textproduct: NWS Flagstaff

SYNOPSIS

Storm activity will be confined to eastern Arizona today before gradually spreading back westward through the week. Widespread shower and thunderstorm activity could develop by Friday and Friday night with a passing weather disturbance. Temperatures warming to above normal today through Thursday, then cooling off over the weekend.

DISCUSSION...Today through Thursday

As the ridge to our east begins to retrograde, warming aloft will act to limit much of the storm potential over northern Arizona through the next couple of days. While moisture does remain, PWATS around 0.75 to 1.00 inches, the threat is not totally removed. Daily chances for isolated to scattered storms look to continue, mainly over the Mogollon Rim and White Mountains today, increasing in coverage slightly by Wednesday. Any activity that does develop will be fairly minor, and isolated in nature, as the cap aloft will inhibit any substantial convective development. Coverage looks to further increase on Thursday, especially along and south of the Mogollon Rim.

Friday through Monday...As a trough mover through the Pacific Northwest, moisture looks to be pulled northward through the day Friday. PWATs look to increase to around an inch across the Four Corners, to near 1.40-1.50 inches across central Arizona. Guidance as of now has the greatest potential for storms on Friday, initially north of the Mogollon Rim during the afternoon. Storms look to then move off the higher terrain, southwestward into central Arizona through the evening and overnight hours. This overnight activity looks to be aided by a weak shortwave passing to the north, potentially adding some upper-level dynamics to support the nocturnal convection. This in turn will likely lead to a heightened flash flood risk Friday afternoon into Saturday morning.

As the trough continues to move eastward, the ridge becomes suppressed further south. Confidence beyond this period remains low, as the operational guidance continues to flip flop in the exact setup. However, more of the EPS, CMCE, and GEFS members do seem to be in agreement with a decrease in moisture late in the weekend into early next week. Thus, a downward tick in thunderstorm potential seems to be the most likely scenario at this time, however thing could certainly change. Otherwise, breezier and cooler conditions look to set in across northern Arizona over the weekend as the ridge loosens it's grip.

AVIATION...Tuesday 08/18Z through Wednesday 09/18Z

VFR conditions continue with SCT mid-level clouds. Isolated showers and thunderstorms are forecast along the eastern Mogollon Rim and into the White Mountains from 19Z-01Z. Outside of any gusty and erratic outflow winds from storms, expect west-northwest winds, 5-15 kts, through 01Z.

OUTLOOK...Wednesday 09/18Z through Friday 11/18Z...VFR conditions with variable cloud cover persists through the week. Monsoonal moisture looks to gradually increase each day with widespread chances forecast by Friday afternoon. Plan on west-northwest winds, 5-15 kts, on Wednesday, followed by west winds, 10-20 kts, for Thursday and Friday.

FIRE WEATHER...Wednesday and Thursday

Isolated showers and thunderstorms are expected along the Mogollon Rim and the White Mountains each afternoon on Wednesday and Thursday. Outside of any gusty and erratic outflow winds from storms, plan on northwest winds, 5 to 15 mph, on Wednesday, followed by west winds, 10 to 20 mph, on Thursday. Minimum humidity will be 10 to 15% in the lower deserts and 20 to 30% in the mountains each afternoon.

Friday through Sunday...Increasing monsoonal moisture from the south with a passing weak disturbance towards the north, will lead to scattered to widespread shower and thunderstorm activity Friday into early Saturday. Gusty and erratic outflow winds along with periods of heavy rain and the potential for severe hail and lightning will be the main threats. Moisture begins to decrease Saturday and Sunday with showers and storms confined to the higher terrain. Winds will be primarily out of the west to southwest, 20 to 30 mph, each afternoon.

FGZ WATCHES/WARNINGS/ADVISORIES

None.