textproduct: NWS Flagstaff

SYNOPSIS

A high pressure system remains centered over northern Arizona, supporting above normal daytime highs, while allowing monsoonal moisture to slowly move northward across the state. Greatest potential for showers and thunderstorms will be along and near the higher terrain. Extreme heat will continue for the Grand Canyon, Glen Canyon and Marble Canyon through at least Friday. The high pressure system is expected to shift slightly toward the Four Corners late this weekend or early next week.

DISCUSSION

Visible satellite imagery shows the mid to upper-level cloud deck that extended from about the I-40 corridor southward, is thinning from south to north. This cloud cover has likely delayed the development of showers and thunderstorms along the higher terrain, especially closer to the I-40 corridor, to early this afternoon, while the White Mountains are currently starting to see showers and thunderstorms develop. The latest sounding from Flagstaff shows decent instability with Mixed-layered CAPE around 1100 J/KG and a little bit of shear, so we could see a handful of severe storms similar to yesterday. Storm motion will likely be slow (around 5 mph) and some guidance suggesting a westward motion. This could lead to a concern for training storms and lead to localized flash flooding.

Guidance continues to support that the area of high pressure is projected to settle over the Four Corners late this weekend or early next week. This would allow more Monsoon moisture to lift northward and increase showers and thunderstorm coverage across northern Arizona. Prior to the incoming active monsoon days, we could see a brief downward trend in convective activity Friday and Saturday. The NBM still has chances for showers/storms across the higher elevation locations, but we are not anticipating more widespread activity until Sunday onward. This pattern could also lead to an extension of the extreme heat warnings the Grand Canyon (below 4000 ft), Glen Canyon and Marble Canyon through at Sunday.

AVIATION...Thursday 06/18Z through Friday 07/18Z

VFR conditions, MVFR near heavier showers/storms. Shower/storms develop around 18Z mainly along a KGCN-KFLG-KSOW line and expand south and west through 03-06Z. Winds variable 5-15kts daytime, light and variable or terrain driven overnight. Gusty and erratic winds possible near showers/storms.

OUTLOOK...Friday 07/18Z through Sunday 09/18Z...VFR likely, MVFR possible near heavier showers/storms. Scattered showers/storms possible between 18Z-03Z each day. Winds variable 5-15kts daytime, light and variable or terrain driven overnight. Gusty and erratic winds possible near showers/storms.

FIRE WEATHER...Friday and Saturday

Warm with temperatures 5-10 degrees above average. Scattered showers and thunderstorms will develop over the higher terrain each afternoon and move off to the west and southwest as the day progresses. Winds variable 5-15 mph with gusty and erratic winds near storms. Minimum RH values 7-15% deserts, 20-30% high terrain.

Sunday through Tuesday...Daytime highs will gradually cool next week, but still remain a few degrees above normal. Storm coverage increases with scattered showers/thunderstorms possible across the whole region. Gusty/erratic winds possible from showers/storms, otherwise expect variable winds 5-15 mph. Minimum RH's increase as the week progresses, 10-30% Sunday, 15-40% Monday, 20-50% Tuesday.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST /9 PM MDT/ Friday for AZZ005- 006.