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-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...Friday 07/00Z through Saturday 08/00Z

Expect VFR conditions outside of thunderstorms. SCT-NMRS SHRA/TSRA along and west of the Mogollon Rim/White Mtns through 02Z-04Z, dissipating overnight. Mainly ISOLD cells north and northeast of these areas. Heavier storms will produce brief MVFR/IFR and wind gusts to 40kts. Expect less coverage on Friday, mainly AFT 19Z. Sfc winds generally light outside of thunderstorms and outflows.

OUTLOOK...Saturday 08/00Z through Monday 10/00Z...Expect mainly VFR conditions outside of thunderstorms. SCT-NMRS SHRA/TSRA from 18Z-03Z each day, especially along and near the Mogollon Rim and White Mtns. Heavier storms will produce brief MVFR/IFR and wind gusts to 40kts. Sfc winds generally light outside of thunderstorms and outflows.

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.