textproduct: NWS Flagstaff

SYNOPSIS

Northern Arizona will see an increase in shower and thunderstorm activity from later tonight through Thursday, when a Flash Flood Watch is in effect. Expect multiple rounds of rain and thunderstorms, with a few stronger storms possible. We'll see a drying trend with less thunderstorm activity over the weekend. Outside of precipitation, look for seasonable temperatures and breezy southwest winds.

DISCUSSION

An active monsoon pattern continues across Arizona as monsoonal moisture lingers across the state. Confidence continues to increase today in an even more active period of rain and thunderstorms developing from late tonight through early Thursday morning and a Flash Flood Watch has been issued for all of northern Arizona.

For today, we expect scattered showers and thunderstorms to develop with prime daytime heating. Most of this activity looks to favor the Mogollon Rim and areas north/east. Storm motion around 15 mph should limit the flash flood threat, though isolated heavy rain leading to flooding cannot be ruled out. Thunderstorm activity looks to increase substantially after midnight tonight and through the day on Wednesday as increasing moisture interacts with a shortwave feature that's expected to move across northern Mexico and through Arizona over the next 48 hours. This pattern is favorable for multiple rounds of shower and thunderstorm activity, and that's very consistent with what the latest CAM (convection allowing) model guidance suggests. The first round will likely develop after midnight tonight and move north through the morning hours, followed by multiple additional rounds on Wednesday. Storms will be capable of producing heavy rain, and the repeated nature of activity will increase the threat of flash flooding, thus a Flash Flood Watch has been issued for all of Apache, Navajo, Coconino, Yavapai and northern Gila counties. The potential for the highest rainfall amounts are in-line with WPC's "Moderate" risk of excessive rainfall across eastern Yavapai and Gila counties. The areas that see the more persistent bands of rainfall could see amounts of 1-3+ inches over the next 48 hours. The persistent trough across the Pac. Northwest is adding some wind shear to the environment as well. Though flash flooding will be the primary threat, there will be secondary threat of isolated severe thunderstorms that could produce large hail and damaging wind.

Storm coverage will decrease Thursday, but we still expect to see at least scattered thunderstorm coverage. By Friday, the aforementioned trough begins to progress through the western U.S. and will begin to spread drier air across the state. Expect a downturn in activity over the weekend with mostly isolated showers/storms.

Forecast confidence decreases dramatically early next week as additional troughs move into the southwest and the guidance is split on potential interactions with additional moisture.

AVIATION...Tuesday 15/18Z through Wednesday 16/18Z

ISOLD-SCT SHRA/TSRA through 02Z Wednesday, then ISOLD -SHRA/-TSRA or partial clearing through 08Z-10Z. AFT 08Z-10Z, NMRS SHRA/TSRA and ISOLD +TSRA moving south to north through the remainder of the period. Areas MVFR CIGS due to low clouds and TSRA through the period. Sfc winds S-SW5-15g20kts.

OUTLOOK...Wednesday 16/18Z through Friday 18/18Z...Expect SCT-NMRS SHRA/TSRA and ISOLD +TSRA through the period. Areas MVFR CIGS due to low clouds and TSRA through the period. Sfc winds outside of stronger convection generally light.

FIRE WEATHER...Wednesday and Thursday

An increase in shower/storm activity is expected from late tonight through Thursday morning with widespread wetting rain likely. There is an elevated risk of flash flooding, especially over recent burn scars. A few isolated severe storms are also possible. Outside of storm activity, expect near to below average temperatures and south to southwest winds 10-15 mph gusting up to 25 mph. Expect gusty and erratic winds in/near storms.

Friday through Sunday...A drying trend will lead to decreasing storm coverage over the weekend. Temperatures will remain near average with south to southwest winds around 10 mph during the daytime hours, becoming light overnight.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch from late tonight through late Wednesday night for AZZ004>018-037>040.