textproduct: NWS Flagstaff

SYNOPSIS

Above average temperatures expected for most of the week. Moisture starts moving in with thunderstorm chances beginning as soon as Tuesday, but better chances arrive Wednesday and Thursday. Dry and windy weather is expected Friday through Sunday, elevating fire weather concerns.

DISCUSSION

Strong high pressure centered near El Paso will persist through Thursday, bringing above normal temperatures that should peak Tuesday before dropping slightly Wed/Thu due to some moisture moving in. This moisture is forecast to move up from the south, starting Tuesday with some isolated high-based convection developing during the afternoon and evening, primarily along and north of the Mogollon Rim. This activity should only produce spotty light rain amounts, but gusty winds are likely with any showers or storms. Very hot temperatures will continue through Tuesday at the lower elevations of the Grand Canyon where an Extreme Heat Warning continues. Temperatures at the bottom of the canyon will reach near 112F, hiking at the lower parts of the canyon is dangerous and discouraged in this heat. By Wednesday and Thursday, moisture values increase a bit more, with mean precipitable water values reaching 0.80" to 1.00" area wide which is well above normal for this time of year. Isolated to scattered showers and thunderstorms are forecast each afternoon and evening, with PoPs up to 30-50% mostly along/north of the Mogollon Rim.

Friday through Sunday - strong low pressure for this time of year is forecast to drop down into the northwest United States. This is likely to bring windy conditions along with a drying trend, leading to a high chance of critical fire weather conditions over nearly all of northern Arizona. Combined with a potential for some new lightning-caused fire starts the preceding few days, this fire weather pattern is concerning. In our latest forecasts, southwest wind gusts of 30-40 mph are expected Friday afternoon, increasing to 40-50 mph Saturday and then 35-45 mph Sunday. Daytime temperatures will be decreasing as this trough moves into the western US and pushes the ridge well to the south. Highs over the weekend should drop to near or even a bit below normal.

AVIATION...Monday 22/18Z through Tuesday 23/18Z

VFR conditions, no precipitation expected. Winds SW 5-15kts, gusts to 25kts daytime, light and variable or terrain driven overnight.

OUTLOOK...Tuesday 23/18Z through Thursday 25/18Z...VFR conditions, isolated SHRA/TSRA along the and north of the Mogollon Rim Tuesday and Wednesday afternoon/evening. Brief MVFR possible near heaviest storms. Winds SW-W 10-20kts daytime, light and variable or terrain driven overnight.

FIRE WEATHER...Tuesday and Wednesday

An increase in moisture brings a slight chance of thunderstorms (10-20%) Tuesday afternoon and a (20-40%) chance of thunderstorms Wednesday afternoon. Areas with the best chances for storms is the Mogollon Rim northward. Temperatures will be on the warm side, about 10 degrees above average. Winds are SW-W 10-20 mph with gusts around 25 mph each day, though gusty and erratic winds are expected near storms. Minimum RH values 10-20% Tuesday. 15-25% Wednesday.

Thursday through Saturday...Thunderstorm chances peak on Thursday at 20-50% with the best chances for storms being the Mogollon Rim northward. By Friday things dry back out and winds pick up substantially, with critical fire weather almost a certainty for most of northern Arizona through the weekend. Winds SW-W 10-20 mph with gusts to 30 mph Thursday, SW-W 15-25 mph with gusts to 35 mph Friday and SW-W 20-30 mph, gusts 40-45 mph on Saturday. Minimum RH values 15-25% Thursday, 10-20% Friday, 5-15% Saturday.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 7 PM MST Tuesday for AZZ006.