textproduct: NWS Flagstaff

SYNOPSIS

Temperatures warm up to 5 to 10 degrees above average throughout the week. Low grade monsoon conditions continue today with only isolated storms over the White Mountains. By midweek, thunderstorm coverage begins to increase across the area as additional monsoon moisture is drawn across the state. A bit cooler temperatures arriver for the weekend.

DISCUSSION

The axis of high pressure aloft extended from over Arizona eastward into Texas Tuesday afternoon. Over the coming week high pressure aloft will gradually consolidate and wobble from over Arizona across the Four Corners eventually landing over the New Mexico/Texas border. The high position will initially deliver high temperatures 5 to 10 degrees above average but as the high shifts eastward the door will open to an active monsoon weather pattern.

For Wednesday...The center of high pressure aloft will become focused over Arizona. The result will be downright hot weather at mid- to lower-elevations. However, every location in northern Arizona, including the mountains, will range from 5-10 degrees warmer than average. For this reason, an Extreme Heat Warning is in effect for elevations below 4000 feet in the Grand Canyon through Thursday. Monsoon moisture begin it's upward trend (partly due to outflow from thunderstorms over northwest Mexico Tuesday night/Wednesday morning) with isolated to scattered showers and thunderstorm anticipated midday and afternoon over the Mogollon Rim and White Mountains then locations southward guided by northeast flow around the high.

From Thursday into early next week...As the high shifts eastward the door opens to active monsoon weather. The primary reasons for the moisture increase will be enhanced low-level flow from over the Gulf of California and and easier path for thunderstorm outflow over northwest Mexico and southeast Arizona to spread across the state. In addition, with high center moving eastward subsidence aloft will weaken putting an end to the capping/stabilizing layer aloft. On Thursday, as the high becomes established over the Four Corners look for scattered to numerous showers and thunderstorms area wide, most numerous from the Mogollon Rim/White Mountains to the Grand Canyon and Kaibab Plateau. For Friday and over the coming weekend full monsoon activity is forecast with scattered to numerous showers and thunderstorms across the area likely lasting well into the overnight hours. Otherwise, temperatures cooling to seasonal averages by Thursday or Friday with a light wind environment continuing.

AVIATION...Wednesday 19/00Z through Thursday 20/00Z

Expect mainly VFR conditions. ISOLD-SCT SHRA/-TSRA mainly east of a KPAN-KINW-KRQE line through 02Z, then dissipating. SCT SHRA/TSRA and ISOLD +TSRA along, south and east of a KPRC-KFLG-KRQE AFT 18Z-20Z Wednesday. Any stronger storms are capable of brief MVFR/IFR conditions and erratic wind gusts as high as 40-45kts. Outside of storms, expect daytime sfc winds W-SW-5-15kts.

OUTLOOK...Thursday 20/00Z through Saturday 22/00Z...Coverage will increase during this time frame. Expect SCT-NMRS SHRA/TSRA and ISOLD +TSRA throughout the period, especially in the afternoon and evening hours. Any stronger storms are capable of brief MVFR/IFR conditions and erratic wind gusts as high as 40-45kts. Sfc winds outside of storms generally variable 5-15kts.

FIRE WEATHER...Wednesday and Thursday

Temperatures rise to 5-10 degrees above average. Expect isolated to scattered showers and thunderstorms each day with the best coverage over the eastern Mogollon Rim and White Mountains. Winds SW-W at 5-10 mph Wednesday and W-NW at 5-15 mph Thursday. Gusty and erratic winds possible near storms. Minimum RH values 10-15% over the lower deserts to 30-35% in the White Mountains.

Friday through Sunday...Temperatures around 5 degrees above average Friday, cooling to near normal over the weekend. Scattered showers and thunderstorms increasing in coverage each day with most of the area seeing a chance for shower/storms by the weekend. Winds S-SW at 5-15 mph. Gusty and erratic winds possible near storms.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST Thursday for AZZ006 below 4000 feet.