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 tonight 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 the rest of 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, although 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. There is moderate confidence that this area just brushes 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 slightly warmer than normal for early September.

AVIATION...Saturday 05/18Z through Sunday 06/18Z

VFR conditions expected. Only a few isolated thunderstorms expected over the White Mountains today from 18Z-00Z. A band of light rain moves into northwest Arizona after 09Z Sunday extending as far east as the Grand Canyon region with dry conditions elsewhere. Winds S-SW 10-20kts daytime, light and variable or terrain driven overnight.

OUTLOOK...Sunday 06/18Z through Tuesday 08/18Z...Mainly VFR conditions, brief MVFR possible under heavier thunderstorms. Some scattered showers/storms Sunday over northwestern Arizona throughout the day, with a few isolated afternoon thunderstorms over the Rim and White Mountains. Some isolated afternoon thunderstorms over the eastern third of Arizona Monday with the rest of the state being dry. Winds SW-W 5-15kts daytime, light and variable or terrain driven overnight.

FIRE WEATHER...Sunday and Monday

A band of moisture from Hurricane Marie will bring some showers and thunderstorms in northwestern Arizona including the Grand Canyon region. A few isolated afternoon thunderstorms are possible in the Rim and White Mountains on Sunday as well, otherwise the rest of the region remains dry. On Monday the eastern third of Arizona will see a few isolated afternoon showers and thunderstorms. High temperatures near normal to five degrees above normal. Winds S-SW 5-15 mph with gusts to 25 mph each afternoon.

Tuesday through Thursday...High pressure builds in from the east with increasing moisture and monsoon activity Tuesday through Thursday across northern Arizona. Temperatures warming to 5-10 degrees above average. Winds S-SW 5-15 mph each day, light and variable overnight.

FGZ WATCHES/WARNINGS/ADVISORIES

None.