textproduct: NWS Flagstaff

SYNOPSIS

Somewhat diminished monsoonal activity is expected through this weekend as high pressure builds overhead. Very hot temperatures are expected, 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

Strong high pressure will shift westward and build over Arizona today. Monsoon activity will continue to diminish due to subsidence under the ridge plus drier air gradually working into region. However, there remains enough moisture and instability for isolated to scattered showers and thunderstorms today. Coverage will be mostly restricted to the high terrain from Flagstaff southward, and will be maximized around the White Mountains. With very slow storm motion and PW still near the 75th percentile, a low-end flash flood threat over burn scars remains a factor. This somewhat suppressed period of monsoonal activity is forecast to continue through at least the weekend. Showers and thunderstorms will not fully shut off each day, but remain isolated to scattered with the best coverage in the White Mountains.

Outside of storm activity, the primary hazard over the next few days will be heat. With the declination in moisture, above normal heights at 500mb will lead to the warmest temperatures of the year so far for all of northern AZ. As a result, a variety of heat headlines will be in effect. An Extreme Heat Warning for the Grand Canyon below 4000 ft will remain in effect until Sunday with daytime temperatures up to 110-115 F. Additional Extreme Heat Warnings will be in effect today through Sunday for Glen/Marble canyon and low elevation areas south of the Mogollon Rim, where temperatures will approach or exceed 110 F. Valleys north of the Rim will have a Heat Advisory on Saturday and Sunday, with daytime temperatures up to 100-105 F.

By the early to middle part of next week, ensemble guidance is leaning towards the high weakening and shifting east. This would allow monsoonal activity to increase again. There is still some uncertainty on the exact timing and nature of this transition, and there is potential that heat headlines will be extended past Sunday. Right now the forecast calls for continued hot temperatures with diminished monsoonal activity on Monday and Tuesday.

AVIATION...Friday 31/18Z through Saturday 01/18Z

VFR conditions, isolated showers/storms from 18Z-03Z along Rim and White Mountains. Winds light and variable 5-15kts day and night. Gusty erratic winds possible near storms.

OUTLOOK...Saturday 01/18Z through Monday 03/18Z...VFR conditions, isolated showers/storms from 18Z-03Z near the White Mountains. Winds light and variable 5-15kts day and night. Gusty erratic winds possible near storms.

FIRE WEATHER...Today and Saturday

Very hot, with the warmest temperatures of the year so far. Isolated to scattered showers and thunderstorms each afternoon/evening over the high terrain Flagstaff eastward, best coverage in the White Mountains. Winds generally west to northwest at 5-15 mph. Minimum RH values as low as 10-15% in the deserts, 15-25% mountains.

Sunday through Tuesday...Very hot temperatures again on Sunday, with a gradual cooling trend thereafter. Isolated showers and storms over the high terrain of eastern AZ on Sunday and Monday, with coverage increasing and expanding westward on Tuesday. Daytime winds generally southwest to west at 5-15 mph each day.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST /9 PM MDT/ Sunday for AZZ005- 006-018-037-038.

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