textproduct: NWS Flagstaff

SYNOPSIS

High pressure will build into the area through the weekend. This will lead to some decrease in monsoonal moisture as well as hotter temperatures. A return to increased monsoon moisture is possible by the beginning of next week.

DISCUSSION

The weak upper low that moved through eastern AZ Tue/Wed has exited the region this morning. The strong area of high pressure centered over the southern plains will expand and shift westward over the next few days, with 500 mb heights generally 596-598 dam over our region through at least Sunday which is well above the median values for late July. Monsoon moisture levels will decrease somewhat but still remain elevated enough for isolated to scattered afternoon and evening showers and thunderstorms today through Saturday. Daytime temperatures look to peak Friday and Saturday at 5-10 degrees above normal. By Sunday through Tuesday - the center of the high is forecast to shift back east a bit and allow for an increase in monsoon moisture from the southeast into our area. Daily rain chances go back up to 40-60% for higher terrain and 20-30% for lower elevations. This may also result in temperatures backing off for all but far northern Arizona. We issued an Extreme Heat Warning for the lower elevations of the Grand Canyon and Marble/Glen Canyons from Friday through Sunday where highs may reach as high as 112-114 near the Colorado River. Lower elevations of Yavapai County also look to be rather hot through this period, though confidence in extreme heat is lower there due to moisture/clouds possibly keeping temperatures from reaching their potential with such a strong ridge in place. We will continue to monitor the temperature forecast in this area to evaluate the need for a heat warning there also.

AVIATION...Thursday 23/12Z through Friday 24/12Z

Mainly VFR through the period. Isolated to scattered SHRA/TSRA after 18Z, decreasing after 02Z. Brief MVFR/IFR conditions, gusty/erratic winds, and hail possible in stronger storms. Outside of storms, expect light and variable or terrain driven winds.

OUTLOOK...Friday 24/12Z through Sunday 26/12Z...Chances for SHRA/TSRA, mainly between 18Z-03Z each day. Coverage of SHRA/TSRA decreases each day, remaining focused over the higher terrain. Brief MVFR/IFR conditions, gusty/erratic winds, and hail possible in stronger storms. Outside of storms, expect light and variable or terrain driven winds.

FIRE WEATHER...Today through Friday

Scattered afternoon and evening showers and thunderstorms are expected over the higher terrain, with only isolated activity at lower elevations. Winds are generally light through the period outside of outflow and thunderstorm activity. Expect a strong warming trend through the period.

Saturday through Monday...Continued isolated to scattered thunderstorm activity Saturday, with an increasing trend Sunday and Monday. Generally light winds outside of outflow and thunderstorm activity. Expect warm temperatures with minimum RH 20-40%.

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.