Area Forecast Discussion
Issued by NWS Phoenix, AZ
Issued by NWS Phoenix, AZ
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878 FXUS65 KPSR 111720 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1020 AM MST Tue Jun 11 2024 .UPDATE...Updated Aviation Discussion... && .SYNOPSIS... Temperatures will warm up over the next couple of days with highs warming near or in excess of 110 degrees across the lower deserts, especially across south-central Arizona. As a result, an Excessive Heat Warning is in effect for much of south-central Arizona today through Thursday. Temperatures briefly cool down Friday before warming back up again for the weekend. && .DISCUSSION... Current WV imagery and objective analysis show the weak upper low that had previously moved across the Southwest for the start of the week is now situated over the Texas Panhandle while a cutoff low resides off the coast of northern Baja. Over Arizona, heights are rising in response to a building ridge of high pressure over the region downstream of the cutoff low. Going through the day today, 500 mb heights will continue to rise to around 590 dm and will lead to temperatures warming up to around 106-111 degrees this afternoon across the lower deserts. The cutoff low will continue to meander off the coast of northern Baja through the middle part of the week while the upper level ridge strengthens/amplifies over the Southwest. By Wednesday, ensemble and deterministic guidance show 500 mb heights over south-central Arizona peaking around 592-594 dm, which is above the 90th climatological percentile. The greater height anomalies Wednesday will exist further to the east, climbing in excess of the 99th percentile near the AZ/NM border where the ridge axis and center of the anticyclone will be situated. With heights peaking Wednesday, temperatures will respond accordingly with Wednesday forecast to be the hottest day through the rest of the workweek. Lower desert highs Wednesday will rise to around 109-113 across south-central Arizona. Temperatures will flirt with the record high in Phoenix on Wednesday, which is 113 degrees set back in 2022. While the greatest coverage of Major HeatRisk across south- central Arizona will occur Wednesday, temperatures today and Thursday will also be pretty similar and near Major HeatRisk thresholds. As a result, an Excessive Heat Warning is in effect for much of south-central Arizona today through Thursday. Going into the end of the workweek, ensemble clusters remain in great agreement with the aforementioned cutoff low progressing inland across southern California into Arizona late Thursday into Friday. This will lead to temperatures dropping back closer to near to slightly above normal readings Friday across south-central Arizona. There will be an increase in moisture ahead of the upper low Thursday into early Friday, which may lead to some shower/thunderstorm development across mainly high terrain areas of Arizona. NBM PoPs have trended up during this time period with the greatest chances currently focused across the high terrain east of Phoenix. Additionally, breezy conditions will increase late in the week, which combined with hot and dry weather will lead to enhanced fire weather conditions. Following the passage of the upper low, ensembles favor flat ridging prevailing for the upcoming weekend, leading to temperatures increasing once again. According to the latest NBM deterministic output, highs will once again approach or exceed 110 degrees across the lower deserts. Anyone with outdoor weekend plans should plan accordingly such as limiting time outdoors and maintaining adequate cooling and hydration. Uncertainty increases heading into early next week as a trough pushes into the Pacific Northwest with ensemble cluster analysis showing disagreement in the depth and timing of this trough. For now, the NBM indicates highs briefly "cooling" back closer to near normal readings early next week. && .AVIATION...Updated at 1720Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT; VFR conditions at all terminals under some passing high clouds can be expected through the TAF period. Winds will continue to exhibit diurnal tendencies with speeds generally remaining aob 10 kts, although some occasional afternoon/early evening gusts into the mid-teens cannot be ruled out. Southeast California/Southwest Arizona including KIPL and KBLH: VFR conditions at both terminals under some passing high clouds can be expected through the TAF period. At KIPL, winds will be out of the southeast through this afternoon before shifting out of a westerly direction by this evening. At KBLH, winds will generally be out of the south to southwest. Wind speeds will remain aob 10 kts at both sites through this evening becoming light and variable in the early morning hours. && .FIRE WEATHER... Hot and seasonably dry conditions will continue to support a high fire danger across the area through the week. Temperatures will heat up over the next couple of days with afternoon highs across the lower deserts approaching or exceeding 110 degrees through Thursday. Winds will continue to generally favor diurnal tendencies with occasional afternoon breeziness of 20-25 mph expected across most of the region. MinRHs will range between 5-10% with overnight Max RHs between 15-35% expected. Going into the end of the work week, a weather system is expected to traverse the region and bring increasing breeziness, which will act to promote elevated fire weather conditions. Additionally, the weather system will bring a low chance (less than 10%) for dry thunder to the high terrain east of Phoenix. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Thursday for AZZ534- 537>555-559-560-562. CA...None. && $$ DISCUSSION...Smith AVIATION...95/Lojero FIRE WEATHER...Smith/Whittock