textproduct: NWS Flagstaff

SYNOPSIS

A strong high pressure system over Arizona will deliver low-grade monsoon conditions as well as hot daytime temperatures through Friday. Look for, isolated to scattered showers and thunderstorms to continue over the higher terrain each afternoon and evening. On Saturday deeper moisture will start to return, bringing back moderate monsoon activity with increasing showers and thunderstorms heading into early next week.

DISCUSSION

A strong high pressure system will remain centered over the Arizona/New Mexico border through Friday resulting in daytime temperatures in the mid 80 to lower 90s in the mountains to 105 to 110 at elevations below 4000 feet in our forecast area. A few record high temperatures will likely be set. Due to the hot temperatures an Extreme Heat Warning remains in effect for the lower portions of the Grand Canyon and Yavapai County through Friday. Enough moisture will remain for the daily development of afternoon into the evening showers and thunderstorms, mainly at higher elevations.

Starting Saturday and lasting into early next week...The high pressure center shifts eastward in response to a trough moving over the western states. The trough will remain just far enough north and west to allow monsoon moisture from over the Gulf of California to stream northward across Arizona. Look for the daily influence of daytime heating on thunderstorm development but with the addition of passing shortwave disturbances interacting with this moisture (classic transition season stuff). Shower and thunderstorms coverage will become scattered to numerous with some level of overnight activity continuing. We're confident that the pattern will contain decent vertical wind shear with the potential for organized and severe thunderstorm development. In addition, about 10-20% percent of model ensemble members are pointing toward a deeper tropical moisture tap, perhaps being pulled off a dying tropical system over the Pacific. If the deeper moisture tap develops then a serious flash flood threat could develop. However, the timing of various players in the flash flood scenario remains uncertain and thus our confidence remains low. Stay tuned.

Later next week...Looks like monsoon moisture lingers and unsettled conditions remain with at least low-grade monsoon activity continuing.

AVIATION...Friday 28/06Z through Saturday 29/06Z

Mainly VFR conditions, brief MVFR possible in storms. Dry overnight. Scattered showers/storms begin around 18Z in the higher terrain on Friday. Showers and storms could last through 06Z south of the Mogollon Rim while areas north of the Mogollon Rim dry out. Winds light and variable or terrain driven overnight, SW-W 5-15kts daytime Friday. Light and variable or terrain driven Friday night. Gusty and erratic winds possible near storms.

OUTLOOK...Saturday 29/06Z through Monday 31/06Z...VFR conditions with MVFR possible in heavier storms. Nocturnal thunderstorms possible Friday night into Saturday morning. Scattered to numerous showers/storms Saturday afternoon across all of northern Arizona with some of these storms lasting overnight Saturday into Sunday morning. Another round of scattered showers/storms on Sunday with most of northern Arizona seeing coverage. Winds SW-W 10-15kts daytime, light and variable or terrain driven overnight. Gusty and erratic winds near storms.

FIRE WEATHER...This afternoon through Saturday

Isolated to scattered showers and thunderstorms this afternoon and Friday afternoon, then humidity and storm coverage increasing for Saturday. Storms may persist through the overnight hours Saturday night. Outside of gusty and erratic storm driven winds, expect southwest to west winds around 10-15 mph during the day, becoming variable at night.

Sunday through Tuesday...Increasing moisture with scattered to numerous showers and thunderstorms, possibly extending through the evening and overnight hours. The increase in showers and thunderstorms will cause high temperatures to cool to slightly below normal. Outside of storms, expect southwest to west winds around 10-15 mph each afternoon, becoming variable at night.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST Friday for AZZ006-037.