textproduct: NWS Flagstaff

SYNOPSIS

Showers and thunderstorms are starting to develop off of the higher terrain due to daytime heating, but are currently isolated in coverage. The potential for showers and thunderstorms will be limited through this weekend as high pressure builds over Arizona. This will cause our daytime high temperatures to soar, likely reaching the warmest readings so far this year. Monsoon moisture is then expected to start moving back into the region next week as the high moves into a more favorable position.

DISCUSSION

Mostly sunny skies, along with the moisture still present within the forecast area, will trigger isolated to low-end scattered showers and thunderstorms over the higher terrain this afternoon and into the early evening hours, as the high to our east moves west and strengthens. Storm motion expected to be toward the northeast to east, and around 10 to 15 mph. Overall coverage and motion of the showers and thunderstorms will help to limit the threat for flash flooding, but if any storms start to back-build, this will created localized areas of higher risk for flash flooding.

Overall forecast guidance continues to support a slow down of the Monsoon as the high shifts westward and strengthens over Arizona. This will cause daytime temperatures to soar, with many areas reaching the warmest reading so far this year. Extreme Heat Warnings are already in effect for the Grand Canyon, below 4000 ft today, and starting 10 AM MST/11 AM MDT Friday, for Yavapai and northern Gila Counties below 4000 ft, as well for Marble and Glen Canyon, including the city of Page, and Oak Creek and Sycamore Canyons, including the city of Sedona. The Extreme Heat Warning was extended today for the lower elevations of northeast Arizona, starting at 10 AM MST/11 AM MDT Saturday, when daytime temperatures are expected to range from 100 to 105. Currently, all heat warnings are set to end 8 PM MST/9 PM MST Sunday.

Max daytime temperatures are expected to start decreasing next week as the high pressure system is expected to shift back toward the east and eventually moving into a favorable location that should allow for the return of more monsoonal moisture. Some guidance has the happening as soon as Monday, while others delay this closer to middle of the week. A slower transition could lead to the heat products being extended into early next week, while a faster transition would favor the current Sunday evening expiration. These forecast trends will be monitored over the next couple of days and a we should be able to have a better idea on which trend is more likely by Saturday.

AVIATION...Thursday 30/18Z through Friday 31/18Z

VFR conditions, brief MVFR possible near showers/storms. Isolated showers/storms possible along Mogollon Rim and White Mountains between 19Z-03Z. Winds SW-W 5-15kts daytime, light and variable or terrain driven overnight. Gusty and erratic winds possible near storms.

OUTLOOK...Friday 31/18Z through Sunday 02/18Z...VFR conditions, isolated showers/storms possible 18Z-03Z each day near the White Mountains, dry elsewhere. Winds VRB 5-15kts. Gusty and erratic winds possible near storms.

FIRE WEATHER...Friday and Saturday

Hot with temperatures warming to 10-15 degrees above average. Isolated showers or storms become confined mainly to the White Mountains region. Winds light and variable at 5-15 mph. Minimum RH values 10-15% deserts to 20-30% mountains Friday, dropping to 7% deserts to 20% mountains.

Sunday through Tuesday...Hot with temperatures 10-15 degrees above average with a cooling trend starting on Tuesday. Dry with the only area seeing isolated showers/storms is the White Mountains region on Sunday and Monday. Storm chances start to spread westward along the Rim on Tuesday. Winds light and variable 5-15 mph. Minimum RH values 7-20% Sunday and Monday, 10-25% Tuesday.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from 10 AM MST /11 AM MDT/ Friday to 8 PM MST /9 PM MDT/ Sunday for AZZ005-018-037-038.

Extreme Heat Warning until 8 PM MST Sunday for AZZ006.

Extreme Heat Warning from 10 AM MST /11 AM MDT/ Saturday to 8 PM MST /9 PM MDT/ Sunday for AZZ009-010-012>014-040.