Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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607 FXUS65 KPSR 131709 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1010 AM MST Thu Jun 13 2024 .UPDATE... Updated Aviation && .SYNOPSIS... Very hot and overall dry conditions will persist through the 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 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 1710Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Variable and potentially erratic wind directions will be the greatest weather issue through Friday afternoon with 15-20K AGL cigs today giving way to clear skies Friday. Confidence is good that east winds will prevail into the early afternoon, however highly variable directions are probable into the mid-afternoon during the typical transition to a westerly direction. This variability may be exacerbated by isolated, elevated convection resulting in virga and isold SHRA; and west winds may not become truly established until very late afternoon. While coverage and confidence of any more direct impacts are too low to include in this TAF package, low probabilities (~10%) exist of gusty, erratic (up to 30kt) winds during the late afternoon through the evening. Southeast California/Southwest Arizona including KIPL and KBLH: A period of afternoon/evening gusty winds will be the main weather issue through Friday afternoon as midlevel cloud decks stream north along and east of the Colorado River. S/SE winds will be preferred through the early evening with gusts 20-25kt initially materializing at KBLH, then stronger westerly sundowner winds up to 30kt sweeping into KIPL. Confidence is good that wind directions will have the tendency to veer towards a W/SW direction through the overnight, then trending more towards a light and variable character Friday morning. && .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...18 FIRE WEATHER...Kuhlman