textproduct: NWS Flagstaff

SYNOPSIS

A strong high pressure system over Arizona will deliver low-grade monsoon conditions as well as hot daytime temperatures today through at least Friday. Mainly isolated showers and thunderstorms will develop along the higher terrain each afternoon and evening. Moisture will start to return this weekend, bringing back moderate monsoon activity.

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. Due to the hot temperatures at lower elevations an Extreme Heat Warning is in effect for the lower portions of the Grand Canyon as well as Yavapai county through Friday. Enough moisture will remain for the daily development of afternoon into the evening thunderstorm, mainly at higher elevations but nothing too impactful is anticipated.

Starting Saturday and lasting into early next week...The high pressure center will shift eastward in response to a longwave trough and embedded disturbances moving over the western states. The trough will remain just far enough north and west to allow monsoon moisture 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). Its too far out to say much but the pattern will contain a decent amount of vertical wind shear which could lead to more organized thunderstorms with an elevated potential to become severe. In addition, about 10-20% percent of model ensemble members are pointing toward a deeper moisture tap. If the deeper moisture tap develops cooler trough related temperatures aloft, organized vertical wind shear and passing enhancements to upward motion by the weak disturbances could lead to a quite active weekend. Stay tuned.

AVIATION...Thursday 27/00Z through Friday 28/00Z

VFR conditions, brief MVFR possible in storms. A few isolated to scattered showers/storms possible until 03Z. Winds light and variable or terrain driven overnight. SW-W 5-15 mph daytime. Gusty and erratic winds possible near storms.

OUTLOOK...Friday 28/00Z through Sunday 30/00Z...Mainly VFR conditions, brief MVFR possible near storms. Isolated afternoon showers/storms possible over the higher terrain between 18Z and 03Z Friday. Storms become more numerous and widespread on Saturday. Daytime winds SW-W 5-15kts, nighttime winds light and variable or terrain driven. Gusty and erratic winds possible near storms.

FIRE WEATHER...Today through Friday

Hotter and drier conditions, with isolated showers and thunderstorms along the higher terrain each afternoon. Outside of gusty and erratic storm driven winds, expect southwest to west winds around 5-15 mph during the day, becoming variable at night. Minimum RH will range from 10-15% for the lower deserts to 30-35% in the White Mountains and San Francisco Peaks.

Saturday through Monday...Scattered showers and thunderstorms each day, especially in the afternoon and across the higher terrain. The increase in showers and thunderstorms will cause high temperatures to cool closer to normal. Outside of storms, expect southwest to west winds around 5-15 mph each afternoon, becoming variable at night.

FGZ WATCHES/WARNINGS/ADVISORIES

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