textproduct: NWS Flagstaff

SYNOPSIS

High pressure will build into the area through the weekend. This will lead to a slight decrease in monsoonal moisture, though expect continued showers and thunderstorms each day. Also expect hotter temperatures. A return to increased monsoon moisture is possible by the beginning of next week.

DISCUSSION

The easterly wave that rippled through our area over the past few days has fully departed. Heights aloft are quickly building today as the ridge strengthens and expands westward. The location of the ridge is less optimal for moisture advection into Northern Arizona, however plenty of moisture still lingers with dewpoints in the 50s and PW near the 90th percentile. Surface heating has been uninhibited this morning under clear skies, and scattered showers thunderstorms are firing along terrain features as of 1230 MST. The flash flooding threat is lesser than previous days, but still remains the primary hazard given the moist profile, saturated ground conditions, and very slow storm motion.

The ridge remains strong while moisture continues to trend downward on Friday. Monsoon activity will be more low-medium grade with isolated to scattered storms in the forecast. By late Saturday into Sunday, the ridge begins to back of a bit and center towards the Four Corners. Another complicating factor will be the potential arrival of an easterly wave associated with the remains of Tropical Storm Bertha, though this may follow a trajectory too far south. With heights at 500 mb reaching well above normal through the period, hot temperatures are expected over the the lower elevations of our forecast area. An Extreme Heat Warning will be in effect Friday through Sunday for the lower elevations of the Grand Canyon and Marble/Glen Canyons.

On Monday through the middle of next week, the ridge looks to stay centered to our east and the door remains open for good moisture advection into northern AZ.

AVIATION...Thursday 23/18Z through Friday 24/18Z

Mainly VFR conditions, MVFR near heavier showers/storms. Isolated to scattered showers/storms from 18Z to 02Z. Winds light and variable except near storms where winds will be gusty and erratic.

OUTLOOK...Friday 24/18Z through Sunday 26/18Z...Mainly VFR conditions, MVFR near heavier showers/storms. Isolated to scattered showers/storms over the higher terrain (i.e. Mogollon Rim, White Mountains) between 18Z-02Z each day. Winds light and variable except near storms where winds will be gusty and erratic.

FIRE WEATHER...Friday through Saturday

Scattered afternoon and evening showers and thunderstorms are expected over the higher terrain, with only isolated activity at lower elevations. High temperatures warm close to 10 degrees above average. Winds are generally light through the period outside of outflow and thunderstorm activity. Minimum RH's 15-20% in the lower deserts to 35% higher terrain.

Sunday through Tuesday...Monsoon trends upward Sunday through Tuesday with scattered showers and thunderstorms expanding coverage outside the higher terrain and into the deserts. Temperatures 5-10 degrees above average Sunday trend back towards average Monday and tuesday. Generally light winds outside of outflow and thunderstorm activity. Minimum RH 15-25% lower deserts to 40-50% higher terrain.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from 10 AM MST /11 AM MDT/ Friday to 8 PM MST /9 PM MDT/ Sunday for AZZ005-006.