textproduct: NWS Flagstaff

SYNOPSIS

Look for isolated showers and thunderstorms from the White Mountains and Mogollon Rim southward through early this evening and again Thursday. Widespread shower and thunderstorm activity could develop by Friday and Friday night with a passing weather disturbance. Temperatures warming to above normal through Thursday, then cooling off over the weekend.

DISCUSSION

A strong area of high pressure is centered over our area this afternoon, bringing hot temperatures from 5 to 10 degrees above average for this time of year. The flow around the ridge is bringing drier air to areas north of I-40 where surface dewpoints have fallen to the 30s/low 40s. Sufficient moisture remains along/south of I-40 for isolated to scattered showers and thunderstorms, with the highest coverage around the White Mountains, where some storms will contain heavy rainfall. Expect today's activity to be mainly diurnal, dissipating by around sunset if not before. By Thursday - the center of high pressure is forecast to slide to our south-southwest, resulting in the drier air moving a bit farther south into our area. Isolated storms will be possible across the White Mountains and Yavapai/Gila counties, with dry weather elsewhere. The hot temperatures will continue on Thursday afternoon.

Friday into Saturday - a passing disturbance is forecast to move west to east across our area, with moisture increasing along and ahead of it. This will bring higher shower and thunderstorm chances, in the 30-60% range by later Friday afternoon through Friday night. Storm chances fall to 10-30% by Saturday as the disturbance moves to the east. Sunday through Tuesday - troughing in the northwest US will increase southwest flow across our region, with gusty surface winds reaching 25-35 mph. The western edge of the moisture will also be nearby though there is some uncertainty this far out regarding where it will set up. This will allow for daily storm chances, highest in eastern AZ and tapering off to 10% or less in western AZ. Daytime temperatures are forecast to be around seasonal averages.

AVIATION...Wednesday 09/18Z through Thursday 10/18Z

Mainly VFR conditions. Slight chance for ISOLD -SHRA/-TSRA 19Z-02Z INVOF KSOW/KJTC, and potentially KFLG/KCMR as well. Brief gusty winds possible in and around TS. Winds W-NW 5-15 kts through 02Z, then becoming light and VRB.

OUTLOOK...Thursday 10/18Z through Saturday 12/18Z...Mainly VFR conditions. ISOLD -SHRA/-TSRA possible south of a KPRC-KJTC line on Thursday, then becoming likely with SCT SHRA/TSRA across much of northern AZ on Friday. Brief MVFR conditions and gusty winds possible in and around +TS. Daytime winds W-NW 5-15 kts on Thursday, becoming W/SW 10-20 kts on Friday. Overnight winds light and VRB.

FIRE WEATHER...Thursday and Friday

Isolated showers and storms will be possible south of the Mogollon Rim on Thursday, becoming scattered on Friday across much of northern Arizona. Winds west/northwest 5-15 mph on Thursday, becoming west/southwest 10-20 mph on Friday.

Saturday through Monday...Chances for isolated to scattered showers and thunderstorms remain through the weekend into Monday, mainly over the higher terrain. Winds southwest 10-20 mph on Saturday, increasing on 15-25 mph on Sunday, then subsiding to 10-20 mph for Monday.

FGZ WATCHES/WARNINGS/ADVISORIES

None.