textproduct: NWS Flagstaff

SYNOPSIS

Moderate monsoon activity will continue through today, mainly along the higher terrain during the afternoon and evening hours. As high pressure builds over Arizona, expect hot temperatures and a decrease in storm activity to develop as moisture diminishes across the region.

DISCUSSION

An area of high pressure over New Mexico is starting to drift westward today through Tuesday before becoming centered over Arizona. As we move through the rest of the week, the high starts to sink further to the south and east.

Today and Tuesday...Shower activity lifted north this morning, which was in response to outflows from storms across the valley overnight. Increased cloud cover as a result is limiting instability as evidenced in the 18Z sounding, with most thunderstorm activity early this afternoon over western Coconino county where there was partial clearing. Going through the rest of today, we see monsoon moisture remaining in place with another fairly active afternoon/evening across the region. Best chances will be across the higher terrain and across western portions of the forecast area as moisture is advected up from the Gulf of California in the continued southerly flow. Storm motions remain on the slower side which will keep flash flooding as the main hazard for the day. As the high pushes back to the west, we will lose some of that good moisture advection into the region and storm chances will start to decrease. Expect storms to develop mainly across the higher terrain for Tuesday.

Wednesday through Friday...As the high becomes centered over Arizona, we see the moisture start to get cut off as subsidence wins out with drier conditions expected. Best chances for any storms will remain mainly across the higher terrain with the highest chances towards the White Mountains. The other factor of the strengthening high will be the increasing temperatures, which will be hot across the region. With highs reaching back into the 100s and heat risk increasing, we have issued an Extreme Heat Warning for the lower elevations of the Grand Canyon and Yavapai County, for areas below 4000 feet, in effect for Wednesday through Friday.

Saturday and Sunday...Models show the high elongating and sliding to the east of the region by the weekend. This shift may help to usher moisture back into our area with better chances for showers and thunderstorms returning along with slightly cooler temperatures.

AVIATION...Tuesday 25/06Z through Wednesday 26/06Z

Mainly VFR conditions, brief MVFR possible near thunderstorms. For Tuesday, isolated to scattered showers/storms along the Rim and White Mountains from 18Z-00Z. Winds variable 5-15kts daytime, light and variable or terrain driven overnight.

OUTLOOK...Wednesday 26/06Z through Friday 28/06Z...Mainly VFR conditions, isolated showers/storms possible along the Rim and White Mountains between 18Z and 00Z each afternoon. Winds SW-W 5-15kts daytime, light and variable or terrain driven overnight.

FIRE WEATHER...Today through Wednesday

Becoming warmer with decreasing moisture. Scattered showers and thunderstorms continue through this evening with the best coverage across far northern and western AZ. Coverage becomes isolated to scattered along the higher terrain each afternoon/evening on Tuesday and Wednesday. Outside of gusty and erratic storm driven winds, expect southwest to west winds around 5-15 mph during the day, becoming variable at night.

Thursday through Saturday...Hot temperatures continue. Low-grade monsoonal conditions on Thursday and Friday, with isolated showers and thunderstorms mainly across the higher terrain. Coverage of showers and thunderstorms begins to increase by Saturday. Winds are southwest through west 5-15 mph each afternoon.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Friday for AZZ006-037.