textproduct: NWS Flagstaff

SYNOPSIS

High pressure will dominate the weather across Arizona through the coming week. This pattern will allow for above normal temperatures and daily chances for showers and storms. Greatest coverage will be across the higher terrain each afternoon and evening.

DISCUSSION

Strong high pressure aloft remained centered over the New Mexico/Colorado border Sunday afternoon. As mentioned in previous discussions, the high will wobble in place through Wednesday before shifting westward to a position centered over Arizona/Utah by next weekend.

For today and tonight...Cloud cover suppressed thunderstorm coverage through midday Sunday, especially from a Prescott to Four Corners line northward. South of this line sunny skies allowing convective development to proceed as normal. We're thinking that north of the Prescott to Four corners line shower and storm activity will be suppressed to isolated and weak storms. South of this line, as showers and storm developing over the mountains, the flow aloft has shifted enough so the storm motion will be to the west to northwest. This storm motion will inhibit any organized line of storms from moving from the Mogollon Rim south across Gila and Yavapai counties (as they did on Saturday). Yet still, where it is sunny enough, storms will build over the mountains and move off. Storms on the sunny side of the line will be stronger with localized flash flooding possible. In any case, activity will subside by mid evening leaving behind isolated showers and a very slight chance of thunderstorms. With strong high pressure nearby light winds and hot temperatures continue with an Extreme Heat Warning in effect until 9 PM this evening below 4000 feet from the Grand Canyon to Page.

From Monday into Wednesday...Monsoon moisture will remain stationed across northern Arizona. Strong high pressure will wobble in place with daily rounds of mountain thunderstorms from late morning into the afternoon then rolling out into the lower elevations later in the afternoon into the evening. Each day will be a little different so no sense getting into those details. The primary influence will be that the strong high pressure will start to have a capping/stabilizing influence with low to medium (at best) levels of monsoon activity. In addition, temperatures will begin to climb toward Wednesday as high pressure begins to shift over Arizona.

From Thursday onward...Models insist that the strong high pressure system over Colorado/New Mexico will shift over Arizona. While monsoon moisture will remain in place, with strong high pressure centered over Arizona we can probably expect low grade monsoon activity, generally of the isolated afternoon and early evening variety. In addition, temperatures are expected to climb further with extreme heat returning to our lower elevation locations.

AVIATION...Sunday 26/18Z through Monday 27/18Z

Another round of scattered SHRA/TSRA is expected this afternoon through early evening. Brief MVFR/IFR and gusty erratic winds can be expected in the stronger storm cells. Outside of storms, expect light winds 10 kt or less and primarily VFR conditions.

OUTLOOK...Monday 27/18Z through Wednesday 29/18Z...Mainly VFR conditions. Scattered SHRA/TSRA between 18Z-03Z each day, with greatest coverage across the higher terrain. Brief MVFR/IFR conditions and gusty, erratic winds in stronger storms. Outside of storms, expect westerly winds 5-15 kts, becoming light and variable overnight.

FIRE WEATHER...Monday and Tuesday

A low to moderate monsoonal pattern will continue into next week with daily rounds of isolated to scattered thunderstorms. Greatest storm coverage will be over the higher terrain. Isolated areas of heavy rain and gusty outflow winds will be the main storm threats. Outside of storm activity, expect warm temperatures and westerly winds around 10 mph.

Wednesday through Thursday...Expect a downward trend in monsoon thunderstorm activity late next week with increasingly hot temperatures. Storm activity will favor the high terrain, with only isolated coverage by Friday. Daytime humidity will see a decreasing trend to 15-25% by Friday. Outside of storm activity, expect light westerly winds 5-15 mph.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST /9 PM MDT/ this evening for AZZ005-006.