329 FXUS65 KPSR 081012 AFDPSR Area Forecast Discussion National Weather Service Phoenix AZ 312 AM MST Wed Aug 8 2018 .SYNOPSIS... Temperatures will cool to more seasonable, but still hot, levels today. With increased moisture across the region and a favorable atmospheric pattern, precipitation chances will remain elevated through early next week. && .DISCUSSION... In the latest NHC public advisory, Hurricane John was located 230 miles south-southwest of the southern tip of Baja California with maximum sustained wind speeds near 100 mph. John, a feature that will help to increase the moisture across the desert southwest this week, is expected to continue moving toward the northwest and pass to the southwest of Baja California Sur Wednesday and Thursday. Simultaneously, the 500 mb high will migrate to the northwest tomorrow, becoming nearly stationary around Nevada/Utah through the end of the week. With increased moisture across the region and favorable mid-level easterly flow, precipitation chances will remain elevated through early next week. Activity from last night will continue to dissipate overnight, with skies gradually clearing during the morning hours. The aforementioned 500 mb high will shift northwest today, placing our forecast area under deep easterly mid-level flow. As a result, heights will be a tad bit lower today and mid-level temperatures will be slightly cooler. In addition, another gulf surge underway tonight will result in even more boundary layer moisture across the region today. PWAT values in Phoenix are forecast to rise from 1.31 inches this afternoon to near 1.5 inches tomorrow afternoon, in Yuma values are forecast to rise from close to 1.5 inches this afternoon to close to 1.9 inches tomorrow afternoon, and in Imperial values are forecast to rise from close to 1.2 inches this afternoon to close to 1.5 inches tomorrow afternoon. At the 250 mb level, there is weak westerly flow which will help to keep anvil clouds from overspreading the region ahead of the storms later this afternoon. In addition, there is pretty decent divergence at the 250 mb level with the flow separating across the eastern half of the state between a trough in northern Arizona and a ridge in in southern Arizona. This divergence aloft will provide extra dynamical support to enhance thunderstorm updrafts. With the combination of increased moisture and sufficient day time heating, MLCAPE values are forecast to be around 1000 to 2000 J/kg this afternoon, with the greatest instability along the higher terrain of south-central Arizona as well as along and west of the Colorado River. Storms will start to develop during the late morning/ early afternoon hours along the higher terrain in eastern Arizona. With very robust CAPE values in this region, steeper lapse rates, and very high DCAPE values, expect storms that develop to have the potential to produce severe winds, hail, and frequent lightning. The steering flow is pretty weak, so some areas could also see some localized flooding. Storm motion will be to the west, so the big question is, will these storms be able to sustain themselves as they move towards the lower deserts. For that to happen, there would need to be a strong enough outflow to overcome the convective inhibition that will be in place during the afternoon hours. With the environment out east being favorable for stronger storms, it's not out of the question we will get a strong enough outflow to move into the lower deserts and regenerate storms. The CAMs don't really look to optimistic though, and seem to think the environment will be way too worked over from last nights activity. However, there is a little bit more dynamical support today than there was yesterday, so once again, storms in the lower deserts can't be ruled out. In fact, any storm that does develop across the lower deserts will have the potential to be strong and produce gusty winds, frequent lightning, hail, and localized flooding. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Converging thunderstorm outflows over metro Phoenix will make for erratic surface winds and provide lift for at least isolated thunderstorms through 07Z along with areas of visibility below 6SM but above 3SM due to dust (localized 2-3SM). Expect isolated weaker showers through 09Z. Anticipate southwesterly surface winds to begin reestablishing after 07Z. Expect ceilings to remain AOA FL100 except in showers. An active Monsoon pattern is expected through at least Thursday. There are indications that Wednesday will be more active than Today (Tuesday) has been. Southeast California/Southwest Arizona including KIPL and KBLH: South and southeasterly breeziness will continue overnight and through the day Wednesday. Other than some mid and high clouds, no thunderstorm activity is anticipated except perhaps for portions of La Paz County Wednesday afternoon and evening. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Thursday through Monday: Significant moisture will return to the area from the east and bring an increase in thunderstorm activity through the period. Storms are expected to be most prevalent over the higher terrain north and east of Phoenix but even lower elevations will have a shot at precipitation each afternoon. Minimum humidities will end up between 20 to 30 percent over the deserts each day following fair to good overnight recoveries. Apart from thunderstorms, winds will be light except for typical afternoon and evening upslope breeziness. Temperatures each day will remain at or just below seasonal normals although portions of the south-central deserts may drop to around 100 Thursday into Saturday as thicker clouds and moisture affect the region. && .SPOTTER INFORMATION STATEMENT... Spotter reports may be needed later this week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Hernandez AVIATION...AJ FIRE WEATHER...Iniguez/Hirsch/Wilson/Kuhlman/CB