Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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365 FXUS65 KPSR 131117 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 417 AM MST Thu Jun 13 2024 .UPDATE...Updated 12z Aviation Discussion... && .SYNOPSIS... Very hot and overall dry conditions will persist through the coming weekend with an Excessive Heat Warning in effect through Sunday for the lower deserts of south-central Arizona. A weak area of low pressure will move over the region later today and tonight leading to increased cloud cover, breezy conditions, and perhaps a few light showers focused more across central Arizona. Temperatures will eventually cool down early next week with readings closer to normal for the first half of next week. && .DISCUSSION... The main forecast concern continues to be the near record heat across portions of the area through the upcoming weekend. For today, the strong sub-tropical ridge currently centered over southern New Mexico will continue to shift to the east of the region while a weak cut-off low approaches southern California. The heat dome over the region will largely stay in place despite increasing mid-level moisture and clouds across Arizona as the cut-off low approaches the region. Forecast highs of 107-111 degrees today may not be realized across south-central Arizona if the clouds are thick and expansive enough to greatly impede insolation, but breezier conditions very well could counteract the clouds with increased mixing. We also anticipate narrow bands of mostly virga showers developing as early as sunrise this morning, but more so during the afternoon and evening hours across western Pinal, Maricopa and eastern La Paz and Yuma counties. Model soundings continue to show cloud bases above 12K feet with a very dry sub-cloud layer evaporating the majority of any rainfall from the shower activity. However, would not be surprised to see a stationary narrow band of showers allowing for enough top-down saturation for a hundredth of an inch or so in a few spots. As the cut-off low quickly exits to the northeast during the day Friday, the temporary lower heights over Arizona will drop temperatures to below 110 degrees across the south-central lower deserts. However, building heights will quickly be seen across the western deserts leading to forecast highs between 108-112 degrees across southeast California. The sub-tropical ridge will build back over the southern part of the Desert Southwest late Friday into Saturday with H5 heights back to between 590-592dm, or easily into the 90th percentile of climatology. As a result, NBM forecast highs Saturday rise to 109-114 degrees reaching Major HeatRisk again for portions of the area. This renewed heat will however be temporary as a large Pacific trough is expected to enter the Pacific Northwest this weekend with the southern extent of the trough reaching our region starting Sunday. Temperatures Sunday will still be quite hot over the area, especially across south-central Arizona where readings are expected to be around 110 degrees. With widespread Moderate HeatRisk and localized Major HeatRisk over portions of the lower deserts over the next several days, we decided to extend the Excessive Heat Warning in Arizona through Sunday while upgrading the Excessive Heat Watch to a Warning across portions of southeast California on Friday and Saturday. Gradually lower heights and temperatures are expected early next week as the Pacific trough slowly slides by just to our north. By Monday, highs are likely to fall back closer to seasonal normals before bottoming out on Tuesday with highs between 100-105 degrees. The relief from the excessive heat will however be short-lived as the sub-tropical ridge is expected to build back over the region during the latter half of the week. Eventually it seems likely highs will reach or exceed 110 degrees again by next Thursday or Friday as the center of the ridge moves near or even over the region. && .AVIATION...Updated at 1110Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will be following diurnal tendencies through the period. A period of variable winds (140v250) will be common late morning through mid-afternoon before fully switching out of the west, especially at KPHX. Wind speeds will be light through the morning before picking up in the afternoon and lasting into the early evening hours with gusts ranging between 15-20 kts. SCT-BKN mid to high-level aoa 15 kft will prevail through tonight. Under these clouds, some virga showers will be possible, which could create gusty and erratic winds of up to 30 kts. However, confidence in occurrence is low at time and not included in the TAF. Southeast California/Southwest Arizona including KIPL and KBLH: At KIPL, light and variable winds this morning will become southeasterly by early afternoon before a westerly sundowner switch occurs by late this afternoon. At KBLH, winds will generally be out of south to southwest. Wind speeds this morning will generally be light before picking up later this afternoon as gusts approach 20-25 kts, with the highest gusts expected at KIPL where up to 30 kts are possible this evening. Generally mostly clear skies will prevail through the period with just a FEW mid- level passing clouds. && .FIRE WEATHER... Hot and overall dry conditions will prevail over the next few days. A weak weather system moving through later today and tonight will bring some high based light showers, but much of the rain will not reach the surface due to the very dry lower levels. Some of these virga showers may produce locally gusty winds in excess of 30 mph. Outside of any shower activity, gusts 20-25 mph will be fairly common this afternoon and evening, resulting in locally enhanced fire weather conditions. MinRH values will range between 5-10%, while poor overnight recoveries can be expected with MaxRHs only reaching towards 15-35%. The above normal temperatures will continue through the upcoming weekend, while winds increase further with afternoon gusts of 20-30 mph likely on Sunday and Monday. The combination of the increased winds and low RHs will continue to bring elevated fire danger across the area into early next week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ534-537>555- 559-560-562. CA...Excessive Heat Warning from 10 AM Friday to 8 PM PDT Saturday for CAZ562-563-566-567-570. && $$ DISCUSSION...Kuhlman AVIATION...Lojero FIRE WEATHER...Kuhlman