through the the morning with FEW-SCT high clouds moving in this afternoon. && .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 from 10 AM this morning to 8 PM MST Friday for AZZ530. Blowing Dust Advisory from 4 PM this afternoon to 10 PM MST this evening for AZZ553. CA...Excessive Heat Warning from 10 AM this morning to 8 PM PDT Friday for CAZ562-566-567-569-570. && $$ DISCUSSION...Kuhlman AVIATION...Berislavich/Salerno FIRE WEATHER...Kuhlman