textproduct: NWS Flagstaff

SYNOPSIS

There will be a gradual increase in shower and thunderstorm coverage today into the weekend, as moisture starts to push northward. The highest chances will be in eastern Arizona today, shifting toward northwest Arizona by Sunday. Expect breezy southwest winds to start easing this weekend, along with slightly below normal temperatures continuing into early next week.

DISCUSSION

A large upper low will remain over the NW United States through the weekend with high pressure to our east. This results in continued south-southwesterly flow over our region. Some shallow moisture has been pulled northward into Gila and southern Navajo/Apache counties, resulting in a few showers. This moisture is forecast to shift eastward through the day, with the highest chances for additional showers and thunderstorms (30-60%) east of a Payson to four corners line, with only low chances (5-15%) farther west. A few storms could contain heavy rainfall around the White Mountains. By Saturday, moisture is forecast to increase from south to north through the day with isolated to scattered showers and thunderstorms. Some of this moisture is surging northward from distant Hurricane Marie, which is forecast to be around 700 miles west of the southern tip of the Baja Peninsula by Saturday afternoon and heading northwestward. Extensive cloud cover may limit instability for many areas, so storm intensity remains uncertain. By Sunday, a shortwave disturbance is shown by much of the guidance moving across southern NV into UT while even deeper moisture is shown in the latest grand ensemble moving into northwest Arizona. Mean precipitable water values from the 00Z ensembles are in the 1.00"-1.25" range for much of our area, highest in northwest Arizona. These values are in the 85-95th percentile, with values around the 98th percentile in northwest Coconino County. Even with extensive cloud cover, the shortwave may provide enough lift for some heavier showers and thunderstorms in the northwest corner of the state. Storm chances are up to 50-70% in this area which includes the Grand Canyon/Supai. WPC has included this area in a slight risk for excessive rainfall/flash flooding on Sunday, and this will need to be monitored closely. The placement of the heavier rainfall risk is still not certain, and could end up being farther northwest into NV/UT. By Monday and Tuesday, rainfall chances shift to mainly eastern Arizona. Mid to late next week are looking active again as a favorable monsoon pattern sets up.

AVIATION...Friday 04/18Z through Saturday 05/18Z

Expect mainly VFR conditions. Scattered -SHRA/-TSRA along/south of a KPAN-KRQE line, only isolated -SHRA/-TSRA west of this line. All activity diminishing by 03Z. Daytime winds southwest 15-25 kts gusting up to 30 kts, decreasing to light and vartiable 5-10 kts after 02Z.

OUTLOOK...Saturday 05/18Z through Monday 07/18Z...Expect mainly VFR conditions. Isolated to scattered -SHRA/-TSRA for Saturday and Sunday. Activity most likely west of a KFLG-KPGA line. Daytime winds southwest at 5-15 kts, light and variable overnight periods.

FIRE WEATHER...Today and Saturday

Mainly dry and breezy conditions today west of a Payson to Four Corners line with scattered showers and thunderstorms along and east of this line. On Saturday, isolated to scattered activity spreads area wide. Winds today southwest 10-20 mph with gusts 25 to 35 mph, strongest across northwest Arizona. Saturday's winds southwest 10-15 with gusts to 25 mph. Little change in temperatures.

Sunday through Tuesday...Increasing moisture will cause shower and thunderstorm coverage to expand. Highest chances for rainfall will be seen on Sunday, especially in northwest 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.