Area Forecast Discussion

SYNOPSIS

Monsoon moisture remains in place, but high pressure remains centered over New Mexico. This is keeping the potential for showers and thunderstorm mostly contained to the higher terrain during the afternoon and evening hours today. Chances for afternoon and evening showers and thunderstorms will continue Wednesday, mainly for the higher terrain, before temperatures start rising Thursday and remaining elevated this weekend.

DISCUSSION

Visible satellite imagery shows a developing cumulus field over the higher terrain, but the development into showers and thunderstorms appears to be suppressed by the high over New Mexico, despite the presence of the monsoonal moisture. Still expecting isolated to scattered showers and thunderstorms to develop over the higher terrain later this afternoon, with storm motion pushing convection toward the north-northeast today. Convection south of the Mogollon Rim is expected to be limited, mostly associated with any outflows that push activity southward.

Forecast guidance continues to support the high pressure weakening slightly Tuesday and Wednesday, before strengthening again as it moves westward later this week. This may allow a slight increase in showers and thunderstorms Tueday and Wednesday, thought the greatest chance remains over and near the higher terrain. As the high strengthens and shifts westward later this week, temperatures will begin to climb Thursday and continuing into the weekend. Based on the consistency of guidance supporting increasing temperatures, and drier air for later this week and weekend, an Extreme Heat Warning was issued for the Grand Canyon, below 4000 feet, starting 10 AM MST Thursday, and then extending to Yavapai County valleys and basins below 4000 feet and to Marble and Glen Canyons, and Oak Creek and Sycamore Canyons, including Sedona, starting 10 AM MST/11 AM MDT Friday. These hazards are expected to continue trough 8 PM MST/9PM MDT Sunday.

AVIATION...Tuesday 28/00Z through Wednesday 29/00Z

Mainly VFR conditions. ISO-SCT SHRA/TSRA through 03Z then SCT SHRA/TSRA return after 18Z. Brief MVFR/IFR conditions and gusty, erratic winds in stronger storms. Outside of storms, expect generally light or terrain driven winds.

OUTLOOK...Wednesday 29/00Z through Friday 31/00Z...Mainly VFR conditions. ISO-SCT SHRA/TSRA from 18Z-03Z each day, with greatest coverage across or near higher terrain features. Brief MVFR/IFR conditions and gusty, erratic winds in stronger storms. Outside of storms, expect generally light or terrain driven winds.

FIRE WEATHER...Tuesday and Wednesday

Expect an active Monsoon pattern to continue through the period, with afternoon/evening showers and thunderstorms each day. Highest coverage of storms will be over the higher terrain of central Arizona, with isolated to scattered activity elsewhere. Gusty and erratic winds, hail, and flash flooding are continued threats within stronger storms. Away from storms, winds will be generally southwest to west at 10 mph or less. Temperatures will be slightly above normal for locations that do not receive rainfall.

Thursday through Saturday...A downtrend in Monsoon activity is expected through the period, with isolated storms along the higher terrain each day. Away from cloud cover and rainfall, temperatures will rise to possibly the warmest of the year so far. Winds will be generally light and variable at 5 to 15 mph.

FGZ WATCHES / WARNINGS / ADVISORIES

Extreme Heat Warning from 10 AM MST /11 AM MDT/ Friday to 8 PM MST /9 PM MDT/ Sunday for AZZ005-037-038.

Extreme Heat Warning from 10 AM Thursday to 8 PM MST Sunday for AZZ006.