textproduct: NWS Flagstaff

SYNOPSIS

Isolated showers and thunderstorms are expected this weekend, with scattered activity by Sunday in northwest Arizona and the White Mountains. Storm activity will be confined to far eastern Arizona Monday before spreading back westward through next week. Temperatures will be close to normal.

DISCUSSION

A large upper low over the northwest United States will linger through the weekend, with ridging to our east. This setup keeps south-southwesterly flow over our region which will allow for an increase in moisture starting later today and through Sunday. While precipitable water values will increase above normal for early September, instability does not look high as much of the moisture is in the mid/upper levels bringing clouds and limiting surface heating. Some of this moisture, especially by Sunday in northwest AZ, is getting pulled northward from Hurricane Marie located around 700 miles west of the tip of the Baja peninsula. For today, mainly just isolated showers or thunderstorms are expected, with the vast majority of locations remaining dry. Later tonight through Sunday, the deeper moisture will move into northwest Arizona and portions of NV/UT but again instability is lacking and much of the activity may just be light to moderate showers. The main band of precipitation has also continued to trend farther westward and is now forecast by much of the guidance to be from southern CA to Las Vegas and into UT, possibly just brushing far northwest Coconino County where there is around a 40% chance of rain Sunday.

Monday - the northwest US low is forecast to shift eastward allowing for some significantly drier air to move into our area from the west. Storm chances will be limited to areas along the AZ/NM line with dry weather elsewhere. Starting Tuesday and continuing through next week - an elongated ridge covering most of the southern US will gradually shift westward. The flow around this ridge looks favorable for monsoon moisture to shift back into our region. Storm chances increase to 30-50% each afternoon from Wednesday onward, highest for the mountains. Temperatures should be near normal for early September.

AVIATION...Saturday 05/12Z through Sunday 06/12Z

Mainly VFR conditions. Isolated -SHRA/-TSRA after 18Z-20Z Saturday, ending for most areas by 02Z with a slight chance continuing through the night NW of KGCN-KPGA. Light winds becoming S-SW 10-20 kts from 18Z to 02Z, then light again.

OUTLOOK...Sunday 06/12Z through Tuesday 08/12Z...Mainly VFR conditions. Isolated to scattered -SHRA/-TSRA Sunday, with highest coverage west of a KCMR-KPGA line and over southern Apache County. Mainly dry Monday, with a chance of -SHRA/-TSRA over southern Apache County. Daytime winds mainly SW-W 5-15 kts.

FIRE WEATHER...Today and Sunday

Increasing moisture will result in mainly isolated showers and thunderstorms today and Sunday, with higher coverage over northwest Arizona and the White Mountains. Winds south to southwest 5-15 mph with gusts to 25 mph each afternoon. Little change in temperatures.

Monday through Wednesday...A bit drier air will push across northern Arizona on Monday with showers and thunderstorms mainly confined to the White Mountains area. High pressure builds in from the east with increasing moisture and monsoon activity Tuesday and especially Wednesday across northern Arizona. Winds south through southwest 5- 15 mph each day, then generally light and variable overnight. Little change in temperatures.

FGZ WATCHES/WARNINGS/ADVISORIES

None.