Area Forecast Discussion
Issued by NWS Phoenix, AZ

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065 FXUS65 KPSR 150500 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 1000 PM MST Fri Jun 14 2024 .UPDATE... Updated Aviation section. && .SYNOPSIS... Dry conditions with above normal temperatures will persist through the weekend with local Excessive Heat Warnings remaining in effect. The hottest day will be Saturday with highs at least 5 degrees above normal and breaching 110 degrees for many lower desert communities. Readings will retreat several degrees back closer to normal levels early next week as a series of weather disturbances stream north of the area. A return to warmer than normal conditions is likely during the latter half of next week. && .DISCUSSION... While a compact low pressure system ejects through the four corners early this afternoon, dry anti-cyclonic flow was building into the SW Conus with modest height rises. In fact, HREF members suggest H5 heights rising into a 590-593dm range tonight and Saturday with notable midtropospheric warming behind the departing cold core. This evolution will result in temperatures once again reaching 4F-8F above normal Saturday with local excessive heat warnings remaining in place, though readings should hover several degrees below daily records. Although HeatRisk will only briefly touch a major category over very localized areas this weekend, warnings in the Phoenix metro are mandated through Sunday despite temperatures already quickly retreating closer to the seasonal normal. Forecast confidence is excellent that broad longwave troughing currently over the NE Pacific will progress into the western Conus with individual shortwaves carving out a deeper trough axis resulting in notable midlevel height falls into the forecast area during the first half of next week. Ensemble means suggest H5 heights retreating into a 580-582dm range with minimal temperature guidance spread equating to readings falling near or even a couple degrees below the daily normal. The approach of this larger trough and passing shortwaves will also induce periods of stronger afternoon wind gusts (particularly Monday). While not terribly anomalous for the early summer season, combined with warm temperatures and low humidity levels, a dangerous fire weather scenario may materialize (see Fire Weather section). The near normal temperatures will be rather short lived as strong subtropical ridging impacting the eastern Conus early next week will retrograde towards the SW Conus later in the week as longwave troughing becomes repositioned over the northern plains and Great Lakes. The haste of this transition and eventual position/magnitude of the high pressure center remains rather uncertain with subtle, but very important differences among ensemble members. There is general ensemble agreement that the H5 ridge core in a 590-592dm range will drift along the southern Arizona border towards the end of next week resulting in another period of locally excessive heat. However, a minority of ensemble output suggests more dampened ridging with renewed troughing and lower heights affecting the region. On the opposite end of the spectrum another minority of models indicates ridging building poleward allowing better quality moisture to seep into southern Arizona setting the stage for deeper mountain convection. At this time, feel the preponderance of evidence supports an NBM mean solution of H5 heights in a 590-592dm range advancing directly over the CWA yielding temperatures 5F-10F above normal during the latter part of next week. && .AVIATION...
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Updated at 0500Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: Surface winds have begun to transition to downvalley/drainage patterns which will prevail through mid morning. Winds will transition to predominantly southwesterly directions in the afternoon with some minor gustiness (15-20kts). As for sky cover, skies will be clear except for some afternoon cumulus near and north of the Mogollon Rim. Southeast California/Southwest Arizona including KIPL and KBLH: Familiar nocturnal wind patterns have developed (favoring west/southwest directions). Winds will weaken toward morning becoming southeasterly at KIPL and light and variable at KBLH. During the afternoon, expect for some enhanced southerly breeziness at KBLH (gusts to 25kts) with more minor southeasterly gustiness (15-20kts) at KIPL. Saturday evening, directions at KIPL will shift to southwest/westerly with some gusts up to 20kts (more subtle change at KBLH to SSWly). Otherwise, clear skies.
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&& .FIRE WEATHER... Hot and dry conditions with low humidity levels will continue to yield a slightly elevated fire danger this weekend with the typical daytime upslope gustiness. A weather disturbance moving through the Great Basin early next week will allow temperatures to cool closer to normal, however strengthening afternoon winds will create an environment of heightened fire weather concern during the first part of next week. In fact, there is at least a 30% chance of critical conditions materializing over eastern districts Monday with widespread, frequent gusts 25-30mph possible. Minimum afternoon humidity levels will generally fall into a 5-10% through the weekend with only modest improvement closer into a 10-15% range early next week. This will follow primarily poor overnight recovery of 15-30%. Strong high pressure should build back over the districts during the latter half of next week resulting in warming temperatures, but also weakening winds. There are a few models suggesting somewhat better moisture sneaking into eastern Arizona beyond next weekend yielding a few thunderstorms over mountain areas, yet confidence is very low given any early season activity typically results in little actual wetting rainfall. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ534-537>555- 559-560-562. CA...Excessive Heat Warning until 8 PM PDT Saturday for CAZ562-563- 566-567-570. && $$ DISCUSSION...18/Kuhlman AVIATION...AJ FIRE WEATHER...18