textproduct: NWS Flagstaff

SYNOPSIS

This morning's disturbance is continuing to produce extensive cloud cover, along with showers and thunderstorms across the central portion of northern AZ, while skies remained mostly clear over northern and eastern portions of Arizona, allowing new showers and thunderstorms to develop ahead and east of the disturbance this afternoon. Chances for afternoon and evening showers and thunderstorms will continue Wednesday, mainly for the higher terrain, before temperatures start rising Thursday and remaining elevated this weekend as the monsoon activity decreases.

DISCUSSION

Visible satellite and radar imagery shows the center of the MCV is passing west of Flagstaff, near Williams, and moving in a north- northwest direction, producing a quick burst of showers and thunderstorms, and then leaving behind a layer of mid- to upper- level cloud cover. This cloud layer is helping to suppress new convection across Prescott, Sedona, Flagstaff, and surrounding areas this afternoon. However, areas that have remain mostly clear this morning, especially areas north to northwest of Flagstaff, near the Grand Canyon, and eastern portions of the CWA, including most of Navajo and Apache counties, are starting to see new showers and thunderstorms develop near higher terrain and where daytime heating was the greatest today. This activity is expected to continue through the rest of the afternoon and early evening hours before settling down tonight.

For Wednesday onward, the high pressure that was over New Mexico will strengthen and shift westward and over Arizona, leading to an overall decrease in showers and thunderstorms as subsidence increases and drier, mid-level air moves into the region. However, this will not completely stop the low-level monsoonal moisture, so isolated to low-end scattered showers and thunderstorms will still be possible over the higher terrain during the late morning and afternoon hours. The decrease in Monsoon, along with the strengthening and relocation of the area of high pressure, will cause temperatures to rise above normal by Thursday, with a more significant rise for Friday through Sunday. An Extreme Heat Warning for the Grand Canyon (below 4000 ft) will start at 10 MST Thursday, with additional warnings starting 10 MST/ 11 AM MDT Friday for Yavapai County and northern Gila County (both below 4000 ft), Marble and Glen Canyon, including the city of Page, and Oak Creek and Sycamore Canyons, including the city of Sedona.

AVIATION...Tuesday 28/18Z through Wednesday 29/18Z

Ongoing SCT SHRA/TSRA will move through the KFLG-KSEZ-KPRC area from 18Z to 22Z, creating MVFR/IFR conditions and gusty winds. SHRA/TSRA has pushed west of KINW but 30kt gusts are still being reported, but gusts should start to relax around 21Z. Otherwise, ISOLD-SCT SHRA TSRA are possible from 21Z-06Z, primarily across or near higher terrain features. Brief MVFR/IFR conditions and gusty, erratic winds in stronger storms. Away from storms, expect light or terrain light winds.

OUTLOOK...Wednesday 29/18Z through Friday 31/18Z...Mainly VFR conditions. ISO-SCT SHRA/TSRA from 18Z-03Z each day, with greatest coverage across or near higher terrain features. Brief MVFR/IFR conditions and gusty, erratic winds in stronger storms. Outside of storms, expect generally light or terrain driven winds.

FIRE WEATHER...Rest of Today through Thursday

Active monsoonal conditions are expected through the rest of today, with a slow downturn through Thursday, with isolated to scattered showers and thunderstorms mainly over the higher terrain. Expect mainly light winds outside of thunderstorms, but trending toward westerly through southwest 5 to 15 mph over higher terrain. Daytime temperatures rise to above normal by Thursday.

Friday through Sunday...A continued downturn in Monsoonal activity is expected through this period, although isolated showers and thunderstorms remain possible over higher terrain. Temperatures will rise significantly during this period, with many areas seeing the warmest conditions so far this year. Winds will be generally light and variable, at 5 to 15 mph.

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 from 10 AM Thursday to 8 PM MST Sunday for AZZ006.